Multiple stratigraphic classification and correlation of the Devonian-Triassic in the Jiuzhaigou area, Sichuan, and its sedimentary environment

Abstract：A sequence of carbonate rocks with a total thickness of over 6000 m is developed in Jiuzhaigou in the border region between the eastern margin of the Qinghai-Tibet Plateau and Sichuan basin. Based on the 1∶50000 regional geological survey and a series of special-subject surveys in this areas, nine formation-complexes are recognized in the lithostratigraphic context, and 3 coral assemblage-zones, 3 assemblage-zones and 1 acme-zone of brachiopods, 2 bivalve acme-zones and 1 assemblage-zones and 1 acme-zone of foraminifers are distinguished in the biostratigraphic context. In terms of ecostratigraphy, 2 communities are established. According to the characteristics of geochemical elements, 11 geochemical intervals are identified. In addition, the authors have studied the major element and carbon isotopic features and conducted microfacies analysis of carbonate rocks. Through integrating various sedimentary indicators, the authors have made discrimination of sedimentary environments, of which the sedimentary environment of the Minhe Formation is unique, belonging to a mixed carbonate and terrestrial clastic sedimentary system.