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
Ordovician black shales are widely distributed in the Tarim Basin and its peripheral regions,and some of them may serve as potential hydrocarbon source rocks.The present study of the Ordovician graptolite fauna from t...Ordovician black shales are widely distributed in the Tarim Basin and its peripheral regions,and some of them may serve as potential hydrocarbon source rocks.The present study of the Ordovician graptolite fauna from these shales,together with the yielded conodonts and chitinozoans etc.,permits a refined correlation of the rocks.Based mainly on a new collecting of the graptolites and a study of the faunas in Kalpin and Kuruktag regions,and the successful identification of the new graptolite material from a few drill cores within the basin,we are able to update our knowledge of the Ordovician in the regions,and draw some conclusions:(1) The most widespread distribution of the black shales in the Tarim Basin and its peripheral regions,which correspond to the Nemagraptus gracilis Zone,may be related to a global sea-level rise during this time interval.(2) Black shales of Ordovician occur most frequently and extensively in the Kuruktag(also spelled as Quruq Tagh) region in east-ern Tianshan Mountains,spanning Tremadocian to mid-Katian(D.spiniferus Zone) temporally and extending southeastwards into Manjiaer Depression.The black shales of the D.spiniferus Zone may even extend into the central Tarim Basin.(3) Three different bio-and litho-facies belts(Bachu:carbonate platform and reef belt;Kalpin-Aksu:marginal platform and upper slope belt;Wushi:slope belt) are recognized in the northwestern Tarim Basin.(4) The internationally well-correlated Saergan black shale,which has been considered to possess high potential for hydrocarbon source rock,may possess a restricted distribution in the Kalpin and Aksu areas.展开更多
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supported by Chinese Academy of Sci-ences (Grant Nos. KZCX2-EW-111 and KZCX2-YW-Q05-01)China Geological Survey (Grant No.1212011120116)
文摘Ordovician black shales are widely distributed in the Tarim Basin and its peripheral regions,and some of them may serve as potential hydrocarbon source rocks.The present study of the Ordovician graptolite fauna from these shales,together with the yielded conodonts and chitinozoans etc.,permits a refined correlation of the rocks.Based mainly on a new collecting of the graptolites and a study of the faunas in Kalpin and Kuruktag regions,and the successful identification of the new graptolite material from a few drill cores within the basin,we are able to update our knowledge of the Ordovician in the regions,and draw some conclusions:(1) The most widespread distribution of the black shales in the Tarim Basin and its peripheral regions,which correspond to the Nemagraptus gracilis Zone,may be related to a global sea-level rise during this time interval.(2) Black shales of Ordovician occur most frequently and extensively in the Kuruktag(also spelled as Quruq Tagh) region in east-ern Tianshan Mountains,spanning Tremadocian to mid-Katian(D.spiniferus Zone) temporally and extending southeastwards into Manjiaer Depression.The black shales of the D.spiniferus Zone may even extend into the central Tarim Basin.(3) Three different bio-and litho-facies belts(Bachu:carbonate platform and reef belt;Kalpin-Aksu:marginal platform and upper slope belt;Wushi:slope belt) are recognized in the northwestern Tarim Basin.(4) The internationally well-correlated Saergan black shale,which has been considered to possess high potential for hydrocarbon source rock,may possess a restricted distribution in the Kalpin and Aksu areas.
