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John P Grotzinger - One of the best experts on this subject based on the ideXlab platform.
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depositional facies and platform architecture of microbialite dominated carbonate reservoirs ediacaran cambrian ara group sultanate of oman
AAPG Bulletin, 2014Co-Authors: John P Grotzinger, Zuwaina AlrawahiAbstract:Intrasalt carbonates of the Ediacaran–Cambrian Ara Group constitute a significant reservoir element of the intrasalt “stringer” play in Oman, in which dolomitic carbonates are encased in salt at depths of 3 to 7 km (1.9 to 4.3 mi). These reservoir carbonates have significant microbial influences. Although Ara Group reservoirs are mostly latest Precambrian, the models developed here may be applicable to younger microbially dominated carbonate reservoirs in basins of higher salinity when higher organisms are excluded, in lacustrine settings where calcified invertebrates are not a significant source of carbonate, or after periods of mass extinction before faunal recovery. A broad range of carbonate facies provides the context in which to understand the origin of the microbialite-dominated reservoirs developed across both ramp and rimmed shelf profiles. Major facies associations include carbonate-evaporite transition zone, deep ramp and slope, subtidal microbialites, clastic-textured carbonates, and restricted peritidal carbonates. Microbialites are subdivisible into a number of facies that all have significance in terms of understanding environmental history as well as reservoir properties, and that help in predicting the location of reservoir fairways. Microbially influenced facies include shallow subtidal Thrombolites with massive clotted textures and very high initial porosities (>50%), shallow subtidal pustular laminites with cm-scale variability of lamina morphology, deeper subtidal crinkly laminites that show mm-scale variability of lamina morphology, and intertidal tufted laminates that show mm- to cm-scale tufted textures. Other reservoir facies are more conventional grainy carbonates including ripple cross-stratified grainstone–packstone, hummocky cross-stratified grainstone–packstone, flat pebble conglomerate, ooid and intraclast grainstone–packstone, and Cloudina grainstone–packstone. These facies are almost invariably dolomitized and all have moderate to excellent reservoir quality. These facies comprise carbonate platforms, broken up during salt tectonics, that range up to 160 m (525 ft) in thickness and extended laterally, prior to halokinesis, for tens to over 50 km (31 mi). The distribution of reservoir facies follows sequence stratigraphic predictions, with microbialites occurring in every accommodation profile. Late highstand and early transgressive systems tracts favor greater lateral extent of Thrombolite build-ups, whereas later transgressive to early highstand system tracts favor greater lateral discontinuity and compartmentalization of buildup reservoir facies. Pustular laminites occur in close association with Thrombolite buildups but form laterally extensive sheets in late transgressive to late highstand periods. Crinkly laminites form during late transgressive to early highstand systems tracts and may represent maximum flooding intervals when the flux of carbonate sediment was greatly reduced allowing pelagically derived organics to accumulate.
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digital characterization of Thrombolite stromatolite reef distribution in a carbonate ramp system terminal proterozoic nama group namibia
AAPG Bulletin, 2005Co-Authors: Erwin W Adams, John P Grotzinger, W A Watters, Stefan Schroder, David S Mccormick, Hisham A AlsiyabiAbstract:The stratigraphic architecture of a terminal Proterozoic carbonate ramp system (ca. 550 Ma, Nama Group, Namibia) was mapped quantitatively with digital surveying technologies. The carbonate ramp consists of a shoaling-upward ramp sequence in which Thrombolite-stromatolite reefs developed at several stratigraphic levels. The reefs are associated with grainstone and heterolithic facies and exhibit diverse geometries and dimensions related to the position in the sequence-stratigraphic framework. Laterally extensive reefs with a tabular geometry developed when accommodation was relatively low, whereas discontinuous oblate dome-shaped reefs developed during times when accommodation space was relatively high. Collecting sedimentological and stratigraphic data digitally in an extensive canyon system allowed a comprehensive documentation of the three-dimensional (3-D) architecture and dimensions of the reefal buildups. Both deterministic and stochastic methods were used to extend outcrop observations to construct 3-D models that honor the observed stratigraphy. In particular, the accuracy with which dimensions of reefal buildups can be measured is critically important in the statistical modeling of the dome-shaped buildups. Calculations and corrections can be applied directly to the digital data set and serve as input during model building. The final 3-D model faithfully reproduces the outcrop distribution of facies and geological objects and has a high spatial resolution, compared with petroleum industry reservoir models. The organization of the reefal buildups in the stratigraphic framework has direct implications for reservoir continuity and connectivity in analogous settings. The digital characterization and 3-D outcrop models presented in this article can be subsequently used to condition dynamic reservoir-simulation modeling of geologically similar areas.
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digital reconstruction and stratigraphic evolution of a microbial dominated isolated carbonate platform terminal proterozoic nama group namibia
Journal of Sedimentary Research, 2004Co-Authors: Erwin W Adams, John P Grotzinger, Stefan Schroder, David S MccormickAbstract:ABSTRACT A terminal Proterozoic (ca. 550 Ma) isolated carbonate platform developed downdip on a carbonate ramp of the Nama Group of southern Namibia. The stratigraphic evolution of the platform was reconstructed from an extensive dataset that was compiled by using digital surveying technologies and traditional outcrop observations. Digital field geology techniques enabled rapid and accurate mapping over the 10 km outcrop belt, with spatial and geological information captured at scales ranging from centimeters to kilometers. Furthermore, these digital geology techniques made the reconstruction and interpretation of the development of the carbonate platform considerably more efficient and quantitative. The carbonate platform deposits encompass three accommodation cycles in which each subsequent cycle experienced progressively greater influence of a long-term accommodation increase. Aggradation and progradation during the first cycle produced a flat-topped, sheet-like platform. Deposits of the first cycle show a coarsening-upward motif grading from dominantly columnar stromatolitic Thrombolites and interbedded mudstone-grainstone at the base, to dominantly massive and cross-bedded dolostones toward the top. The second cycle features aggradation and is typified by the formation of a distinct margin and development of a bucket-shaped geometry. The margin contained Thrombolite mounds and domes, whereas columnar stromatolitic Thrombolites dominated the platform interior. The third and last cycle records a gradual deepening trend with initial aggradation and formation of well-bedded, thin deposits in the interior and microbial mounds at the margins. While the interior drowned, the platform margins kept up with rising sea level and complex pinnacle reefs formed, which contained fused and coalesced Thrombolite mounds flanked by bioclastic grainstones and collapse breccias. The top of the unit consists of a set of isolated large Thrombolite mounds flanked by shale, and is interpreted to indicate the final stage of the carbonate platform before drowning. The overall geometric evolution and spatial scale of this platform, from flat-topped to bucket-shaped with elevated margins, is recorded in many Proterozoic and Phanerozoic isolated carbonate platforms. This study clearly illustrates that accommodation changes are a fundamental control on the development of carbonate platforms, regardless of whether they are formed from microbial or metazoan components, or are of Precambrian or Phanerozoic age. Significantly, the architectural elements and spatial dimensions are comparable throughout earth history.
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calcified metazoans in Thrombolite stromatolite reefs of the terminal proterozoic nama group namibia
Paleobiology, 2000Co-Authors: John P Grotzinger, W A Watters, Andrew H KnollAbstract:Abstract Reefs containing abundant calcified metazoans occur at several stratigraphic levels within carbonate platforms of the terminal Proterozoic Nama Group, central and southern Namibia. The reef-bearing strata span an interval ranging from approximately 550 Ma to 543 Ma. The reefs are composed of Thrombolites (clotted internal texture) and stromatolites (laminated internal texture) that form laterally continuous biostromes, isolated patch reefs, and isolated pinnacle reefs ranging in scale from a meter to several kilometers in width. Stromatolite-dominated reefs occur in depositionally updip positions within carbonate ramps, whereas Thrombolite-dominated reefs occur broadly across the ramp profile and are well developed as pinnacle reefs in downdip positions. The three-dimensional morphology of reef-associated fossils was reconstructed by computer, based on digitized images of sections taken at 25-micron intervals through 15 fossil specimens and additionally supported by observations of over 90 sets o...
Andrew H Knoll - One of the best experts on this subject based on the ideXlab platform.
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environmental covariation of metazoans and microbialites in the lower ordovician boat harbour formation newfoundland
Palaeogeography Palaeoclimatology Palaeoecology, 2017Co-Authors: Sara B Pruss, Andrew H KnollAbstract:Abstract An antagonistic view of the relationship between microbialites and metazoans has long been inferred, in part because of the large scale anticorrelation of these two groups through geologic time. The nexus of this relationship occurs in the Early Paleozoic Era: stromatolites declined in abundance as complex animals and algae diversified, but Thrombolites, a type of microbialite little known before the Proterozoic-Cambrian boundary, proliferated for the first time. Well-preserved parasequences in the basal portion of the Lower Ordovician Boat Harbour Formation, western Newfoundland, contain a succession of stromatolites and Thrombolites that permit an investigation into the role metazoans played in shaping the nature and abundance of microbialites in Early Paleozoic carbonate seas. Sessile benthic animals colonized Thrombolite surfaces, but are nearly absent from stromatolites. Bioturbation rarely co-occurred with microbialites, but is widespread in clastic carbonates that lack microbialites. Our results, thus, support the hypothesis of ecological antagonism between microbial communities and motile benthic animals, but also demonstrate biological facilitation between Thrombolites and both sessile benthic animals and nekton.
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calcified metazoans in Thrombolite stromatolite reefs of the terminal proterozoic nama group namibia
Paleobiology, 2000Co-Authors: John P Grotzinger, W A Watters, Andrew H KnollAbstract:Abstract Reefs containing abundant calcified metazoans occur at several stratigraphic levels within carbonate platforms of the terminal Proterozoic Nama Group, central and southern Namibia. The reef-bearing strata span an interval ranging from approximately 550 Ma to 543 Ma. The reefs are composed of Thrombolites (clotted internal texture) and stromatolites (laminated internal texture) that form laterally continuous biostromes, isolated patch reefs, and isolated pinnacle reefs ranging in scale from a meter to several kilometers in width. Stromatolite-dominated reefs occur in depositionally updip positions within carbonate ramps, whereas Thrombolite-dominated reefs occur broadly across the ramp profile and are well developed as pinnacle reefs in downdip positions. The three-dimensional morphology of reef-associated fossils was reconstructed by computer, based on digitized images of sections taken at 25-micron intervals through 15 fossil specimens and additionally supported by observations of over 90 sets o...
Diego C Garciabellido - One of the best experts on this subject based on the ideXlab platform.
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geobiology of a lower cambrian carbonate platform pedroche formation ossa morena zone spain
Palaeogeography Palaeoclimatology Palaeoecology, 2013Co-Authors: Jessica R Creveling, D C Fernandezremolar, Marta Rodriguezmartinez, Silvia Menendez, Kristin D Bergmann, Benjamin C Gill, John Abelson, Ricardo Amils, B L Ehlmann, Diego C GarciabellidoAbstract:The Cambrian Pedroche Formation comprises a mixed siliciclastic–carbonate succession recording subtidal deposition on a marine platform. Carbonate carbon isotope chemostratigraphy confirms previous biostratigraphic assignment of the Pedroche Formation to the Atdabanian regional stage of Siberia, correlative to Cambrian Series 2. At the outcrop scale, thrombolitic facies comprise ~ 60% of carbonate-normalized stratigraphy and coated-grains another ~ 10%. Petrographic point counts reveal that skeletons contribute at most 20% to thrombolitic inter-reef and reef-flank lithologies; on average, archaeocyath clasts make up 68% of skeletal materials. In contrast, petrographic point counts show that skeletons comprise a negligible volume of biohermal and biostromal Thrombolite, associated nodular carbonate facies, and ooid, oncoid and peloid grainstone facies. As such, archaeocyathan reefal bioconstructions represent a specific and limited locus of skeletal carbonate production and deposition. Consistent with data from coeval, globally dispersed lower Cambrian successions, our analysis of the Pedroche Formation supports the view that lower Cambrian carbonates have more in common with earlier, Neoproterozoic deposits than with younger carbonates dominated by skeletal production and accumulation.
James G Ogg - One of the best experts on this subject based on the ideXlab platform.
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a permian triassic boundary microbialite deposit from the eastern yangtze platform jiangxi province south china geobiologic features ecosystem composition and redox conditions
Palaeogeography Palaeoclimatology Palaeoecology, 2017Co-Authors: Yuheng Fang, Yu Pei, Hao Yang, James G OggAbstract:Abstract A Permian-Triassic (P-Tr) boundary microbialite (PTB-microbialite) deposit occurs near Xiushui on the southern margin of the eastern Yangtze Platform, South China. This 2-m-thick microbialite overlies uppermost Permian bioclastic limestone with a 5-cm-thick oolite-like grainstone layer at the contact. This PTB-microbialite consists of lower Thrombolite (1.5-m thick) and an upper dendrolite (0.5-m thick). The Thrombolite interval is characterized by a clotted texture of reddish sparitic patches embedded in a gray micritic matrix, whereas the dendrolite texture consists of brownish sparitic patches embedded within a yellow micritic matrix. Abundant calcified microbes occur in both the Thrombolite and the dendrolite, including 1) columnar and clustered fabrics, which are especially rich in the Thrombolite, assigned as products of Gakhumella or related microorganisms and 2) microspheroids, 40–60 μm in diameter, with different interior structures. These calcimicrobes are considered to have played an important role in constructing the Xiushui PTB-microbialite. The demise of the microbialite was likely due to a sea-level fall during the early Griesbachian (lowermost Triassic), which resulted in a lowering of the wave base thereby destroying the microbialite frameworks and facilitating the deposition of winnowed skeletal grainstone. Metazoan community structures within the microbialite changed sharply across the end-Permian extinction horizon, which is placed at a sharp negative shift in δ 13 C carb . Quantitative analyses show that the Xiushui microbialite community is similar to that of Chongyang and Cili microbialites. This is probably because all of these microbialites grew along the margins of the Lower Yangtze region during the P-Tr transition. However, unlike other PTB-microbialites, the Xiushui ecosystem contains fairly abundant metazoans, which are dominated by ostracods with minor occurrences of foraminifers, microgastropods and microconchids. Both the ostracod assemblage and the pyrite framboid analyses indicate an upper dysoxic zone to a well-oxygenated condition for the Xiushui microbialite. This implies that some PTB-microbialite ecosystems developed in conditions that were not always harsh; instead, some were hospitable for some metazoans to survive immediately after the end-Permian crisis. Considering that the redox conditions indicated by PTB-microbialites are quite variable, we infer that oxygen levels probably were not the crucial factor affecting the growth of the PTB-microbialites.
Zuwaina Alrawahi - One of the best experts on this subject based on the ideXlab platform.
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depositional facies and platform architecture of microbialite dominated carbonate reservoirs ediacaran cambrian ara group sultanate of oman
AAPG Bulletin, 2014Co-Authors: John P Grotzinger, Zuwaina AlrawahiAbstract:Intrasalt carbonates of the Ediacaran–Cambrian Ara Group constitute a significant reservoir element of the intrasalt “stringer” play in Oman, in which dolomitic carbonates are encased in salt at depths of 3 to 7 km (1.9 to 4.3 mi). These reservoir carbonates have significant microbial influences. Although Ara Group reservoirs are mostly latest Precambrian, the models developed here may be applicable to younger microbially dominated carbonate reservoirs in basins of higher salinity when higher organisms are excluded, in lacustrine settings where calcified invertebrates are not a significant source of carbonate, or after periods of mass extinction before faunal recovery. A broad range of carbonate facies provides the context in which to understand the origin of the microbialite-dominated reservoirs developed across both ramp and rimmed shelf profiles. Major facies associations include carbonate-evaporite transition zone, deep ramp and slope, subtidal microbialites, clastic-textured carbonates, and restricted peritidal carbonates. Microbialites are subdivisible into a number of facies that all have significance in terms of understanding environmental history as well as reservoir properties, and that help in predicting the location of reservoir fairways. Microbially influenced facies include shallow subtidal Thrombolites with massive clotted textures and very high initial porosities (>50%), shallow subtidal pustular laminites with cm-scale variability of lamina morphology, deeper subtidal crinkly laminites that show mm-scale variability of lamina morphology, and intertidal tufted laminates that show mm- to cm-scale tufted textures. Other reservoir facies are more conventional grainy carbonates including ripple cross-stratified grainstone–packstone, hummocky cross-stratified grainstone–packstone, flat pebble conglomerate, ooid and intraclast grainstone–packstone, and Cloudina grainstone–packstone. These facies are almost invariably dolomitized and all have moderate to excellent reservoir quality. These facies comprise carbonate platforms, broken up during salt tectonics, that range up to 160 m (525 ft) in thickness and extended laterally, prior to halokinesis, for tens to over 50 km (31 mi). The distribution of reservoir facies follows sequence stratigraphic predictions, with microbialites occurring in every accommodation profile. Late highstand and early transgressive systems tracts favor greater lateral extent of Thrombolite build-ups, whereas later transgressive to early highstand system tracts favor greater lateral discontinuity and compartmentalization of buildup reservoir facies. Pustular laminites occur in close association with Thrombolite buildups but form laterally extensive sheets in late transgressive to late highstand periods. Crinkly laminites form during late transgressive to early highstand systems tracts and may represent maximum flooding intervals when the flux of carbonate sediment was greatly reduced allowing pelagically derived organics to accumulate.