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Yang W.,State Key Laboratory of Oil and Reservoir Geology and Exploitation | Zhang T.S.,State Key Laboratory of Oil and Reservoir Geology and Exploitation | Liu Z.C.,State Key Laboratory of Oil and Reservoir Geology and Exploitation | Huang H.,State Key Laboratory of Oil and Reservoir Geology and Exploitation | And 2 more authors.
Acta Petrologica Sinica | Year: 2014

According to the strata characters, lithological features, palaeontologic assemblages, geochemistry index and the result of predecessors' research in the northwest of the Upper Yangtze plate in the Middle Permian. Due to the crustal doming affected by Emeishan mantle plume activity in the Middle Permian, Sichuan Basin was characterized by high relief in the southwestern part of the Upper Yangtze platform, converted into flat paleogeomorphic features eastward and northeastward, and poorly developed steep slope and distinct slope transition zone. The paleogeographical feature of this kind, and local sea level change directly controlled the paleogeographic pattern and evolution, forming a unique pattern of carbonate ramp platform. Emeishan mantle plume activity caused the sedimentary and environmental responses included lithology, paleontology and geochemistry characters. According to the sedimentary lithology, paleotogical assemblages, structure features and geochemistry characters in various parts of submarine doming, the study area in a broad environment with a high water energy is the subfacies open platform, located at the higher part of the submarine dome shaped area in the southwestern Upper Yangtze platform, and gradually transformed eastward and northeastward into developing area of the shallow and deep ramp facies. There are enriched of paleontological in the open platform and shallow ramp developing area. The Palaeotextularia assemblages, Ungdarella assemblages located in open platform. The Mizzia-Pseudovermoporella assemblages, Glomospira-Eolasiodiscus assemblages and Nodosarinae assemblages, and so on, represent the shallow ramp environment, the palaeontology gradually decreased to eastward and northeastward. There are only a small amounts of paleontology distributed in the upper deep ramp facies developing area. Changes in the abundances of trace elements also reflect the paleogeographic characteristics. From the open platform to deep ramp facies developing area, the sedimentary environment also transform from oxidizing environment to reducing environment. In the process of environmental changes, the average abundances for Ba, Sr, V, Cu etc., are gradually increased.

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