Black shale event during the Late Triassic Carnian Age: Implications from sedimentary and palaeontological records in Longmen Mountains region
Shi Zhiqiang， born in 1972， is an associate professor of Chengdu University of Technology. He is mainly engaged in teaching and researhes of sedimentary geology.
A set of darkgray， grayishblack or black calcareous shale(bearing shell sometimes)occurred at the Upper Triassic Carnian—Norian Maantang Formation in the Longmen Mountains region， Sichuan Province. Numerous bivalves， primary divalent metal sulfides(pyrite)， thinintermediate layers and horizontal bedding observed in the shale indicated an anoxic lowenergy environment. The Late Carnian sediments mainly mudstone，shale or silty slate， calcareous slate which are timeequvalent to this black shale，can be found in the east Paleotethys including Songpan—Ganzi Area， Changdu Area，and Hoh Xil Area. We considered that they reflected a black shale event which strongly influenced the marine sediments in the eastern Paleotethys of west China. The global correlation indicated that the dark color mudstone（shale）were widely distributed in western China， Indian Himalayas， Eastern Alps， and overlied on the Early Carnian carbonate rocks. Thus we proposed a Tethyswide black shale event， which caused the late Early Carnian global carbonate production crisis occurred， while the dark color mudstone(shale)developed in the middle part of the Maantang Formation is a reflection of this event along the western margin of the Yangtze Platform. Based on investigation and studies of the Upper Triassic sections in Hanwang， Jushui， and Maantang areas in northwestern Sichuan， it is concluded that the Carnian limestone(ie. oolid limestone， sponge reef limestone in the middlelower Maantang Formation)was deposited before the anoxic event， and the Norian gray siltstone and fine sandstone was laid down after the event. The black mudstone(shale)triggered by the event not only indicated the significant lithological change， but also was the turning point of sudden paleontological and paleoecological changes. Marine fossils such as hexactinellida， crinoid， bryozoa，and coral were abundant in the limestones of the lower Maantang Formation， but they suddenly disappeared in the black shales in the Maantang Formation. Shell fauna fossils such as rich bivalves， ammonoids，and brachiopods occurred in the middleupper Maantang Formation.
. Black shale event during the Late Triassic Carnian Age: Implications from sedimentary and palaeontological records in Longmen Mountains region[J]. JOPC, 2009, 11(4): 375-.
