Located northwest of the Jiangshan-Shaoxing Fault Zone,western and northwestern Zhejiang and northeastern Jiangxi provinces experienced major changes in bio-and litho-facies and paleogeography through the Ordovician-S...Located northwest of the Jiangshan-Shaoxing Fault Zone,western and northwestern Zhejiang and northeastern Jiangxi provinces experienced major changes in bio-and litho-facies and paleogeography through the Ordovician-Silurian transition (late Katian,Hirnantian,and early Rhuddanian),as manifested by stratigraphic,paleontologic and synecologic records.Three geographic units under consideration are South,Central,and North areas.The western margin of the South area was occupied by the Huaiyu Mountains,whereas the other two parts were covered by the Zhe-Gan Sea during late Katian (Late Ordovician) time.In the early stage of the Changwu Formation deposition (late Katian),the sea was deepening northeastward,but with shallower conditions in the southwest and deeper conditions in the northeast.During mid to late stages of Changwu Formation deposition (latest Katian),the sea became much shallower and the sea bottom was uplifted substantially,which occurred somewhat prior to the global trend.During the Hirnantian (latest Ordovician) and early Rhuddanian (earliest Silurian),the study region became a shallow bay under expansion of the Cathaysian Oldland.There occurred a major drop of sea level and great changes in benthic biota with the occurrence of many new immigrants through the Ordovician-Silurian transition,which are closely related to a unique regional orogeny.The Yangtze and Cathaysian blocks may have amalgamated within the South China Paleoplate during this interval to cause the continuous uplifting and northwestward expansion of the Cathaysian Oldland.展开更多
More than 20 K-bentonite beds were discovered from the Wufeng Formation and the lowest Longmaxi Formation in two sections, both adjacent to the Ordovician-Silurian (O-S) bound-ary and located in Tongzi, Guizhou Provin...More than 20 K-bentonite beds were discovered from the Wufeng Formation and the lowest Longmaxi Formation in two sections, both adjacent to the Ordovician-Silurian (O-S) bound-ary and located in Tongzi, Guizhou Province and Yichang, Hubei Province, some 500 km apart from each other in South China. This indicates that many volcanic eruptions occurred near the southeast margin of the Yangtze Platform between the latest Ordovician and the earliest Silurian. Mainly through biostratigraphic and sequence stratigraphic studies, it was found that almost all these far-apart K-bentonite beds may be correlated with each other. This is the first time that a succession of volcanic ash deposits with high potential of correlation was discovered within a strata interval on the main platforms of China. Therefore, these K-bentonite beds may afford ex-cellent event-marker beds helpful to high-resolution research in integrated stratigraphy as well as other lines of research on the O-S boundary in South China.展开更多
Based on the new material of seven Ordovician-Silurian boundary sections investigated recently, together with previously published data, we analyze the temporal and spatial distributions of the Lungmachi black shales,...Based on the new material of seven Ordovician-Silurian boundary sections investigated recently, together with previously published data, we analyze the temporal and spatial distributions of the Lungmachi black shales, a key petroleum source bed widely distributed in South China. The Lungmachi black shales range in age from the Normalograptus persculptus Biozone of the uppermost Ordovician to the Spirograptus guerichi Biozone of the lower Telychian, and ten graptolite biozones can be recognized within this unit. The basal and upper contacts of the Lungmachi black shales are diachronous. The basal contact ranges from the N. persculptus to the C. cyphus biozones, a span of five graptolite biozones over two stages. The upper contact ranges from the D. pectinatus-M. argenteus Biozone to the Spirograptus guerichi Biozone, which spans four graptolite biozones over two stages. The Yichang Uplift resulted in the formation of the Hunan-Hubei Submarine High in the border area of Hubei, Hunan, and Chongqing. This is supported by a break in sedimentation in this area spanning all or part of the Hirnantian, and in many areas extending into the underlying Katian and overlying Rhuddanian. Comparison of the distribution of the Katian to Rhuddanian strata in this area indicates a growth and subsequent reduction in area of the Hunan-Hubei Submarine High particularly in the Hirnantian to early Rhuddanian. This may partly represent the influence of the process of formation and melting of ice sheet in Ordovician South Pole and consequent sea level change.展开更多
The Global boundary Stratotype Section and Point (GSSP) for the base of the Hirnantian Stage (the latest stage of the Ordovician System) is defined at a point 0.39m below the base of the Kuanyinchiao Bed in the Wangji...The Global boundary Stratotype Section and Point (GSSP) for the base of the Hirnantian Stage (the latest stage of the Ordovician System) is defined at a point 0.39m below the base of the Kuanyinchiao Bed in the Wangjiawan North Section, which is the upper most "golden spike" of the Ordovician. However, this "golden spike" is lack of reliable geochronology data. This article gives a sensitive high resolution ion microprobe (SHRIMPII) zircon U-Pb dating for a K-bentonite sample from the Kuany-inchiao Bed in the Wangjiawan North Section. The age of the K-bentonite sample is 443.2±1.6 Ma, that is to say, the isotopic age of the uppermost of Hirnantian Stage, the point of Ordovician-Silurian boundary, should be near to, but slightly younger than 443.2±1.6 Ma. This age is identical to the Ordovi-cian-Silurian boundary age 443.7±1.5 Ma as declared by International Commission on Stratigraphy (ICS). So, this research provides some good geochronlogical data for the Hirnantian Stage and the Ordovician-Silurian boundary as well as the global correlation.展开更多
The trace element and rare earth element(REE) variations across the Ordovician-Silurian succession are presented from two outcrop sections on the Yangtze Platform:the Nanbazi section,Guizhou Province,deposited in a sh...The trace element and rare earth element(REE) variations across the Ordovician-Silurian succession are presented from two outcrop sections on the Yangtze Platform:the Nanbazi section,Guizhou Province,deposited in a shallow platform interior setting,and the Wangjiawan section,Hubei Province,deposited in a deeper basinal environment.Geochemical analysis of closely spaced samples through three intervals,the Wufeng,Guanyinqiao and Longmaxi,revealed vast palaeoceanographic changes.Some geochemical proxies,including Th/U,Ni/Co,V/Cr,and V/(V+Ni) ratios,together with sedimentary facies and biotic data,indicate that an anoxic condition on the most of the Yangtze Platform during the Wufeng and Longmaxi intervals,but an oxic condition during the Guanyinqiao time.The shift of the anoxic to the oxic environment during the Guanyinqiao time coincided with a global sea-level lowstand,in parallel with the global glaciation.The Longmaxian anoxic environment was a result of a global sea-level rise,which may be synchronized with a mainly catastrophic event in the latest Ordovician.Although the two sections generally show similar variation patterns of trace and REE concentrations and some element ratios,a minor difference occurs between the Wangjiawan and Nanbazi sections,likely reflecting a difference in depositional setting during the accumulation.Such an oceanic oxygen-level variation may add a useful constraint to the current arguments on the cause and consequence of the latest Ordovician mass extinction.展开更多
Survivor, Lazarus and progenitor taxa are sources of biotic recovery following mass extinction. Investigations of the benthic brachiopods through the latest Ordovician mass extinction shows that progenitors developed ...Survivor, Lazarus and progenitor taxa are sources of biotic recovery following mass extinction. Investigations of the benthic brachiopods through the latest Ordovician mass extinction shows that progenitors developed many evolutionary novelties and successful surviving mechanisms. They are superior to survivors and Lazarus taxa in their ability to adapt to environmental changes. They are the primary source of macroevolution and the ancestors of a number of new taxa. Three kinds of progenitors are recognized based on the Ordovician-Silurian brachiopods from South China: survivor-progenitors, crisis-progenitors and Lazarus-progenitors; the last has the strongest ability to resist adverse environments, and is the most diverse and abundant.展开更多
A continuous Ordovician-Silurian boundary section from the upper Wufeng Formation through the Kuanyinchiao Formation to the lower Lungmachi Formation has been carefully measured and collected at Shuanghe of Changning,...A continuous Ordovician-Silurian boundary section from the upper Wufeng Formation through the Kuanyinchiao Formation to the lower Lungmachi Formation has been carefully measured and collected at Shuanghe of Changning, southern Sichuan Province. For the first time, the temporal changes of α- and β-diversities of the Hirnantia fauna have been discussed in great detail. The general trend of brachiopod diversity change, increasing upward, is consistent with the regional trend of the Yangtze Platform, which had been controlled by both intrinsic and extrinsic factors. However, the sudden drop of diversity for a short period in the upper Kuanyinchiao Formation might have been controlled by environmental factors rather than normal faunal turnover. Synecological analysis using numerical methods recognizes two brachiopod-dominated associations of the Hirnantia fauna, the Dalmanella-Kinnella Association and the Mirorthis Association, both living in an offshore, deeper water environment corresponding to BA3-upper BA4, particularly lower BA3.展开更多
New total organic carbon （TOC） data from the two Ordovician-Silurian transitional graptolite-bearing black shale intervals, the Wufeng （五峰） Formation and the Longmaxi （龙马溪） Formation in Central Guizhou （...New total organic carbon （TOC） data from the two Ordovician-Silurian transitional graptolite-bearing black shale intervals, the Wufeng （五峰） Formation and the Longmaxi （龙马溪） Formation in Central Guizhou （贵州） and West Hubei （湖北）, respectively, as well as previously reported TOC data from the same intervals in other places on the Yangtze platform of South China, have been used to produce an initial estimate of the primary paleoproductivity via a conventional inverse method （i.e., Rpp.inverse）. The values of the Rpp.inverse are estimated to be 32 （43-21） gC/（m^2·a）（Wufeng Formation） and 21 （27-16） gC/（m^2·a） （Longmaxi Formation）. Also, simultaneously, the habitat types （i.e., HT; cf., BA： benthic assemblage） and their temporal and spatial changes have been documented from the same succession, and an initial estimate of the primary paleoproductivity has been produced using a forward method （i.e., Rpp-forward） Beingbounded mainly by the peritidal to inner-shelf environment shelly-facies or mixed-facies successions with BA1 to BA3 faunas both at the top and the base, which indicates the habitat types from HT Ⅱ to HT Ⅲ2, the biohabitat type of the two graptolite-bearing black shale intervals can be limited to HT III to HT IV, corresponding to the inner shelf to the outer shelf, with depths from roughly 60 m to 200-300 m. Based on the current data from the South China Sea and the southern part of the East China Sea, values of Rpp-forward should be about 100 to 400 gC/（m^2·a）. The difference in the results via the two methods suggests that paleoproductivity estimates from the geological strata need to be made cautiously, with particular attention paid to the paleogeographic setting, oxic-anoxic conditions, as also the preservation factor of organic carbon.展开更多
Systematic Ce anomalies for whole-rock have been obtained from the shale-dominated, continuous, and pelagic sedimentary sequences spanning the Ordovician/Silurian （O/S） boundary at the Tieshui （铁水） of Xiushan ...Systematic Ce anomalies for whole-rock have been obtained from the shale-dominated, continuous, and pelagic sedimentary sequences spanning the Ordovician/Silurian （O/S） boundary at the Tieshui （铁水） of Xiushan （秀山）, Chongqing （重庆）, South China. Ce anomalies across the O/S boundary are recognized in three intervals, Wufeng （五峰）, Guanyinqiao （观音桥） and Longmaxi （龙马溪）. The calculated Ce/Ce＊ values of Wufeng Formation range from 0.84 to 0.96 （avg. 0.90）. In the Guanyinqiao Formation, the values of calculated Ce/Ce＊ range from 0.73 to 0.85 （avg. 0.79）. The Ce/Ce＊ values of uppermost Longmaxi Formation range from 0.87 to 0.96 （avg. 0.91）. All along the section, the magnitude of the Ce anomaly is always negative, but is more significant in the Guanyinqiao Formation. The relatively higher Ce/Ce＊ values in the Wufeng and Longmaxi shales are likely to be due to the sediments deposited under rather reducing conditions. The Ce anomaly apparently does play some regular roles in the anoxic events that accompany prominent mass extinctions, and this work provides new data of critical importance for constraining models on the end-Ordovician anoxic events and mass extinctions.展开更多
基金supported by Chinese Academy of Sciences (Grant No.KZCX2-YW-Q05-01)National Natural Science Foundation of China(Grant No.40825006)+1 种基金Ministry of Science and Technology (Grant Nos.2006CB806402,2006 FY120300-5)Department of Land and Resources of Zhejiang (Grant No.200711)
文摘Located northwest of the Jiangshan-Shaoxing Fault Zone,western and northwestern Zhejiang and northeastern Jiangxi provinces experienced major changes in bio-and litho-facies and paleogeography through the Ordovician-Silurian transition (late Katian,Hirnantian,and early Rhuddanian),as manifested by stratigraphic,paleontologic and synecologic records.Three geographic units under consideration are South,Central,and North areas.The western margin of the South area was occupied by the Huaiyu Mountains,whereas the other two parts were covered by the Zhe-Gan Sea during late Katian (Late Ordovician) time.In the early stage of the Changwu Formation deposition (late Katian),the sea was deepening northeastward,but with shallower conditions in the southwest and deeper conditions in the northeast.During mid to late stages of Changwu Formation deposition (latest Katian),the sea became much shallower and the sea bottom was uplifted substantially,which occurred somewhat prior to the global trend.During the Hirnantian (latest Ordovician) and early Rhuddanian (earliest Silurian),the study region became a shallow bay under expansion of the Cathaysian Oldland.There occurred a major drop of sea level and great changes in benthic biota with the occurrence of many new immigrants through the Ordovician-Silurian transition,which are closely related to a unique regional orogeny.The Yangtze and Cathaysian blocks may have amalgamated within the South China Paleoplate during this interval to cause the continuous uplifting and northwestward expansion of the Cathaysian Oldland.
基金the National Natural Science Foundation of China(Grant No.49802002)the State Key Project of Sequence Stratigraphy and Earth Rhythms the Lab of Earth Surface Systems of Hubei Province.
文摘More than 20 K-bentonite beds were discovered from the Wufeng Formation and the lowest Longmaxi Formation in two sections, both adjacent to the Ordovician-Silurian (O-S) bound-ary and located in Tongzi, Guizhou Province and Yichang, Hubei Province, some 500 km apart from each other in South China. This indicates that many volcanic eruptions occurred near the southeast margin of the Yangtze Platform between the latest Ordovician and the earliest Silurian. Mainly through biostratigraphic and sequence stratigraphic studies, it was found that almost all these far-apart K-bentonite beds may be correlated with each other. This is the first time that a succession of volcanic ash deposits with high potential of correlation was discovered within a strata interval on the main platforms of China. Therefore, these K-bentonite beds may afford ex-cellent event-marker beds helpful to high-resolution research in integrated stratigraphy as well as other lines of research on the O-S boundary in South China.
基金supported by Chinese Academy of Sciences (Grant No. KZCX2-EW-111)National Natural Science Foundation of China (Grant Nos. 40839910 and 40772002)Natural Sciences and Engineering Research Council of Canada (MJM)
文摘Based on the new material of seven Ordovician-Silurian boundary sections investigated recently, together with previously published data, we analyze the temporal and spatial distributions of the Lungmachi black shales, a key petroleum source bed widely distributed in South China. The Lungmachi black shales range in age from the Normalograptus persculptus Biozone of the uppermost Ordovician to the Spirograptus guerichi Biozone of the lower Telychian, and ten graptolite biozones can be recognized within this unit. The basal and upper contacts of the Lungmachi black shales are diachronous. The basal contact ranges from the N. persculptus to the C. cyphus biozones, a span of five graptolite biozones over two stages. The upper contact ranges from the D. pectinatus-M. argenteus Biozone to the Spirograptus guerichi Biozone, which spans four graptolite biozones over two stages. The Yichang Uplift resulted in the formation of the Hunan-Hubei Submarine High in the border area of Hubei, Hunan, and Chongqing. This is supported by a break in sedimentation in this area spanning all or part of the Hirnantian, and in many areas extending into the underlying Katian and overlying Rhuddanian. Comparison of the distribution of the Katian to Rhuddanian strata in this area indicates a growth and subsequent reduction in area of the Hunan-Hubei Submarine High particularly in the Hirnantian to early Rhuddanian. This may partly represent the influence of the process of formation and melting of ice sheet in Ordovician South Pole and consequent sea level change.
基金the Notional Natural Science Foundation of China (Grant No.40525010)
文摘The Global boundary Stratotype Section and Point (GSSP) for the base of the Hirnantian Stage (the latest stage of the Ordovician System) is defined at a point 0.39m below the base of the Kuanyinchiao Bed in the Wangjiawan North Section, which is the upper most "golden spike" of the Ordovician. However, this "golden spike" is lack of reliable geochronology data. This article gives a sensitive high resolution ion microprobe (SHRIMPII) zircon U-Pb dating for a K-bentonite sample from the Kuany-inchiao Bed in the Wangjiawan North Section. The age of the K-bentonite sample is 443.2±1.6 Ma, that is to say, the isotopic age of the uppermost of Hirnantian Stage, the point of Ordovician-Silurian boundary, should be near to, but slightly younger than 443.2±1.6 Ma. This age is identical to the Ordovi-cian-Silurian boundary age 443.7±1.5 Ma as declared by International Commission on Stratigraphy (ICS). So, this research provides some good geochronlogical data for the Hirnantian Stage and the Ordovician-Silurian boundary as well as the global correlation.
基金Supported by National Basic Research Program of China (Grant No.2005CB422101)
文摘The trace element and rare earth element(REE) variations across the Ordovician-Silurian succession are presented from two outcrop sections on the Yangtze Platform:the Nanbazi section,Guizhou Province,deposited in a shallow platform interior setting,and the Wangjiawan section,Hubei Province,deposited in a deeper basinal environment.Geochemical analysis of closely spaced samples through three intervals,the Wufeng,Guanyinqiao and Longmaxi,revealed vast palaeoceanographic changes.Some geochemical proxies,including Th/U,Ni/Co,V/Cr,and V/(V+Ni) ratios,together with sedimentary facies and biotic data,indicate that an anoxic condition on the most of the Yangtze Platform during the Wufeng and Longmaxi intervals,but an oxic condition during the Guanyinqiao time.The shift of the anoxic to the oxic environment during the Guanyinqiao time coincided with a global sea-level lowstand,in parallel with the global glaciation.The Longmaxian anoxic environment was a result of a global sea-level rise,which may be synchronized with a mainly catastrophic event in the latest Ordovician.Although the two sections generally show similar variation patterns of trace and REE concentrations and some element ratios,a minor difference occurs between the Wangjiawan and Nanbazi sections,likely reflecting a difference in depositional setting during the accumulation.Such an oceanic oxygen-level variation may add a useful constraint to the current arguments on the cause and consequence of the latest Ordovician mass extinction.
基金Project supported by the National Natural Science Foundation of China (Grant No. 49672083)Major Project of the Chinese Academy of Sciences (CAS) (Grant KZ952-J1-023).
文摘Survivor, Lazarus and progenitor taxa are sources of biotic recovery following mass extinction. Investigations of the benthic brachiopods through the latest Ordovician mass extinction shows that progenitors developed many evolutionary novelties and successful surviving mechanisms. They are superior to survivors and Lazarus taxa in their ability to adapt to environmental changes. They are the primary source of macroevolution and the ancestors of a number of new taxa. Three kinds of progenitors are recognized based on the Ordovician-Silurian brachiopods from South China: survivor-progenitors, crisis-progenitors and Lazarus-progenitors; the last has the strongest ability to resist adverse environments, and is the most diverse and abundant.
基金supported by the Chinese Academy of Sciences (KZCX2-YW-Q05-01)the Ministry of Science and Technology of China (2006FY120300-5)the National Natural Science Foundation of China (40825006, 40972020), and the State Key Laboratory of Palaeobiology and Stratigraphy of NIGPAS
文摘A continuous Ordovician-Silurian boundary section from the upper Wufeng Formation through the Kuanyinchiao Formation to the lower Lungmachi Formation has been carefully measured and collected at Shuanghe of Changning, southern Sichuan Province. For the first time, the temporal changes of α- and β-diversities of the Hirnantia fauna have been discussed in great detail. The general trend of brachiopod diversity change, increasing upward, is consistent with the regional trend of the Yangtze Platform, which had been controlled by both intrinsic and extrinsic factors. However, the sudden drop of diversity for a short period in the upper Kuanyinchiao Formation might have been controlled by environmental factors rather than normal faunal turnover. Synecological analysis using numerical methods recognizes two brachiopod-dominated associations of the Hirnantia fauna, the Dalmanella-Kinnella Association and the Mirorthis Association, both living in an offshore, deeper water environment corresponding to BA3-upper BA4, particularly lower BA3.
基金supported by the National Natural Science Foundation of China (Nos. 40372057, 40772076)the SINOPEC project (G0800-06-ZS-319)
文摘New total organic carbon （TOC） data from the two Ordovician-Silurian transitional graptolite-bearing black shale intervals, the Wufeng （五峰） Formation and the Longmaxi （龙马溪） Formation in Central Guizhou （贵州） and West Hubei （湖北）, respectively, as well as previously reported TOC data from the same intervals in other places on the Yangtze platform of South China, have been used to produce an initial estimate of the primary paleoproductivity via a conventional inverse method （i.e., Rpp.inverse）. The values of the Rpp.inverse are estimated to be 32 （43-21） gC/（m^2·a）（Wufeng Formation） and 21 （27-16） gC/（m^2·a） （Longmaxi Formation）. Also, simultaneously, the habitat types （i.e., HT; cf., BA： benthic assemblage） and their temporal and spatial changes have been documented from the same succession, and an initial estimate of the primary paleoproductivity has been produced using a forward method （i.e., Rpp-forward） Beingbounded mainly by the peritidal to inner-shelf environment shelly-facies or mixed-facies successions with BA1 to BA3 faunas both at the top and the base, which indicates the habitat types from HT Ⅱ to HT Ⅲ2, the biohabitat type of the two graptolite-bearing black shale intervals can be limited to HT III to HT IV, corresponding to the inner shelf to the outer shelf, with depths from roughly 60 m to 200-300 m. Based on the current data from the South China Sea and the southern part of the East China Sea, values of Rpp-forward should be about 100 to 400 gC/（m^2·a）. The difference in the results via the two methods suggests that paleoproductivity estimates from the geological strata need to be made cautiously, with particular attention paid to the paleogeographic setting, oxic-anoxic conditions, as also the preservation factor of organic carbon.
基金This study was supported by the National Natural ScienceFoundation of China (No. 40903032)the Research Foundationfor Outstanding Young Teachers,China University of Geo-sciences (Wuhan)Key Laboratory of Biogeology and En-vironmental Geology of Ministry of Education,China University of Geosciences (No.BGEGF200810)
文摘Systematic Ce anomalies for whole-rock have been obtained from the shale-dominated, continuous, and pelagic sedimentary sequences spanning the Ordovician/Silurian （O/S） boundary at the Tieshui （铁水） of Xiushan （秀山）, Chongqing （重庆）, South China. Ce anomalies across the O/S boundary are recognized in three intervals, Wufeng （五峰）, Guanyinqiao （观音桥） and Longmaxi （龙马溪）. The calculated Ce/Ce＊ values of Wufeng Formation range from 0.84 to 0.96 （avg. 0.90）. In the Guanyinqiao Formation, the values of calculated Ce/Ce＊ range from 0.73 to 0.85 （avg. 0.79）. The Ce/Ce＊ values of uppermost Longmaxi Formation range from 0.87 to 0.96 （avg. 0.91）. All along the section, the magnitude of the Ce anomaly is always negative, but is more significant in the Guanyinqiao Formation. The relatively higher Ce/Ce＊ values in the Wufeng and Longmaxi shales are likely to be due to the sediments deposited under rather reducing conditions. The Ce anomaly apparently does play some regular roles in the anoxic events that accompany prominent mass extinctions, and this work provides new data of critical importance for constraining models on the end-Ordovician anoxic events and mass extinctions.
