Iridium anomaly

@article{doi10113000167606197788367ucmsag20co2,
    author = "Arthur, Michael A. and Fischer, Alfred G.",
    title = "Upper Cretaceous–Paleocene magnetic stratigraphy at Gubbio, Italy I. Lithostratigraphy and sedimentology",
    year = "1977",
    journal = "Geological Society of America Bulletin",
    url = "https://doi.org/10.1130/0016-7606(1977)88<367:ucmsag>2.0.co;2",
    doi = "10.1130/0016-7606(1977)88<367:ucmsag>2.0.co;2",
    openalex = "W2112488864"
}

@article{doi10113000167606197788374ucmsag20co2,
    author = "Lowrie, William and Álvarez, Walter",
    title = "Upper Cretaceous–Paleocene magnetic stratigraphy at Gubbio, Italy III. Upper Cretaceous magnetic stratigraphy",
    year = "1977",
    journal = "Geological Society of America Bulletin",
    url = "https://doi.org/10.1130/0016-7606(1977)88<374:ucmsag>2.0.co;2",
    doi = "10.1130/0016-7606(1977)88<374:ucmsag>2.0.co;2",
    openalex = "W2030003066"
}

@article{doi10113000167606197788383ucmsag20co2,
    author = "Álvarez, Walter and Arthur, Michael A. and Fischer, Alfred G. and Lowrie, William and Napoleone, Giovanni and Silvá, Isabella Premoli and Roggenthen, William",
    title = "Upper Cretaceous–Paleocene magnetic stratigraphy at Gubbio, Italy V. Type section for the Late Cretaceous-Paleocene geomagnetic reversal time scale",
    year = "1977",
    journal = "Geological Society of America Bulletin",
    url = "https://doi.org/10.1130/0016-7606(1977)88<383:ucmsag>2.0.co;2",
    doi = "10.1130/0016-7606(1977)88<383:ucmsag>2.0.co;2",
    openalex = "W2149596606"
}

Paleomagnetic evidence suggests that the Cretaceous/Tertiary transition at DSDP Site 384 is continuous. Quantitative taxonomic analysis of the nannolith assemblages indicates that all taxa within the Cretaceous assemblage became extinct simultaneously. The evolutionary sequence of the Tertiary assemblages at Site 384 is characterized by an initial dominance of Thoracosphaera, Zygodiscus sigmoides and Markalius astroporus, a following Braarudosphaera bloom, and a subsequent gradual increase of Cruciplacolithus primus and C. tenuis. The preserved nannolith record can be explained by benthic mixing with an incompletely homogenized mixed layer of 21 cm in thickness. The carbonate record in the deep North Atlantic documents a major excursion (>2 km) of the carbonate compensation surface to abyssal paleodepths from middle Maestrichtian to middle Danian time. Comparison with the scanty sedimentary evidence from the deep Pacific and Indian oceans suggests a late Mesozoic deep water fractionation between the Pacific and the Atlantic oceans with deep circulation reversals just prior and subsequent to the evolutionary Cretaceous/Tertiary boundary extinction event.

@incollection{doi102973dsdpproc431221979,
    author = "Thierstein, Hans R. and Okada, Hakuyu",
    title = "The Cretaceous/Tertiary Boundary Event in the North Atlantic",
    year = "1979",
    booktitle = "U.S. Government Printing Office eBooks",
    abstract = "Paleomagnetic evidence suggests that the Cretaceous/Tertiary transition at DSDP Site 384 is continuous. Quantitative taxonomic analysis of the nannolith assemblages indicates that all taxa within the Cretaceous assemblage became extinct simultaneously. The evolutionary sequence of the Tertiary assemblages at Site 384 is characterized by an initial dominance of Thoracosphaera, Zygodiscus sigmoides and Markalius astroporus, a following Braarudosphaera bloom, and a subsequent gradual increase of Cruciplacolithus primus and C. tenuis. The preserved nannolith record can be explained by benthic mixing with an incompletely homogenized mixed layer of 21 cm in thickness. The carbonate record in the deep North Atlantic documents a major excursion (>2 km) of the carbonate compensation surface to abyssal paleodepths from middle Maestrichtian to middle Danian time. Comparison with the scanty sedimentary evidence from the deep Pacific and Indian oceans suggests a late Mesozoic deep water fractionation between the Pacific and the Atlantic oceans with deep circulation reversals just prior and subsequent to the evolutionary Cretaceous/Tertiary boundary extinction event.",
    url = "https://doi.org/10.2973/dsdp.proc.43.122.1979",
    doi = "10.2973/dsdp.proc.43.122.1979",
    openalex = "W2498884602"
}

Platinum metals are depleted in the earth's crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may thus indicate influxes of extraterrestrial material. Deep-sea limestones exposed in Italy, Denmark, and New Zealand show iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago. Reasons are given to indicate that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is suggested which accounts for the extinctions and the iridium observations. Impact of a large earth-crossing asteroid would inject about 60 times the object's mass into the atmosphere as pulverized rock; a fraction of this dust would stay in the stratosphere for several years and be distributed worldwide. The resulting darkness would suppress photosynthesis, and the expected biological consequences match quite closely the extinctions observed in the paleontological record. One prediction of this hypothesis has been verified: the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the Cretaceous and Tertiary limestones, which are chemically similar to each other. Four different independent estimates of the diameter of the asteroid give values that lie in the range 10 ± 4 kilometers.

@article{alvarez1980extraterrestrial,
    author = "Alvarez, Luis W. and Alvarez, Walter and Asaro, Frank and Michel, Helen V.",
    title = "Extraterrestrial Cause for the Cretaceous-Tertiary Extinction",
    year = "1980",
    journal = "Science",
    abstract = "Platinum metals are depleted in the earth's crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may thus indicate influxes of extraterrestrial material. Deep-sea limestones exposed in Italy, Denmark, and New Zealand show iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago. Reasons are given to indicate that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is suggested which accounts for the extinctions and the iridium observations. Impact of a large earth-crossing asteroid would inject about 60 times the object's mass into the atmosphere as pulverized rock; a fraction of this dust would stay in the stratosphere for several years and be distributed worldwide. The resulting darkness would suppress photosynthesis, and the expected biological consequences match quite closely the extinctions observed in the paleontological record. One prediction of this hypothesis has been verified: the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the Cretaceous and Tertiary limestones, which are chemically similar to each other. Four different independent estimates of the diameter of the asteroid give values that lie in the range 10 ± 4 kilometers.",
    url = "https://doi.org/10.1126/science.208.4448.1095",
    doi = "10.1126/science.208.4448.1095",
    number = "4448",
    openalex = "W2110619496",
    pages = "1095-1108",
    volume = "208",
    references = "doi101007bf00212446, doi1010160016703773900665, doi1010160031018268900473, doi101038242032a0, doi101038267403a0, doi1010970001069419540800000019, doi101126science18441411079, doi10113000167606197788367ucmsag20co2, doi10113000167606197788374ucmsag20co2, doi10113000167606197788383ucmsag20co2, doi101146annurevea07050179001115, hays1971faunal"
}

Evidence for a major meteorite impact on the earth 65 million years ago is shown by the presence of meteoritic debris in the "fish clay" from Denmark representing the Cretaceous-Tertiary boundary. Noble metals (iridium, osmium, gold, platinum, rhenium, ruthenium, palladium, nickel, and cobalt), which are sensitive indicators of meteorites and are normally depleted on the terrestrial surface by factors of 10(4) to 10(2) relative to cosmic abundances, are enriched in this boundary clay by factors of 5 to 100 over the expected abundances. With the exception of rhenium, all the enriched noble metals in the clay are present in cosmic proportions, indicating that the impacting celestial body had not undergone gross chemical differentiation. The major extinction of life on the earth at the end of the Cretaceous Period may be related to the meteorite impact.

@article{doi101126science2094459921,
    author = "Ganapathy, R.",
    title = "A Major Meteorite Impact on the Earth 65 Million Years Ago: Evidence from the Cretaceous-Tertiary Boundary Clay",
    year = "1980",
    journal = "Science",
    abstract = {Evidence for a major meteorite impact on the earth 65 million years ago is shown by the presence of meteoritic debris in the "fish clay" from Denmark representing the Cretaceous-Tertiary boundary. Noble metals (iridium, osmium, gold, platinum, rhenium, ruthenium, palladium, nickel, and cobalt), which are sensitive indicators of meteorites and are normally depleted on the terrestrial surface by factors of 10(4) to 10(2) relative to cosmic abundances, are enriched in this boundary clay by factors of 5 to 100 over the expected abundances. With the exception of rhenium, all the enriched noble metals in the clay are present in cosmic proportions, indicating that the impacting celestial body had not undergone gross chemical differentiation. The major extinction of life on the earth at the end of the Cretaceous Period may be related to the meteorite impact.},
    url = "https://doi.org/10.1126/science.209.4459.921",
    doi = "10.1126/science.209.4459.921",
    openalex = "W2011916250"
}

In Gubbio, Italy, a l em layer of clay between extensive limestone formations marks the boundary between the Cretaceous and Tertiary Periods. This clay layer was known to have been deposited about 65 million years ago when many life forms became extinct, but the length of time associated with the deposition was not known. In an attempt to measure this time with normally deposited meteoritic material as a clock, extensive measurements of iridium abundances (and those of many other elements) were made on the Gubbio rocks. Neutron activation analysis was the principal tool used in these studies. About 50 elements are searched for in materials like the earth's crust, about 40 are detected and about 30 are measured with useful precision. We were not able to determine exactly how long the clay deposition took. Instead the laboratory studies on the chemical and physical nature of the Cretaceous-Tertiary boundary led to the theory that an asteroid collision with the earth was responsible for the extinction of many forms of life including the dinosaurs.

@article{openalexw274971555,
    author = "Asaro, Frank and Michel, Helen V. and Alvarez, Luis W. and Álvarez, Walter",
    title = "RESULTS OF A DATING ATTEMPT -CHEMICAL AND PHYSICAL MEASUREMENTS RELEVANT TO THE CASE OF THE CRETACEOUS TERTIARY EXTINCTIONS",
    year = "1980",
    journal = "University of North Texas Digital Library (University of North Texas)",
    abstract = "In Gubbio, Italy, a l em layer of clay between extensive limestone formations marks the boundary between the Cretaceous and Tertiary Periods. This clay layer was known to have been deposited about 65 million years ago when many life forms became extinct, but the length of time associated with the deposition was not known. In an attempt to measure this time with normally deposited meteoritic material as a clock, extensive measurements of iridium abundances (and those of many other elements) were made on the Gubbio rocks. Neutron activation analysis was the principal tool used in these studies. About 50 elements are searched for in materials like the earth's crust, about 40 are detected and about 30 are measured with useful precision. We were not able to determine exactly how long the clay deposition took. Instead the laboratory studies on the chemical and physical nature of the Cretaceous-Tertiary boundary led to the theory that an asteroid collision with the earth was responsible for the extinction of many forms of life including the dinosaurs.",
    openalex = "W274971555"
}

An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater swamp conditions in the Raton Basin of northeastern New Mexico. The anomaly occurs at the base of a coal bed, at the same stratigraphic position at which several well-known species of Cretaceous-age pollen became extinct.

@article{doi101126science21445271341,
    author = "Orth, C. J. and Gilmore, J. S. and Knight, J.D. and Pillmore, Charles L. and Tschudy, Robert H. and Fassett, James E.",
    title = "An Iridium Abundance Anomaly at the Palynological Cretaceous-Tertiary Boundary in Northern New Mexico",
    year = "1981",
    journal = "Science",
    abstract = "An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater swamp conditions in the Raton Basin of northeastern New Mexico. The anomaly occurs at the base of a coal bed, at the same stratigraphic position at which several well-known species of Cretaceous-age pollen became extinct.",
    url = "https://doi.org/10.1126/science.214.4527.1341",
    doi = "10.1126/science.214.4527.1341",
    openalex = "W1980328862",
    references = "alvarez1980extraterrestrial, doi101038285198a0, doi101126science2094459921, doi1021724365567, doi103133gq823"
}

@article{ganapathy1981iridium,
    author = "GANAPATHY, R and GARTNER, S and JIANG, M",
    title = "Iridium anomaly at the Cretaceous-Tertiary boundary in Texas",
    year = "1981",
    journal = "Earth and Planetary Science Letters",
    url = "https://doi.org/10.1016/0012-821x(81)90055-8",
    doi = "10.1016/0012-821x(81)90055-8",
    number = "3",
    openalex = "W2013795681",
    pages = "393-396",
    volume = "54",
    references = "alvarez1980extraterrestrial, doi101029eo061i026p00505, doi101038285198a0, doi101038288651a0, doi101126science2094459921, doi102973dsdpproc431221979, openalexw274971555"
}

Iridium is depleted in the earth’s crust relative to its normal solar system abundance. Several hundred measurements by at least seven laboratories have disclosed an iridium abundance anomaly at the Cretaceous/Tertiary (C/T) boundary in 36 sites worldwide. Discovery of the first iridium anomaly in nonmarine sediments, by Charles Orth and his colleagues, shows that the iridium was not extracted from sea water. Sediment starvation and a nearby supernova have also been eliminated as possible sources. Impact of a large extraterrestrial object is now widely accepted as the best explanation of the iridium anomaly. Paleomagnetic reversal stratigraphy of four marine and five non-marine C/T boundary sections is consistent with simultaneous extinction worldwide, but does not prove it. Ultra-high-resolution stratigraphic studies at Caravaca, in southern Spain, by Jan Smit, gave an unparalleled record of the extinction of the planktonic foraminifera and the associated geochemical patterns. Au/Ir and Pt/Ir ratios from two C/T boundary clays indicate a type I carbonaceous chondrite composition for the impacting object. Iridium anomalies are known from two other stratigraphic horizons, in each case associated with direct evidence for an extraterrestrial impact: in the Pliocene, with chondritic ablation debris, and in the late Eocene with microtektites. The C/T impact site has not been located. Two interesting candidate sites are the circular sea-floor features west of Portugal and the Deccan Traps of India. There is a 20% probability that impact occurred on sea floor that has subsequently been subducted. Recent computer modeling of impact processes is yielding important information. The killing mechanism has not yet been established, but both temperature changes and darkness due to atmospheric dust are probable contributors. Darkness would have lasted a few months, rather than our originally suggested few years; this is indicated by (1) calculated rapid dispersal of dust in ballistic trajectories, (2) more rapid settling of heavier, coagulated dust particles, (3) calculated effects of darkness on phytoplankton, and (4) compatibility of the plant record with a few months—but not with a few years—of darkness.

@incollection{doi101130spe190p305,
    author = "Álvarez, Walter and Alvarez, Luis W. and Asaro, Frank and Michel, Helen V.",
    title = "Current status of the impact theory for the terminal Cretaceous extinction",
    year = "1982",
    booktitle = "Geological Society of America eBooks",
    abstract = "Iridium is depleted in the earth’s crust relative to its normal solar system abundance. Several hundred measurements by at least seven laboratories have disclosed an iridium abundance anomaly at the Cretaceous/Tertiary (C/T) boundary in 36 sites worldwide. Discovery of the first iridium anomaly in nonmarine sediments, by Charles Orth and his colleagues, shows that the iridium was not extracted from sea water. Sediment starvation and a nearby supernova have also been eliminated as possible sources. Impact of a large extraterrestrial object is now widely accepted as the best explanation of the iridium anomaly. Paleomagnetic reversal stratigraphy of four marine and five non-marine C/T boundary sections is consistent with simultaneous extinction worldwide, but does not prove it. Ultra-high-resolution stratigraphic studies at Caravaca, in southern Spain, by Jan Smit, gave an unparalleled record of the extinction of the planktonic foraminifera and the associated geochemical patterns. Au/Ir and Pt/Ir ratios from two C/T boundary clays indicate a type I carbonaceous chondrite composition for the impacting object. Iridium anomalies are known from two other stratigraphic horizons, in each case associated with direct evidence for an extraterrestrial impact: in the Pliocene, with chondritic ablation debris, and in the late Eocene with microtektites. The C/T impact site has not been located. Two interesting candidate sites are the circular sea-floor features west of Portugal and the Deccan Traps of India. There is a 20\% probability that impact occurred on sea floor that has subsequently been subducted. Recent computer modeling of impact processes is yielding important information. The killing mechanism has not yet been established, but both temperature changes and darkness due to atmospheric dust are probable contributors. Darkness would have lasted a few months, rather than our originally suggested few years; this is indicated by (1) calculated rapid dispersal of dust in ballistic trajectories, (2) more rapid settling of heavier, coagulated dust particles, (3) calculated effects of darkness on phytoplankton, and (4) compatibility of the plant record with a few months—but not with a few years—of darkness.",
    url = "https://doi.org/10.1130/spe190-p305",
    doi = "10.1130/spe190-p305",
    openalex = "W1950866488"
}

The mass-extinction event at the Cretaceous/Tertiary boundary (C/T in text; K-T on figures) exterminated all but one species of the planktonic Foraminifera (Guembelitria cretaceaCushman). Although not all details have been clarified yet, all Paleocene planktonic Foraminifera may have evolved from this sole survivor. Globigerina minutulaLuterbacher and Premoli Silva is the first true Paleocene species to appear; it develops into Globigerina fringaSubbotina, and later on probably into Globigerina eugubinaLuterbacher and Premoli Silva. Essentially, the stratigraphy of several complete sections shows a similar pattern: abrupt extinction of plankton followed by deposition of a thin lamina with high concentrations of siderophile elements, considered as the direct fallout level of the impact event. This lamina is followed by a 1- to 30-cm-thick clay or marl layer (which represents the normal background supply of hemipelagic clay) and a gradual return to calcareous sedimentation associated with the appearance of the first new Paleocene species. The biostratigraphy of the Gredero section in southeast Spain is analyzed in detail, complemented with data from the Kef section in Northern Tunisia. A new zone, the Guembelitria cretaceaZone, which contains only G. cretacea,and possibly Globotruncanella monmouthensis(Olsson) and Globigerinelloides messinaeBrönnimann in situ, is established at the base of the Tertiary. It is essentially the same as the C/T boundary clay. New taxonomic descriptions are given of G. cretacea, Globigerina minutula, G. fringa, G. eugubina,and Globotruncanella caravacaensisn. sp. Preliminary results of a paleomagnetic survey are used to calculate sediment accumulation rates, from which the mass extinction is inferred to have occurred within 50 years and a new stable planktonic fauna re-established within 35,000 years. The earliest Paleocene faunas are highly unstable. Different species successively become dominant and show a rapid evolutionary development. The initial development thus is both explosive and unstable and seems to be consistent with the punctuated mode of evolution.

@incollection{doi101130spe190p329,
    author = "Smit, Jan",
    title = "Extinction and evolution of planktonic foraminifera after a major impact at the Cretaceous/Tertiary boundary",
    year = "1982",
    booktitle = "Geological Society of America eBooks",
    abstract = "The mass-extinction event at the Cretaceous/Tertiary boundary (C/T in text; K-T on figures) exterminated all but one species of the planktonic Foraminifera (Guembelitria cretaceaCushman). Although not all details have been clarified yet, all Paleocene planktonic Foraminifera may have evolved from this sole survivor. Globigerina minutulaLuterbacher and Premoli Silva is the first true Paleocene species to appear; it develops into Globigerina fringaSubbotina, and later on probably into Globigerina eugubinaLuterbacher and Premoli Silva. Essentially, the stratigraphy of several complete sections shows a similar pattern: abrupt extinction of plankton followed by deposition of a thin lamina with high concentrations of siderophile elements, considered as the direct fallout level of the impact event. This lamina is followed by a 1- to 30-cm-thick clay or marl layer (which represents the normal background supply of hemipelagic clay) and a gradual return to calcareous sedimentation associated with the appearance of the first new Paleocene species. The biostratigraphy of the Gredero section in southeast Spain is analyzed in detail, complemented with data from the Kef section in Northern Tunisia. A new zone, the Guembelitria cretaceaZone, which contains only G. cretacea,and possibly Globotruncanella monmouthensis(Olsson) and Globigerinelloides messinaeBrönnimann in situ, is established at the base of the Tertiary. It is essentially the same as the C/T boundary clay. New taxonomic descriptions are given of G. cretacea, Globigerina minutula, G. fringa, G. eugubina,and Globotruncanella caravacaensisn. sp. Preliminary results of a paleomagnetic survey are used to calculate sediment accumulation rates, from which the mass extinction is inferred to have occurred within 50 years and a new stable planktonic fauna re-established within 35,000 years. The earliest Paleocene faunas are highly unstable. Different species successively become dominant and show a rapid evolutionary development. The initial development thus is both explosive and unstable and seems to be consistent with the punctuated mode of evolution.",
    url = "https://doi.org/10.1130/spe190-p329",
    doi = "10.1130/spe190-p329",
    openalex = "W2418914985"
}

During the past year we have been measuring trace element abundances and searching for anomalously high iridium (Ir) concentrations in continental sedimentary rocks that span the Cretaceous-Tertiary boundary in the Raton and San Juan Basins of northern New Mexico and southern Colorado. Using neutron activation and radiochemical separations, we have identified anomalous concentrations of Ir in samples from two sites in the Raton Basin: in a drill core at York Canyon, about 50 km west of Raton, New Mexico, and in a road cut near the city of Raton. In both cases the anomaly occurs essentially at the base of thin coal beds, across a thickness span of only a few cm and at the same level at which several species of Cretaceous pollen become extinct and the ratio of angiosperm pollen to fern spores drops sharply. The Ir surface density ranges from 8 to 40 × 10 −9g cm −2. In the York Canyon core the Ir concentration reaches a value of 5.6 × 10 −9g/g of rock over a local background of about 10 −11g/g; the Pt abundance distribution is similar to that for Ir, while Au reaches its maximum concentration about 10 cm below the Ir peak. Se, V, Cr, Mn, Co, and Zn are about two-fold more abundant at the anomaly zone than in adjacent zones, and mass spectrometric 244Pu analysis showed the 244Pu/Ir atom ratio ⩽ 1 × 10 7. In the San Juan Basin we have located a small Ir spike (55 × 10 −12g/g over a local background of 8 × 10 −12g/g) that is accompanied by high concentrations of Co and Mn. It is thought to be due to geochemical enrichment processes.

@incollection{doi101130spe190p423,
    author = "Orth, C. J. and Gilmore, J. S. and Knight, J.D. and Pillmore, Charles L. and Tschudy, Robert H. and Fassett, James E.",
    title = "Iridium abundance measurements across the Cretaceous/Tertiary boundary in the San Juan and Raton Basins of northern New Mexico",
    year = "1982",
    booktitle = "Geological Society of America eBooks",
    abstract = "During the past year we have been measuring trace element abundances and searching for anomalously high iridium (Ir) concentrations in continental sedimentary rocks that span the Cretaceous-Tertiary boundary in the Raton and San Juan Basins of northern New Mexico and southern Colorado. Using neutron activation and radiochemical separations, we have identified anomalous concentrations of Ir in samples from two sites in the Raton Basin: in a drill core at York Canyon, about 50 km west of Raton, New Mexico, and in a road cut near the city of Raton. In both cases the anomaly occurs essentially at the base of thin coal beds, across a thickness span of only a few cm and at the same level at which several species of Cretaceous pollen become extinct and the ratio of angiosperm pollen to fern spores drops sharply. The Ir surface density ranges from 8 to 40 × 10 −9g cm −2. In the York Canyon core the Ir concentration reaches a value of 5.6 × 10 −9g/g of rock over a local background of about 10 −11g/g; the Pt abundance distribution is similar to that for Ir, while Au reaches its maximum concentration about 10 cm below the Ir peak. Se, V, Cr, Mn, Co, and Zn are about two-fold more abundant at the anomaly zone than in adjacent zones, and mass spectrometric 244Pu analysis showed the 244Pu/Ir atom ratio ⩽ 1 × 10 7. In the San Juan Basin we have located a small Ir spike (55 × 10 −12g/g over a local background of 8 × 10 −12g/g) that is accompanied by high concentrations of Co and Mn. It is thought to be due to geochemical enrichment processes.",
    url = "https://doi.org/10.1130/spe190-p423",
    doi = "10.1130/spe190-p423",
    openalex = "W1847538392"
}

Iridium concentrations are anomalously high at the palynological Cretaceous-Tertiary boundary in fluvial sedimentary rocks of the lower part of the Raton Formation at several localities in the Raton Basin of New Mexico and Colorado. The iridium anomaly is associated with a thin bed of kaolinitic claystone in a discontinuous carbonaceous shale and coal sequence.

@article{doi101126science22346411180,
    author = "Pillmore, Charles L. and Tschudy, Robert H. and Orth, C. J. and Gilmore, J. S. and Knight, J.D.",
    title = "Geologic Framework of Nonmarine Cretaceous-Tertiary Boundary Sites, Raton Basin, New Mexico and Colorado",
    year = "1984",
    journal = "Science",
    abstract = "Iridium concentrations are anomalously high at the palynological Cretaceous-Tertiary boundary in fluvial sedimentary rocks of the lower part of the Raton Formation at several localities in the Raton Basin of New Mexico and Colorado. The iridium anomaly is associated with a thin bed of kaolinitic claystone in a discontinuous carbonaceous shale and coal sequence.",
    url = "https://doi.org/10.1126/science.223.4641.1180",
    doi = "10.1126/science.223.4641.1180",
    openalex = "W2033629863"
}

A thin claystone layer found in nonmarine rocks at the palynological Cretaceous-Tertiary boundary in eastern Montana contains an anomalously high value of iridium. The nonclay fraction is mostly quartz with minor feldspar, and some of these grains display planar features. These planar features are related to specific crystallographic directions in the quartz lattice. The shocked quartz grains also exhibit asterism and have lowered refractive indices. All these mineralogical features are characteristic of shock metamorphism and are compelling evidence that the shocked grains are the product of a high velocity impact between a large extraterrestrial body and the earth. The shocked minerals represent silicic target material injected into the stratosphere by the impact of the projectile.

@article{doi101126science2244651867,
    author = "Bohor, B. F. and Foord, Eugene E. and Modreski, Peter J. and Triplehorn, Don M.",
    title = "Mineralogic Evidence for an Impact Event at the Cretaceous-Tertiary Boundary",
    year = "1984",
    journal = "Science",
    abstract = "A thin claystone layer found in nonmarine rocks at the palynological Cretaceous-Tertiary boundary in eastern Montana contains an anomalously high value of iridium. The nonclay fraction is mostly quartz with minor feldspar, and some of these grains display planar features. These planar features are related to specific crystallographic directions in the quartz lattice. The shocked quartz grains also exhibit asterism and have lowered refractive indices. All these mineralogical features are characteristic of shock metamorphism and are compelling evidence that the shocked grains are the product of a high velocity impact between a large extraterrestrial body and the earth. The shocked minerals represent silicic target material injected into the stratosphere by the impact of the projectile.",
    url = "https://doi.org/10.1126/science.224.4651.867",
    doi = "10.1126/science.224.4651.867",
    openalex = "W2038487387",
    references = "alvarez1980extraterrestrial, doi101007bf00377477, doi101016001910356990061x, doi101126science21445271341, doi101130spe127p65, doi101130spe190p305, doi101130spe190p423, doi102475ajs2639786"
}

The palynologically defined Cretaceous-Tertiary boundary in the western interior of North America occurs at the top of an iridium-rich clay layer. The boundary is characterized by the abrupt disappearance of certain pollen species, immediately followed by a pronounced, geologically brief change in the ratio of fern spores to angiosperm pollen. The occurrence of these changes at two widely separated sites implies continentwide disruption of the terrestrial ecosystem, probably caused by a major catastrophic event at the end of the period.

@article{doi101126science22546661030,
    author = "Tschudy, Robert H. and Pillmore, Charles L. and Orth, C. J. and Gilmore, J. S. and Knight, J.D.",
    title = "Disruption of the Terrestrial Plant Ecosystem at the Cretaceous-Tertiary Boundary, Western Interior",
    year = "1984",
    journal = "Science",
    abstract = "The palynologically defined Cretaceous-Tertiary boundary in the western interior of North America occurs at the top of an iridium-rich clay layer. The boundary is characterized by the abrupt disappearance of certain pollen species, immediately followed by a pronounced, geologically brief change in the ratio of fern spores to angiosperm pollen. The occurrence of these changes at two widely separated sites implies continentwide disruption of the terrestrial ecosystem, probably caused by a major catastrophic event at the end of the period.",
    url = "https://doi.org/10.1126/science.225.4666.1030",
    doi = "10.1126/science.225.4666.1030",
    openalex = "W2045965176",
    references = "alvarez1980extraterrestrial, doi101038307224a0, doi101086628630, doi101126science21445271341, doi101126science22346411180, doi101126science2244651867, doi101130spe190p305, doi1023072399088, openalexw2334406281"
}

@article{doi101016037783988590009x,
    author = "Monechi, Simonetta and Thierstein, Hans R.",
    title = "Late Cretaceous-Eocene nannofossil and magnetostratigraphic correlations near Gubbio, Italy",
    year = "1985",
    journal = "Marine Micropaleontology",
    url = "https://doi.org/10.1016/0377-8398(85)90009-x",
    doi = "10.1016/0377-8398(85)90009-x",
    openalex = "W2094054644",
    references = "crossref1982geological, doi1010160012821x77900607, doi1010160033589473900525, doi101016037783988090016x, doi101029jb073i006p02119, doi101029jb084ib02p00615, doi101126science19442701121, doi1011300091761319775400gsolqc20co2, doi102973dsdpproc441341978, openalexw62718268"
}

Iridium measured in 149 samples of a continuous 9-meter section of Pacific abyssal clay covering the time span 33 to 67 million years ago shows a well-defined peak only at the Cretaceous/Tertiary boundary. In the rest of the section iridium ranges from a minimum concentration near 0.35 nanograms per gram in the Paleocene to a maximum near 1.7 in the Eocene; between 63 and 33 million years ago the mean iridium accumulation rate is approximately 13 nanograms per square centimeter per million years. Correction for terrestrial iridium leads to an extraterrestrial flux of9 +/- 3 nanograms of iridium per square centimeter per million years, and an estimated annual global influx of 78 billion grams of chondritic matter, consistent with recent estimates of the influx of dust, meteorites, and crater-producing bodies with masses ranging from 10(-13) to 10(18)grams. Combining the recent flux of objects ranging in mass from 10(6) to 10(7) grams with the flux of 10(14) - to 10(15) -gram objects indicates that the number of objects is equal to 0.54 divided by the radius (in kilometers) to the 2.1 power. Periodic comet showers should increase the cometary iridium flux by a factor of 200 to 600 on a time scale of 1 to 3 million years; the predicted iridium maxima (more than 30 times background) are not present in the intervals associated with the Cretaceous/Tertiary boundary or the tektiteproducing late Eocene events.

@article{doi101126science23247551225,
    author = "Kyte, Frank T. and Wasson, J. T.",
    title = "Accretion Rate of Extraterrestrial Matter: Iridium Deposited 33 to 67 Million Years Ago",
    year = "1986",
    journal = "Science",
    abstract = "Iridium measured in 149 samples of a continuous 9-meter section of Pacific abyssal clay covering the time span 33 to 67 million years ago shows a well-defined peak only at the Cretaceous/Tertiary boundary. In the rest of the section iridium ranges from a minimum concentration near 0.35 nanograms per gram in the Paleocene to a maximum near 1.7 in the Eocene; between 63 and 33 million years ago the mean iridium accumulation rate is approximately 13 nanograms per square centimeter per million years. Correction for terrestrial iridium leads to an extraterrestrial flux of9 +/- 3 nanograms of iridium per square centimeter per million years, and an estimated annual global influx of 78 billion grams of chondritic matter, consistent with recent estimates of the influx of dust, meteorites, and crater-producing bodies with masses ranging from 10(-13) to 10(18)grams. Combining the recent flux of objects ranging in mass from 10(6) to 10(7) grams with the flux of 10(14) - to 10(15) -gram objects indicates that the number of objects is equal to 0.54 divided by the radius (in kilometers) to the 2.1 power. Periodic comet showers should increase the cometary iridium flux by a factor of 200 to 600 on a time scale of 1 to 3 million years; the predicted iridium maxima (more than 30 times background) are not present in the intervals associated with the Cretaceous/Tertiary boundary or the tektiteproducing late Eocene events.",
    url = "https://doi.org/10.1126/science.232.4755.1225",
    doi = "10.1126/science.232.4755.1225",
    openalex = "W2044432443",
    references = "doi101007bf00567511, doi1010160012821x80901776, doi1010160016703762901126, doi1010160016703781901459, doi1010160019103585901216, doi101038307222a0, doi101038308709a0, doi101073pnas813801, doi101126science20944641522, doi101126science21445271341, doi101126science22746911161"
}

@article{montanari1986spherules,
    author = "Montanari, Alessandro",
    title = "Spherules from the Cretaceous/Tertiary boundary clay at Gubbio, Italy: The problem of outcrop contamination",
    year = "1986",
    journal = "Geology",
    url = "https://doi.org/10.1130/0091-7613(1986)14<1024:sftcbc>2.0.co;2",
    doi = "10.1130/0091-7613(1986)14<1024:sftcbc>2.0.co;2",
    number = "12",
    openalex = "W2053828156",
    pages = "1024",
    volume = "14"
}

@article{crocket1988distribution,
    author = "Crocket, James H. and Officer, Charles B. and Wezel, Forese C. and Johnson, Gary D.",
    title = "Distribution of noble metals across the Cretaceous/Tertiary boundary at Gubbio, Italy: Iridium variation as a constraint on the duration and nature of Cretaceous/Tertiary boundary events",
    year = "1988",
    journal = "Geology",
    url = "https://doi.org/10.1130/0091-7613(1988)016<0077:donmat>2.3.co;2",
    doi = "10.1130/0091-7613(1988)016<0077:donmat>2.3.co;2",
    number = "1",
    openalex = "W2040219210",
    pages = "77",
    volume = "16"
}

At sites near the Brazos River, Texas, an iridium anomaly and the paleontologic Cretaceous-Tertiary boundary directly overlie a sandstone bed in which coarse-grained sandstone with large clasts of mudstone and reworked carbonate nodules grades upward to wave ripple-laminated, very fine grained sandstone. This bed is the only sandstone bed in a sequence of uppermost Cretaceous to lowermost Paleocene mudstone that records about 1 million years of quiet water deposition in midshelf to outer shelf depths. Conditions for depositing such a sandstone layer at these depths are most consistent with the occurrence of a tsunami about 50 to 100 meters high. The most likely source for such a tsunami at the Cretaceous-Tertiary boundary is a bolidewater impact.

@article{doi101126science2414865567,
    author = "Bourgeois, Joanne and Hansen, Thor A. and Wiberg, Patricia L. and Kauffman, Erle G.",
    title = "A Tsunami Deposit at the Cretaceous-Tertiary Boundary in Texas",
    year = "1988",
    journal = "Science",
    abstract = "At sites near the Brazos River, Texas, an iridium anomaly and the paleontologic Cretaceous-Tertiary boundary directly overlie a sandstone bed in which coarse-grained sandstone with large clasts of mudstone and reworked carbonate nodules grades upward to wave ripple-laminated, very fine grained sandstone. This bed is the only sandstone bed in a sequence of uppermost Cretaceous to lowermost Paleocene mudstone that records about 1 million years of quiet water deposition in midshelf to outer shelf depths. Conditions for depositing such a sandstone layer at these depths are most consistent with the occurrence of a tsunami about 50 to 100 meters high. The most likely source for such a tsunami at the Cretaceous-Tertiary boundary is a bolidewater impact.",
    url = "https://doi.org/10.1126/science.241.4865.567",
    doi = "10.1126/science.241.4865.567",
    openalex = "W2111233732",
    references = "doi101126science23848311237"
}

High‐resolution planktonic foraminiferal analysis of three Brazos River sections indicates a nearly continuous Cretaceous/Tertiary [K/T] boundary sedimentary record second only to the world's most complete record at El Kef, Tunisia. Species extinctions occur over an extended period of time and with two major extinction episodes. The first extinction episode with 46% of the species extinct occurs at and just below [10–15 cm] a short hiatus at the base of a sandy shell hash and clay‐sand unit which was interpreted by Bourgeois et al. [1988] to represent a tsunami bed generated by the K/T boundary bolide impact. The top of this tsunami bed is about 17–20 cm below the K/T boundary as defined by the first appearance of Tertiary planktonic foraminifera. The second extinction phase with 45% of the species extinct occurs 25 cm above the K/T boundary [Zone P0/P1a boundary]. Of the remaining seven surviving Cretaceous species, six gradually disappear during planktonic foraminiferal Subzones P1a and basal P1b. No species extinctions or major faunal assemblage changes are directly associated with the K/T boundary. Iridium distribution is ambiguous, with one peak in the upper part of the tsunami bed and a second peak at the micropaleontologically defined K/T boundary. Relative abundances of dominant species are stable through the Late Maastrichtian, and only minor abundance changes coincide with the first extinction episode or the K/T boundary. The first major faunal change in the dominant species group coincides with the second extinction episode and leads to decline and eventual extinction of this group in Subzone P1a. Species disappearing at the two extinction episodes [46% and 45%] constitute only a small percentage [8% and 5%] of the individuals of the total planktonic foraminiferal population. This suggests that weakened species with low numbers of individuals and sensitive to relatively minor environmental changes were primarily affected by these extinction episodes. Magnetostratigraphy indicates that the first extinction phase began about 310,000 years before the K/T boundary, and the second extinction phase occurred 50,000 years after the K/T boundary. This stepped pattern of species extinctions suggests a progressively stressed ecosystem in continental shelf settings which may be related to an observed sea level regression and global cooling. The hypothesis of a global catastrophic mass extinction at the K/T boundary caused by a large extraterrestrial impact is not supported by the Brazos River planktonic foraminiferal data.

@article{doi101029pa004i003p00287,
    author = "Keller, Gerta",
    title = "Extended Cretaceous/Tertiary boundary extinctions and delayed population change in planktonic foraminifera from Brazos River, Texas",
    year = "1989",
    journal = "Paleoceanography",
    abstract = "High‐resolution planktonic foraminiferal analysis of three Brazos River sections indicates a nearly continuous Cretaceous/Tertiary [K/T] boundary sedimentary record second only to the world's most complete record at El Kef, Tunisia. Species extinctions occur over an extended period of time and with two major extinction episodes. The first extinction episode with 46\% of the species extinct occurs at and just below [10–15 cm] a short hiatus at the base of a sandy shell hash and clay‐sand unit which was interpreted by Bourgeois et al. [1988] to represent a tsunami bed generated by the K/T boundary bolide impact. The top of this tsunami bed is about 17–20 cm below the K/T boundary as defined by the first appearance of Tertiary planktonic foraminifera. The second extinction phase with 45\% of the species extinct occurs 25 cm above the K/T boundary [Zone P0/P1a boundary]. Of the remaining seven surviving Cretaceous species, six gradually disappear during planktonic foraminiferal Subzones P1a and basal P1b. No species extinctions or major faunal assemblage changes are directly associated with the K/T boundary. Iridium distribution is ambiguous, with one peak in the upper part of the tsunami bed and a second peak at the micropaleontologically defined K/T boundary. Relative abundances of dominant species are stable through the Late Maastrichtian, and only minor abundance changes coincide with the first extinction episode or the K/T boundary. The first major faunal change in the dominant species group coincides with the second extinction episode and leads to decline and eventual extinction of this group in Subzone P1a. Species disappearing at the two extinction episodes [46\% and 45\%] constitute only a small percentage [8\% and 5\%] of the individuals of the total planktonic foraminiferal population. This suggests that weakened species with low numbers of individuals and sensitive to relatively minor environmental changes were primarily affected by these extinction episodes. Magnetostratigraphy indicates that the first extinction phase began about 310,000 years before the K/T boundary, and the second extinction phase occurred 50,000 years after the K/T boundary. This stepped pattern of species extinctions suggests a progressively stressed ecosystem in continental shelf settings which may be related to an observed sea level regression and global cooling. The hypothesis of a global catastrophic mass extinction at the K/T boundary caused by a large extraterrestrial impact is not supported by the Brazos River planktonic foraminiferal data.",
    url = "https://doi.org/10.1029/pa004i003p00287",
    doi = "10.1029/pa004i003p00287",
    openalex = "W2017428397",
    references = "ganapathy1981iridium"
}

The iridium anomaly at the Cretaceous-Tertiary (KT) boundary was discovered in the pelagic limestone sequence at Gubbio on the basis of 12 samples analyzed by neutron activation analysis (NAA) and was interpreted as indicating impact of a large extraterrestrial object at exactly the time of the KT mass extinction. Continuing controversy over the shape of the Ir profile at the Gubbio KT boundary and its interpretation called for a more detailed follow-up study. Analysis of a 57-meter-thick, 10-million-year-old part of the Gubbio sequence using improved NAA techniques revealed that there is only one Ir anomaly at the KT boundary, but this anomaly shows an intricate fine structure, the origin of which cannot yet be entirely explained. The KT Ir anomaly peaks in a 1-centimeter-thick clay layer, where the average Ir concentration is 3000 parts per trillion (ppt); this peak is flanked by tails with Ir concentrations of 20 to 80 ppt that rise above a background of 12 to 13 ppt. The fine structure of the tails is probably due in part to lateral reworking, diffusion, burrowing, and perhaps Milankovitch cyclicity.

@article{alvarez1990iridium,
    author = "Alvarez, Walter and Asaro, Frank and Montanari, Alessandro",
    title = "Iridium Profile for 10 Million Years Across the Cretaceous-Tertiary Boundary at Gubbio (Italy)",
    year = "1990",
    journal = "Science",
    abstract = "The iridium anomaly at the Cretaceous-Tertiary (KT) boundary was discovered in the pelagic limestone sequence at Gubbio on the basis of 12 samples analyzed by neutron activation analysis (NAA) and was interpreted as indicating impact of a large extraterrestrial object at exactly the time of the KT mass extinction. Continuing controversy over the shape of the Ir profile at the Gubbio KT boundary and its interpretation called for a more detailed follow-up study. Analysis of a 57-meter-thick, 10-million-year-old part of the Gubbio sequence using improved NAA techniques revealed that there is only one Ir anomaly at the KT boundary, but this anomaly shows an intricate fine structure, the origin of which cannot yet be entirely explained. The KT Ir anomaly peaks in a 1-centimeter-thick clay layer, where the average Ir concentration is 3000 parts per trillion (ppt); this peak is flanked by tails with Ir concentrations of 20 to 80 ppt that rise above a background of 12 to 13 ppt. The fine structure of the tails is probably due in part to lateral reworking, diffusion, burrowing, and perhaps Milankovitch cyclicity.",
    url = "https://doi.org/10.1126/science.11538083",
    doi = "10.1126/science.11538083",
    number = "4988",
    openalex = "W2029363104",
    pages = "1700-1702",
    volume = "250",
    references = "alvarez1980extraterrestrial, doi1010079783642758294, doi101029pa001i004p00495, doi101038321739a0, doi101126science13334591105, doi101126science23247551225, doi10113000167606197788367ucmsag20co2, doi10113000167606197788383ucmsag20co2, doi101130001676061985961407cg20co2, openalexw2989049194"
}

@misc{alvarez1990iridium1,
    author = "Alvarez, W. and Asaro, F. and Montanari, A",
    title = "Iridium profile for 10 million years across the Cretaceous-Tertiary boundary at Gubbio (Italy)",
    year = "1990",
    howpublished = "Science, v. 250, no. 4988, p. 1700-1702",
    note = "talkorigins\_source = {true}; raw\_reference = {Alvarez, W., Asaro, F., and Montanari, A., 1990, Iridium profile for 10 million years across the Cretaceous-Tertiary boundary at Gubbio (Italy): Science, v. 250, no. 4988, p. 1700-1702.}"
}

The iridium anomaly at the Cretaceous-Tertiary (KT) boundary was discovered in the pelagic limestone sequence at Gubbio on the basis of 12 samples analyzed by neutron activation analysis (NAA) and was interpreted as indicating impact of a large extraterrestrial object at exactly the time of the KT mass extinction. Continuing controversy over the shape of the Ir profile at the Gubbio KT boundary and its interpretation called for a more detailed follow-up study. Analysis of a 57-meter-thick, 10-million-year-old part of the Gubbio sequence using improved NAA techniques revealed that there is only one Ir anomaly at the KT boundary, but this anomaly shows an intricate fine structure, the origin of which cannot yet be entirely explained. The KT Ir anomaly peaks in a 1-centimeter-thick clay layer, where average Ir concentration is 3000 parts per trillion (ppt); this peak is flanked by tails with Ir concentrations of 20 to 80 ppt that rise above a background of 12 to 13 ppt. The fine structure of the tails is probably due in part to lateral reworking, diffusion, burrowing, and perhaps Milankovitch cyclicity.

@article{doi101126science11538083,
    author = "Alvarez, W and Asaro, F and Montanari, A",
    title = "Iridium profile for 10 million years across the Cretaceous-Tertiary boundary at Gubbio (Italy).",
    year = "1990",
    journal = "Science (New York, N.Y.)",
    abstract = "The iridium anomaly at the Cretaceous-Tertiary (KT) boundary was discovered in the pelagic limestone sequence at Gubbio on the basis of 12 samples analyzed by neutron activation analysis (NAA) and was interpreted as indicating impact of a large extraterrestrial object at exactly the time of the KT mass extinction. Continuing controversy over the shape of the Ir profile at the Gubbio KT boundary and its interpretation called for a more detailed follow-up study. Analysis of a 57-meter-thick, 10-million-year-old part of the Gubbio sequence using improved NAA techniques revealed that there is only one Ir anomaly at the KT boundary, but this anomaly shows an intricate fine structure, the origin of which cannot yet be entirely explained. The KT Ir anomaly peaks in a 1-centimeter-thick clay layer, where average Ir concentration is 3000 parts per trillion (ppt); this peak is flanked by tails with Ir concentrations of 20 to 80 ppt that rise above a background of 12 to 13 ppt. The fine structure of the tails is probably due in part to lateral reworking, diffusion, burrowing, and perhaps Milankovitch cyclicity.",
    url = "https://pubmed.ncbi.nlm.nih.gov/11538083/",
    doi = "10.1126/science.11538083",
    openalex = "W2029363104",
    pmid = "11538083",
    references = "alvarez1980extraterrestrial, doi1010079783642758294, doi101029pa001i004p00495, doi101038321739a0, doi101126science13334591105, doi101126science23247551225, doi10113000167606197788367ucmsag20co2, doi10113000167606197788383ucmsag20co2, doi101130001676061985961407cg20co2, openalexw2989049194"
}

Trace element, isotopic, and mineralogic studies indicate that the proposed impact at the Cretaceous-Tertiary (K-T) boundary occurred in an ocean basin, although a minor component of continental material is required. The size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact-wave deposits suggest an impact between the Americas. Coarse boundary sediments at sites 151 and 153 in the Colombian Basin and 5- to 450-meter-thick boundary sediments in Cuba may be deposits of a giant wave produced by a nearby oceanic impact. On the southern peninsula of Haiti, a approximately 50-centimeter-thick ejecta layer occurs at the K-T boundary. This ejecta layer is approximately 25 times as thick as that at any known K-T site and suggests an impact site within approximately 1000 kilometers. Seismic reflection profiles suggest that a buried approximately 300-km-diameter candidate structure occurs in the Colombian Basin.

@article{doi101126science2484957843,
    author = "Hildebrand, A. R. and Boynton, W. V.",
    title = "Proximal Cretaceous-Tertiary Boundary Impact Deposits in the Caribbean",
    year = "1990",
    journal = "Science",
    abstract = "Trace element, isotopic, and mineralogic studies indicate that the proposed impact at the Cretaceous-Tertiary (K-T) boundary occurred in an ocean basin, although a minor component of continental material is required. The size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact-wave deposits suggest an impact between the Americas. Coarse boundary sediments at sites 151 and 153 in the Colombian Basin and 5- to 450-meter-thick boundary sediments in Cuba may be deposits of a giant wave produced by a nearby oceanic impact. On the southern peninsula of Haiti, a approximately 50-centimeter-thick ejecta layer occurs at the K-T boundary. This ejecta layer is approximately 25 times as thick as that at any known K-T site and suggests an impact site within approximately 1000 kilometers. Seismic reflection profiles suggest that a buried approximately 300-km-diameter candidate structure occurs in the Colombian Basin.",
    url = "https://doi.org/10.1126/science.248.4957.843",
    doi = "10.1126/science.248.4957.843",
    openalex = "W2072375792",
    references = "doi1010631881078"
}

Relic tektites are associated with a Pt‐group metal abundance anomaly and shocked minerals in a thin marl bed that marks the K‐T boundary on Haiti. The presence of these three impact‐produced materials at the precise K‐T boundary enormously strengthens the Alvarez impact extinction hypothesis. The tektites occur in smectite spherules that have external shapes typical of tektites. Their chemical and physical properties are broadly similar to those of other tektite groups, except that the Haitian tektites have lower Si and higher Fe, Ca, and Na. On average, they contain more Sc, V, Cu, Zn, Ga, Sr, Sn, and Ba and less Cr, Ni, Co, B, Mn, and Hf than Other tektite groups. Amounts of rare earth elements (REE) in the tektites indicate that their progenitor materials were not melted mafic or ultramafic oceanic crust; rather they were sedimentary deposits having a bulk composition of andesite. Rare tektites contain unusually high amounts of CaO (∼20%) and S (0.4%), and these data suggest that some target materials consisted of CaSO 4. Anhydrite beds occur in the subsurface at two candidate impact sites (Chicxulub and Manson). Sm‐Nd isotopic data for the tektites indicate that the melted precursor sediments were most likely deposited less than −400 m.y. between the Late Cretaceous and Silurian periods. Major chemical changes accompanied the diagenetic change of glass to smectite. The Haitian tektites are the first datable impact products in K‐T boundary rocks, and 40 Ar‐ 39 Ar ages of the glass show that the K‐T boundary and impact event are coeval at 64.5±0.1 Ma.

@article{doi10102991je02249,
    author = "Izett, G. A.",
    title = "Tektites in Cretaceous‐Tertiary boundary rocks on Haiti and their bearing on the Alvarez Impact Extinction Hypothesis",
    year = "1991",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Relic tektites are associated with a Pt‐group metal abundance anomaly and shocked minerals in a thin marl bed that marks the K‐T boundary on Haiti. The presence of these three impact‐produced materials at the precise K‐T boundary enormously strengthens the Alvarez impact extinction hypothesis. The tektites occur in smectite spherules that have external shapes typical of tektites. Their chemical and physical properties are broadly similar to those of other tektite groups, except that the Haitian tektites have lower Si and higher Fe, Ca, and Na. On average, they contain more Sc, V, Cu, Zn, Ga, Sr, Sn, and Ba and less Cr, Ni, Co, B, Mn, and Hf than Other tektite groups. Amounts of rare earth elements (REE) in the tektites indicate that their progenitor materials were not melted mafic or ultramafic oceanic crust; rather they were sedimentary deposits having a bulk composition of andesite. Rare tektites contain unusually high amounts of CaO (∼20\%) and S (0.4\%), and these data suggest that some target materials consisted of CaSO 4. Anhydrite beds occur in the subsurface at two candidate impact sites (Chicxulub and Manson). Sm‐Nd isotopic data for the tektites indicate that the melted precursor sediments were most likely deposited less than −400 m.y. between the Late Cretaceous and Silurian periods. Major chemical changes accompanied the diagenetic change of glass to smectite. The Haitian tektites are the first datable impact products in K‐T boundary rocks, and 40 Ar‐ 39 Ar ages of the glass show that the K‐T boundary and impact event are coeval at 64.5±0.1 Ma.",
    url = "https://doi.org/10.1029/91je02249",
    doi = "10.1029/91je02249",
    openalex = "W2128408803"
}

(40)Ar/(39)Ar dating of tektites discovered recently in Cretaceous-Tertiary (K-T) boundary marine sedimentary rocks on Haiti indicates that the K-T boundary and impact event are coeval at 64.5 +/- 0.1 million years ago. Sanidine from a bentonite that lies directly above the K-T boundary in continental, coal-bearing, sedimentary rocks of Montana was also dated and has a (40)Ar/(39)Ar age of 64.6 +/- 0.2 million years ago, which is indistinguishable statistically from the age of the tektites.

@article{doi101126science25250121539,
    author = "Izett, G. A. and Dalrymple, G. Brent and Snee, Lawrence W.",
    title = "40 Ar/ 39 Ar Age of Cretaceous-Tertiary Boundary Tektites from Haiti",
    year = "1991",
    journal = "Science",
    abstract = "(40)Ar/(39)Ar dating of tektites discovered recently in Cretaceous-Tertiary (K-T) boundary marine sedimentary rocks on Haiti indicates that the K-T boundary and impact event are coeval at 64.5 +/- 0.1 million years ago. Sanidine from a bentonite that lies directly above the K-T boundary in continental, coal-bearing, sedimentary rocks of Montana was also dated and has a (40)Ar/(39)Ar age of 64.6 +/- 0.2 million years ago, which is indistinguishable statistically from the age of the tektites.",
    url = "https://doi.org/10.1126/science.252.5012.1539",
    doi = "10.1126/science.252.5012.1539",
    openalex = "W2011903534"
}

The marker bed at the Cretaceous-Tertiary boundary of the Beloc Formation (southern Haiti) contains abundant coarse-grained microtektites and minor amounts of shocked quartz grains in the basal part. The upper part is composed of medium-grained marl with amalgamated microtektite lenses and finer-grained marl lenses disseminated throughout. Field and petrographic observations, and the distribution of planktonic foraminifera suggest that the bed formed from a complex sequence of events. A bolide impact nearby produced microtektites that sett1led to form a nearly pure layer at the base. Vaporized materials with anomalously high extraterrestrial components settled last, along with carbonate sediments. The entire bed became sparsely consolidated. Subsequently, another major disruptive event, perhaps a giant tsunami, partly reworked the initial deposit. Cohesive fragments of the original marker bed mixed with exotic materials were redeposited as lenticular bodies. This process also may have caused further mixing of Cretaceous and Tertiary microfossils, as observed at Beloc and elsewhere.

@article{doi101126science25250131690,
    author = "Maurrasse, F. J. and Sen, Gautam",
    title = "Impacts, Tsunamis, and the Haitian Cretaceous-Tertiary Boundary Layer",
    year = "1991",
    journal = "Science",
    abstract = "The marker bed at the Cretaceous-Tertiary boundary of the Beloc Formation (southern Haiti) contains abundant coarse-grained microtektites and minor amounts of shocked quartz grains in the basal part. The upper part is composed of medium-grained marl with amalgamated microtektite lenses and finer-grained marl lenses disseminated throughout. Field and petrographic observations, and the distribution of planktonic foraminifera suggest that the bed formed from a complex sequence of events. A bolide impact nearby produced microtektites that sett1led to form a nearly pure layer at the base. Vaporized materials with anomalously high extraterrestrial components settled last, along with carbonate sediments. The entire bed became sparsely consolidated. Subsequently, another major disruptive event, perhaps a giant tsunami, partly reworked the initial deposit. Cohesive fragments of the original marker bed mixed with exotic materials were redeposited as lenticular bodies. This process also may have caused further mixing of Cretaceous and Tertiary microfossils, as observed at Beloc and elsewhere.",
    url = "https://doi.org/10.1126/science.252.5013.1690",
    doi = "10.1126/science.252.5013.1690",
    openalex = "W1973143059",
    references = "alvarez1980extraterrestrial, doi101007springerreference4923, doi1010160025322770900010, doi1010160377839888900059, doi101029jb093ib05p04279, doi101029jb094ib12p17465, doi101038343251a0, doi101086625710, doi101126science2414865567, doi101130spe190p305, doi101144pygs3511, openalexw1570283708"
}

(40)Ar/(39)Ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180-kilometer subsurface Chicxulub crater in Yucatán, Mexico, has yielded well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from (40)Ar/(39)Ar ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The (40)Ar/(39)Ar ages, in conjunction with geochemical and petrological similarities, strengthen the recent suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.

@article{doi101126science2575072954,
    author = "Swisher, Carl C. and Grajales-Nishimura, José Manuel and Montanari, Alessandro and Margolis, Stanley V. and Claeys, Philippe and Álvarez, Walter and Renne, Paul R. and Cedillo-Pardoa, Esteban and Maurrasse, F. J. and Curtis, Garniss H. and Smit, Jan and McWilliams, Michael",
    title = "Coeval 40 Ar/ 39 Ar Ages of 65.0 Million Years Ago from Chicxulub Crater Melt Rock and Cretaceous-Tertiary Boundary Tektites",
    year = "1992",
    journal = "Science",
    abstract = "(40)Ar/(39)Ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180-kilometer subsurface Chicxulub crater in Yucatán, Mexico, has yielded well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from (40)Ar/(39)Ar ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The (40)Ar/(39)Ar ages, in conjunction with geochemical and petrological similarities, strengthen the recent suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.",
    url = "https://doi.org/10.1126/science.257.5072.954",
    doi = "10.1126/science.257.5072.954",
    openalex = "W2087549641",
    references = "doi1010160012821x77900607, doi1010160016703777901843, doi101016016896228790025x, doi101126science25250131690, doi101126science2535016176, doi1011300091761319910190867ccapct23co2, doi1011300091761319920200099tbdwcu23co2, doi1015159781400862924, doi10151597814008629241, doi102475ajs2622145, openalexw1586251589"
}

The hypothesis of Cretaceous-Tertiary (K-T) boundary impact on Yucatán, Mexico, predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves. An outcrop along the Arroyo el Mimbral in northeastern Mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic-marl sequence deposited at more than 400 m water depth. The marls were found to be unsuitable for determining magnetostratigraphy, but foraminiferal biostratigraphy places the clastic unit precisely at the K-T boundary. We interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact. The clastic unit comprises three main subunits. (1) The basal "spherule bed" contains glass in the form of tektites and microtektites, glass spherules replaced by chlorite-smectite and calcite, and quartz grains showing probable shock features. This bed is interpreted as a channelized deposit of proximal ejecta. (2) A set of lenticular, massive, graded "laminated beds" contains intraclasts and abundant plant debris, and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water. (3) At the top, several thin "ripple beds" composed of fine sand are separated by clay drapes; they are interpreted as deposits of oscillating currents, perhaps a seiche. An iridium anomaly (921 +/- 23 pg/g) is observed at the top of the ripple beds. Our observations at the Mimbral locality support the hypothesis of a K-T impact on nearby Yucatán.

@article{doi1011300091761319920200099tbdwcu23co2,
    author = "Smit, Jan and Montanari, Alessandro and Swinburne, Nicola H.M. and Álvarez, Walter and Hildebrand, A. R. and Margolis, Stanley V. and Claeys, Philippe and Lowrie, William and Asaro, Frank",
    title = "Tektite-bearing, deep-water clastic unit at the Cretaceous-Tertiary boundary in northeastern Mexico",
    year = "1992",
    journal = "Geology",
    abstract = {The hypothesis of Cretaceous-Tertiary (K-T) boundary impact on Yucatán, Mexico, predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves. An outcrop along the Arroyo el Mimbral in northeastern Mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic-marl sequence deposited at more than 400 m water depth. The marls were found to be unsuitable for determining magnetostratigraphy, but foraminiferal biostratigraphy places the clastic unit precisely at the K-T boundary. We interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact. The clastic unit comprises three main subunits. (1) The basal "spherule bed" contains glass in the form of tektites and microtektites, glass spherules replaced by chlorite-smectite and calcite, and quartz grains showing probable shock features. This bed is interpreted as a channelized deposit of proximal ejecta. (2) A set of lenticular, massive, graded "laminated beds" contains intraclasts and abundant plant debris, and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water. (3) At the top, several thin "ripple beds" composed of fine sand are separated by clay drapes; they are interpreted as deposits of oscillating currents, perhaps a seiche. An iridium anomaly (921 +/- 23 pg/g) is observed at the top of the ripple beds. Our observations at the Mimbral locality support the hypothesis of a K-T impact on nearby Yucatán.},
    url = "https://doi.org/10.1130/0091-7613(1992)020<0099:tbdwcu>2.3.co;2",
    doi = "10.1130/0091-7613(1992)020<0099:tbdwcu>2.3.co;2",
    openalex = "W1972546096"
}

Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater.

@article{doi1011300091761319920200697pidatc23co2,
    author = "Álvarez, Walter and Smit, Jan and Lowrie, William and Asaro, Frank and Margolis, Stanley V. and Claeys, Philippe and Kastner, Miriam and Hildebrand, A. R.",
    title = "Proximal impact deposits at the Cretaceous-Tertiary boundary in the Gulf of Mexico: A restudy of DSDP Leg 77 Sites 536 and 540",
    year = "1992",
    journal = "Geology",
    abstract = "Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater.",
    url = "https://doi.org/10.1130/0091-7613(1992)020<0697:pidatc>2.3.co;2",
    doi = "10.1130/0091-7613(1992)020<0697:pidatc>2.3.co;2",
    openalex = "W2020692402"
}

From the investigations in the East Balkan area, south of the trust and nappe of the Balkan Mountains until now only on the coast of the Black Sea there has been found a real Cretaceous/Tertiary (T/K) boundary. Cretaceous/Tertiary boundary sections in Bulgaria on the coast of the Black Sea near Bjala, 35 km south of Varna have been identified by micro- and nannofossils, magnetic reversals and event markers. The hemipelagic sediments of profile Bjala 2b and Bjala 2c show an iridium enrichment in the boundary clay, a minimum of CaCO3, shocked quartzes, a mass extinction of Cretaceous nannoplankton species, as well as a bloom of survivors at the K/T boundary and the first appearance of new nannoplankton species after the K/T event. The comparison of biostratigraphic and magnetostratigraphic results provides a time scale for the evolution of these new nannoplankton species.

@article{doi1052321geolbalc2353,
    author = "Preisinger, A. and Aslanian, S. and Stoykova, Kristalina and Grass, Friedrich and Mauritsch, Hermann Johann and Scholger, Robert",
    title = "Cretaceous/Tertiary boundary sections in the East Balkan area, Bulgaria",
    year = "1993",
    journal = "Geologica Balcanica",
    abstract = "From the investigations in the East Balkan area, south of the trust and nappe of the Balkan Mountains until now only on the coast of the Black Sea there has been found a real Cretaceous/Tertiary (T/K) boundary. Cretaceous/Tertiary boundary sections in Bulgaria on the coast of the Black Sea near Bjala, 35 km south of Varna have been identified by micro- and nannofossils, magnetic reversals and event markers. The hemipelagic sediments of profile Bjala 2b and Bjala 2c show an iridium enrichment in the boundary clay, a minimum of CaCO3, shocked quartzes, a mass extinction of Cretaceous nannoplankton species, as well as a bloom of survivors at the K/T boundary and the first appearance of new nannoplankton species after the K/T event. The comparison of biostratigraphic and magnetostratigraphic results provides a time scale for the evolution of these new nannoplankton species.",
    url = "https://doi.org/10.52321/geolbalc.23.5.3",
    doi = "10.52321/geolbalc.23.5.3",
    openalex = "W2733508872",
    references = "alvarez1980extraterrestrial, doi1010160012821x9090115e, doi101016037783988590009x, doi101038322794a0, doi101038352420a0, doi101038359819a0, doi101126science23247551225, doi1011300091761319910190867ccapct23co2, doi103929ethza000502199, openalexw62718268"
}

Observations on shocked quartz in Cretaceous-Tertiary (K-T) boundary sediments compellingly tied to Chicxulub crater raise three problems. First, in North America shocked quartz occurs above the main K-T ejecta layer. Second, shocked quartz is more abundant west than east of Chicxulub. Third, shocked quartz reached distances requiring initial velocities up to 8 kilometers per second, corresponding to shock pressures that would produce melt, not the moderate-pressure shock lamellae observed. Shock devolatilization and the expansion of carbon dioxide and water from impacted wet carbonate, producing a warm, accelerating fireball after the initial hot fireball of silicate vapor, may explain all three problems.

@article{doi101126science2695226930,
    author = "Álvarez, Walter and Claeys, Philippe and Kieffer, S. W.",
    title = "Emplacement of Cretaceous-Tertiary Boundary Shocked Quartz from Chicxulub Crater",
    year = "1995",
    journal = "Science",
    abstract = "Observations on shocked quartz in Cretaceous-Tertiary (K-T) boundary sediments compellingly tied to Chicxulub crater raise three problems. First, in North America shocked quartz occurs above the main K-T ejecta layer. Second, shocked quartz is more abundant west than east of Chicxulub. Third, shocked quartz reached distances requiring initial velocities up to 8 kilometers per second, corresponding to shock pressures that would produce melt, not the moderate-pressure shock lamellae observed. Shock devolatilization and the expansion of carbon dioxide and water from impacted wet carbonate, producing a warm, accelerating fireball after the initial hot fireball of silicate vapor, may explain all three problems.",
    url = "https://doi.org/10.1126/science.269.5226.930",
    doi = "10.1126/science.269.5226.930",
    openalex = "W1976136691",
    references = "doi101111j194551001995tb01113x"
}

@article{openalexw2611647714,
    author = "Silvá, Isabella Premoli and Sliter, William V.",
    title = "Cretaceous planktonic foraminiferal biostratigraphy and evolutionary trends from the Bottaccione Section, Gubbio, Italy",
    year = "1995",
    openalex = "W2611647714"
}

@article{ebihara1996chemical,
    author = "Ebihara, Mitsuru and Miura, Tsutomu",
    title = "Chemical characteristics of the Cretaceous-Tertiary boundary layer at Gubbio, Italy",
    year = "1996",
    journal = "Geochimica et Cosmochimica Acta",
    url = "https://doi.org/10.1016/s0016-7037(96)00282-7",
    doi = "10.1016/s0016-7037(96)00282-7",
    number = "24",
    openalex = "W2004246145",
    pages = "5133-5144",
    volume = "60",
    references = "alvarez1980extraterrestrial, doi1010160012821x86901184, doi1010160016703781901848, doi1010160016703784902989, doi1010160016703785900894, doi101016001670378990286x, doi101016001670379290315a, doi101029jz068i014p04209, doi101038285198a0, doi1011300091761319910190867ccapct23co2"
}

The devastating effect on terrestrial plant communities of a bolide impact at the Cretaceous-Tertiary boundary is shown in fossil pollen and spore assemblages by a diverse flora being abruptly replaced by one dominated by a few species of fern. Well documented in North America, this fern spike signals widespread deforestation due to an impact winter or massive wildfires. A Southern Hemisphere record of a fern spike, together with a large iridium anomaly, indicates that the devastation was truly global. Recovery of New Zealand plant communities followed a pattern consistent with major climatic perturbations occurring after an impact winter that was possibly preceded by global wildfires.

@article{doi101126science1064706,
    author = "Vajda, Vivi and Raine, J. Ian and Hollis, Christopher J.",
    title = "Indication of Global Deforestation at the Cretaceous-Tertiary Boundary by New Zealand Fern Spike",
    year = "2001",
    journal = "Science",
    abstract = "The devastating effect on terrestrial plant communities of a bolide impact at the Cretaceous-Tertiary boundary is shown in fossil pollen and spore assemblages by a diverse flora being abruptly replaced by one dominated by a few species of fern. Well documented in North America, this fern spike signals widespread deforestation due to an impact winter or massive wildfires. A Southern Hemisphere record of a fern spike, together with a large iridium anomaly, indicates that the devastation was truly global. Recovery of New Zealand plant communities followed a pattern consistent with major climatic perturbations occurring after an impact winter that was possibly preceded by global wildfires.",
    url = "https://doi.org/10.1126/science.1064706",
    doi = "10.1126/science.1064706",
    openalex = "W2073161320",
    references = "doi10102997je01743, doi101038323253a0, doi101038324148a0, doi101038334665a0, doi101038343251a0, doi101038352420a0, doi101126science22546661030, doi101126science2304722167, doi105962bhltitle60647, openalexw1555522030"
}

Analysis of tetrapod footprints and skeletal material from more than 70 localities in eastern North America shows that large theropod dinosaurs appeared less than 10,000 years after the Triassic-Jurassic boundary and less than 30,000 years after the last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated with an iridium anomaly (up to 285 parts per trillion, with an average maximum of 141 parts per trillion) and a fern spore spike, suggesting that a bolide impact was the cause. Eastern North American dinosaurian diversity reached a stable maximum less than 100,000 years after the boundary, marking the establishment of dinosaur-dominated communities that prevailed for the next 135 million years.

@article{doi101126science1065522,
    author = "Olsen, Paul E. and Kent, Dennis V. and Sues, Hans‐Dieter and Koeberl, Christian and Huber, Heinz and Montanari, Alessandro and Rainforth, Emma C. and Fowell, Sarah J. and Szajna, Michael J. and Hartline, B. W.",
    title = "Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic Boundary",
    year = "2002",
    journal = "Science",
    abstract = "Analysis of tetrapod footprints and skeletal material from more than 70 localities in eastern North America shows that large theropod dinosaurs appeared less than 10,000 years after the Triassic-Jurassic boundary and less than 30,000 years after the last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated with an iridium anomaly (up to 285 parts per trillion, with an average maximum of 141 parts per trillion) and a fern spore spike, suggesting that a bolide impact was the cause. Eastern North American dinosaurian diversity reached a stable maximum less than 100,000 years after the boundary, marking the establishment of dinosaur-dominated communities that prevailed for the next 135 million years.",
    url = "https://doi.org/10.1126/science.1065522",
    doi = "10.1126/science.1065522",
    openalex = "W2107051375",
    references = "doi1010160031018295001719, doi101126science22546661030, doi101126science3616622, doi1023073514751, doi105860choice332752, doi107312lock90868"
}

Micropaleontology studies across the Cretaceous-Tertiary (K-T) boundary from sections at La Ceiba, Bochil, Mexico, and El Kef, Tunisia, suggest a close cause and effect relationship between the Chicxulub impact and the K-T planktic foraminiferal mass extinction. The K-T planktic foraminiferal biostratigraphy and assemblage turnover in Mexico was examined and the approximate deposition timing of K-T-related material (clastic unit) was estimated. On the basis of established biomagnetochronologic calibrations, the first appearance datum (FAD) of Parvularugoglobigerina longiapertura occurred 3.5–5 k.y. after the K-T boundary, and the FADs of Parvularugoglobigerina eugubina, Eoglobigerina simplicissima, and Parasubbotina pseudobulloides occurred 15–17.5 k.y., 28–31 k.y., and 45–55 k.y., respectively, after the K-T boundary. According to estimated average sedimentation rates and estimated age, the K-T red layer at El Kef was probably formed in 20 yr and the deposition of the K-T clastic unit in the Gulf of Mexico was geologically instantaneous. The last appearance of most Maastrichtian species is just below the K-T impact-generated bed, clearly implying a catastrophic planktic foraminiferal mass extinction.

@incollection{doi1011300813723566253,
    author = "Arenillas, Ignacio and Alegret, Laia and Arz, José Antonio and Liesa, Carlos L. and Meléndez, Alfonso and Molina, Eustoquio and Soria, Ana R. and Cedillo-Pardo, E. and Grajales-Nishimura, José Manuel and Rosales-Domínguez, Carmen",
    title = "Cretaceous-Tertiary boundary planktic foraminiferal mass extinction and biochronology at La Ceiba and Bochil, Mexico, and El Kef, Tunisia",
    year = "2002",
    booktitle = "Geological Society of America eBooks",
    abstract = "Micropaleontology studies across the Cretaceous-Tertiary (K-T) boundary from sections at La Ceiba, Bochil, Mexico, and El Kef, Tunisia, suggest a close cause and effect relationship between the Chicxulub impact and the K-T planktic foraminiferal mass extinction. The K-T planktic foraminiferal biostratigraphy and assemblage turnover in Mexico was examined and the approximate deposition timing of K-T-related material (clastic unit) was estimated. On the basis of established biomagnetochronologic calibrations, the first appearance datum (FAD) of Parvularugoglobigerina longiapertura occurred 3.5–5 k.y. after the K-T boundary, and the FADs of Parvularugoglobigerina eugubina, Eoglobigerina simplicissima, and Parasubbotina pseudobulloides occurred 15–17.5 k.y., 28–31 k.y., and 45–55 k.y., respectively, after the K-T boundary. According to estimated average sedimentation rates and estimated age, the K-T red layer at El Kef was probably formed in 20 yr and the deposition of the K-T clastic unit in the Gulf of Mexico was geologically instantaneous. The last appearance of most Maastrichtian species is just below the K-T impact-generated bed, clearly implying a catastrophic planktic foraminiferal mass extinction.",
    url = "https://doi.org/10.1130/0-8137-2356-6.253",
    doi = "10.1130/0-8137-2356-6.253",
    openalex = "W2335107662",
    references = "doi1010160012821x9190113v"
}

The mineralogical, sedimentological, and geochemical information in a large database on the Cretaceous-Tertiary (K-T) boundary is used to document the distribution of impact debris derived from the Chicxulub crater. The database is coupled with a geographic information system (GIS) allowing the plotting of the information on a latest Cretaceous paleogeographic map. The database will be available in part on the internet in the near future, and contains data from 345 K-T boundary sites worldwide. However, relatively few sites are known in South America, Australia, Africa, and in the high latitudes. Major disturbances of sedimentation, such as massive debris flows, failure of platform margins, or significant erosion of Upper Cretaceous layers, occur throughout the Gulf of Mexico. Mass wasting of material also took place in the western and eastern parts of the Atlantic Ocean. Almost 100 K-T boundary sites analyzed for Ir recorded the positive anomaly; Ir is spread homogeneously throughout the world, but is diluted at proximal sites because of the high volume of sediment that was in suspension in the Gulf of Mexico after the impact. Shocked quartz is more common, and maybe larger in size west of the crater. The main advantage of the database is to provide a convenient method to manage the huge amount of data available in the literature, and to reveal patterns or characteristics of the data. The database can help refine the variables used in mathematical models and documents the origin, transport, and deposition of ejecta during a cratering event.

@incollection{doi101130081372356655,
    author = "Claeys, Philippe and Kiessling, Wolfgang and Álvarez, Walter",
    title = "Distribution of Chicxulub ejecta at the Cretaceous-Tertiary boundary",
    year = "2002",
    booktitle = "Geological Society of America eBooks",
    abstract = "The mineralogical, sedimentological, and geochemical information in a large database on the Cretaceous-Tertiary (K-T) boundary is used to document the distribution of impact debris derived from the Chicxulub crater. The database is coupled with a geographic information system (GIS) allowing the plotting of the information on a latest Cretaceous paleogeographic map. The database will be available in part on the internet in the near future, and contains data from 345 K-T boundary sites worldwide. However, relatively few sites are known in South America, Australia, Africa, and in the high latitudes. Major disturbances of sedimentation, such as massive debris flows, failure of platform margins, or significant erosion of Upper Cretaceous layers, occur throughout the Gulf of Mexico. Mass wasting of material also took place in the western and eastern parts of the Atlantic Ocean. Almost 100 K-T boundary sites analyzed for Ir recorded the positive anomaly; Ir is spread homogeneously throughout the world, but is diluted at proximal sites because of the high volume of sediment that was in suspension in the Gulf of Mexico after the impact. Shocked quartz is more common, and maybe larger in size west of the crater. The main advantage of the database is to provide a convenient method to manage the huge amount of data available in the literature, and to reveal patterns or characteristics of the data. The database can help refine the variables used in mathematical models and documents the origin, transport, and deposition of ejecta during a cratering event.",
    url = "https://doi.org/10.1130/0-8137-2356-6.55",
    doi = "10.1130/0-8137-2356-6.55",
    openalex = "W1866467814",
    references = "alvarez1990iridium, doi1010160012821x9190113v, doi101126science11538083, doi101126science2244651867, doi101126science2414865567, doi101126science25250131690, doi101126science2575072954, doi10113000917613198614535scaia20co2, doi1011300091761319980260331tctbcc23co2, doi101130spe190p187, doi101130spe307, doi101146annurevearth27175, doi102110pec98020003, openalexw2687631996"
}

Since the early l990s the Chicxulub crater on Yucatan, Mexico, has been hailed as the smoking gun that proves the hypothesis that an asteroid killed the dinosaurs and caused the mass extinction of many other organisms at the Cretaceous-Tertiary (K-T) boundary 65 million years ago. Here, we report evidence from a previously uninvestigated core, Yaxcopoil-1, drilled within the Chicxulub crater, indicating that this impact predated the K-T boundary by approximately 300,000 years and thus did not cause the end-Cretaceous mass extinction as commonly believed. The evidence supporting a pre-K-T age was obtained from Yaxcopoil-1 based on five independent proxies, each with characteristic signals across the K-T transition: sedimentology, biostratigraphy, magnetostratigraphy, stable isotopes, and iridium. These data are consistent with earlier evidence for a late Maastrichtian age of the microtektite deposits in northeastern Mexico.

@article{doi101073pnas0400396101,
    author = "Keller, Gerta and Adatte, Thierry and Stinnesbeck, Wolfgang and Rebolledo‐Vieyra, M. and Fucugauchi, Jaime Urrutia and Kramar, U. and Stüben, Doris",
    title = "Chicxulub impact predates the K-T boundary mass extinction",
    year = "2004",
    journal = "Proceedings of the National Academy of Sciences",
    abstract = "Since the early l990s the Chicxulub crater on Yucatan, Mexico, has been hailed as the smoking gun that proves the hypothesis that an asteroid killed the dinosaurs and caused the mass extinction of many other organisms at the Cretaceous-Tertiary (K-T) boundary 65 million years ago. Here, we report evidence from a previously uninvestigated core, Yaxcopoil-1, drilled within the Chicxulub crater, indicating that this impact predated the K-T boundary by approximately 300,000 years and thus did not cause the end-Cretaceous mass extinction as commonly believed. The evidence supporting a pre-K-T age was obtained from Yaxcopoil-1 based on five independent proxies, each with characteristic signals across the K-T transition: sedimentology, biostratigraphy, magnetostratigraphy, stable isotopes, and iridium. These data are consistent with earlier evidence for a late Maastrichtian age of the microtektite deposits in northeastern Mexico.",
    url = "https://doi.org/10.1073/pnas.0400396101",
    doi = "10.1073/pnas.0400396101",
    openalex = "W1710439440",
    references = "alvarez1980extraterrestrial, doi1010079783642859168, doi101016s0012821x0000159x, doi101038359819a0, doi101126science2575072954, doi1011300091761319910190867ccapct23co2, doi1011300091761319920200099tbdwcu23co2, doi1011300091761319950230873ynssia23co2, doi1011300091761319980260995adswat23co2, doi101144gsjgs15420265"
}

The sedimentary deposits of the New Jersey Coastal Plain span the Cretaceous/Tertiary boundary and reveal a complex stratigraphy in the northeastern part of their outcrop belt. Newly discovered exposures of the New Egypt Formation in northeastern Monmouth County, New Jersey, indicate that a tongue of this formation, previously thought to be restricted in outcrop to southwestern Monmouth County, extends to the northeast. This formation is sandwiched between the Tinton Formation below and the Hornerstown Formation above. The upper contact is unconformable. Fossils occur in the upper part of the New Egypt Formation and the basal part of the Hornerstown Formation and are concentrated at the formational contactthis accumulation is known as the Main Fossiliferous Layer. The Discoscaphites minardi Assemblage Zone occurs in the New Egypt Formation approximately 2 m below the base of the Hornerstown Formation and contains Discoscaphites minardi

@article{doi1012060003009020042870001cfttbi20co2,
    author = "Landman, Neil H. and Johnson, Ralph O. and Edwards, Lucy E.",
    title = "CEPHALOPODS FROM THE CRETACEOUS/TERTIARY BOUNDARY INTERVAL ON THE ATLANTIC COASTAL PLAIN, WITH A DESCRIPTION OF THE HIGHEST AMMONITE ZONES IN NORTH AMERICA. PART 2. NORTHEASTERN MONMOUTH COUNTY, NEW JERSEY",
    year = "2004",
    journal = "Bulletin of the American Museum of Natural History",
    abstract = "The sedimentary deposits of the New Jersey Coastal Plain span the Cretaceous/Tertiary boundary and reveal a complex stratigraphy in the northeastern part of their outcrop belt. Newly discovered exposures of the New Egypt Formation in northeastern Monmouth County, New Jersey, indicate that a tongue of this formation, previously thought to be restricted in outcrop to southwestern Monmouth County, extends to the northeast. This formation is sandwiched between the Tinton Formation below and the Hornerstown Formation above. The upper contact is unconformable. Fossils occur in the upper part of the New Egypt Formation and the basal part of the Hornerstown Formation and are concentrated at the formational contactthis accumulation is known as the Main Fossiliferous Layer. The Discoscaphites minardi Assemblage Zone occurs in the New Egypt Formation approximately 2 m below the base of the Hornerstown Formation and contains Discoscaphites minardi",
    url = "https://doi.org/10.1206/0003-0090(2004)287<0001:cfttbi>2.0.co;2",
    doi = "10.1206/0003-0090(2004)287<0001:cfttbi>2.0.co;2",
    openalex = "W4231123077",
    references = "doi1011300091761320010291055mctbsi20co2, doi103133pp151, ganapathy1981iridium"
}

Carbon stable-isotope variation through the Cenomanian–Santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven Chalk successions in England. The sections show consistent stratigraphic trends and δ 13 C values that provide a basis for high-resolution correlation. Positive and negative δ 13 C excursions and inflection points on the isotope profiles are used to define 72 isotope events. Key markers are provided by positive δ 13 C excursions of up to +2‰: the Albian/Cenomanian Boundary Event; Mid-Cenomanian Event I; the Cenomanian/Turonian Boundary Event; the Bridgewick, Hitch Wood and Navigation events of Late Turonian age; and the Santonian/Campanian Boundary Event. Isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons. An age-calibrated composite δ 13 C reference curve and an isotope event stratigraphy are constructed using data from the English Chalk. The isotope stratigraphy is applied to successions in Germany, France, Spain and Italy. Correlation with pelagic sections at Gubbio, central Italy, demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the Cenomanian–Turonian stages, confirming established relationships between Tethyan planktonic foraminiferal and Boreal macrofossil biozonations. Correlation of the Coniacian–Santonian stages is less clear cut: magnetostratigraphic evidence for placing the base of Chron 33r near the base of the Upper Santonian is in good agreement with the carbon-iso-tope correlation, but generates significant anomalies regarding the placement of the Santonian and Campanian stage boundaries with respect to Tethyan planktonic foraminiferal and nannofossil zones. Isotope stratigraphy offers a more reliable criterion for detailed correlation of Cenomanian–Santonian strata than biostratigraphy. With the addition of Campanian δ 13 C data from one of the English sections, a composite Cenomanian–Campanian age-calibrated reference curve is presented that can be utilized in future chemostratigraphic studies. The Cenomanian–Campanian carbon-isotope curve is remarkably similar in shape to supposedly eustatic sea-level curves: increasing δ 13 C values accompanying sea-level rise associated with transgression, and falling δ 13 C values characterizing sea-level fall and regression. The correlation between carbon isotopes and sea-level is explained by variations in epicontinental sea area affecting organic-matter burial fluxes: increasing shallow sea-floor area and increased accommodation space accompanying sea-level rise allowed more efficient burial of marine organic matter, with the preferential removal of 12 C from the marine carbon reservoir. During sea-level fall, reduced seafloor area, marine erosion of previously deposited sediments, and exposure of basin margins led to reduced organic-carbon burial fluxes and oxidation of previously deposited organic matter, causing falling δ 13 C values. Additionally, drowning of carbonate platforms during periods of rapid sea-level rise may have reduced the global inorganic relative to the organic carbon flux, further enhancing δ 13 C values, while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition. Variations in nutrient supply, changing rates of oceanic turnover, and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon-isotope ratios.

@article{doi101017s0016756806002421,
    author = "Jarvis, Ian and Gale, Andrew S. and Jenkyns, Hugh C. and Pearce, Martin A.",
    title = "Secular variation in Late Cretaceous carbon isotopes: a new δ 13 C carbonate reference curve for the Cenomanian–Campanian (99.6–70.6 Ma)",
    year = "2006",
    journal = "Geological Magazine",
    abstract = "Carbon stable-isotope variation through the Cenomanian–Santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven Chalk successions in England. The sections show consistent stratigraphic trends and δ 13 C values that provide a basis for high-resolution correlation. Positive and negative δ 13 C excursions and inflection points on the isotope profiles are used to define 72 isotope events. Key markers are provided by positive δ 13 C excursions of up to +2‰: the Albian/Cenomanian Boundary Event; Mid-Cenomanian Event I; the Cenomanian/Turonian Boundary Event; the Bridgewick, Hitch Wood and Navigation events of Late Turonian age; and the Santonian/Campanian Boundary Event. Isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons. An age-calibrated composite δ 13 C reference curve and an isotope event stratigraphy are constructed using data from the English Chalk. The isotope stratigraphy is applied to successions in Germany, France, Spain and Italy. Correlation with pelagic sections at Gubbio, central Italy, demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the Cenomanian–Turonian stages, confirming established relationships between Tethyan planktonic foraminiferal and Boreal macrofossil biozonations. Correlation of the Coniacian–Santonian stages is less clear cut: magnetostratigraphic evidence for placing the base of Chron 33r near the base of the Upper Santonian is in good agreement with the carbon-iso-tope correlation, but generates significant anomalies regarding the placement of the Santonian and Campanian stage boundaries with respect to Tethyan planktonic foraminiferal and nannofossil zones. Isotope stratigraphy offers a more reliable criterion for detailed correlation of Cenomanian–Santonian strata than biostratigraphy. With the addition of Campanian δ 13 C data from one of the English sections, a composite Cenomanian–Campanian age-calibrated reference curve is presented that can be utilized in future chemostratigraphic studies. The Cenomanian–Campanian carbon-isotope curve is remarkably similar in shape to supposedly eustatic sea-level curves: increasing δ 13 C values accompanying sea-level rise associated with transgression, and falling δ 13 C values characterizing sea-level fall and regression. The correlation between carbon isotopes and sea-level is explained by variations in epicontinental sea area affecting organic-matter burial fluxes: increasing shallow sea-floor area and increased accommodation space accompanying sea-level rise allowed more efficient burial of marine organic matter, with the preferential removal of 12 C from the marine carbon reservoir. During sea-level fall, reduced seafloor area, marine erosion of previously deposited sediments, and exposure of basin margins led to reduced organic-carbon burial fluxes and oxidation of previously deposited organic matter, causing falling δ 13 C values. Additionally, drowning of carbonate platforms during periods of rapid sea-level rise may have reduced the global inorganic relative to the organic carbon flux, further enhancing δ 13 C values, while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition. Variations in nutrient supply, changing rates of oceanic turnover, and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon-isotope ratios.",
    url = "https://doi.org/10.1017/s0016756806002421",
    doi = "10.1017/s0016756806002421",
    openalex = "W2117913067",
    references = "doi101007978940156861618, doi101007bf01821208, doi1010160195667188900031, doi101016jcretres200501006, doi101017cbo9780511536045020, doi10113000167606197788383ucmsag20co2, doi101144gsjgs13620175, doi102110pec98020003, doi1037570bgsd19843313, doi1037570bgsd19843319"
}

Geological investigations in the upper Manasquan River Basin, central Monmouth County, New Jersey, reveal a Cretaceous/Tertiary (= Cretaceous/Paleogene) succession consisting of approximately 2 m of the Tinton Formation overlain by 2 m of the Hornerstown Formation. The top of the Tinton Formation consists of a very fossiliferous unit, approximately 20 cm thick, which we refer to as the Pinna Layer. It is laterally extensive and consists mostly of glauconitic minerals and some angular quartz grains. The Pinna Layer is truncated at the top and is overlain by the Hornerstown Formation, which consists of nearly equal amounts of glauconitic minerals and siderite. The base of the Hornerstown Formation is marked by a concentration of siderite nodules containing reworked fossils. This layer also contains a few fossils of organisms that were living in the environment during the time of reworking. At some downdip sites, there is an additional layer (the Burrowed Unit), which is sandwiched between the top of the Pinna Layer and the concentrated bed of nodules. This unit is very thin and is characterized by large burrows piping down material from above.The Pinna Layer is abundantly fossiliferous and represents a diverse, nearshore marine community. It contains approximately 110 species of bivalves, gastropods, cephalopods, echinoids, sponges, annelids, bryozoans, crustaceans, and dinoflagellates. The cephalopods include Eutrephoceras dekayi (Morton, 1834), Pachydiscus (Neodesmoceras) mokotibensis Collignon, 1952, Sphenodiscus lobatus (Tuomey, 1856), Eubaculites carinatus (Morton, 1834), Eubaculites latecarinatus (Brunnschweiler, 1966), Discoscaphites iris (Conrad, 1858), Discoscaphites sphaeroidalis Kennedy and Cobban, 2000, Discoscaphites minardi Landman et al., 2004b, Discoscaphites gulosus (Morton, 1834), and Discoscaphites jerseyensis, n.sp. The dinoflagellates include Palynodinium grallator Gocht, 1970, Thalassiphora pelagica (Eisenack, 1954) Eisenack & Gocht, 1960, Deflandrea galeata (Lejeune-Carpentier, 1942) Lentin & Williams, 1973, and Disphaerogena carposphaeropsis Wetzel, 1933. These ammonites and dinoflagellates are indicative of the uppermost Maastrichtian, corresponding to the upper part of calcareous nannofossil Subzone CC26b.The mode of occurrence of the fossils in the Pinna Layer suggests an autochthonous accumulation with little or no postmortem transport. Many of the benthic organisms are preserved in life position. For example, specimens of Pinna laqueata Conrad, 1858, are oriented in a vertical position, similar to that of modern members of this genus. The echinoids also occur in aggregations of hundreds of individuals, suggesting gregarious feeding behavior. In addition, there are monospecific clusters of baculites and scaphites. These clusters are biological in origin and could not have been produced by hydraulic means. Scaphite jaws are also present, representing the first reports of these structures in the Upper Cretaceous of the Atlantic Coastal Plain. They occur both as isolated specimens and inside the body chamber, and indicate little or no postmortem transport.The Pinna Layer represents a geologically short interval of time. The fact that most of the animals are mature suggests that the community persisted for at least 5–10 years. If multiple generations of animals are present, perhaps reflecting multiple episodes of colonization and burial, then this unit probably represents more time, amounting to several tens of years. The fact that the Pinna Layer is truncated at the top implies a still longer period of time, amounting to hundreds of years. These age estimates are consistent with observed rates of sedimentation in nearshore environments.Iridium analyses of 37 samples of sediment from three sites in the Manasquan River Basin reveal an elevated concentration of iridium of 520 pg/g, on average, at the base of the Pinna Layer. The iridium profile is aymmetric with an abrupt drop off above the base of this u

@article{doi1012060003009020073031cfttbi20co2,
    author = "Landman, Neil H. and Johnson, Ralph O. and Garb, Matthew P. and Edwards, Lucy E. and Kyte, Frank T.",
    title = "CEPHALOPODS FROM THE CRETACEOUS/TERTIARY BOUNDARY INTERVAL ON THE ATLANTIC COASTAL PLAIN, WITH A DESCRIPTION OF THE HIGHEST AMMONITE ZONES IN NORTH AMERICA. PART III. MANASQUAN RIVER BASIN, MONMOUTH COUNTY, NEW JERSEY",
    year = "2007",
    journal = "Bulletin of the American Museum of Natural History",
    abstract = "Geological investigations in the upper Manasquan River Basin, central Monmouth County, New Jersey, reveal a Cretaceous/Tertiary (= Cretaceous/Paleogene) succession consisting of approximately 2 m of the Tinton Formation overlain by 2 m of the Hornerstown Formation. The top of the Tinton Formation consists of a very fossiliferous unit, approximately 20 cm thick, which we refer to as the Pinna Layer. It is laterally extensive and consists mostly of glauconitic minerals and some angular quartz grains. The Pinna Layer is truncated at the top and is overlain by the Hornerstown Formation, which consists of nearly equal amounts of glauconitic minerals and siderite. The base of the Hornerstown Formation is marked by a concentration of siderite nodules containing reworked fossils. This layer also contains a few fossils of organisms that were living in the environment during the time of reworking. At some downdip sites, there is an additional layer (the Burrowed Unit), which is sandwiched between the top of the Pinna Layer and the concentrated bed of nodules. This unit is very thin and is characterized by large burrows piping down material from above.The Pinna Layer is abundantly fossiliferous and represents a diverse, nearshore marine community. It contains approximately 110 species of bivalves, gastropods, cephalopods, echinoids, sponges, annelids, bryozoans, crustaceans, and dinoflagellates. The cephalopods include Eutrephoceras dekayi (Morton, 1834), Pachydiscus (Neodesmoceras) mokotibensis Collignon, 1952, Sphenodiscus lobatus (Tuomey, 1856), Eubaculites carinatus (Morton, 1834), Eubaculites latecarinatus (Brunnschweiler, 1966), Discoscaphites iris (Conrad, 1858), Discoscaphites sphaeroidalis Kennedy and Cobban, 2000, Discoscaphites minardi Landman et al., 2004b, Discoscaphites gulosus (Morton, 1834), and Discoscaphites jerseyensis, n.sp. The dinoflagellates include Palynodinium grallator Gocht, 1970, Thalassiphora pelagica (Eisenack, 1954) Eisenack \& Gocht, 1960, Deflandrea galeata (Lejeune-Carpentier, 1942) Lentin \& Williams, 1973, and Disphaerogena carposphaeropsis Wetzel, 1933. These ammonites and dinoflagellates are indicative of the uppermost Maastrichtian, corresponding to the upper part of calcareous nannofossil Subzone CC26b.The mode of occurrence of the fossils in the Pinna Layer suggests an autochthonous accumulation with little or no postmortem transport. Many of the benthic organisms are preserved in life position. For example, specimens of Pinna laqueata Conrad, 1858, are oriented in a vertical position, similar to that of modern members of this genus. The echinoids also occur in aggregations of hundreds of individuals, suggesting gregarious feeding behavior. In addition, there are monospecific clusters of baculites and scaphites. These clusters are biological in origin and could not have been produced by hydraulic means. Scaphite jaws are also present, representing the first reports of these structures in the Upper Cretaceous of the Atlantic Coastal Plain. They occur both as isolated specimens and inside the body chamber, and indicate little or no postmortem transport.The Pinna Layer represents a geologically short interval of time. The fact that most of the animals are mature suggests that the community persisted for at least 5–10 years. If multiple generations of animals are present, perhaps reflecting multiple episodes of colonization and burial, then this unit probably represents more time, amounting to several tens of years. The fact that the Pinna Layer is truncated at the top implies a still longer period of time, amounting to hundreds of years. These age estimates are consistent with observed rates of sedimentation in nearshore environments.Iridium analyses of 37 samples of sediment from three sites in the Manasquan River Basin reveal an elevated concentration of iridium of 520 pg/g, on average, at the base of the Pinna Layer. The iridium profile is aymmetric with an abrupt drop off above the base of this u",
    url = "https://doi.org/10.1206/0003-0090(2007)303[1:cfttbi]2.0.co;2",
    doi = "10.1206/0003-0090(2007)303[1:cfttbi]2.0.co;2",
    openalex = "W2122840541",
    references = "doi101002qj49707532417, doi101016s0031018299000887, doi101017s0016756800083710, doi101017s0022336000024331, doi101017s0022336000061096, doi101038017199b0, doi101038114085a0, doi101038141548c0, doi101086273307, doi101093nqs5vi146318i, doi101093oso97801985491780010001, doi1011300091761320010291055mctbsi20co2, doi102110pec95040129, doi103133pp151, doi103133pp331b, ganapathy1981iridium, openalexw2751580477, openalexw52563376, openalexw657396478, sohl1960archeogastropoda"
}

Results of investigation of the cosmic matter in the transitional clay layer at the Cretaceous-Paleogene boundary in the Gams section, Eastern Alps, are presented. A great diversity of iron microspherules and particles of different morphologies, pure nickel spherules, awaruite (Fe3Ni) particles, and diamond crystals are discovered. Iron microspherules are also met in the overlying Paleocene deposits, but their diversity there is not great. The discovered metallic microspherules and particles are described, their chemical compositions are presented, and their origin is discussed.

@article{doi101134s1069351308070069,
    author = "Grachev, A. F. and Korchagin, O. A. and Tselmovich, V. A. and Kollmann, Heinz A.",
    title = "Cosmic dust and micrometeorites in the transitional clay layer at the Cretaceous-Paleogene boundary in the gams section (Eastern Alps): Morphology and chemical composition",
    year = "2008",
    journal = "Izvestiya Physics of the Solid Earth",
    abstract = "Results of investigation of the cosmic matter in the transitional clay layer at the Cretaceous-Paleogene boundary in the Gams section, Eastern Alps, are presented. A great diversity of iron microspherules and particles of different morphologies, pure nickel spherules, awaruite (Fe3Ni) particles, and diamond crystals are discovered. Iron microspherules are also met in the overlying Paleocene deposits, but their diversity there is not great. The discovered metallic microspherules and particles are described, their chemical compositions are presented, and their origin is discussed.",
    url = "https://doi.org/10.1134/s1069351308070069",
    doi = "10.1134/s1069351308070069",
    openalex = "W2149151658",
    references = "ebihara1996chemical"
}

The present paper completes a restudy of the main lava pile in the Deccan flood basalt province (trap) of India. Chenet et al. (2008) reported results from the upper third, and this paper reports the lower two thirds of the 3500‐m‐thick composite section. The methods employed are the same, i.e., combined use of petrology, volcanology, chemostratigraphy, morphology, K‐Ar absolute dating, study of sedimentary alteration horizons, and as the main correlation tool, analysis of detailed paleomagnetic remanence directions. The thickness and volume of the flood basalt province studied in this way are therefore tripled. A total of 169 sites from eight new sections are reported in this paper. Together with the results of Chenet et al. (2008), these data represent in total 70% of the 3500‐m combined section of the main Deccan traps province. This lava pile was erupted in some 30 major eruptive periods or single eruptive events (SEE), each with volumes ranging from 1000 to 20,000 km 3 and 41 individual lava units with a typical volume of 1300 km 3. Paleomagnetic analysis shows that some SEEs with thicknesses attaining 200 m were emplaced over distances in excess of 100 km (both likely underestimates, due to outcrop conditions) and up to 800 km. The total time of emission of all combined SEEs could have been (much) less than 10 ka, with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence (so‐called “big red boles”). The number of boles, thickness of the pulses, and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end. On the basis of geochronologic results published by Chenet et al. (2007) and paleontological results from Keller et al. (2008), we propose that volcanism occurred in three rather short, discrete phases or megapulses, an early one at ∼67.5 ± 1 Ma near the C30r/C30n transition and the two largest around 65 ± 1 Ma, one entirely within C29r just before the K‐T boundary, the other shortly afterward spanning the C29r/C29n reversal. We next estimate sulfur dioxide (likely a major agent of environmental stress) amounts and fluxes released by SEEs: they would have ranged from 5 to 100 Gt and 0.1 to 1 Gt/a, respectively, over durations possibly as short as 100 years for each SEE. The chemical input of the Chicxulub impact would have been on the same order as that of a very large single pulse. The impact, therefore, appears as important but incremental, neither the sole nor main cause of the Cretaceous‐Tertiary mass extinctions.

@article{doi1010292008jb005644,
    author = "Chenet, A. and Courtillot, Vincent and Fluteau, Frédéric and Gérard, Martine and Quidelleur, Xavier and Khadri, S. and Subbarao, Κ. V. and Thórdarson, T.",
    title = "Determination of rapid Deccan eruptions across the Cretaceous‐Tertiary boundary using paleomagnetic secular variation: 2. Constraints from analysis of eight new sections and synthesis for a 3500‐m‐thick composite section",
    year = "2009",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The present paper completes a restudy of the main lava pile in the Deccan flood basalt province (trap) of India. Chenet et al. (2008) reported results from the upper third, and this paper reports the lower two thirds of the 3500‐m‐thick composite section. The methods employed are the same, i.e., combined use of petrology, volcanology, chemostratigraphy, morphology, K‐Ar absolute dating, study of sedimentary alteration horizons, and as the main correlation tool, analysis of detailed paleomagnetic remanence directions. The thickness and volume of the flood basalt province studied in this way are therefore tripled. A total of 169 sites from eight new sections are reported in this paper. Together with the results of Chenet et al. (2008), these data represent in total 70\% of the 3500‐m combined section of the main Deccan traps province. This lava pile was erupted in some 30 major eruptive periods or single eruptive events (SEE), each with volumes ranging from 1000 to 20,000 km 3 and 41 individual lava units with a typical volume of 1300 km 3. Paleomagnetic analysis shows that some SEEs with thicknesses attaining 200 m were emplaced over distances in excess of 100 km (both likely underestimates, due to outcrop conditions) and up to 800 km. The total time of emission of all combined SEEs could have been (much) less than 10 ka, with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence (so‐called “big red boles”). The number of boles, thickness of the pulses, and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end. On the basis of geochronologic results published by Chenet et al. (2007) and paleontological results from Keller et al. (2008), we propose that volcanism occurred in three rather short, discrete phases or megapulses, an early one at ∼67.5 ± 1 Ma near the C30r/C30n transition and the two largest around 65 ± 1 Ma, one entirely within C29r just before the K‐T boundary, the other shortly afterward spanning the C29r/C29n reversal. We next estimate sulfur dioxide (likely a major agent of environmental stress) amounts and fluxes released by SEEs: they would have ranged from 5 to 100 Gt and 0.1 to 1 Gt/a, respectively, over durations possibly as short as 100 years for each SEE. The chemical input of the Chicxulub impact would have been on the same order as that of a very large single pulse. The impact, therefore, appears as important but incremental, neither the sole nor main cause of the Cretaceous‐Tertiary mass extinctions.",
    url = "https://doi.org/10.1029/2008jb005644",
    doi = "10.1029/2008jb005644",
    openalex = "W2066351018",
    references = "doi1010160012821x86901184, doi101016jepsl200801015, doi101016s0012825200000374, doi101016s1631071303000063, doi1010292000jb000050, doi10102994jb03098, doi10108008120090500170393, doi101098rspa19530064, doi101111j1365246x1980tb02601x, openalexw1520428197, openalexw1575579655, openalexw2974218786"
}

The Cretaceous-Paleogene boundary approximately 65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.

@article{doi101126science1177265,
    author = "Schulte, Peter and Alegret, Laia and Arenillas, Ignacio and Arz, José Antonio and Barton, P. J. and Bown, Paul R. and Bralower, Timothy J. and Christeson, Gail and Claeys, Philippe and Cockell, Charles S. and Collins, G. S. and Deutsch, A. and Goldin, Tamara and Goto, Kazuhisa and Grajales-Nishimura, José Manuel and Grieve, R. A. F. and Gulick, S. P. S. and Johnson, Kirk R. and Kiessling, Wolfgang and Koeberl, Christian and Kring, D. A. and MacLeod, Kenneth G. and Matsui, Takafumi and Melosh, J. and Montanari, Alessandro and Morgan, Joanna and Neal, C. R. and Nichols, Douglas J. and Norris, Richard D. and Pierazzo, E. and Ravizza, Greg and Rebolledo‐Vieyra, M. and Reimold, W. U. and Robin, Éric and Salge, T. and Speijer, Robert P. and Sweet, A R and Urrutia‐Fucugauchi, J. and Vajda, Vivi and Whalen, Michael T. and Willumsen, Pi Suhr",
    title = "The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary",
    year = "2010",
    journal = "Science",
    abstract = "The Cretaceous-Paleogene boundary approximately 65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.",
    url = "https://doi.org/10.1126/science.1177265",
    doi = "10.1126/science.1177265",
    openalex = "W2160490562",
    references = "alvarez1980extraterrestrial, doi101016jepsl200605041, doi101016jepsl200607020, doi101016jepsl200902019, doi101016jpalaeo200702037, doi101016jpalaeo200709016, doi101017cbo9780511535536, doi1010292008jb005644, doi10102996rg03038, doi10102997je01743, doi101038285198a0, doi101073pnas0802597105, doi101126science1064706, doi101126science20844481095, doi1011300091761319910190867ccapct23co2, doi101130081372356655, doi1011302007242401, doi101146annurevearth27175, doi101146annurevecolsys35021103105715"
}

Abstract The La Popa Basin in north‐eastern Mexico features outstanding, continuous three‐dimensional exposures of the Cretaceous–Palaeogene boundary event deposit in shallow shelf environments pierced by salt stocks. In the area to the south‐east of the El Papalote diapir, the Cretaceous–Palaeogene deposit consists of two superimposed sedimentary units and erosively overlies upper Maastrichtian sand‐siltstones with soft‐sediment deformation and liquefaction structures. The basal unit 1 is an up to 8 m thick chaotic, carbonate‐rich bed that discontinuously fills incised gutters and channels. Besides abundant silicic and carbonate ejecta spherules from the Chicxulub impact, unit 1 includes large sandstone boulders and abundant shallow‐water debris (for example, mud clasts, algae, bivalve shells, gastropod shells and vertebrate remains). Unit 1 is conformably overlain by unit 2. Distal to the diapir, unit 2 consists of a centimetre to decimetre‐thick conglomeratic, coarse bioclast and spherule‐bearing sandstone bed. Closer to the diapir, unit 2 becomes a metre‐thick series of four to eight conglomeratic to fine‐grained graded sandstone beds rich in shell debris and ejecta spherules. Unit 2 is conformably overlain by structureless to parallel laminated sandstone beds that may mark the return to the pre‐event depositional regime. The sedimentary characteristics of the Cretaceous–Palaeogene deposit, including its erosive base, its sheet‐like geometry, the presence of multiple, graded beds, evidence for upper flow regime conditions and the absence of bioturbation, support an origin by a short‐term multiphase depositional event. The occurrence of soft‐sediment deformation structures (for example, liquefaction) below the Cretaceous–Palaeogene deposit suggests that earthquakes were the first to occur at La Popa. Then, shelf collapse and strong backflow from the first tsunami waves may have triggered erosion and deposition by violent ejecta‐rich hyperconcentrated density flows (unit 1). Subsequently, a series of concentrated density flows resulting from tsunami backwash surges may have deposited the multiple‐graded bedding structures of unit 2. The specific depositional sequence and the Fe‐Mg‐rich as well as Si‐K‐rich composition of the ejecta spherules both provide a critical link to the well‐known deep marine Cretaceous–Palaeogene boundary sites in the adjacent Burgos basin in north‐eastern Mexico. Moreover, the pulse‐like input of Chicxulub ejecta material at the base of the event deposit allows for correlation with other Cretaceous–Palaeogene boundary sites in the Gulf of Mexico and the Atlantic, as well as in Central and Northern America. The presence of diverse dinosaur and mosasur bones and teeth in the event deposit is the first observation of such remains together with Chicxulub ejecta material. These findings indicate that dinosaurs lived in the area during the latest Maastrichtian and suggest that the tsunami waves not only eroded deltas and estuaries but the coastal plain as well.

@article{doi101111j13653091201101274x,
    author = "Schulte, P. and Smit, Jan and Deutsch, A. and Salge, T. and Friese, Andrea and Beichel, Kilian",
    title = "Tsunami backwash deposits with Chicxulub impact ejecta and dinosaur remains from the Cretaceous–Palaeogene boundary in the La Popa Basin, Mexico",
    year = "2011",
    journal = "Sedimentology",
    abstract = "Abstract The La Popa Basin in north‐eastern Mexico features outstanding, continuous three‐dimensional exposures of the Cretaceous–Palaeogene boundary event deposit in shallow shelf environments pierced by salt stocks. In the area to the south‐east of the El Papalote diapir, the Cretaceous–Palaeogene deposit consists of two superimposed sedimentary units and erosively overlies upper Maastrichtian sand‐siltstones with soft‐sediment deformation and liquefaction structures. The basal unit 1 is an up to 8 m thick chaotic, carbonate‐rich bed that discontinuously fills incised gutters and channels. Besides abundant silicic and carbonate ejecta spherules from the Chicxulub impact, unit 1 includes large sandstone boulders and abundant shallow‐water debris (for example, mud clasts, algae, bivalve shells, gastropod shells and vertebrate remains). Unit 1 is conformably overlain by unit 2. Distal to the diapir, unit 2 consists of a centimetre to decimetre‐thick conglomeratic, coarse bioclast and spherule‐bearing sandstone bed. Closer to the diapir, unit 2 becomes a metre‐thick series of four to eight conglomeratic to fine‐grained graded sandstone beds rich in shell debris and ejecta spherules. Unit 2 is conformably overlain by structureless to parallel laminated sandstone beds that may mark the return to the pre‐event depositional regime. The sedimentary characteristics of the Cretaceous–Palaeogene deposit, including its erosive base, its sheet‐like geometry, the presence of multiple, graded beds, evidence for upper flow regime conditions and the absence of bioturbation, support an origin by a short‐term multiphase depositional event. The occurrence of soft‐sediment deformation structures (for example, liquefaction) below the Cretaceous–Palaeogene deposit suggests that earthquakes were the first to occur at La Popa. Then, shelf collapse and strong backflow from the first tsunami waves may have triggered erosion and deposition by violent ejecta‐rich hyperconcentrated density flows (unit 1). Subsequently, a series of concentrated density flows resulting from tsunami backwash surges may have deposited the multiple‐graded bedding structures of unit 2. The specific depositional sequence and the Fe‐Mg‐rich as well as Si‐K‐rich composition of the ejecta spherules both provide a critical link to the well‐known deep marine Cretaceous–Palaeogene boundary sites in the adjacent Burgos basin in north‐eastern Mexico. Moreover, the pulse‐like input of Chicxulub ejecta material at the base of the event deposit allows for correlation with other Cretaceous–Palaeogene boundary sites in the Gulf of Mexico and the Atlantic, as well as in Central and Northern America. The presence of diverse dinosaur and mosasur bones and teeth in the event deposit is the first observation of such remains together with Chicxulub ejecta material. These findings indicate that dinosaurs lived in the area during the latest Maastrichtian and suggest that the tsunami waves not only eroded deltas and estuaries but the coastal plain as well.",
    url = "https://doi.org/10.1111/j.1365-3091.2011.01274.x",
    doi = "10.1111/j.1365-3091.2011.01274.x",
    openalex = "W2153888939",
    references = "doi101016jepsl200607020, doi101016s0037073896000577, doi101111j194551001995tb01113x"
}

In the light of integrated biostratigraphic and geochemical data, a complete shallow-marine succession across the Cretaceous—Palaeogene (K—Pg) boundary, with the critical boundary clay coupled with a burrowed siliceous chalk (“opoka” in Polish geological literature), possibly equivalent of the basal Danian Cerithium Limestone in Denmark, has been discovered at Lechowka near Chelm, SE Poland. An extraterrestrial signature marking the K—Pg boundary is confirmed by anomalously high amounts of iridium (up to 9.8 ppb) and other siderophile elements (especially Au and Ni), as well as by an elevated Ir/Au ratio consistent with a chondrite meteoritic composition. The major positive iridium spike surprisingly occurs in Maastrichtian marls, 10 cm below the boundary clay interval, which can be explained by diagenetic mobilisation and re-concentration of the impact-derived components. Thus, intensively infiltrating, humic acid-rich ground waters during the long-lasting Palaeogene weathering in tropical humid regimes...

@article{doi104202app20100062,
    author = "Racki, Grzegorz and Machalski, Marcin and Koeberl, Christian and Harasimiuk, Marian",
    title = "The Weathering-Modified Iridium Record of a New Cretaceous—Palaeogene Site at Lechówka Near Chełm, SE Poland, and Its Palaeobiologic Implications",
    year = "2011",
    journal = "Acta Palaeontologica Polonica",
    abstract = "In the light of integrated biostratigraphic and geochemical data, a complete shallow-marine succession across the Cretaceous—Palaeogene (K—Pg) boundary, with the critical boundary clay coupled with a burrowed siliceous chalk (“opoka” in Polish geological literature), possibly equivalent of the basal Danian Cerithium Limestone in Denmark, has been discovered at Lechowka near Chelm, SE Poland. An extraterrestrial signature marking the K—Pg boundary is confirmed by anomalously high amounts of iridium (up to 9.8 ppb) and other siderophile elements (especially Au and Ni), as well as by an elevated Ir/Au ratio consistent with a chondrite meteoritic composition. The major positive iridium spike surprisingly occurs in Maastrichtian marls, 10 cm below the boundary clay interval, which can be explained by diagenetic mobilisation and re-concentration of the impact-derived components. Thus, intensively infiltrating, humic acid-rich ground waters during the long-lasting Palaeogene weathering in tropical humid regimes...",
    url = "https://doi.org/10.4202/app.2010.0062",
    doi = "10.4202/app.2010.0062",
    openalex = "W2021476555",
    references = "ebihara1996chemical"
}

@article{hull2011mechanisms,
    author = "Hull, Pincelli M. and Franks, Peter J.S. and Norris, Richard D.",
    title = "Mechanisms and models of iridium anomaly shape across the Cretaceous–Paleogene boundary",
    year = "2011",
    journal = "Earth and Planetary Science Letters",
    url = "https://doi.org/10.1016/j.epsl.2010.10.031",
    doi = "10.1016/j.epsl.2010.10.031",
    number = "1-2",
    openalex = "W2079087978",
    pages = "98-106",
    volume = "301",
    references = "crocket1988distribution, doi1010160012821x86901184, doi101016jepsl200707011, doi101016jjmarsys200803011, doi101016jpalaeo200709016, doi101029jc080i021p03032, doi101126science1089209, doi101126science1177265, doi101126science22746911161, doi101146annurevearth27175, doi103354meps158275"
}

An impact‐induced osmium (Os) isotope excursion provides a unique means of assessing the completeness of marine Cretaceous‐Paleogene (K‐Pg) boundary sections, and surmounting challenges associated with constraining the time scale of the Earth system recovery from this extreme perturbation. A model of the recovery of seawater 187 Os/ 188 Os following the impact event allows independent estimates of the time elapsed since the impact, which can be directly compared to time estimates derived from biostratigraphy, magnetostratigraphy and cyclostratigraphy. This approach is tested using data from three deep ocean sites cored by the Ocean Drilling Program (ODP). Data from ODP 1262B (South Atlantic) and ODP 690C (Southern Ocean) display the expected 187 Os/ 188 Os minimum very close to the biostratigraphically defined K‐Pg boundary and yield Os‐based accumulation rate estimates similar to those obtained from magnetostratigraphy and orbital tuning. In contrast, the 187 Os/ 188 Os minimum in ODP 1209C (Western Pacific) occurs ≈9 cm below the K‐Pg boundary. Low Os concentrations throughout the boundary interval and an implausibly rapid recovery to higher, pre‐impact 187 Os/ 188 Os ratios provide strong evidence for a previously unrecognized gap in the K‐Pg interval of Site 1209. Results presented here provide strong empirical evidence that Os isotope data are uniquely valuable in assessing the completeness and accumulation rates of earliest Paleogene sediments from the deep sea. They are of broad interest because they have implications for astronomical tuning of the geologic time scale and illustrate that whole ocean geochemical perturbations can provide an alternative to biostratigraphy for correlation and timekeeping during abrupt biotic events.

@article{doi1010292012pa002301,
    author = "Ravizza, Greg and VonderHaar, D.L.",
    title = "A geochemical clock in earliest Paleogene pelagic carbonates based on the impact‐induced Os isotope excursion at the Cretaceous‐Paleogene boundary",
    year = "2012",
    journal = "Paleoceanography",
    abstract = "An impact‐induced osmium (Os) isotope excursion provides a unique means of assessing the completeness of marine Cretaceous‐Paleogene (K‐Pg) boundary sections, and surmounting challenges associated with constraining the time scale of the Earth system recovery from this extreme perturbation. A model of the recovery of seawater 187 Os/ 188 Os following the impact event allows independent estimates of the time elapsed since the impact, which can be directly compared to time estimates derived from biostratigraphy, magnetostratigraphy and cyclostratigraphy. This approach is tested using data from three deep ocean sites cored by the Ocean Drilling Program (ODP). Data from ODP 1262B (South Atlantic) and ODP 690C (Southern Ocean) display the expected 187 Os/ 188 Os minimum very close to the biostratigraphically defined K‐Pg boundary and yield Os‐based accumulation rate estimates similar to those obtained from magnetostratigraphy and orbital tuning. In contrast, the 187 Os/ 188 Os minimum in ODP 1209C (Western Pacific) occurs ≈9 cm below the K‐Pg boundary. Low Os concentrations throughout the boundary interval and an implausibly rapid recovery to higher, pre‐impact 187 Os/ 188 Os ratios provide strong evidence for a previously unrecognized gap in the K‐Pg interval of Site 1209. Results presented here provide strong empirical evidence that Os isotope data are uniquely valuable in assessing the completeness and accumulation rates of earliest Paleogene sediments from the deep sea. They are of broad interest because they have implications for astronomical tuning of the geologic time scale and illustrate that whole ocean geochemical perturbations can provide an alternative to biostratigraphy for correlation and timekeeping during abrupt biotic events.",
    url = "https://doi.org/10.1029/2012pa002301",
    doi = "10.1029/2012pa002301",
    openalex = "W1556125941",
    references = "hull2011mechanisms"
}

Mass extinctions manifest in Earth's geologic record were turning points in biotic evolution. We present (40)Ar/(39)Ar data that establish synchrony between the Cretaceous-Paleogene boundary and associated mass extinctions with the Chicxulub bolide impact to within 32,000 years. Perturbation of the atmospheric carbon cycle at the boundary likely lasted less than 5000 years, exhibiting a recovery time scale two to three orders of magnitude shorter than that of the major ocean basins. Low-diversity mammalian fauna in the western Williston Basin persisted for as little as 20,000 years after the impact. The Chicxulub impact likely triggered a state shift of ecosystems already under near-critical stress.

@article{doi101126science1230492,
    author = "Renne, Paul R. and Deino, Alan L. and Hilgen, F.J. and Kuiper, Klaudia F. and Mark, Darren F. and Mitchell, William S. and Morgan, Leah E. and Mundil, Roland and Smit, Jan",
    title = "Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary",
    year = "2013",
    journal = "Science",
    abstract = "Mass extinctions manifest in Earth's geologic record were turning points in biotic evolution. We present (40)Ar/(39)Ar data that establish synchrony between the Cretaceous-Paleogene boundary and associated mass extinctions with the Chicxulub bolide impact to within 32,000 years. Perturbation of the atmospheric carbon cycle at the boundary likely lasted less than 5000 years, exhibiting a recovery time scale two to three orders of magnitude shorter than that of the major ocean basins. Low-diversity mammalian fauna in the western Williston Basin persisted for as little as 20,000 years after the impact. The Chicxulub impact likely triggered a state shift of ecosystems already under near-critical stress.",
    url = "https://doi.org/10.1126/science.1230492",
    doi = "10.1126/science.1230492",
    openalex = "W1964523361",
    references = "doi101007s1091400569434, doi101016jchemgeo200503011, doi101016jcretres200805030, doi101016jepsl200902019, doi101016jepsl201107015, doi101016jgca2006061563, doi101016jgca201006017, doi101016jgca201106021, doi101016s0009254197001599, doi101016s0012821x03005570, doi101016s1631071303000063, doi1010292008jb005644, doi101038nature08227, doi101038nature11018, doi1010510004636120041335, doi10105100046361201116836, doi101073pnas802627, doi101126science1116412, doi101126science1154339, doi101126science1177265, doi101126science22346411177, doi101126science25250131690, doi101126science2575072954, doi1011270078042120120020, doi10113000917613198614279ssaedt20co2, doi1011300091761319910190867ccapct23co2, doi101130spe332, doi101146annurevecolsys35021103105715, doi101666070341, openalexw610180004"
}

The mass extinction at the Cretaceous-Paleogene boundary, ∼ 66 Ma, is thought to be caused by the impact of an asteroid at Chicxulub, present-day Mexico. Although the precise mechanisms that led to this mass extinction remain enigmatic, most postulated scenarios involve a short-lived global cooling, a so-called "impact winter" phase. Here we document a major decline in sea surface temperature during the first months to decades following the impact event, using TEX86 paleothermometry of sediments from the Brazos River section, Texas. We interpret this cold spell to reflect, to our knowledge, the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere, blocking incoming solar radiation. This impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis.

@article{doi101073pnas1319253111,
    author = "Vellekoop, Johan and Sluijs, Appy and Smit, Jan and Schouten, Stefan and Weijers, Johan W.H. and Damsté, Jaap S. Sinninghe and Brinkhuis, Henk",
    title = "Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary",
    year = "2014",
    journal = "Proceedings of the National Academy of Sciences",
    abstract = {The mass extinction at the Cretaceous-Paleogene boundary, ∼ 66 Ma, is thought to be caused by the impact of an asteroid at Chicxulub, present-day Mexico. Although the precise mechanisms that led to this mass extinction remain enigmatic, most postulated scenarios involve a short-lived global cooling, a so-called "impact winter" phase. Here we document a major decline in sea surface temperature during the first months to decades following the impact event, using TEX86 paleothermometry of sediments from the Brazos River section, Texas. We interpret this cold spell to reflect, to our knowledge, the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere, blocking incoming solar radiation. This impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis.},
    url = "https://doi.org/10.1073/pnas.1319253111",
    doi = "10.1073/pnas.1319253111",
    openalex = "W2105771959",
    references = "alvarez1980extraterrestrial, doi101016jgca201005027, doi101016jorggeochem200607018, doi101016jpalaeo200702037, doi101016s0012821x02009792, doi10102997je01743, doi101038285198a0, doi10103835097000, doi101073pnas0802597105, doi101126science1177265, doi101126science2414865567, doi101130081372356655, doi101146annurevearth33092203122654, ganapathy1981iridium"
}

ABSTRACT The Cretaceous and Paleogene pelagic limestone and marl formations of the Umbria-Marche Apennines of north-central Italy have proven to be exceptional recorders of the history of Earth and of life on Earth, and they have been the subject of numerous geological and paleontological studies over the last several decades. Founded a quarter century ago, in 1992, the Geological Observatory of Coldigioco is a research and teaching center focused on these exceptional rocks. This chapter is a historical introduction that briefly reviews the highlights of the lithologic, biostratigraphic, sedimentologic, magnetostratigraphic, impact-stratigraphic, geochemical, geochronological, time-scale, and cyclostratigraphical research done on the Umbria-Marche stratigraphic sequence, much of it facilitated by the Geological Observatory of Coldigioco. This review covers work up to the Coldigioco 25th anniversary Penrose conference in September 2017; it does not treat work presented at that conference or done since then. A remarkable irony is that a century ago, the Umbria-Marche Cretaceous–Paleogene sequence was so difficult to date that early work contained an error of ~35 m.y., but now there is a reasonable hope that this entire section may eventually be dated to an accuracy and precision of ~10,000 yr. This review begins with an homage to the little medieval city of Gubbio, its wild Festa dei Ceri, and its Bottaccione Gorge, where much of the research described here has been done. The review ends with three points of perspective. The first is the notion that sometimes geology can be done by looking up at the sky, and astronomy can be done by looking down at Earth, with much of the Coldigioco-based research being of this latter kind. The second is the observation that geology and paleontology are contributing far more new information to Big History—to our integrated knowledge of the past—than any other historical field in the humanities or sciences. The third is that three of the major scientific revolutions of geology in the twentieth century have direct connections to the Umbria-Marche stratigraphic sequence—the turbidite revolution, the development of plate tectonics, and the downfall of strict uniformitarianism.

@misc{doi1011302019254201,
    author = "Álvarez, Walter",
    title = "A review of the Earth history record in the Cretaceous, Paleogene, and Neogene pelagic carbonates of the Umbria-Marche Apennines (Italy): Twenty-five years of the Geological Observatory of Coldigioco",
    year = "2019",
    booktitle = "Geological Society of America eBooks",
    abstract = "ABSTRACT The Cretaceous and Paleogene pelagic limestone and marl formations of the Umbria-Marche Apennines of north-central Italy have proven to be exceptional recorders of the history of Earth and of life on Earth, and they have been the subject of numerous geological and paleontological studies over the last several decades. Founded a quarter century ago, in 1992, the Geological Observatory of Coldigioco is a research and teaching center focused on these exceptional rocks. This chapter is a historical introduction that briefly reviews the highlights of the lithologic, biostratigraphic, sedimentologic, magnetostratigraphic, impact-stratigraphic, geochemical, geochronological, time-scale, and cyclostratigraphical research done on the Umbria-Marche stratigraphic sequence, much of it facilitated by the Geological Observatory of Coldigioco. This review covers work up to the Coldigioco 25th anniversary Penrose conference in September 2017; it does not treat work presented at that conference or done since then. A remarkable irony is that a century ago, the Umbria-Marche Cretaceous–Paleogene sequence was so difficult to date that early work contained an error of \textasciitilde 35 m.y., but now there is a reasonable hope that this entire section may eventually be dated to an accuracy and precision of \textasciitilde 10,000 yr. This review begins with an homage to the little medieval city of Gubbio, its wild Festa dei Ceri, and its Bottaccione Gorge, where much of the research described here has been done. The review ends with three points of perspective. The first is the notion that sometimes geology can be done by looking up at the sky, and astronomy can be done by looking down at Earth, with much of the Coldigioco-based research being of this latter kind. The second is the observation that geology and paleontology are contributing far more new information to Big History—to our integrated knowledge of the past—than any other historical field in the humanities or sciences. The third is that three of the major scientific revolutions of geology in the twentieth century have direct connections to the Umbria-Marche stratigraphic sequence—the turbidite revolution, the development of plate tectonics, and the downfall of strict uniformitarianism.",
    url = "https://doi.org/10.1130/2019.2542(01)",
    doi = "10.1130/2019.2542(01)",
    openalex = "W3112503786",
    references = "montanari1986spherules"
}

ABSTRACT The complete and well-studied pelagic carbonate successions from the Umbria-Marche basin (Italy) permit the study of the event-rich stratigraphic interval around the Cretaceous-Paleogene boundary (e.g., Deccan volcanism, boundary impact, Paleocene recovery, and climate). To test the robustness of various proxy records (bulk carbonate δ13C, δ18O, 87Sr/86Sr, and Ca, Fe, Sr, and Mn concentrations) inside the Umbria-Marche basin, several stratigraphically equivalent sections were investigated (Bottaccione Gorge, Contessa Highway, Fornaci East quarry, Frontale, Morello, and Petriccio core). Besides the classical Gubbio sections of Bottaccione and Contessa, the new Morello section is put forward as an alternative location for this stratigraphic interval because it is less altered by burial diagenesis. Elemental profiles (Ca, Fe, Sr, Mn) acquired by handheld X-ray fluorescence (pXRF) efficiently provide regional chemostratigraphic and paleoenvironmental information. The Deccan volcanism, the Cretaceous-Paleogene boundary, the characteristic pattern of the Sr/Ca profile across the boundary driven by the extinction and recovery of coccolithophores, and the Dan-C2 hyperthermal event are examples of such recorded paleoenvironmental events. Moreover, cyclostratigraphic analyses of proxies of detrital input (magnetic susceptibility and Fe concentrations) show the imprint in the sedimentary record of a 2.4 m.y. eccentricity minimum around 66.45–66.25 Ma, and suggest that the occurrence of the Dan-C2 hyperthermal event was astronomically paced.

@incollection{doi1011302019254207,
    author = "Sinnesael, Matthias and Montanari, Alessandro and Frontalini, Fabrizio and Coccioni, Rodolfo and Gattacceca, J. and Snoeck, Christophe and Wegner, Wencke and Koeberl, Christian and Morgan, Leah E. and de Winter, Niels J. and DePaolo, Donald J. and Claeys, Philippe",
    title = "Multiproxy Cretaceous-Paleogene boundary event stratigraphy: An Umbria-Marche basinwide perspective",
    year = "2019",
    booktitle = "Geological Society of America eBooks",
    abstract = "ABSTRACT The complete and well-studied pelagic carbonate successions from the Umbria-Marche basin (Italy) permit the study of the event-rich stratigraphic interval around the Cretaceous-Paleogene boundary (e.g., Deccan volcanism, boundary impact, Paleocene recovery, and climate). To test the robustness of various proxy records (bulk carbonate δ13C, δ18O, 87Sr/86Sr, and Ca, Fe, Sr, and Mn concentrations) inside the Umbria-Marche basin, several stratigraphically equivalent sections were investigated (Bottaccione Gorge, Contessa Highway, Fornaci East quarry, Frontale, Morello, and Petriccio core). Besides the classical Gubbio sections of Bottaccione and Contessa, the new Morello section is put forward as an alternative location for this stratigraphic interval because it is less altered by burial diagenesis. Elemental profiles (Ca, Fe, Sr, Mn) acquired by handheld X-ray fluorescence (pXRF) efficiently provide regional chemostratigraphic and paleoenvironmental information. The Deccan volcanism, the Cretaceous-Paleogene boundary, the characteristic pattern of the Sr/Ca profile across the boundary driven by the extinction and recovery of coccolithophores, and the Dan-C2 hyperthermal event are examples of such recorded paleoenvironmental events. Moreover, cyclostratigraphic analyses of proxies of detrital input (magnetic susceptibility and Fe concentrations) show the imprint in the sedimentary record of a 2.4 m.y. eccentricity minimum around 66.45–66.25 Ma, and suggest that the occurrence of the Dan-C2 hyperthermal event was astronomically paced.",
    url = "https://doi.org/10.1130/2019.2542(07)",
    doi = "10.1130/2019.2542(07)",
    openalex = "W2979263928",
    references = "montanari1986spherules"
}

The local structure around antimony (Sb) atoms in Cretaceous–Tertiary (K–T) boundary sediments from Stevns Klint in Denmark was studied using Sb K–edge X–ray absorption fine structure (XAFS) spectroscopy to obtain information about the chemical state and coordination environment. We also performed arsenic (As) K–edge XAFS measurements. The Sb K–edge X–ray absorption near edge structure (XANES) spectrum of K–T boundary sediments was compared with those of various kinds of reference Sb minerals, such as Sb sulfides and Sb5+ complex oxides, and soils containing ferrihydrite (schwertmannite), Sb2O3, and Sb2O5. The XANES pattern and threshold energy of K–T boundary sediments are similar to those of ferrihydrite (schwertmannite) soil samples. There is no chemical shift in the threshold energies among K–T boundary sediments, Sb5+ oxide complex minerals, and Sb2O5. In As XAFS analyses, the threshold energy of K–T boundary sediments is approximately similar to those of As5+ minerals, and the XANES pattern of K–T boundary sediments is almost similar to those of ferrihydrite (schwertmannite) soil samples. The oxidation states of Sb and As of K–T boundary sediments are estimated to be Sb5+ and As5+, respectively. Sb and As in K–T boundary sediments are coordinated with oxide ions, and Sb and As exist in the same local structure positions as Sb and As in ferrihydrite (schwertmannite). The XANES spectra and radial structure function for Sb atoms also showed that Sb in K–T boundary sediments is stored in a SbO6 octahedral coordination environment. The Sb–O interatomic distance in the K–T boundary sediments sample is 1.99(1) Å. Abundant ferric hydroxides occur in K–T boundary sediments. Sb is considered to be coprecipitated with As and Fe ions, and Sb and As in K–T boundary sediments are incorporated in low crystalline ferrihydrite (schwertmannite) throughout precipitation and sedimentation. The environment at K–T boundary sediments resembles that of soil contaminated by Sb and As in local areas at the present age. However, in an unusual environment, such as widely distributed K–T boundary sediments in the world, unusually high concentrations of Sb5+ and As5+ could become an index of the soiling of the global environment with dust and ashes derived from asteroid impact ejecta falls.

@article{doi102465jmps180927,
    author = "Hongu, Hidetomo and Yoshiasa, Akira and Tobase, Tsubasa and Okube, Maki and Sugiyama, Kazumasa and Satō, Tsutomu",
    title = "XAFS study of Sb and As in Cretaceous–Tertiary boundary sediments: an index of soiling of the global environment with dust and ashes from impact ejecta falls",
    year = "2019",
    journal = "Journal of Mineralogical and Petrological Sciences",
    abstract = "The local structure around antimony (Sb) atoms in Cretaceous–Tertiary (K–T) boundary sediments from Stevns Klint in Denmark was studied using Sb K–edge X–ray absorption fine structure (XAFS) spectroscopy to obtain information about the chemical state and coordination environment. We also performed arsenic (As) K–edge XAFS measurements. The Sb K–edge X–ray absorption near edge structure (XANES) spectrum of K–T boundary sediments was compared with those of various kinds of reference Sb minerals, such as Sb sulfides and Sb5+ complex oxides, and soils containing ferrihydrite (schwertmannite), Sb2O3, and Sb2O5. The XANES pattern and threshold energy of K–T boundary sediments are similar to those of ferrihydrite (schwertmannite) soil samples. There is no chemical shift in the threshold energies among K–T boundary sediments, Sb5+ oxide complex minerals, and Sb2O5. In As XAFS analyses, the threshold energy of K–T boundary sediments is approximately similar to those of As5+ minerals, and the XANES pattern of K–T boundary sediments is almost similar to those of ferrihydrite (schwertmannite) soil samples. The oxidation states of Sb and As of K–T boundary sediments are estimated to be Sb5+ and As5+, respectively. Sb and As in K–T boundary sediments are coordinated with oxide ions, and Sb and As exist in the same local structure positions as Sb and As in ferrihydrite (schwertmannite). The XANES spectra and radial structure function for Sb atoms also showed that Sb in K–T boundary sediments is stored in a SbO6 octahedral coordination environment. The Sb–O interatomic distance in the K–T boundary sediments sample is 1.99(1) Å. Abundant ferric hydroxides occur in K–T boundary sediments. Sb is considered to be coprecipitated with As and Fe ions, and Sb and As in K–T boundary sediments are incorporated in low crystalline ferrihydrite (schwertmannite) throughout precipitation and sedimentation. The environment at K–T boundary sediments resembles that of soil contaminated by Sb and As in local areas at the present age. However, in an unusual environment, such as widely distributed K–T boundary sediments in the world, unusually high concentrations of Sb5+ and As5+ could become an index of the soiling of the global environment with dust and ashes derived from asteroid impact ejecta falls.",
    url = "https://doi.org/10.2465/jmps.180927",
    doi = "10.2465/jmps.180927",
    openalex = "W2985710519",
    references = "ebihara1996chemical"
}

The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing. We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change. Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from postextinction volcanism.

@article{doi101126scienceaay5055,
    author = "Hull, Pincelli M. and Bornemann, André and Penman, Donald E. and Henehan, Michael J. and Norris, Richard D. and Wilson, Paul A. and Blum, Peter and Alegret, Laia and Batenburg, Sietske J. and Bown, Paul R. and Bralower, Timothy J. and Cournède, C. and Deutsch, A. and Donner, Barbara and Friedrich, Oliver and Jehle, Sofie and Kim, Hojung and Kroon, Dick and Lippert, Peter C. and Loroch, Dominik and Moebius, Iris and Moriya, Kazuyoshi and Peppe, Daniel J. and Ravizza, G. and Röhl, Ursula and Schueth, Jonathan D. and Sepúlveda, Julio and Sexton, Philip F. and Sibert, Elizabeth C and Śliwińska, Kasia K. and Summons, Roger E. and Thomas, Ellen and Westerhold, Thomas and Whiteside, Jessica H. and Yamaguchi, Tatsuhiko and Zachos, James C.",
    title = "On impact and volcanism across the Cretaceous-Paleogene boundary",
    year = "2020",
    journal = "Science",
    abstract = "The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing. We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change. Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from postextinction volcanism.",
    url = "https://doi.org/10.1126/science.aay5055",
    doi = "10.1126/science.aay5055",
    openalex = "W2999541819",
    references = "doi101016jepsl200902019, doi1010292008jb005644, doi101073pnas1319253111, doi101098rspb20181194, doi101126science2825387276, doi101126scienceaaa0118, doi101126scienceaau2422, doi1011300091761319980260995adswat23co2, doi101130b318901"
}

The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide.

@article{doi101126sciadvabe3647,
    author = "Goderis, Steven and Sato, Honami and Ferrière, L. and Schmitz, Birger and Burney, D. and Kaskes, Pim and Vellekoop, Johan and Wittmann, A. and Schulz, Toni and Chernonozhkin, Stepan M. and Claeys, Philippe and de Graaff, Sietze J. and Déhais, Thomas and de Winter, Niels J. and Elfman, M. and Feignon, Jean–Guillaume and Ishikawa, Akira and Koeberl, Christian and Kristiansson, P. and Neal, C. R. and Owens, Jeremy D. and Schmieder, M. and Sinnesael, Matthias and Vanhaecke, Frank and Malderen, Stijn J. M. Van and Bralower, Timothy J. and Gulick, S. P. S. and Kring, D. A. and Lowery, Christopher M. and Morgan, Joanna and Smit, Jan and Whalen, Michael T. and Scientists, IODP-ICDP Expedition 364",
    title = "Globally distributed iridium layer preserved within the Chicxulub impact structure",
    year = "2021",
    journal = "Science Advances",
    abstract = "The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide.",
    url = "https://doi.org/10.1126/sciadv.abe3647",
    doi = "10.1126/sciadv.abe3647",
    openalex = "W3130273201",
    references = "doi101016jgca201306010, doi101130b318901"
}

Abstract Untangling the timing of the environmental effects of Deccan volcanism with respect to the Chicxulub impact is instrumental to fully assessing the contributions of both to climate change over the Cretaceous-Paleogene boundary (KPB) interval. Despite recent improvements in radiometric age calibrations, the accuracy of age constraints and correlations is insufficient to resolve the exact mechanisms leading to environmental and climate change in the 1 m.y. across the KPB. We present new high-resolution planktic foraminiferal, geochemical, and geophysical data from the Zumaia section (Spain), calibrated to an updated orbitally tuned age model. We provide a revised chronology for the major carbon isotope excursions (CIEs) and planktic foraminiferal events and test temporal relationships with different models of the eruptive phases of the Deccan Traps. Our data show that the major CIEs near the KPB, i.e., the late Maastrichtian warming event (66.25–66.10 Ma) and the Dan-C2 event (65.8–65.7 Ma), are synchronous with the last and the first 405 k.y. eccentricity maximum of the Maastrichtian and the Danian, respectively, and that the minor Lower C29n event (65.48–65.41 Ma) is well constrained to a short eccentricity maximum. Conversely, we obtained evidence of abrupt environmental change likely related to Deccan volcanism at ca. 65.9 Ma, based on a bloom of opportunistic triserial guembelitriids (Chiloguembelitria). The orbital, isotopic, and paleobiological temporal relationships with Deccan volcanism established here provide new insights into the role of Deccan volcanism in climate and environmental change in the 1 m.y. across the KPB.

@article{doi101130g492141,
    author = "Gilabert, Vicente and Batenburg, Sietske J. and Arenillas, Ignacio and Arz, José Antonio",
    title = "Contribution of orbital forcing and Deccan volcanism to global climatic and biotic changes across the Cretaceous-Paleogene boundary at Zumaia, Spain",
    year = "2021",
    journal = "Geology",
    abstract = "Abstract Untangling the timing of the environmental effects of Deccan volcanism with respect to the Chicxulub impact is instrumental to fully assessing the contributions of both to climate change over the Cretaceous-Paleogene boundary (KPB) interval. Despite recent improvements in radiometric age calibrations, the accuracy of age constraints and correlations is insufficient to resolve the exact mechanisms leading to environmental and climate change in the 1 m.y. across the KPB. We present new high-resolution planktic foraminiferal, geochemical, and geophysical data from the Zumaia section (Spain), calibrated to an updated orbitally tuned age model. We provide a revised chronology for the major carbon isotope excursions (CIEs) and planktic foraminiferal events and test temporal relationships with different models of the eruptive phases of the Deccan Traps. Our data show that the major CIEs near the KPB, i.e., the late Maastrichtian warming event (66.25–66.10 Ma) and the Dan-C2 event (65.8–65.7 Ma), are synchronous with the last and the first 405 k.y. eccentricity maximum of the Maastrichtian and the Danian, respectively, and that the minor Lower C29n event (65.48–65.41 Ma) is well constrained to a short eccentricity maximum. Conversely, we obtained evidence of abrupt environmental change likely related to Deccan volcanism at ca. 65.9 Ma, based on a bloom of opportunistic triserial guembelitriids (Chiloguembelitria). The orbital, isotopic, and paleobiological temporal relationships with Deccan volcanism established here provide new insights into the role of Deccan volcanism in climate and environmental change in the 1 m.y. across the KPB.",
    url = "https://doi.org/10.1130/g49214.1",
    doi = "10.1130/g49214.1",
    openalex = "W3197872458",
    references = "doi101016jepsl200607020"
}