The Pennsylvanian unconformity,which is a detrital surface,separates the beds of the Permian-aged strata from the Lower Paleozoic in the Central Basin Platform.Seismic data interpretation indicates that the unconformi...The Pennsylvanian unconformity,which is a detrital surface,separates the beds of the Permian-aged strata from the Lower Paleozoic in the Central Basin Platform.Seismic data interpretation indicates that the unconformity is an angular unconformity,overlying multiple normal faults,and accompanied with a thrust fault which maximizes the region's structural complexity.Additionally,the Pennsylvanian angular unconformity creates pinch-outs between the beds above and below.We computed the spectral decomposition and reflector convergence attributes and analyzed them to characterize the angular unconformity and faults.The spectral decomposition attribute divides the broadband seismic data into different spectral bands to resolve thin beds and show thickness variations.In contrast,the reflector convergence attribute highlights the location and direction of the pinch-outs as they dip south at angles between 2° and 6°.After reviewing findings from RGB blending of the spectrally decomposed frequencies along the Pennsylvanian unconformity,we observed channel-like features and multiple linear bands in addition to the faults and pinch-outs.It can be inferred that the identified linear bands could be the result of different lithologies associated with the tilting of the beds,and the faults may possibly influence hydrocarbon migration or act as a flow barrier to entrap hydrocarbon accumulation.The identification of this angular unconformity and the associated features in the study area are vital for the following reasons:1)the unconformity surface represents a natural stratigraphic boundary;2)the stratigraphic pinch-outs act as fluid flow connectivity boundaries;3)the areal extent of compartmentalized reservoirs'boundaries created by the angular unconformity are better defined;and 4)fault displacements are better understood when planning well locations as faults can be flow barriers,or permeability conduits,depending on facies heterogeneity and/or seal effectiveness of a fault,which can affect hydrocarbon production.The methodol展开更多
The metasedimentary sequence of the Cushamen Formation in the western North Patagonian Massif is540 m thick and comprises six sedimentary lithofacies associations related to a glacimarine environment.Four of these lit...The metasedimentary sequence of the Cushamen Formation in the western North Patagonian Massif is540 m thick and comprises six sedimentary lithofacies associations related to a glacimarine environment.Four of these lithofacies represent distal glacimarine environments, whereas another one was deposited in proximal glacimarine environments, and the last includes subglacial environments. The organization and configuration of these lithofacies associations represent the advance and retreat of the glacier masses. The maximum glacial advance is correlatable with the G2 glacial interval of the Pennsylvanian Pampa de Tepuel, Las Salinas and Valley Chico, formations of the Extraandean Chubut, and the southern part of Neuquen Cordillera. Contemporaneously, in southern Chile there are marine and glacimarine sediments. The chronostratigraphic relationships between the Silurian to Permian units allow five paleogeographic stages to be distinguished. The middle Silurian-late Devonian igneous rocks represent the first magmatic stage. The second stage, which is transitional to the first, is represented by a marine basin that includes the late Devonian-early Carboniferous Esquel and Rio Pescado formations and the Llanquihue Complex. The third stage(early-late Carboniferous) includes granitoids of the second magmatic event that partially overlapped the first magmatic igneous belt. The fourth stage belongs to the late Carboniferous sedimentation of the Cushamen and equivalent formations. The extended early Permian magmatism was the last Paleozoic event in the studied area.展开更多
Concentrations of redox-sensitive trace-element(RSTE) in marine shales have long been interpreted simply as redox proxies. However, the impact of other non-redox factors(e.g., sea-level fluctuation and seawater chemis...Concentrations of redox-sensitive trace-element(RSTE) in marine shales have long been interpreted simply as redox proxies. However, the impact of other non-redox factors(e.g., sea-level fluctuation and seawater chemistry) on the enrichment of RSTE, especially molybdenum(Mo) and uranium(U), in sediments has been rarely reported. This study presents newly obtained RSTE datasets from the Upper Pennsylvanian organic-rich Cline Shale in the silled Midland Basin, U.S., to illustrate the influence of sea-level fluctuation on the authigenic accumulation of RSTE in marine sediments. A previously established transgressive-regressive sequence of the Cline Shale, a well-constrained high-amplitude glacio-eustatic fluctuation curve, and an accompanying episodic resupply of aqueous RSTE from the Panthalassic Ocean provide an ideal stratigraphic framework for determining the spatial and temporal variations of sediment RSTE enrichment patterns that responded to the episodic variations of seawater chemistry in this marginal silled paleomarine basin. Results suggest that although slightly higher median RSTE concentrations were observed in sediments from more reducing environments, the overall variation ranges of RSTE concentrations largely overlap among sediments deposited from a wide redox spectrum(from oxic to euxinic conditions) or different sea-level statuses in the Cline Shale. In contrast to the sediment RSTE enrichment patterns, the variations of sediment Mo/TOC and U/TOC ratios are coupled with glacio-eustatic fluctuation. The highest Mo/TOC and U/TOC ratios are commonly observed in sediments deposited during the highest relative sea-level(RSTE resupply), whereas the lowest Mo/TOC and U/TOC ratios usually appear in sediments deposited during the lowest relative sea-level(RSTE depletion). Our findings suggest that the benthic redox conditions recorded in sediment Mo and U concentrations can be greatly obscured and weakened by depleted aqueous Mo and U concentrations in highly restricted basins. Thus, the use of sediment Mo a展开更多
Based on drill core and thin section observation,major geochemical element analysis and con-ventional well log analysis,this study summarizes the characteristics and thickness of weathering crust of Pennsylvanian volc...Based on drill core and thin section observation,major geochemical element analysis and con-ventional well log analysis,this study summarizes the characteristics and thickness of weathering crust of Pennsylvanian volcanic rocks(Carboniferous)in Shixi area,Junggar Basin.The weathering crust is identified and divided into three types according to the petrological characteristics and well log interpretations in Shixi area,and the isopach of weathering crust is mapped.The results show that:(1)With the increase of depth,the weathering weakens,and the rocks become less fractured with decreased porosity;(2)the weathering crust of the Upper Carboniferous volcanic rocks can be divided into strongly weathered and mildly weathered layers in Shixi area;(3)the weathering crust is relatively thicker in Dinan uplift and Shixi uplift.This study provides research basis for further evaluation of Upper Carboniferous volcanic reservoir,and will benefit for well location deployment and potential oilfield development in the Shixi area.展开更多
In this work,we intend to investigate the kerogen composition of the Tabenken coal hence,its palaeo-depositional environment and age.Tabenken is one of the three areas in the continental sectors of the CVL(Cameroon Vo...In this work,we intend to investigate the kerogen composition of the Tabenken coal hence,its palaeo-depositional environment and age.Tabenken is one of the three areas in the continental sectors of the CVL(Cameroon Volcanic Line)where coal occurs in between a granitic basement and volcanic outpours.Samples of coal from this seam were studied to determine the organic matter richness,maturity,depositional environment and its age through organic geochemical techniques such as Rock-Eval pyrolysis and palynological studies.HI(Hydrogen Index)obtained is less than 200 mgHC/gTOC for most of the samples indicating Type III kerogen for these samples(gas prone)and terrestrial source of the original peat-forming organic matter.One sample presents a HI of 462 mgHC/gTOC indicating organic matter type II,prone to producing oil.Palynological studies reveal the presence of hydrogen-rich AOM(Amorphous Organic Matter)indicating preservation under dysoxic-anoxic conditions.High values of TOC ranging from 0.29 to 1.98 are suggestive of AOM of terrestrial origin.The remarkable absence of pollen suggestive of deposition before the Pennsylvanian during which the earliest forms of flowering plants first appeared displays a relative abundance of spores in the organic residue suggestive of deposition from the mid-Ordovician.Careful interpretation of palynological data suggests the coal was laid down from the mid-Ordovician to the Pennsylvanian age.展开更多
Based on detailed measurement in the field and a comprehensive analysis of carbonate microfacies,the Pennsylvanian reefal microfacies characteristic and sedimentary environment from Longjiangdong,Guangxi,China are ana...Based on detailed measurement in the field and a comprehensive analysis of carbonate microfacies,the Pennsylvanian reefal microfacies characteristic and sedimentary environment from Longjiangdong,Guangxi,China are analyzed. The twelve carbonate microfacies have been recognized including micritic / microsparitic limestone,peloidal / aggregate-grain grainstone,bioclastic wackestone / packstone,laminated mudstone,boundstone,bioclastic wackestone / packstone with single shell,coral framestone / bafflestone,bioclastic packstones /grainstones with abundant benthic foraminifera or crinoids,wackestone / mudstone with calcispheres,bioclastic packstone / grainstone,unname reef-building organism framestone and brachiopod grainstone. In addition,four facies have been identified including open platform facies,restricted platform facies,coral reefal facies and shoal facies. According to analysis of microfacies combination and facies evolution,three stages and three reef units during the reef formation process have been noted. The evolution of each stage indicates a repeating fluctuation of the sea-level,but the water energy is still relatively low overall,which represents frequent changes of paleoclimate in the early Late Carboniferous.展开更多
The Upper Carboniferous-Lower Permian （Upper Pennsylvanian-Asselian） Tobra Formation is exposed in the Salt and Trans Indus ranges of Pakistan. The formation exhibits an alluvial plain （alluvial fan-piedmont alluvi...The Upper Carboniferous-Lower Permian （Upper Pennsylvanian-Asselian） Tobra Formation is exposed in the Salt and Trans Indus ranges of Pakistan. The formation exhibits an alluvial plain （alluvial fan-piedmont alluvial plain） facies association in the Salt Range and Khisor Range. In addition, a stream flow facies association is restricted to the eastern Salt Range. The alluvial plain facies association is comprised of clast-supported massive conglomerate （Gmc）, diamictite （Dm） facies, and massive sandstone （Sm） iithofacies whereas the stream flow-dominated alluvial plain facies association includes fine-grained sandstone and sUtstone （Fss）, fining upwards pebbly sandstone （Sf）, and massive mudstone （Fro） lithofacies. The lack of glacial signatures （particularly glacial grooves and striations） in the deposits in the Tobra Formation, which are, in contrast, present in their time-equivalent and palaeogeographically nearby strata of the Arabian peninsula, e.g. the Al Khlata Formation of Oman and Unayzah B member of the Sandi Arabia, suggests a pro-to periglacial, i.e. glaciofluvial depositional setting for the Tobra Formation. The sedimentology of the Tobra Formation attests that the Salt Range, Pakistan, occupied a palaeogeographic position just beyond the maximum glacial extent during Upper Pennsylvanian-Asselian time.展开更多
文摘The Pennsylvanian unconformity,which is a detrital surface,separates the beds of the Permian-aged strata from the Lower Paleozoic in the Central Basin Platform.Seismic data interpretation indicates that the unconformity is an angular unconformity,overlying multiple normal faults,and accompanied with a thrust fault which maximizes the region's structural complexity.Additionally,the Pennsylvanian angular unconformity creates pinch-outs between the beds above and below.We computed the spectral decomposition and reflector convergence attributes and analyzed them to characterize the angular unconformity and faults.The spectral decomposition attribute divides the broadband seismic data into different spectral bands to resolve thin beds and show thickness variations.In contrast,the reflector convergence attribute highlights the location and direction of the pinch-outs as they dip south at angles between 2° and 6°.After reviewing findings from RGB blending of the spectrally decomposed frequencies along the Pennsylvanian unconformity,we observed channel-like features and multiple linear bands in addition to the faults and pinch-outs.It can be inferred that the identified linear bands could be the result of different lithologies associated with the tilting of the beds,and the faults may possibly influence hydrocarbon migration or act as a flow barrier to entrap hydrocarbon accumulation.The identification of this angular unconformity and the associated features in the study area are vital for the following reasons:1)the unconformity surface represents a natural stratigraphic boundary;2)the stratigraphic pinch-outs act as fluid flow connectivity boundaries;3)the areal extent of compartmentalized reservoirs'boundaries created by the angular unconformity are better defined;and 4)fault displacements are better understood when planning well locations as faults can be flow barriers,or permeability conduits,depending on facies heterogeneity and/or seal effectiveness of a fault,which can affect hydrocarbon production.The methodol
文摘The metasedimentary sequence of the Cushamen Formation in the western North Patagonian Massif is540 m thick and comprises six sedimentary lithofacies associations related to a glacimarine environment.Four of these lithofacies represent distal glacimarine environments, whereas another one was deposited in proximal glacimarine environments, and the last includes subglacial environments. The organization and configuration of these lithofacies associations represent the advance and retreat of the glacier masses. The maximum glacial advance is correlatable with the G2 glacial interval of the Pennsylvanian Pampa de Tepuel, Las Salinas and Valley Chico, formations of the Extraandean Chubut, and the southern part of Neuquen Cordillera. Contemporaneously, in southern Chile there are marine and glacimarine sediments. The chronostratigraphic relationships between the Silurian to Permian units allow five paleogeographic stages to be distinguished. The middle Silurian-late Devonian igneous rocks represent the first magmatic stage. The second stage, which is transitional to the first, is represented by a marine basin that includes the late Devonian-early Carboniferous Esquel and Rio Pescado formations and the Llanquihue Complex. The third stage(early-late Carboniferous) includes granitoids of the second magmatic event that partially overlapped the first magmatic igneous belt. The fourth stage belongs to the late Carboniferous sedimentation of the Cushamen and equivalent formations. The extended early Permian magmatism was the last Paleozoic event in the studied area.
基金supported by the State of Texas Advanced Resource Recovery (STARR) program at the Bureau of Economic Geology (BEG)minor financial support from the China Scholarship Council (Grant No. 201606440062)the Geological Society of America Graduate Student Research Grant (Grant No. 9244823)。
文摘Concentrations of redox-sensitive trace-element(RSTE) in marine shales have long been interpreted simply as redox proxies. However, the impact of other non-redox factors(e.g., sea-level fluctuation and seawater chemistry) on the enrichment of RSTE, especially molybdenum(Mo) and uranium(U), in sediments has been rarely reported. This study presents newly obtained RSTE datasets from the Upper Pennsylvanian organic-rich Cline Shale in the silled Midland Basin, U.S., to illustrate the influence of sea-level fluctuation on the authigenic accumulation of RSTE in marine sediments. A previously established transgressive-regressive sequence of the Cline Shale, a well-constrained high-amplitude glacio-eustatic fluctuation curve, and an accompanying episodic resupply of aqueous RSTE from the Panthalassic Ocean provide an ideal stratigraphic framework for determining the spatial and temporal variations of sediment RSTE enrichment patterns that responded to the episodic variations of seawater chemistry in this marginal silled paleomarine basin. Results suggest that although slightly higher median RSTE concentrations were observed in sediments from more reducing environments, the overall variation ranges of RSTE concentrations largely overlap among sediments deposited from a wide redox spectrum(from oxic to euxinic conditions) or different sea-level statuses in the Cline Shale. In contrast to the sediment RSTE enrichment patterns, the variations of sediment Mo/TOC and U/TOC ratios are coupled with glacio-eustatic fluctuation. The highest Mo/TOC and U/TOC ratios are commonly observed in sediments deposited during the highest relative sea-level(RSTE resupply), whereas the lowest Mo/TOC and U/TOC ratios usually appear in sediments deposited during the lowest relative sea-level(RSTE depletion). Our findings suggest that the benthic redox conditions recorded in sediment Mo and U concentrations can be greatly obscured and weakened by depleted aqueous Mo and U concentrations in highly restricted basins. Thus, the use of sediment Mo a
基金Supported by 14th Five-year Major Project of CNPC(No.2021DJ0206).
文摘Based on drill core and thin section observation,major geochemical element analysis and con-ventional well log analysis,this study summarizes the characteristics and thickness of weathering crust of Pennsylvanian volcanic rocks(Carboniferous)in Shixi area,Junggar Basin.The weathering crust is identified and divided into three types according to the petrological characteristics and well log interpretations in Shixi area,and the isopach of weathering crust is mapped.The results show that:(1)With the increase of depth,the weathering weakens,and the rocks become less fractured with decreased porosity;(2)the weathering crust of the Upper Carboniferous volcanic rocks can be divided into strongly weathered and mildly weathered layers in Shixi area;(3)the weathering crust is relatively thicker in Dinan uplift and Shixi uplift.This study provides research basis for further evaluation of Upper Carboniferous volcanic reservoir,and will benefit for well location deployment and potential oilfield development in the Shixi area.
文摘In this work,we intend to investigate the kerogen composition of the Tabenken coal hence,its palaeo-depositional environment and age.Tabenken is one of the three areas in the continental sectors of the CVL(Cameroon Volcanic Line)where coal occurs in between a granitic basement and volcanic outpours.Samples of coal from this seam were studied to determine the organic matter richness,maturity,depositional environment and its age through organic geochemical techniques such as Rock-Eval pyrolysis and palynological studies.HI(Hydrogen Index)obtained is less than 200 mgHC/gTOC for most of the samples indicating Type III kerogen for these samples(gas prone)and terrestrial source of the original peat-forming organic matter.One sample presents a HI of 462 mgHC/gTOC indicating organic matter type II,prone to producing oil.Palynological studies reveal the presence of hydrogen-rich AOM(Amorphous Organic Matter)indicating preservation under dysoxic-anoxic conditions.High values of TOC ranging from 0.29 to 1.98 are suggestive of AOM of terrestrial origin.The remarkable absence of pollen suggestive of deposition before the Pennsylvanian during which the earliest forms of flowering plants first appeared displays a relative abundance of spores in the organic residue suggestive of deposition from the mid-Ordovician.Careful interpretation of palynological data suggests the coal was laid down from the mid-Ordovician to the Pennsylvanian age.
基金supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20120042110027,20110042120043)the National Natural Science Foundation of China(No.41202018)
文摘Based on detailed measurement in the field and a comprehensive analysis of carbonate microfacies,the Pennsylvanian reefal microfacies characteristic and sedimentary environment from Longjiangdong,Guangxi,China are analyzed. The twelve carbonate microfacies have been recognized including micritic / microsparitic limestone,peloidal / aggregate-grain grainstone,bioclastic wackestone / packstone,laminated mudstone,boundstone,bioclastic wackestone / packstone with single shell,coral framestone / bafflestone,bioclastic packstones /grainstones with abundant benthic foraminifera or crinoids,wackestone / mudstone with calcispheres,bioclastic packstone / grainstone,unname reef-building organism framestone and brachiopod grainstone. In addition,four facies have been identified including open platform facies,restricted platform facies,coral reefal facies and shoal facies. According to analysis of microfacies combination and facies evolution,three stages and three reef units during the reef formation process have been noted. The evolution of each stage indicates a repeating fluctuation of the sea-level,but the water energy is still relatively low overall,which represents frequent changes of paleoclimate in the early Late Carboniferous.
基金the Higher Education Commission of Pakistan's National Research Program for Universities(NRPU) grant to Dr.Irfan U.Jan,principal investigator on the project via grant number 20-2706
文摘The Upper Carboniferous-Lower Permian （Upper Pennsylvanian-Asselian） Tobra Formation is exposed in the Salt and Trans Indus ranges of Pakistan. The formation exhibits an alluvial plain （alluvial fan-piedmont alluvial plain） facies association in the Salt Range and Khisor Range. In addition, a stream flow facies association is restricted to the eastern Salt Range. The alluvial plain facies association is comprised of clast-supported massive conglomerate （Gmc）, diamictite （Dm） facies, and massive sandstone （Sm） iithofacies whereas the stream flow-dominated alluvial plain facies association includes fine-grained sandstone and sUtstone （Fss）, fining upwards pebbly sandstone （Sf）, and massive mudstone （Fro） lithofacies. The lack of glacial signatures （particularly glacial grooves and striations） in the deposits in the Tobra Formation, which are, in contrast, present in their time-equivalent and palaeogeographically nearby strata of the Arabian peninsula, e.g. the Al Khlata Formation of Oman and Unayzah B member of the Sandi Arabia, suggests a pro-to periglacial, i.e. glaciofluvial depositional setting for the Tobra Formation. The sedimentology of the Tobra Formation attests that the Salt Range, Pakistan, occupied a palaeogeographic position just beyond the maximum glacial extent during Upper Pennsylvanian-Asselian time.
