Based on the lithologies,sedimentary structures,graptolite zones,inorganic geochemical characteristics,electrical data of 110 shale gas wells in southern Sichuan Basin and the mineral quantitative analysis technology ...Based on the lithologies,sedimentary structures,graptolite zones,inorganic geochemical characteristics,electrical data of 110 shale gas wells in southern Sichuan Basin and the mineral quantitative analysis technology of scanning electron microscope,the stratigraphic sequences of the Upper Ordovician Katian Stage-Himantian Stage-Silurian Rhuddanian Stage-Aeronian Stage are divided,the sedimentary characteristics and fourth-order sequence evolution are analyzed.The target layer can be divided into two sequences,namely SQ1 and SQ2.According to Ordovician-Silurian sedimentary background,the gamma value of the target layer and U/Th,5 maximum flooding surfaces and 12 system tracts are identified.According to system tracts and their combinations,eight fourth-order sequences are identified,namely,Pss1-Pss8 from old to new.The development period and scale of dominant shale facies from Katian stage to Aeronian stage in southern Sichuan are restored.The best-quality dolomite/calcite-bearing siliceous shale facies,siliceous shale facies,clay-bearing siliceous shale facies and feldspar-bearing siliceous shale facies mainly occur in Pss3-Pss5 of Weiyuan,Western Chongqing and Luzhou,Pss6 of Western Changning-Northern Luzhou-Central Western Chongqing and Pss3-Pss4 of Changning.The siliceous clay shale facies second in quality mainly occurs in Pss6 of Southern Luzhou-Changning area(excluding Western Changning area),Pss7 of Eastern Weiyuan-Northern Western Chongqing-Southern Luzhou and Pss8 of Northern Luzhou-Weiyuan-Western Chongqing.The fourth-order sequence evolution model of Katian stage-Aeronian stage in southern Sichuan is established.During the depositional period of Pss1-Pss8,the sea level had six regressions and five transgressions,and the first transgression SQ2-MFS1 after glaciation was the largest flooding surface.展开更多
Three positive carbon isotope excursions are reported from Middle-Upper Ordovician in Tahe oil-gas field, northern Tarim Basin. Based on conodont biostratigraphy, the Middle Darriwilian Isotope Carbon Excursion（MDICE...Three positive carbon isotope excursions are reported from Middle-Upper Ordovician in Tahe oil-gas field, northern Tarim Basin. Based on conodont biostratigraphy, the Middle Darriwilian Isotope Carbon Excursion（MDICE） and the Guttenberg Carbon Isotope Excursion（GICE） are identified from Darriwilian to Early Katian by the aid of whole-rock carbon isotope data from two well cores. Positive excursion within conodont Pygodus anserinus zone is developed in Early Sandbian, and the fluctuation range is no less than MDICE. Because the range of this excursion in the generalized global carbon isotope curve is short, previous studies paid little attention to it, and named Early Sandbian Isotope Carbon Excursion（ESICE） in this paper. Furthermore, these positive excursions are not directly related to sea level fluctuations and the MDICE and GICE identified in northern Tarim can be globally correlated to that in southern China, North America, South America, and Europe. The Saergan Fm. source rocks of Middle-Upper Ordovician in Kalpin Dawangou outcrop are in accord with the geologic time of MDICE and ESICE, and GICE have strong ties to the source rock of Lianglitag Fm. in basin. Abundant organic carbon burial is an important factor in genesis of positive isotope carbon excursions. Positive oxygen isotope excursion, conodont fauna turnover, decreased conodont total diversity, and the change of sedimentary facies indicated that dramatic changes of paleoceanographic environment of Early-Middle Ordovician in Tarim Basin started from the end of Darriwillian, and an obvious icehouse climate of Late Ordovician occurred in ESICE.展开更多
Stable carbon isotope ratio （δ13Ccarb） analysis has been widely applied to the study of the inter-conti- nental or global marine carbonate correlation. Large-scale Cambrian-Ordovician carbonate platforms were devel...Stable carbon isotope ratio （δ13Ccarb） analysis has been widely applied to the study of the inter-conti- nental or global marine carbonate correlation. Large-scale Cambrian-Ordovician carbonate platforms were developed in the Tarim Basin. But research on fluctuation character- istics and global correlation of δ13Ccarb is still weak. Based on conodont biostratigraphy and whole-rock δ13Ccarb data in the Tahe oil-gas field of the northern Tarim Basin, the global correlation and genesis of positive carbon isotope excursions in the Darriwilian--Early Katian was exam- ined. Three positive excursions were identified in the Tahe oil-gas field including the middle Darriwilian carbon iso- tope excursion （MDICE）, the Guttenberg carbon isotope excursion （GICE）, and a positive excursion within the Pygodus anserinus conodont zone which is named the Early Sandbian carbon isotope excursion （ESICE） in this paper. Furthermore, these positive excursions had no direct relation with sea level fluctuations. MDICE and GICE could be globally correlated. The Middle-Upper Ordovi- cian Saergan Formation source rocks of the Kalpin outcrops were in accordance with the geological time of MDICE and ESICE. GICE had close relationship with the source rock of the Lianglitag Formation in the basin.Massive organic carbon burial was an important factor controlling the genesis of these positive excursions.展开更多
Seven Cornulites species,including a new one—Cornulites leonei n.sp.,are described from the Upper Ordovician Portixeddu Formation(Katian,stage slices Ka2-3)of Sardinia and the Cavá(lower Katian,stage slice Ka2)a...Seven Cornulites species,including a new one—Cornulites leonei n.sp.,are described from the Upper Ordovician Portixeddu Formation(Katian,stage slices Ka2-3)of Sardinia and the Cavá(lower Katian,stage slice Ka2)and Estana(upper Katian,stage slices Ka3-4)formations of the Pyrenees.The Sardinian and Pyrenean cornulitids represent an adaptation to live in environments with high sedimentation rates and limited hard substrates availability.Their prominent annuli could have had a stabilizing function in the soft sediment that helped cornulitids to keep a favourable position in the sediment to enable suspension feeding.The known Late Ordovician cornulitid diversity in different Gondwana areas is low,usually ranging from one to three taxa,being higher(seven)in Sardinia.Like other benthic groups during the Late Ordovician,the cornulitid tubeworm faunas within the high-latitude peri-Gondwana Province indicate a certain endemism and share morphological and ecological affinities,such as a small body size and tubes with a strikingly small apical angle.Although essentially endemic,some links with cornulitids from the Late Ordovician of Scotland are revealed.展开更多
The Kwangsian Orogeny originated along the southeast coast of China and stepwise developed in a northwest direction.It includes two stages,a long locally varying uplift from the Late Ordovician to the early Silurian a...The Kwangsian Orogeny originated along the southeast coast of China and stepwise developed in a northwest direction.It includes two stages,a long locally varying uplift from the Late Ordovician to the early Silurian and a finally tectonic movement near the Silurian and Devonian transition.The Kwangsian uplift event shows a stepwise delay northwestwards from the southeastern coast area in Nemagraptus gracilis Biozone(Sa1)to the south side of the Xuefeng Mountains in or later than Cystograptus vesiculosus Biozone(R3)to Coronograptus cyphus Biozone(R4).In the southern of Yangtze Platform,the Yichang Uplift was droved by the Kwangsian Orogeny forming a diachronous stratigraphical break through Rhuddanian and Aeronian.The distribution of the early Telychian lower marine red beds indicates a northwestward increase of the Cathaysian Oldland.Stratigraphical evidence may explain why the Kwangsian movement was marked by an angular disconformity during the Pridoli to earliest Devonian interval.展开更多
基金Supported by the Petro China Major Engineering Technology Field Test Project(2019F-31-01)Postdoctoral Project of Petro China Southwest Oil and Gas Field Company(20200304-03)。
文摘Based on the lithologies,sedimentary structures,graptolite zones,inorganic geochemical characteristics,electrical data of 110 shale gas wells in southern Sichuan Basin and the mineral quantitative analysis technology of scanning electron microscope,the stratigraphic sequences of the Upper Ordovician Katian Stage-Himantian Stage-Silurian Rhuddanian Stage-Aeronian Stage are divided,the sedimentary characteristics and fourth-order sequence evolution are analyzed.The target layer can be divided into two sequences,namely SQ1 and SQ2.According to Ordovician-Silurian sedimentary background,the gamma value of the target layer and U/Th,5 maximum flooding surfaces and 12 system tracts are identified.According to system tracts and their combinations,eight fourth-order sequences are identified,namely,Pss1-Pss8 from old to new.The development period and scale of dominant shale facies from Katian stage to Aeronian stage in southern Sichuan are restored.The best-quality dolomite/calcite-bearing siliceous shale facies,siliceous shale facies,clay-bearing siliceous shale facies and feldspar-bearing siliceous shale facies mainly occur in Pss3-Pss5 of Weiyuan,Western Chongqing and Luzhou,Pss6 of Western Changning-Northern Luzhou-Central Western Chongqing and Pss3-Pss4 of Changning.The siliceous clay shale facies second in quality mainly occurs in Pss6 of Southern Luzhou-Changning area(excluding Western Changning area),Pss7 of Eastern Weiyuan-Northern Western Chongqing-Southern Luzhou and Pss8 of Northern Luzhou-Weiyuan-Western Chongqing.The fourth-order sequence evolution model of Katian stage-Aeronian stage in southern Sichuan is established.During the depositional period of Pss1-Pss8,the sea level had six regressions and five transgressions,and the first transgression SQ2-MFS1 after glaciation was the largest flooding surface.
基金supported by the National Key Scientific Project of China (No. 2011ZX05005-0042016ZX05005-002)the National Basic Research Program of China (973 Program) (No. 2012CB214806)
文摘Three positive carbon isotope excursions are reported from Middle-Upper Ordovician in Tahe oil-gas field, northern Tarim Basin. Based on conodont biostratigraphy, the Middle Darriwilian Isotope Carbon Excursion（MDICE） and the Guttenberg Carbon Isotope Excursion（GICE） are identified from Darriwilian to Early Katian by the aid of whole-rock carbon isotope data from two well cores. Positive excursion within conodont Pygodus anserinus zone is developed in Early Sandbian, and the fluctuation range is no less than MDICE. Because the range of this excursion in the generalized global carbon isotope curve is short, previous studies paid little attention to it, and named Early Sandbian Isotope Carbon Excursion（ESICE） in this paper. Furthermore, these positive excursions are not directly related to sea level fluctuations and the MDICE and GICE identified in northern Tarim can be globally correlated to that in southern China, North America, South America, and Europe. The Saergan Fm. source rocks of Middle-Upper Ordovician in Kalpin Dawangou outcrop are in accord with the geologic time of MDICE and ESICE, and GICE have strong ties to the source rock of Lianglitag Fm. in basin. Abundant organic carbon burial is an important factor in genesis of positive isotope carbon excursions. Positive oxygen isotope excursion, conodont fauna turnover, decreased conodont total diversity, and the change of sedimentary facies indicated that dramatic changes of paleoceanographic environment of Early-Middle Ordovician in Tarim Basin started from the end of Darriwillian, and an obvious icehouse climate of Late Ordovician occurred in ESICE.
基金supported by the National Key Scientific Project of China(No.2011ZX05005-0042016ZX05005-002)the National Basic Research Program of China(973 Program)(No.2012CB214806)
文摘Stable carbon isotope ratio （δ13Ccarb） analysis has been widely applied to the study of the inter-conti- nental or global marine carbonate correlation. Large-scale Cambrian-Ordovician carbonate platforms were developed in the Tarim Basin. But research on fluctuation character- istics and global correlation of δ13Ccarb is still weak. Based on conodont biostratigraphy and whole-rock δ13Ccarb data in the Tahe oil-gas field of the northern Tarim Basin, the global correlation and genesis of positive carbon isotope excursions in the Darriwilian--Early Katian was exam- ined. Three positive excursions were identified in the Tahe oil-gas field including the middle Darriwilian carbon iso- tope excursion （MDICE）, the Guttenberg carbon isotope excursion （GICE）, and a positive excursion within the Pygodus anserinus conodont zone which is named the Early Sandbian carbon isotope excursion （ESICE） in this paper. Furthermore, these positive excursions had no direct relation with sea level fluctuations. MDICE and GICE could be globally correlated. The Middle-Upper Ordovi- cian Saergan Formation source rocks of the Kalpin outcrops were in accordance with the geological time of MDICE and ESICE. GICE had close relationship with the source rock of the Lianglitag Formation in the basin.Massive organic carbon burial was an important factor controlling the genesis of these positive excursions.
基金The financial supported was provided by a Sepkoski Grant from the Paleontological SocietyKing Saud University,Riyadh,Saudi Arabia,Researchers Supporting Project Number RSP 2024R140Project PDI2021-125585NB-100 of the Spanish Ministry for Science Innovation (MICINN)。
文摘Seven Cornulites species,including a new one—Cornulites leonei n.sp.,are described from the Upper Ordovician Portixeddu Formation(Katian,stage slices Ka2-3)of Sardinia and the Cavá(lower Katian,stage slice Ka2)and Estana(upper Katian,stage slices Ka3-4)formations of the Pyrenees.The Sardinian and Pyrenean cornulitids represent an adaptation to live in environments with high sedimentation rates and limited hard substrates availability.Their prominent annuli could have had a stabilizing function in the soft sediment that helped cornulitids to keep a favourable position in the sediment to enable suspension feeding.The known Late Ordovician cornulitid diversity in different Gondwana areas is low,usually ranging from one to three taxa,being higher(seven)in Sardinia.Like other benthic groups during the Late Ordovician,the cornulitid tubeworm faunas within the high-latitude peri-Gondwana Province indicate a certain endemism and share morphological and ecological affinities,such as a small body size and tubes with a strikingly small apical angle.Although essentially endemic,some links with cornulitids from the Late Ordovician of Scotland are revealed.
基金supported by Chinese Academy of Sciences(Grant No.KZCX2-EW-111)the State Key Laboratory of Palaeontology and Stratigraphy and Key Laboratory of Economic Stratigraphy and Paleogeography(Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences)National Natural Science Foundation of China(Grant No.41272042)
文摘The Kwangsian Orogeny originated along the southeast coast of China and stepwise developed in a northwest direction.It includes two stages,a long locally varying uplift from the Late Ordovician to the early Silurian and a finally tectonic movement near the Silurian and Devonian transition.The Kwangsian uplift event shows a stepwise delay northwestwards from the southeastern coast area in Nemagraptus gracilis Biozone(Sa1)to the south side of the Xuefeng Mountains in or later than Cystograptus vesiculosus Biozone(R3)to Coronograptus cyphus Biozone(R4).In the southern of Yangtze Platform,the Yichang Uplift was droved by the Kwangsian Orogeny forming a diachronous stratigraphical break through Rhuddanian and Aeronian.The distribution of the early Telychian lower marine red beds indicates a northwestward increase of the Cathaysian Oldland.Stratigraphical evidence may explain why the Kwangsian movement was marked by an angular disconformity during the Pridoli to earliest Devonian interval.
