Engineering

Abstract Predominantly nonmarine early Tertiary sediments of the Wilcox Group in Texas include numerous local lignite deposits. Recent subsurface mapping has defined several interrelated depositional systems representing six sedimentary environments, in outcropping and subsurface Wilcox in Texas. Lignite occurs in three of the environments so defined; these are (1) fluvial, (2) deltaic, and (3) lagoonal. Plant microfossils and coal macerals from the Wilcox lignites comprise a relatively homogenous, recurring association, but substantial differences also exist between the lignites from the various environments. Petrographic differences include: (1) greater abundances of certain lithotypes, (2) predominance of certain macerals, (3) relative abundance of mineral matter. Palynologic differences can be summarized in terms of distribution of assemblages and species groups within the flora. Assemblages recognized are the (1) Corylus‐Sphagnum Assemblage, (2) Palm Assemblage, and (3) Marine Influence Assemblage. Species groups include (1) locally indigenous forms, (2) reworked forms, (3) temperate genera and (4) tropical genera. Quantitative distinctions within the flora are suggested by species diversity indices. Paleoecologic inferences derived from this study suggest agreement with environmental interpretations based on mapping. This study is seen as a basis for further biostratigraphic and paleoecologic investigations in the Gulf Coast Tertiary.

@article{doi1010800072139519719989707,
    author = "Nichols, Douglas J. and Traverse, Alfred",
    title = "Palynology, petrology, and depositional environments of some early tertiary lignites in Texas",
    year = "1971",
    journal = "Geoscience and Man",
    abstract = "Abstract Predominantly nonmarine early Tertiary sediments of the Wilcox Group in Texas include numerous local lignite deposits. Recent subsurface mapping has defined several interrelated depositional systems representing six sedimentary environments, in outcropping and subsurface Wilcox in Texas. Lignite occurs in three of the environments so defined; these are (1) fluvial, (2) deltaic, and (3) lagoonal. Plant microfossils and coal macerals from the Wilcox lignites comprise a relatively homogenous, recurring association, but substantial differences also exist between the lignites from the various environments. Petrographic differences include: (1) greater abundances of certain lithotypes, (2) predominance of certain macerals, (3) relative abundance of mineral matter. Palynologic differences can be summarized in terms of distribution of assemblages and species groups within the flora. Assemblages recognized are the (1) Corylus‐Sphagnum Assemblage, (2) Palm Assemblage, and (3) Marine Influence Assemblage. Species groups include (1) locally indigenous forms, (2) reworked forms, (3) temperate genera and (4) tropical genera. Quantitative distinctions within the flora are suggested by species diversity indices. Paleoecologic inferences derived from this study suggest agreement with environmental interpretations based on mapping. This study is seen as a basis for further biostratigraphic and paleoecologic investigations in the Gulf Coast Tertiary.",
    url = "https://doi.org/10.1080/00721395.1971.9989707",
    doi = "10.1080/00721395.1971.9989707",
    openalex = "W2065825799",
    references = "doi101130gsab541713, doi1013065ceae1c616bb11d78645000102c1865d"
}

@misc{tourtelot1971the,
    author = "Tourtelot, Harry Allison and Tailleur, Irvin L.",
    title = "The Shublik Formation and adjacent strata in northeastern Alaska description, minor elements, depositional environments and diagenesis",
    year = "1971",
    booktitle = "Open-File Report",
    url = "https://doi.org/10.3133/ofr71284",
    doi = "10.3133/ofr71284"
}

@article{harrywdodge1983depositional,
    author = "Harry W. Dodge, Jr., Thomas M. Cran",
    title = "Depositional Environments of Upper Cretaceous Fox Hills Formation, Niobrara and Weston Counties, East-Central Wyoming: ABSTRACT",
    year = "1983",
    journal = "AAPG Bulletin",
    url = "https://doi.org/10.1306/03b5b835-16d1-11d7-8645000102c1865d",
    doi = "10.1306/03b5b835-16d1-11d7-8645000102c1865d",
    volume = "67"
}

@article{darrensdueitt1985depositional,
    author = "Darren S. Dueitt, Franz Froelicher",
    title = "Depositional Environments of Wilcox Lignites in Choctaw and Winston Counties, Mississippi: ABSTRACT",
    year = "1985",
    journal = "AAPG Bulletin",
    url = "https://doi.org/10.1306/ad462cb3-16f7-11d7-8645000102c1865d",
    doi = "10.1306/ad462cb3-16f7-11d7-8645000102c1865d",
    volume = "69"
}

The Shublik Formation is a heterogeneous unit consisting of several distinct facies, including: 1) fossiliferous sandstone or siltstone: 2) glauconitic sandstone or siltstone: 3) siltstone, calcareous mudstone, or limestone with phosphate nodules; and 4) black, calcareous mudstone or black limestone, usually fossiliferous. This sequence of lithologies is interpreted as having been deposited along an onshore-offsh ore (north to south) gradient. Bioturbation of the sediments is variable, but generally decreases offshore. Organic carbon increases offshore and phosphate increases from the paleoshoreline and decreases again farthest offshore. The distribution of glauconite, phosphate, and organic-carbon-rich rock is consistent with the facies expected in an upwelling zone that has a well-developed oxygen minimum. Glauconite is consistent with dysoxic conditions and well-laminated, organiccarbon-rich rock in the offshore facies is consistent with anoxic conditions. High biologic productivity coupled with normal oceanic circulation may have caused the basin's low-oxygen conditions, as indicated by the presence of phosphate nodules and the extreme abundance of bivalves that have been interpreted to be pelagic. Phosphate indicates a high rate of supply of organic matter to the sediment-water interface, where it was mobilized from the organic matter within the anoxic zone and reprecipitated at the zone's edges. Pelagic bivalves (Monotis and Halobia) are present in such huge numbers as to suggest unusually abundant food supply; in addition, their distribution is consistent with mass kills, which are common among fish in upwelling zones. Although an open-ocean divergence was predicted previously for the North Slope region in the Triassic, the distribution of the facies of the Shublik Formation relative to the paleoshoreline and the rapidity of the facies change onshore to offshore are more consistent with a coastal upwelling zone.

@article{openalexw2140021650,
    author = "Parrish, Judith Totman",
    title = "Lithology, Geochemistry, and Depositional Environment of the Triassic Shublik Formation, Northern Alaska",
    year = "1987",
    abstract = "The Shublik Formation is a heterogeneous unit consisting of several distinct facies, including: 1) fossiliferous sandstone or siltstone: 2) glauconitic sandstone or siltstone: 3) siltstone, calcareous mudstone, or limestone with phosphate nodules; and 4) black, calcareous mudstone or black limestone, usually fossiliferous. This sequence of lithologies is interpreted as having been deposited along an onshore-offsh ore (north to south) gradient. Bioturbation of the sediments is variable, but generally decreases offshore. Organic carbon increases offshore and phosphate increases from the paleoshoreline and decreases again farthest offshore. The distribution of glauconite, phosphate, and organic-carbon-rich rock is consistent with the facies expected in an upwelling zone that has a well-developed oxygen minimum. Glauconite is consistent with dysoxic conditions and well-laminated, organiccarbon-rich rock in the offshore facies is consistent with anoxic conditions. High biologic productivity coupled with normal oceanic circulation may have caused the basin's low-oxygen conditions, as indicated by the presence of phosphate nodules and the extreme abundance of bivalves that have been interpreted to be pelagic. Phosphate indicates a high rate of supply of organic matter to the sediment-water interface, where it was mobilized from the organic matter within the anoxic zone and reprecipitated at the zone's edges. Pelagic bivalves (Monotis and Halobia) are present in such huge numbers as to suggest unusually abundant food supply; in addition, their distribution is consistent with mass kills, which are common among fish in upwelling zones. Although an open-ocean divergence was predicted previously for the North Slope region in the Triassic, the distribution of the facies of the Shublik Formation relative to the paleoshoreline and the rapidity of the facies change onshore to offshore are more consistent with a coastal upwelling zone.",
    openalex = "W2140021650"
}

@article{bergan1988shoreline,
    author = "Bergan, Gail R.",
    title = "Shoreline Depositional Environments of Glen Rose Formation (Lower Cretaceous) in Type Area, Somervell and Hood Counties, Texas: ABSTRACT",
    year = "1988",
    journal = "AAPG Bulletin",
    url = "https://doi.org/10.1306/703c97e4-1707-11d7-8645000102c1865d",
    doi = "10.1306/703c97e4-1707-11d7-8645000102c1865d",
    volume = "72"
}

@misc{leipzig1990the1,
    author = "Leipzig, M. R",
    title = "The stratigraphy, electrofacies and depositional environments of the Reklaw Formation of Goliad and adjacent counties, south Texas",
    year = "1990",
    howpublished = "American Association of Petroleum Geologists, v. 215, no. 1, p. 76- 84",
    note = "talkorigins\_source = {true}; raw\_reference = {Leipzig, M. R., 1990, The stratigraphy, electrofacies and depositional environments of the Reklaw Formation of Goliad and adjacent counties, south Texas: American Association of Petroleum Geologists, v. 215, no. 1, p. 76- 84.}"
}

ABSTRACT The Upper Triassic Shublik Formation within the Prudhoe Bay field unit, North Slope, Alaska, is a potentially economic hydrocarbon reservoir comprised of mixed lithology and mineralogy. Its composition includes limestone, phosphate, shale, siltstone, and sandstone, as well as accessory amounts of siderite, glauconite, pyrite, kaolinite, and dolomite. Within the Prudhoe Bay field unit, the Shublik has been subdivided into four zones, lettered from base to top, D through A, which become thinner and show evidence of deposition under higher energy conditions toward the northeast. The formation is truncated to the east by the regional Lower Cretaceous unconformity. Zones within the Shublik comprise a basal transgressive systems tract (conglomerate lag at the Shublik Formation/Ivishak Formation contact through basal zone C shales) and two highstand shallowing-upward parasequences (zones C through B, and zone A, respectively). The parasequences are bounded by shales interpreted to represent deposition during periods of marine flooding. The contact between the Shublik and the overlying Sag River Formation juxtaposes comparatively deeper marine Shublik with shallower water glauconitic sandstones of the Sag River Formation. The contact is unconformable and is interpreted to represent a regional sequence boundary. Lithofacies of the Shublik are interpreted to have been coeval depositional facies of an upwelling system. Relative sea level changes during Shublik deposition are interpreted to have caused the observed vertical and lateral variability in lithofacies via systematic changes between anaerobic, dysaerobic, and aerobic upwelling conditions. Dissolution of carbonate allochems resulted in the creation of moldic porosity that positively affected reservoir quality (i.e., permeability) in the carbonate packstone/grainstone facies. Areas of highest porosity are in the northern and northeastern parts of the field, which correspond to a combination of facies-controlled reservoir quality improvement toward the northeast and carbonate dissolution along the Lower Cretaceous unconformity and the North Prudhoe Bay fault zone. Oil in place for the Shublik within the Prudhoe Bay unit is estimated to be between 250 and 500 million bbl. Although permeabilities are generally low throughout the field area, the Shublik Formation has the potential to add significant reserves to the Prudhoe Bay field unit.

@article{doi1013067834d4ae172111d78645000102c1865d,
    author = "Kupecz, Julie A.",
    title = "Depositional Setting, Sequence Stratigraphy, Diagenesis, and Reservoir Potential of a Mixed-Lithology, Upwelling Deposit: Upper Triassic Shublik Formation, Prudhoe Bay, Alaska",
    year = "1995",
    journal = "AAPG Bulletin",
    abstract = "ABSTRACT The Upper Triassic Shublik Formation within the Prudhoe Bay field unit, North Slope, Alaska, is a potentially economic hydrocarbon reservoir comprised of mixed lithology and mineralogy. Its composition includes limestone, phosphate, shale, siltstone, and sandstone, as well as accessory amounts of siderite, glauconite, pyrite, kaolinite, and dolomite. Within the Prudhoe Bay field unit, the Shublik has been subdivided into four zones, lettered from base to top, D through A, which become thinner and show evidence of deposition under higher energy conditions toward the northeast. The formation is truncated to the east by the regional Lower Cretaceous unconformity. Zones within the Shublik comprise a basal transgressive systems tract (conglomerate lag at the Shublik Formation/Ivishak Formation contact through basal zone C shales) and two highstand shallowing-upward parasequences (zones C through B, and zone A, respectively). The parasequences are bounded by shales interpreted to represent deposition during periods of marine flooding. The contact between the Shublik and the overlying Sag River Formation juxtaposes comparatively deeper marine Shublik with shallower water glauconitic sandstones of the Sag River Formation. The contact is unconformable and is interpreted to represent a regional sequence boundary. Lithofacies of the Shublik are interpreted to have been coeval depositional facies of an upwelling system. Relative sea level changes during Shublik deposition are interpreted to have caused the observed vertical and lateral variability in lithofacies via systematic changes between anaerobic, dysaerobic, and aerobic upwelling conditions. Dissolution of carbonate allochems resulted in the creation of moldic porosity that positively affected reservoir quality (i.e., permeability) in the carbonate packstone/grainstone facies. Areas of highest porosity are in the northern and northeastern parts of the field, which correspond to a combination of facies-controlled reservoir quality improvement toward the northeast and carbonate dissolution along the Lower Cretaceous unconformity and the North Prudhoe Bay fault zone. Oil in place for the Shublik within the Prudhoe Bay unit is estimated to be between 250 and 500 million bbl. Although permeabilities are generally low throughout the field area, the Shublik Formation has the potential to add significant reserves to the Prudhoe Bay field unit.",
    url = "https://doi.org/10.1306/7834d4ae-1721-11d7-8645000102c1865d",
    doi = "10.1306/7834d4ae-1721-11d7-8645000102c1865d",
    openalex = "W2006860727",
    references = "doi104095100966"
}

@article{jamescslone12000abstract,
    author = "James C Slone1, Jim Mazzullo1",
    title = "Abstract: Facies and depositional environments of the Permian Queen Formation, Howard Glasscock Field, Glasscock and Sterling Counties, Texas",
    year = "2000",
    journal = "AAPG Bulletin",
    url = "https://doi.org/10.1306/a9672eec-1738-11d7-8645000102c1865d",
    doi = "10.1306/a9672eec-1738-11d7-8645000102c1865d",
    volume = "84 (2000)"
}

Abstract The Shublik Formation (Triassic, North Slope, Alaska) is an organic-, phosphate-, and glauconite-rich unit with abundant fossils of marine vertebrates and mollusks. Five lithofacies, generalized around significant chemical constituents or lack thereof, are identified in the Shublik Formation:nonglauconitic sandstone - thin- to medium-bedded, fine, quartzose, calcareous to noncalcareous sandstone or silty to muddy sandstone, fossiliferous in places;glauconitic - thin- to medium-bedded, fine, quartzose sandstone, muddy sandstone, or siltstone containing 10% to > 50% glauconite grainsphosphatic - thin- to medium-bedded siltstone or sandstone or laminated, black silty limestone or limestone containing phosphate nodules; andorganic-rich - laminated, black limestone, marl, and mudstonenonphosphatic, nonorganic-rich limestone - bioclastic wackestone, or argillaceous grainstone and packstone or graded grainstone and packstone. Ichnofabrics provide evidence of fluctuating oxygen levels within the facies, especially the nonglauconitic sandstone and glauconitic facies. The organic-rich facies and, to a lesser extent, the phosphatic facies contain abundant, pristine, disarticulated shells of the clam Halobia. The lithofacies, ichnofabrics, and taphonomy are interpreted to be related to onshore-offshore gradients in biologic productivity and redox conditions. The Shublik Formation is interpreted as an upwelling-zone deposit formed on a shallow shelf. The Shublik Formation in the Prudhoe Bay region is interpreted to comprise three sequences; these have been extended to outcrop but not to cores in the National Petroleum Reserve. Facies stacking patterns indicate that siliclastic facies are most common during lowstand and transgression, organic-rich facies are characteristic of transgression, and carbonate-rich facies are more prevalent during highstand. Phosphatic facies occur along transgressive and maximum flooding surfaces and are thus integral to subdividing sequences into systems tracts.

@incollection{doi102110cor01010089,
    author = "Parrish, Judith Totman and Whalen, Michael T. and Hulm, Erik",
    title = "Shublik Formation Lithofacies, Environments, and Sequence Stratigraphy, Arctic Alaska, U.S.A.",
    year = "2001",
    booktitle = "SEPM (Society for Sedimentary Geology) eBooks",
    abstract = "Abstract The Shublik Formation (Triassic, North Slope, Alaska) is an organic-, phosphate-, and glauconite-rich unit with abundant fossils of marine vertebrates and mollusks. Five lithofacies, generalized around significant chemical constituents or lack thereof, are identified in the Shublik Formation:nonglauconitic sandstone - thin- to medium-bedded, fine, quartzose, calcareous to noncalcareous sandstone or silty to muddy sandstone, fossiliferous in places;glauconitic - thin- to medium-bedded, fine, quartzose sandstone, muddy sandstone, or siltstone containing 10\% to \> 50\% glauconite grainsphosphatic - thin- to medium-bedded siltstone or sandstone or laminated, black silty limestone or limestone containing phosphate nodules; andorganic-rich - laminated, black limestone, marl, and mudstonenonphosphatic, nonorganic-rich limestone - bioclastic wackestone, or argillaceous grainstone and packstone or graded grainstone and packstone. Ichnofabrics provide evidence of fluctuating oxygen levels within the facies, especially the nonglauconitic sandstone and glauconitic facies. The organic-rich facies and, to a lesser extent, the phosphatic facies contain abundant, pristine, disarticulated shells of the clam Halobia. The lithofacies, ichnofabrics, and taphonomy are interpreted to be related to onshore-offshore gradients in biologic productivity and redox conditions. The Shublik Formation is interpreted as an upwelling-zone deposit formed on a shallow shelf. The Shublik Formation in the Prudhoe Bay region is interpreted to comprise three sequences; these have been extended to outcrop but not to cores in the National Petroleum Reserve. Facies stacking patterns indicate that siliclastic facies are most common during lowstand and transgression, organic-rich facies are characteristic of transgression, and carbonate-rich facies are more prevalent during highstand. Phosphatic facies occur along transgressive and maximum flooding surfaces and are thus integral to subdividing sequences into systems tracts.",
    url = "https://doi.org/10.2110/cor.01.01.0089",
    doi = "10.2110/cor.01.01.0089",
    openalex = "W2209195447",
    references = "doi1010160016703796000415, doi10113000917613198614535scaia20co2, doi101130dnaggnag149, doi10130603b5a30e16d111d78645000102c1865d, doi101306bdff8aa6171811d78645000102c1865d, doi101306m26490c14, doi102110pec88010039, doi102110pec88010183, doi102110pec9412, doi102110pec94120045, doi104095100966, tourtelot1971the"
}

@incollection{crossref2003depositional,
    title = "Depositional Environments of Clay Seal Formation",
    year = "2003",
    booktitle = "Clay Seals of Oil and Gas Deposits",
    url = "https://doi.org/10.1201/noe9058095831.ch4",
    doi = "10.1201/noe9058095831.ch4",
    pages = "120-135"
}

The hydrocarbon potential of the Three Forks Formation in North Dakota is poorly known due to limited stratigraphic, geochemical, and petrophysical data. This study presents a methodology and results of a reservoir characterization study of the stratigraphy, lithofacies distribution, petroleum potential, and paleo-environments of the Three Forks Formation in North Dakota as a potential for hydrocarbon exploration with the principal objective to evaluate the Three Forks Formation’s potential for future developments. The detailed lithology is computed by employing a probabilistic interpretation approach calibrated with lab results and five major lithofacies of the Three Forks Formation in North Dakota, which display a variety of diagenetic characteristics including dolomitization and precipitation of hematite, are identified and presented. These facies correlate well with electrofacies predicted by employing principal component analysis and clustering techniques to selected lithology-sensitive logs. Hydrocarbon source rock analysis, including type and quantity of kerogen, and thermal maturity on all five facies using Rock-Eval 6 pyrolysis and LECO TOC shows that these facies have poor to fair petroleum potential and contain immature Type II and Type III kerogens. In addition, samples from three lithofacies are analyzed by thin section and SEM petrography, plus combined bulk and clay XRD analyses and key aspects controlling the porosity and permeability of this formation are revealed by focusing on the detailed mineralogy, rock type, diagenetic mineral distribution plus overall reservoir quality and the fluid sensitivity. Results show that the Three Forks mineralogy is dominated by dolomite, along with substantial hematite, monocrystalline quartz and mica flakes with trace feldspar, calcite, and pyrite. EDX spectra show that the element distribution is influenced by the lithotype composition, mainly Ca, Mg, and Fe with additional Si, Al, and K. Three stages of the dolomitization process are identified and discussed. Clays mainly consist of illite together with minor chlorite, and kaolinite and are associated with the scattered clasts of quartz and feldspars. The reservoir quality is controlled by intercrystalline, rare micro-vuggy, plus microporosity types that result from diagenetic and depositional events. Six members of the Three Forks are identified and log-derived porosities, water saturations, and net-togross values for each Member calculated and areas with high reservoir quality and potential pay zones highlighted. Also, core data are quantitatively compared with results from the Archie, Simandoux, Modified Simandoux, Indonesia, and Dual-Water models. A proposed depositional model is constructed based on detailed core examination and petrographical analysis and sufficient evidence is provided to show that the Three Forks Formation is of peritidal to sabkha-like origin. A proposed hypothesis is that dolomitization commenced soon after deposition and was pervasive that no original carbonate texture is detectable.

@article{openalexw2276499054,
    author = "Ashu, Richard A.",
    title = "Stratigraphy, depositional environments, and petroleum potential of the Three Forks Formation -- Williston Basin, North Dakota",
    year = "2014",
    journal = "UND Scholarly Commons (University of North Dakota)",
    abstract = "The hydrocarbon potential of the Three Forks Formation in North Dakota is poorly known due to limited stratigraphic, geochemical, and petrophysical data. This study presents a methodology and results of a reservoir characterization study of the stratigraphy, lithofacies distribution, petroleum potential, and paleo-environments of the Three Forks Formation in North Dakota as a potential for hydrocarbon exploration with the principal objective to evaluate the Three Forks Formation’s potential for future developments. The detailed lithology is computed by employing a probabilistic interpretation approach calibrated with lab results and five major lithofacies of the Three Forks Formation in North Dakota, which display a variety of diagenetic characteristics including dolomitization and precipitation of hematite, are identified and presented. These facies correlate well with electrofacies predicted by employing principal component analysis and clustering techniques to selected lithology-sensitive logs. Hydrocarbon source rock analysis, including type and quantity of kerogen, and thermal maturity on all five facies using Rock-Eval 6 pyrolysis and LECO TOC shows that these facies have poor to fair petroleum potential and contain immature Type II and Type III kerogens. In addition, samples from three lithofacies are analyzed by thin section and SEM petrography, plus combined bulk and clay XRD analyses and key aspects controlling the porosity and permeability of this formation are revealed by focusing on the detailed mineralogy, rock type, diagenetic mineral distribution plus overall reservoir quality and the fluid sensitivity. Results show that the Three Forks mineralogy is dominated by dolomite, along with substantial hematite, monocrystalline quartz and mica flakes with trace feldspar, calcite, and pyrite. EDX spectra show that the element distribution is influenced by the lithotype composition, mainly Ca, Mg, and Fe with additional Si, Al, and K. Three stages of the dolomitization process are identified and discussed. Clays mainly consist of illite together with minor chlorite, and kaolinite and are associated with the scattered clasts of quartz and feldspars. The reservoir quality is controlled by intercrystalline, rare micro-vuggy, plus microporosity types that result from diagenetic and depositional events. Six members of the Three Forks are identified and log-derived porosities, water saturations, and net-togross values for each Member calculated and areas with high reservoir quality and potential pay zones highlighted. Also, core data are quantitatively compared with results from the Archie, Simandoux, Modified Simandoux, Indonesia, and Dual-Water models. A proposed depositional model is constructed based on detailed core examination and petrographical analysis and sufficient evidence is provided to show that the Three Forks Formation is of peritidal to sabkha-like origin. A proposed hypothesis is that dolomitization commenced soon after deposition and was pervasive that no original carbonate texture is detectable.",
    url = "https://openalex.org/W2276499054",
    openalex = "W2276499054"
}

Peat depositional environments, the sites where and conditions under which peat accumulates, significantly influence a resultant coal's physical properties, chemical composition, and coal utilization behavior. Recognition of peat depositional environments for coal is a challenging endeavor because coal's observed compositional properties not only result from a variety of geological processes operating during peat accumulation, but also reflect the influence of adjoining or external depositional sedimentary environments and alteration during later diagenesis and/or epigenesis. The maceral or microlithotype composition of any one layer of peat can be the product of years or decades of plant growth, death, decay, and post-burial infiltration by roots in addition to the symbiotic, mutualistic, parasitic, and saprophytic relationships with non-plant biota, such as arthropods, fungi, and bacteria. The overprint of increasing thermal maturation and fluid migration through time on the resulting coal can make these relationships difficult to recognize. Therefore, published models based on maceral composition alone must be used with great caution. Lipid compositions, even from lipid-poor low-rank coals, can provide important information about depositional environments and paleoclimate, especially if combined with the results of organic petrography and paleontological studies. Just as sulfur derived from seawater provides environmental clues, the ratios of two particularly relevant trace elements rather than a single trace element can be used to interpret peat depositional environments. Epigenetic minerals, as well as their corresponding chemical compositions should not be used for such a purpose; similarly, resistant terrigenous minerals deposited during peat accumulation in many cases should be used with considerable caution. The interactions of the biota present in the peat-forming ecosystem, often determined using palynological and geochemical proxies, and their interpretation in the context of geography and paleoclimate are important means for deciphering peat depositional environments. Overall, a combination of evidence from geochemistry, mineralogy, palynology, and petrology of coal and from stratigraphy, sedimentology, and sedimentary facies of related rocks is necessary for accurate and comprehensive determination of depositional environments. The need for interdisciplinary studies is underscored by peat compositional properties, which have been greatly affected by various processes during the syngenetic, diagenetic or epigenetic stages of coal formation.

@article{doi101016jcoal2019103383,
    author = "Dai, Shifeng and Bechtel, Achim and Eble, Cortland F. and Flores, Romeo M. and French, David and Graham, Ian T. and Hood, Madison M. and Hower, James C. and Korasidis, Vera A. and Moore, Tim A. and Püttmann, Wilhelm and Wei, Qiang and Zhao, Lei and O’Keefe, Jennifer M.K.",
    title = "Recognition of peat depositional environments in coal: A review",
    year = "2020",
    journal = "International Journal of Coal Geology",
    abstract = "Peat depositional environments, the sites where and conditions under which peat accumulates, significantly influence a resultant coal's physical properties, chemical composition, and coal utilization behavior. Recognition of peat depositional environments for coal is a challenging endeavor because coal's observed compositional properties not only result from a variety of geological processes operating during peat accumulation, but also reflect the influence of adjoining or external depositional sedimentary environments and alteration during later diagenesis and/or epigenesis. The maceral or microlithotype composition of any one layer of peat can be the product of years or decades of plant growth, death, decay, and post-burial infiltration by roots in addition to the symbiotic, mutualistic, parasitic, and saprophytic relationships with non-plant biota, such as arthropods, fungi, and bacteria. The overprint of increasing thermal maturation and fluid migration through time on the resulting coal can make these relationships difficult to recognize. Therefore, published models based on maceral composition alone must be used with great caution. Lipid compositions, even from lipid-poor low-rank coals, can provide important information about depositional environments and paleoclimate, especially if combined with the results of organic petrography and paleontological studies. Just as sulfur derived from seawater provides environmental clues, the ratios of two particularly relevant trace elements rather than a single trace element can be used to interpret peat depositional environments. Epigenetic minerals, as well as their corresponding chemical compositions should not be used for such a purpose; similarly, resistant terrigenous minerals deposited during peat accumulation in many cases should be used with considerable caution. The interactions of the biota present in the peat-forming ecosystem, often determined using palynological and geochemical proxies, and their interpretation in the context of geography and paleoclimate are important means for deciphering peat depositional environments. Overall, a combination of evidence from geochemistry, mineralogy, palynology, and petrology of coal and from stratigraphy, sedimentology, and sedimentary facies of related rocks is necessary for accurate and comprehensive determination of depositional environments. The need for interdisciplinary studies is underscored by peat compositional properties, which have been greatly affected by various processes during the syngenetic, diagenetic or epigenetic stages of coal formation.",
    url = "https://doi.org/10.1016/j.coal.2019.103383",
    doi = "10.1016/j.coal.2019.103383",
    openalex = "W2998976463",
    references = "doi101016000925419490085x, doi1010160012825287900419, doi1010160031920186900932, doi1010160166516284900193, doi101016jchemgeo200312009, doi101016jcoal200303001, doi101016jcoal201202004, doi101016jcoal201205009, doi101016jcoal2019103304, doi101016jearscirev200810003, doi101016jfbr200709001, doi101016s0009254198001429, doi101016s0166516202001179, doi101017cbo9780511524868, doi101038272216a0, doi10108003115517708527763, doi10113000917613198614535scaia20co2, doi101344105000001619, doi1023071485834, doi1023072844758, doi105860choice301532, doi105860choice302690, doi105860choice444462, openalexw1624806571"
}

In the Yangtze Block, the Early Cambrian Niutitang Formation is mainly composed of mudstone, shale, and carbonates which are important for investigating the depositional environment and evolution of the Early Cambrian rocks. The Niutitang Formation in the study area has a greater geologic interest due to its polymetallic beds, depositional age, variation in environmental conditions, Cambrian explosion, organic matter (OM) enrichment, algal boom, etc. This research represents the sedimentary geochemistry of the Early Cambrian Niutitang Formation to reconstruct the palaeo‐depositional environment and to evaluate the OM enrichment mechanism by means of total organic carbon (TOC), biomarkers, carbon isotopes, mineralogy, scanning electron microscope, etc. Based on the variation in TOC content, the Niutitang Formation is divided into three parts (upper, middle, and lower). The majority of the samples from the middle part of the Niutitang Formation exhibit an excellent source of hydrocarbon (TOC > 4.0 wt%) relative to the upper and the lower part. The lighter carbon isotopic composition (<−30.7%) in these sediments reveals the presence of the I‐amorphous kerogen group. Moreover, these lighter δ 13 C org values suggest the presence of type‐I oil‐prone kerogen. Saturated hydrocarbon in these rocks showed the dominance of short‐chain n ‐alkanes maximizing at C 18. The predominance of these n ‐alkanes represents that the OM is chiefly derived from algal/bacterial input. Similarly, the dissymmetric V shape of C 27 ‐C 28 ‐C 29 steranes with a predominance of C 27 and the higher values of in all three parts reflects that the OM in these rocks is chiefly originated from the lower aquatic marine organisms. Based on the Pr/Ph ratio, it is predicted that the middle part of the Niutitang Formation was deposited in extreme anoxic conditions (Pr/Ph < 0.5), whereas the upper and lower parts were deposited in relatively less anoxic conditions. Some biomarkers have more stable stereochemistry, which cannot be affected by diagenetic processes. These stable configurations are utilized to measure the maturity of OM, that is, Ts/(Ts + Tm), C 29 ββ/(ββ + αα), C 29 αα20S/(20S + 20R) steranes, and homohopane C 31 22S/(22S + 22R). These geochemical indices reveal that the Early Cambrian Niutitang Formation in the studied area is mature to the post‐mature in the gas generation phase. Moreover, the hydrothermal fluids rich in metallic elements (e.g., Mo, Zn, V, and U) from the deeper part of the Earth owing to elongational forces among Yangtze and Cathaysian plates over Early Cambrian time entered the oceanic basin via remnant features (fissure and cracks) and through upwelling phenomena interacted with shelf sediments. At the ocean's surface, these nutrient‐rich fluids enhanced the breeding and evolution of marine life (bio‐productivity), which created hypoxic water conditions suitable for the preservation of OM in these rocks.

@article{doi101002gj4304,
    author = "Awan, Rizwan Sarwar and Liu, Chenglin and Khan, Ashar and Zang, Qibiao and Wu, Yuping and Feng, Dehao",
    title = "Sedimentary geochemistry of the Early Cambrian Niutitang Formation to reconstruct the palaeo‐depositional environments and to evaluate the organic matter enrichment mechanism from the Yangtze Block, South China",
    year = "2021",
    journal = "Geological Journal",
    abstract = "In the Yangtze Block, the Early Cambrian Niutitang Formation is mainly composed of mudstone, shale, and carbonates which are important for investigating the depositional environment and evolution of the Early Cambrian rocks. The Niutitang Formation in the study area has a greater geologic interest due to its polymetallic beds, depositional age, variation in environmental conditions, Cambrian explosion, organic matter (OM) enrichment, algal boom, etc. This research represents the sedimentary geochemistry of the Early Cambrian Niutitang Formation to reconstruct the palaeo‐depositional environment and to evaluate the OM enrichment mechanism by means of total organic carbon (TOC), biomarkers, carbon isotopes, mineralogy, scanning electron microscope, etc. Based on the variation in TOC content, the Niutitang Formation is divided into three parts (upper, middle, and lower). The majority of the samples from the middle part of the Niutitang Formation exhibit an excellent source of hydrocarbon (TOC > 4.0 wt\%) relative to the upper and the lower part. The lighter carbon isotopic composition (<−30.7\%) in these sediments reveals the presence of the I‐amorphous kerogen group. Moreover, these lighter δ 13 C org values suggest the presence of type‐I oil‐prone kerogen. Saturated hydrocarbon in these rocks showed the dominance of short‐chain n ‐alkanes maximizing at C 18. The predominance of these n ‐alkanes represents that the OM is chiefly derived from algal/bacterial input. Similarly, the dissymmetric V shape of C 27 ‐C 28 ‐C 29 steranes with a predominance of C 27 and the higher values of in all three parts reflects that the OM in these rocks is chiefly originated from the lower aquatic marine organisms. Based on the Pr/Ph ratio, it is predicted that the middle part of the Niutitang Formation was deposited in extreme anoxic conditions (Pr/Ph < 0.5), whereas the upper and lower parts were deposited in relatively less anoxic conditions. Some biomarkers have more stable stereochemistry, which cannot be affected by diagenetic processes. These stable configurations are utilized to measure the maturity of OM, that is, Ts/(Ts + Tm), C 29 ββ/(ββ + αα), C 29 αα20S/(20S + 20R) steranes, and homohopane C 31 22S/(22S + 22R). These geochemical indices reveal that the Early Cambrian Niutitang Formation in the studied area is mature to the post‐mature in the gas generation phase. Moreover, the hydrothermal fluids rich in metallic elements (e.g., Mo, Zn, V, and U) from the deeper part of the Earth owing to elongational forces among Yangtze and Cathaysian plates over Early Cambrian time entered the oceanic basin via remnant features (fissure and cracks) and through upwelling phenomena interacted with shelf sediments. At the ocean's surface, these nutrient‐rich fluids enhanced the breeding and evolution of marine life (bio‐productivity), which created hypoxic water conditions suitable for the preservation of OM in these rocks.",
    url = "https://doi.org/10.1002/gj.4304",
    doi = "10.1002/gj.4304",
    openalex = "W3211106031",
    references = "doi102110cor01010089"
}