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Louis A Derry - One of the best experts on this subject based on the ideXlab platform.
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a Burial Diagenesis origin for the ediacaran shuram wonoka carbon isotope anomaly
Earth and Planetary Science Letters, 2010Co-Authors: Louis A DerryAbstract:Marked negative δ13C excursions in Ediacaran-age carbonate sediments have been identified in several sections globally, but are not recognized in all sections of similar age. The presence of δ13Ccarb values as low as −12‰ has been interpreted as recording fundamentally different processes in the global carbon cycle than those recognized today. The δ13Ccarb anomalies are strongly correlated with δ18Ocarb values but are not represented in δ13Corg records. While no primary depositional processes have been identified that can produce the correlated δ18O–δ13C arrays, simulations show that fluid–rock interaction with high-pCO2 fluids is capable of producing such arrays at geologically reasonable pCO2 and water–rock ratios. Variations in the Mg/Ca ratio and sulfate concentration of the altering fluid determine the extent of dolomite vs. calcite and anhydrite in the resulting mineral assemblage. Incorporation of an initially aragonitic mineralogy demonstrates that high Sr, low Mn/Sr and modest alteration of 87Sr/86Sr in ancient carbonates are all compatible with a Burial Diagenesis mechanism for generation of the δ13C anomalies, and do not necessarily imply preservation of primary values. The profound Ediacaran negative δ13C anomalies can be adequately explained by well-understood diagenetic processes, conflated with the difficulty of correlating Precambrian sections independently of chemostratigraphy. They are not a record of primary seawater variations and need not have independent stratigraphic significance.
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A Burial Diagenesis origin for the Ediacaran Shuram–Wonoka carbon isotope anomaly
Earth and Planetary Science Letters, 2010Co-Authors: Louis A DerryAbstract:Marked negative δ13C excursions in Ediacaran-age carbonate sediments have been identified in several sections globally, but are not recognized in all sections of similar age. The presence of δ13Ccarb values as low as −12‰ has been interpreted as recording fundamentally different processes in the global carbon cycle than those recognized today. The δ13Ccarb anomalies are strongly correlated with δ18Ocarb values but are not represented in δ13Corg records. While no primary depositional processes have been identified that can produce the correlated δ18O–δ13C arrays, simulations show that fluid–rock interaction with high-pCO2 fluids is capable of producing such arrays at geologically reasonable pCO2 and water–rock ratios. Variations in the Mg/Ca ratio and sulfate concentration of the altering fluid determine the extent of dolomite vs. calcite and anhydrite in the resulting mineral assemblage. Incorporation of an initially aragonitic mineralogy demonstrates that high Sr, low Mn/Sr and modest alteration of 87Sr/86Sr in ancient carbonates are all compatible with a Burial Diagenesis mechanism for generation of the δ13C anomalies, and do not necessarily imply preservation of primary values. The profound Ediacaran negative δ13C anomalies can be adequately explained by well-understood diagenetic processes, conflated with the difficulty of correlating Precambrian sections independently of chemostratigraphy. They are not a record of primary seawater variations and need not have independent stratigraphic significance.
Ezat Heydari - One of the best experts on this subject based on the ideXlab platform.
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The Role of Burial Diagenesis in Hydrocarbon Destruction and H2S Accumulation, Upper Jurassic Smackover Formation, Black Creek Field, Mississippi
AAPG Bulletin, 1997Co-Authors: Ezat HeydariAbstract:Organic-inorganic interactions during Burial of the Smackover Formation at Black Creek Field, Mississippi, have resulted in nearly complete destruction of hydrocarbons. The formation has been buried to a depth of 6 km, has experienced temperatures of over 200 degrees C, and presently contains 78% H 2 S, 20% CO 2 , and 2% CH 4 . Three distinct stages of Burial Diagenesis correspond to three phases of organic matter maturation. Pre-oil window Diagenesis was dominated by precipitation of prebitumen calcite cement. Diagenesis in the oil window was characterized by precipitation of saddle dolomite and anhydrite in water-filled layers and by formation of solid bitumen in the oil column. Diagenesis in the gas window was dominated by thermochemical sulfate reduction (TSR) resulting in hydrocarbon destruction, anhydrite dissolution, large amounts of H 2 S, CO 2 , and S generation, and postbitumen calcite cementation. During TSR, anhydrite reacted with H 2 S to produce S , which in turn reacted with CH 4 to generate more H 2 S in a self-reinforcing cycle. The lack of metal cations to stabilize H 2 S as metal sulfides, availability of sufficient sulfate to generate H 2 S, and a closed system to prevent H 2 S from escaping resulted in the continuation of the TSR cycle until nearly all hydrocarbons were consumed. In Mississippi, concentration of H 2 S is nearly zero in Smackover hydrocarbon reservoirs that have experienced temperatures of 120 degrees C for more than 50 m.y., suggesting that TSR is not a kinetic (time-dependent) process. High H 2 S concentrations initiate at temperatures above 140 degrees C and increase with temperature, indicating that TSR is a thermodynamic phenomenon. Reported high H 2 S concentrations at low temperatures (80-120 degrees C) from other locations may be explained by the following processes; (1) migration of H 2 S into these reservoirs, (2) high geothermal gradients or local thermal perturbations in the past, (3) a biochemical origin for the H 2 S, or (4) exposure of these reservoirs to temperatures greater than 150 degrees C and a rapid uplift. In Black Creek Field, Burial cementation and pressure solution resulted in total destruction of porosity and permeability in limestone reservoirs, but not in dolomite reservoirs, which still possess up to 20% porosity and 100 md permeability. Secondary porosity was not created as a result of hydrocarbon migration. Abundant CO 2 derived during hydrocarbon destruction resulted in calcite cementation rather than carbonate dissolution. Late, secondary porosity development in carbonates may be related to acids generated by metal sulfide precipitation.
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Burial Diagenesis and Hydrocarbon Migration in Platform Limestones: A Conceptual Model Based on the Upper Jurassic of the Gulf Coast of the USA: Chapter 13: Diagenesis, SEQUENCE STRATIGRAPHY AND CHANGES IN RELATIVE SEA LEVEL
1993Co-Authors: Clyde H. Moore, Ezat HeydariAbstract:Subsurface Upper Jurassic Smackover limestones of the Gulf Coast of the U.S.A. are an ideal laboratory for the study of the Burial Diagenesis of platform carbonates because of the enormous quantity of material available occasioned by extensive hydrocarbon production, the wide range of Burial depths over which they occur, and the relative simplicity of their depositional setting. The model presented is based on several long term studies of these limestones. Pathways for Burial diagenetic fluids were established early on during the sedimentological evolution of the platform and were driven by relative sea level fluctuations. Regionally extensive high porosity trends, that subsequently acted as conduits for diagenetic fluid flow, were generally restricted to siliciclastic lo stand fans and wedges, and highstand blanket carbonate sands. Transgressive systems tracts are generally muddy and act as aquicludes, or in some cases, hydrocarbon source rocks. Relative sea level lowstands can dramatically influence later diagenetic fluid flow by modifying original porosity distribution and permeability characteristics through dissolution and cementation. Carbonate mineralogies are generally stabilized during this early, surface-related diagenetic phase. Burial Diagenesis in platform limestones proceeds in two main phases: pre-hydrocarbon migration Diagenesis and post-hydrocarbon migration Diagenesis. Pre-hydrocarbon migration Diagenesis is driven by chemical compaction in an initially open system, dominated by marine connate and mixed marine connate and meteoric water. This hydrologic system became compartmentalized during hydrocarbon trap formation. New pore fluids, derived from underlying siliciclastics below and from the dewatering of adjacent basinal deposits with faults as conduits, moved into porous platform carbonates and mixed with evolved connate waters. Calcite cements were predominantly sourced from pressure solution End_Page 213------------------------ of host limestones. However, their composition also reflects the importation of Fe, Mn, radiogenic Sr, Pb, Ba, etc., from subjacent lowstand siliciclastic sequences and adjacent basinal deposits. Hydrocarbon precursors, such as H2S and organic acids were also introduced, leading to sulfide formation and minor secondary porosity generation. Migration and trapping of hydrocarbons arrested further Diagenesis within the carbonate reservoir sequence. Post-hydrocarbon migration Diagenesis is driven by thermal destruction of reservoir hydrocarbons under the influence of high temperatures. The resulting high H2S environment led to metal fixation by sulfide precipitation, thermochemical sulfate reduction, late calcite cementation, and sulfur-driven methane destruction. Progressive loss of porosity through compaction as well as the emplacement of the by-products of late Diagenesis, such as calcite cements and pyrobitumen, resulted in progressive closure of the diagenetic system. Trace element and isotopic compositions of late, post-hydrocarbon calcite cements reflect these processes. This model should be applicable to hydrocarbon and sulfate-bearing carbonate shelf-ramp depositional sequences featuring high energy, highstand systems tracts, developed in response to 3rd order relative sea level fluctuations.
Anjiang Shen - One of the best experts on this subject based on the ideXlab platform.
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rare earth element and yttrium rey geochemistry in carbonate reservoirs during deep Burial Diagenesis implications for rey mobility during thermochemical sulfate reduction
Chemical Geology, 2015Co-Authors: Lei Jiang, Richard H. Worden, Chunfang Cai, Lei Xiang, Xuelei Chu, Anjiang ShenAbstract:Abstract The impact of Burial Diagenesis (especially deep Burial-related processes such as thermochemical sulfate reduction, TSR) on the distribution of rare earth elements and yttrium (REY) in diagenetic minerals in carbonate reservoir has gained little attention even though they may be unique indicators of the diagenetic system being closed or open to external influx of material. Trace element and REY concentrations, 87 Sr/ 86 Sr, δ 18 O and δ 13 C have been determined for limestone, host dolomite, pore-filling calcite (calcite-2), and late stage fracture-filling calcite (calcite-3), barite (barite-2) and anhydrite (anhydrite-3) from Lower Triassic Feixianguan Formation reservoirs in northeast Sichuan Basin, China. Calcite-2, calcite-3, barite-2, and anhydrite-3 precipitated during deep Burial (from 110 °C to 220 °C), demonstrated by petrology and fluid inclusion thermometry. Sr isotope analysis revealed that diagenetic carbonate minerals and anhydrite have largely identical 87 Sr/ 86 Sr ratios to Triassic seawater, indicating negligible input of Sr from terrigenous sources and probably a relatively closed diagenetic environment for precipitation of these minerals. Carbon isotope analysis showed that calcite-2 has relatively low δ 13 C values (down to − 18.9‰ V-PDB), suggesting that they are TSR calcites with the carbonate derived from oxidized, isotopically-light hydrocarbons. Unlike the seawater-like REY patterns of the limestone and dolomites, calcite-3 and anhydrite-3 are enriched in rare earth elements (ΣREE) and show light rare earth element enrichment and heavy rare earth element depletion, exhibiting a chevron-like pattern of shale normalized REY trends. In contrast, TSR calcite (calcite-2) has similar ΣREE to the host dolomite but a relatively flat REY SN pattern, suggesting strong variations in elemental and REE compositions of the Burial fluids. Significantly, TSR calcite shows a prominent positive Eu anomaly and an unusually high-chondritic Y/Ho ratio. Both yttrium versus holmium fractionation and Eu 2 + oxidation to Eu 3 + must have occurred during thermochemical sulfate reduction. Hence, a positive Eu anomaly and an elevated Y/Ho ratio may be used as effective proxies to differentiate calcite resulting from TSR from ordinary calcite cement. This is especially useful when carbon isotope analysis cannot be used to give an unambiguous interpretation of the origin of the calcite.
Jan Ilavsky - One of the best experts on this subject based on the ideXlab platform.
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The effects of Burial Diagenesis on multiscale porosity in the St. Peter Sandstone: An imaging, small-angle, and ultra-small-angle neutron scattering analysis
Marine and Petroleum Geology, 2018Co-Authors: Lawrence M. Anovitz, Jared T. Freiburg, Matthew J. Wasbrough, David F. R. Mildner, Kenneth C. Littrell, Vitaliy Pipich, Jan IlavskyAbstract:Abstract To examine the effects of Burial Diagenesis on heirarchical pore structures in sandstone and compare those with the effects of overgrowth formation, we obtained samples of St. Peter Sandstone from drill cores recovered from the Illinois and Michigan Basins. The multiscale pore structure of rocks in sedimentary reservoirs and the mineralogy associated with those pores are critical factors for estimating reservoir properties, including fluid mass in place, permeability, and capillary pressures, as well as geochemical interactions between the rock and the fluid. The combination of small- and ultra-small-angle neutron scattering with backscattered electron imaging, provided a means by which pore structures were quantified at scales ranging from approximately 1 nm to 1 cm—seven orders of magnitude. Larger scale (>10 μm) porosity showed the expected logarithmic decrease in porosity with depth, although there was significant variation in each sample group. However, small- and ultra-small-angle neutron scattering data showed that the proportion of small-scale porosity increased with depth. Porosity distributions were not continuous, but consisted of a series of log normal-like distributions at several distinct scales within these rocks. Fractal dimensions at larger scales decreased (surfaces smoothed) with increasing depth, and those at smaller scales increased (surfaces roughened) and pores become more isolated (higher lacunarity). Data suggest that changes in pore-size distributions are controlled by both physical (compaction) and chemical effects (precipitation, cementation, dissolution).
Lynton S. Land - One of the best experts on this subject based on the ideXlab platform.
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Burial Diagenesis of illite smectite in shales and the origins of authigenic quartz and secondary porosity in sandstones
Geochimica et Cosmochimica Acta, 1997Co-Authors: Leo F Lynch, Lawrence E Mack, Lynton S. LandAbstract:Several gram-size samples of <0.1 {mu}m, nearly monomineralic mixed-layer illite/smectite (I/S) were isolated from nineteen whole-cores of shale of the Frio Formation from the Texas Gulf Coast. Between {approximately}7,000 ft (2133 m) and {approximately}15,000 ft (4572 m) Burial depth I/S changes from random-interstratification (R = 0) with low %1 to ordered-interstratification (R = 3) with high %I. The accompanying chemical changes are loss of Si, Mg, and Fe{sup +3}, gain of K, Al, and Fe{sup +2}, and a shift in the REE content of the mineral. There is no chemical or mineralogical evidence for a cessation of I/S reaction at {approximately}80% I as is commonly accepted; both chemical and mineralogical changes occur throughout Burial. Continuous change in the oxygen isotopic composition of I/S implies that the conversion of smectite-layers to illite-layers is a dissolution and reprecipitation process. Mass balance calculations indicate that Burial Diagenesis of Frio Formation shales is an open-system process that requires addition of K{sub 2}O and Al{sub 2}O{sub 3} and results in loss of SiO{sub 2}. The amount of SiO{sub 2} made available by shale Diagenesis is sufficient to be the source of the quartz-overgrowth cements in the associated Frio sandstones. Iron reduction in I/S is amore » significant source of the acid required for the Diagenesis of both Frio shales and sandstones. 68 refs., 12 figs., 4 tabs.« less
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Burial Diagenesis of argillaceous sediment, south Texas Gulf of Mexico sedimentary basin: A reexamination
Geological Society of America Bulletin, 1997Co-Authors: Lynton S. Land, Kitty L. Milliken, Larry E. Mack, F. Leo LynchAbstract:Cuttings from a well through a thick section of Miocene–Oligocene mudrocks from Kenedy County, Texas, spanning a depth range of 2130 to 5490 m (7000 to 18 000 ft), have been studied petrographically and geochemically. On the basis of whole-rock chemical analyses, the deepest samples have lost ≈18 wt% (and approximately vol%), mostly as CaCO3, mineral-bound H2O, and SiO2, but including additional Ca, as well as Sr, light rare earth elements (REE) (La, Ce, Nd, Sm), Fe, and Li. K2O and Rb have been added to the deeper rocks. The large chemical changes are accompanied mineralogically by loss of detrital calcite, kaolinite, K-feldspar, Ca-plagioclase, and muscovite, gain of chlorite and albite, and continued reaction of smectitic illite/smectite (I/S) to more illitic (and K-rich) compositions throughout the entire depth interval of the well. The large chemical changes in this thick mud-rich interval almost certainly require advection of water (free convection?) to accomplish the mass transfer. Initial variation in sediment composition is ruled out as a cause of the observed compositional changes with increasing depth because (1) a variety of “immobile” elements (Al2O3, TiO2, Zr, Hf, heavy REE [Er, Yb], Th, and Sc) remain constant relative to each other despite their uneven distribution across various particle size fractions in the sediments; (2) deep Frio shales are unlike Quaternary Gulf of Mexico sediments or average shales; and (3) unreasonable primary mineralogic compositions would be necessary to explain the chemical composition of the deep samples. These results indicate that Burial Diagenesis of argillaceous sediment can be a considerably more open chemical process than is conventionally assumed, that it can account for the two major chemical cements (calcite and quartz) in associated sandstones, and that it mirrors secular changes in shales throughout geologic time.
