The Tazhong Uplift of the late Ordovician is a drowned rimmed carbonate platform. The carbonate rock of the late Ordovician Lianglitage Formation in the northern slope of the Tazhong region is one of the significant p...The Tazhong Uplift of the late Ordovician is a drowned rimmed carbonate platform. The carbonate rock of the late Ordovician Lianglitage Formation in the northern slope of the Tazhong region is one of the significant petroliferous intervals. Based on petrofacies, depositional cycles, natural gammaray spectrometry and carbon/oxygen isotope data from the Lianglitage Formation, one 2nd-order, three 3rd-order and several 4th-order sequences have been recognized, and the late Ordovician relative sealevel fluctuation curve has been established. The sequences O3 1-1 and O3 1-2 on the platform are composed of highstand and transgressive systems tracts, but lack the lowstand systems tract. The sequence O3 1-3 is a drowning sequence. The sequence O3 1-1 overlapped the eroded slope and pinched out to the northwest and landward. The highstand systems tract in the sequence O3 1-2 consists of low-angle sigmoid and high-angle shingled progradation configuration. Major sedimentary facies of the Lianglitage Formation include reef and shoal in the platform margin and lagoon, which can be subdivided into coral-sponge-stromatoporoid reef complex, sand shoal, lime mud mound, and intershoal sea. Reefs, sand shoals and their complex are potential reservoir facies. The reefs and sand shoals in the sequence O3 1-1 developed in the upper of its highstand systems tract. In the sequence O3 1-2, the highstand systems tract with an internal prograding configuration is a response to the lateral shifting of the complex of reef and sand shoal. The transgressive systems tract, in particular the sand shoals, developed widely on the slope of the platform margin and interior. The reefs in the sequence O3 1-3 migrated towards high positions and formed retrograding reefs in the western platform and low relief in the platform interior. Basinward lateral migration of the reefs and pure carbonate rock both characterize highstand systems tract and show that the rise of the relative sea-level was very slow. Shingled prograding stacking pattern of the 4th-order sequences and reefs grow horizontally, which represents the late stage of highstand systems tract and implies relative sealevel stillstand. Reefs migrating towards high land and impure carbonate rock both indicate transgressive systems tract and suggest that the relative sea-level rose fast. Erosional truncation and epidiagenetic karstification represent a falling relative sea-level. The relative sea-level fluctuation and antecedent palaeotopography control the development and distribution of reef complexes and unconformity karst zones. Currently, the composite zone of epidiagenetic karstic intervals and high-energy complexes of reefs and sand shoals with prograding configuration is an important oil and gas reservoir in the northern slope of the Tazhong carbonate platform.展开更多
The amplitude of pre-Quaternary sea level drop, H, can be calculated by usingthe formula H = D + To, where To is the original thickness from the top of the tidal deposits onthe reef core to the bottom of the tidal dep...The amplitude of pre-Quaternary sea level drop, H, can be calculated by usingthe formula H = D + To, where To is the original thickness from the top of the tidal deposits onthe reef core to the bottom of the tidal deposits on the reef front, or to the bottom of the ancientmeteoric vadose zone, or to the edge of the mixed-water dolostone zone. The identity and similaritybetween the sea-level drop amplitudes calculated from different reefs far away from each otherindicates that such sea-level changes are eustatic rather than relative changes. Evidence of anend-Permian sea-level drop has been found on the Changxingian (i.e. the end of the Palaeofusulinazone) reefs at Ziyun in South China, including algal laminated deposits, sabkha-related dolostone,desiccation cracks, dissolution collapse breccia. According to calculation based on the meteoricdissolution zone of the reef-core sequence at Ziyun, Guizhou province, the amplitude of thesea-level drop at the end-Permian is about 89.3 m. Calculation via the dolomitized upper part of theChangxingian reef in Lichuan, Hubei Province, yields an 88.9 m amplitude of the sea-level drop atthe end-Permian. Comparison shows that the sea-level drop recorded in the two distantly locatedreefs may be of eustatic type. So the amplitude of the sea level drop of the Tethys Sea at theend-Permian might be at least 89.3 m.展开更多
Methods for calculating ancient eustatic change amplitudes according to reef fabric- facies are proposed, with a new method for determining sediment-loading subsidence. Compared with methods based on non-reefal deposi...Methods for calculating ancient eustatic change amplitudes according to reef fabric- facies are proposed, with a new method for determining sediment-loading subsidence. Compared with methods based on non-reefal deposits, these methods are more accurate in restoration of original sediment thickness, determination of sediment-loading subsidence, as well as restoration of ancient water depth. According to the reef in Guangxi, China, the amplitude of sea-level rise during Middle Permian (Neoschwagerina-Yabeina zone) is 249.5 m. According to the coeval reef of the Guadalupe Mountains, New Mexico and Texas, the coeval sea-level rise is 247 m. With these effective methods available, it is feasible to establish more accurate eustatic curve of Phanerozoic.展开更多
The Monards Marsh is located on the northeastern bank of the Gironde Estuary in France. Lithological, sedimentolngical and mi- cropalacontological investigations were made on four cores to determine the evolution of H...The Monards Marsh is located on the northeastern bank of the Gironde Estuary in France. Lithological, sedimentolngical and mi- cropalacontological investigations were made on four cores to determine the evolution of Holocene sedimentary environments and processes in this area over the last 6 000 a. Three main lithological facies are distinguished from bottom to top: ( 1 ) grey laminated silty-sandy clay ; (2) homogeneous dark grey silty clay ; and ( 3 ) compact silty clay. About 26 benthic foraminifera species are identified and divided into six groups according to their ecological characteristics. In association with lithology, sedimentary structures and grainuiometry, the distribution of foraminifera group is used to define external slikke, internal slikke, external schorre, internal schorre, and continental marsh facies. Combined with 14C(AMS) dating, these data indicate four successive paleoenvironments in the Monards Marsh: ( 1 ) Holocene transgression resuited in the development of a basal schorre facies overlying fluvial deposits that transformed to slikke facies sedimentation; the transgression maximum occurred around 5 600 to 5 4430 a BP and was inferred to be associated with the last phase of the rapid Holocene sea-level rise; (2) post-trangressive maximum sedimentation resuited in a regressive sequence of deposits prograding towards the estuary, corresponding to the stahilisation of sea level after 5 4430 a BP; (3) a slight positive tendency in the sea level around 2 800 a BP recorded in the central part of the marsh; and (4) the wetland to a continental marsh environment. The sequential pattern for the evolution of wetlands in this estuarine area during the Holocene is fluvial facies - blackish schorre facies - slikke facies - blackish schorre facies - continental marsh facies. Characteristics of sedimentary facies distribution and evolution reveal that the development of Holocene salt marsh in this area was controlled by the sea-level change and tidal range. The sedimentary facies show an obvious surficial and vertical banding distribution in which the texture and structure, authigenie mineral, foraminifera distribution and bioturbation indicate many distinct difference characteristics.展开更多
Based on stratigraphic variations of petrology,geochemistry(major,trace elements),and pyrite framboids,we study the sedimentary environment of siliceous rocks of the Wufeng Formation in Wuxi,Northeastern Chongqing,Chi...Based on stratigraphic variations of petrology,geochemistry(major,trace elements),and pyrite framboids,we study the sedimentary environment of siliceous rocks of the Wufeng Formation in Wuxi,Northeastern Chongqing,China.Coupled Al2O3/(Al2O3þFe2O3),SiO2/Al2O3,with AleFeeMn values indicate that Wufeng Formation are deposited in a continental margin and influenced by detrital input.UEF-MoEF and V/CreU/Th cross-plots suggest that the siliceous shale was formed in dysoxic to anoxic conditions.Redox proxies imply that the lower,the middle to upper,and the top part of the Wufeng sediments were deposited in an anoxic,dysoxic and oxic environment,respectively.Accordingly,the average size of pyrite framboids are gradually increased from bottom to top,showing that increased oxidisability.A complete vibratory third-order cycle of sea level fluctuations during the Wufeng deposition can be identified.During Wufeng to Longmaxi transition,the sedimentary environment exhibits a short-scale oscillatory pattern and was probably transformed from an outer shelf to inner shelf.Coupled multi-proxies are considered more reliable proxies for deciphering redox conditions in fine-grained sediment.展开更多
Sedimentary successions in the northwestern Gulf of Suez provide important clues to the understanding of the geological evolution of NE Africa during the middle and late Eocene.This study focuses on detailed facies an...Sedimentary successions in the northwestern Gulf of Suez provide important clues to the understanding of the geological evolution of NE Africa during the middle and late Eocene.This study focuses on detailed facies analyses in order to characterize the depositional environments and system tracts of the Bartonian-Priabonian succession cropping out in this area.Bartonian-Priabonian carbonate deposits in five stratigraphic sections constitute,from base to top,the Gebel Hof,Observatory,Sannur,Qurn,and Wadi Hof Formations.These formations contain four local assemblage zones of larger benthic foraminifers.Analyses of litho-,bio-,and microfacies in the succession resulted in the recognition of 12 lithofacies types.These lithofacies are represented by packages of lime-mudstones,wackestones,packstones,pack-to grainstones,grainstones,rudstones,boundstones and dolomites.These lithofacies have been grouped into four geneticallyrelated facies associations that represent,respectively,tidal flats/shallow subtidal,restricted-shelf/lagoonal,shoal bar,and outer-shelf lagoon/reefal depositional environments in a downslope shallow-marine inner-ramp setting.The vertical transitions of these facies associations,representing facies changes through time,imply fluctuations of the regional sea level.The two peaks in the Bartonian correspond to well-known global eustatic sea-level rises;the pronounced Priabonian regression must be ascribed to the known global eustatic sea-level fall in combination with regional tectonic activity.The facies distribution suggests that the study area was located in the direct vicinity of some islands during the Bartonian-Priabonian.展开更多
基金supported by the National Key Basic Research and Development Program of China (Grant No.2006CB202302)
文摘The Tazhong Uplift of the late Ordovician is a drowned rimmed carbonate platform. The carbonate rock of the late Ordovician Lianglitage Formation in the northern slope of the Tazhong region is one of the significant petroliferous intervals. Based on petrofacies, depositional cycles, natural gammaray spectrometry and carbon/oxygen isotope data from the Lianglitage Formation, one 2nd-order, three 3rd-order and several 4th-order sequences have been recognized, and the late Ordovician relative sealevel fluctuation curve has been established. The sequences O3 1-1 and O3 1-2 on the platform are composed of highstand and transgressive systems tracts, but lack the lowstand systems tract. The sequence O3 1-3 is a drowning sequence. The sequence O3 1-1 overlapped the eroded slope and pinched out to the northwest and landward. The highstand systems tract in the sequence O3 1-2 consists of low-angle sigmoid and high-angle shingled progradation configuration. Major sedimentary facies of the Lianglitage Formation include reef and shoal in the platform margin and lagoon, which can be subdivided into coral-sponge-stromatoporoid reef complex, sand shoal, lime mud mound, and intershoal sea. Reefs, sand shoals and their complex are potential reservoir facies. The reefs and sand shoals in the sequence O3 1-1 developed in the upper of its highstand systems tract. In the sequence O3 1-2, the highstand systems tract with an internal prograding configuration is a response to the lateral shifting of the complex of reef and sand shoal. The transgressive systems tract, in particular the sand shoals, developed widely on the slope of the platform margin and interior. The reefs in the sequence O3 1-3 migrated towards high positions and formed retrograding reefs in the western platform and low relief in the platform interior. Basinward lateral migration of the reefs and pure carbonate rock both characterize highstand systems tract and show that the rise of the relative sea-level was very slow. Shingled prograding stacking pattern of the 4th-order sequences and reefs grow horizontally, which represents the late stage of highstand systems tract and implies relative sealevel stillstand. Reefs migrating towards high land and impure carbonate rock both indicate transgressive systems tract and suggest that the relative sea-level rose fast. Erosional truncation and epidiagenetic karstification represent a falling relative sea-level. The relative sea-level fluctuation and antecedent palaeotopography control the development and distribution of reef complexes and unconformity karst zones. Currently, the composite zone of epidiagenetic karstic intervals and high-energy complexes of reefs and sand shoals with prograding configuration is an important oil and gas reservoir in the northern slope of the Tazhong carbonate platform.
基金financially supported by the National Natural Science Foundation of China(No.40172007)the key project from the Chinese Academy of Sciences(No.K2951-B1-409)the Key Lab of Resources,CAS.
文摘The amplitude of pre-Quaternary sea level drop, H, can be calculated by usingthe formula H = D + To, where To is the original thickness from the top of the tidal deposits onthe reef core to the bottom of the tidal deposits on the reef front, or to the bottom of the ancientmeteoric vadose zone, or to the edge of the mixed-water dolostone zone. The identity and similaritybetween the sea-level drop amplitudes calculated from different reefs far away from each otherindicates that such sea-level changes are eustatic rather than relative changes. Evidence of anend-Permian sea-level drop has been found on the Changxingian (i.e. the end of the Palaeofusulinazone) reefs at Ziyun in South China, including algal laminated deposits, sabkha-related dolostone,desiccation cracks, dissolution collapse breccia. According to calculation based on the meteoricdissolution zone of the reef-core sequence at Ziyun, Guizhou province, the amplitude of thesea-level drop at the end-Permian is about 89.3 m. Calculation via the dolomitized upper part of theChangxingian reef in Lichuan, Hubei Province, yields an 88.9 m amplitude of the sea-level drop atthe end-Permian. Comparison shows that the sea-level drop recorded in the two distantly locatedreefs may be of eustatic type. So the amplitude of the sea level drop of the Tethys Sea at theend-Permian might be at least 89.3 m.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 40172007) the Chinese Academy of Sciences (Grant No. K2951 -B 1 -409).
文摘Methods for calculating ancient eustatic change amplitudes according to reef fabric- facies are proposed, with a new method for determining sediment-loading subsidence. Compared with methods based on non-reefal deposits, these methods are more accurate in restoration of original sediment thickness, determination of sediment-loading subsidence, as well as restoration of ancient water depth. According to the reef in Guangxi, China, the amplitude of sea-level rise during Middle Permian (Neoschwagerina-Yabeina zone) is 249.5 m. According to the coeval reef of the Guadalupe Mountains, New Mexico and Texas, the coeval sea-level rise is 247 m. With these effective methods available, it is feasible to establish more accurate eustatic curve of Phanerozoic.
文摘The Monards Marsh is located on the northeastern bank of the Gironde Estuary in France. Lithological, sedimentolngical and mi- cropalacontological investigations were made on four cores to determine the evolution of Holocene sedimentary environments and processes in this area over the last 6 000 a. Three main lithological facies are distinguished from bottom to top: ( 1 ) grey laminated silty-sandy clay ; (2) homogeneous dark grey silty clay ; and ( 3 ) compact silty clay. About 26 benthic foraminifera species are identified and divided into six groups according to their ecological characteristics. In association with lithology, sedimentary structures and grainuiometry, the distribution of foraminifera group is used to define external slikke, internal slikke, external schorre, internal schorre, and continental marsh facies. Combined with 14C(AMS) dating, these data indicate four successive paleoenvironments in the Monards Marsh: ( 1 ) Holocene transgression resuited in the development of a basal schorre facies overlying fluvial deposits that transformed to slikke facies sedimentation; the transgression maximum occurred around 5 600 to 5 4430 a BP and was inferred to be associated with the last phase of the rapid Holocene sea-level rise; (2) post-trangressive maximum sedimentation resuited in a regressive sequence of deposits prograding towards the estuary, corresponding to the stahilisation of sea level after 5 4430 a BP; (3) a slight positive tendency in the sea level around 2 800 a BP recorded in the central part of the marsh; and (4) the wetland to a continental marsh environment. The sequential pattern for the evolution of wetlands in this estuarine area during the Holocene is fluvial facies - blackish schorre facies - slikke facies - blackish schorre facies - continental marsh facies. Characteristics of sedimentary facies distribution and evolution reveal that the development of Holocene salt marsh in this area was controlled by the sea-level change and tidal range. The sedimentary facies show an obvious surficial and vertical banding distribution in which the texture and structure, authigenie mineral, foraminifera distribution and bioturbation indicate many distinct difference characteristics.
基金This research was funded by the National Major projects of Science and Technology(Grant No.2017ZX05001001-002)the Project of Sichuan Key Laboratory of Natural Gas Geology of China(Grant No.2015trqdz01)
文摘Based on stratigraphic variations of petrology,geochemistry(major,trace elements),and pyrite framboids,we study the sedimentary environment of siliceous rocks of the Wufeng Formation in Wuxi,Northeastern Chongqing,China.Coupled Al2O3/(Al2O3þFe2O3),SiO2/Al2O3,with AleFeeMn values indicate that Wufeng Formation are deposited in a continental margin and influenced by detrital input.UEF-MoEF and V/CreU/Th cross-plots suggest that the siliceous shale was formed in dysoxic to anoxic conditions.Redox proxies imply that the lower,the middle to upper,and the top part of the Wufeng sediments were deposited in an anoxic,dysoxic and oxic environment,respectively.Accordingly,the average size of pyrite framboids are gradually increased from bottom to top,showing that increased oxidisability.A complete vibratory third-order cycle of sea level fluctuations during the Wufeng deposition can be identified.During Wufeng to Longmaxi transition,the sedimentary environment exhibits a short-scale oscillatory pattern and was probably transformed from an outer shelf to inner shelf.Coupled multi-proxies are considered more reliable proxies for deciphering redox conditions in fine-grained sediment.
文摘Sedimentary successions in the northwestern Gulf of Suez provide important clues to the understanding of the geological evolution of NE Africa during the middle and late Eocene.This study focuses on detailed facies analyses in order to characterize the depositional environments and system tracts of the Bartonian-Priabonian succession cropping out in this area.Bartonian-Priabonian carbonate deposits in five stratigraphic sections constitute,from base to top,the Gebel Hof,Observatory,Sannur,Qurn,and Wadi Hof Formations.These formations contain four local assemblage zones of larger benthic foraminifers.Analyses of litho-,bio-,and microfacies in the succession resulted in the recognition of 12 lithofacies types.These lithofacies are represented by packages of lime-mudstones,wackestones,packstones,pack-to grainstones,grainstones,rudstones,boundstones and dolomites.These lithofacies have been grouped into four geneticallyrelated facies associations that represent,respectively,tidal flats/shallow subtidal,restricted-shelf/lagoonal,shoal bar,and outer-shelf lagoon/reefal depositional environments in a downslope shallow-marine inner-ramp setting.The vertical transitions of these facies associations,representing facies changes through time,imply fluctuations of the regional sea level.The two peaks in the Bartonian correspond to well-known global eustatic sea-level rises;the pronounced Priabonian regression must be ascribed to the known global eustatic sea-level fall in combination with regional tectonic activity.The facies distribution suggests that the study area was located in the direct vicinity of some islands during the Bartonian-Priabonian.