ICHNOFABRICS AND THEIR ENVIRONMENTAL SIGNIFICANCE FROM THE UPPER CRETACEOUS JIAGUAN FORMATION IN EMEI MT.AREA,SOUTHWEST SICHUAN BASIN
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Abstract:
The Upper Cretaceous Jiaguan Formation mainly consists of a set of thick-bedded fine-to medium-grained sandstones, with a few intercalations of siltstones and mudstones, and conglomerates at its bottom in the Emei Mt. area, southwest Sichuan Basin. It contains a large amount of trace fossils, which has been attributed to 9 ichnogenera and 11 ichnospecies. Based on the characteristic trace fossils and their tiering patterns, they are divided into 5 types of ichnofabrics: Palaeophycus ichnofabric, Arenicolites ichnofabric, Skolithos ichnofabric, Planolites ichnofabric and Scoyenia ichnofabric. Palaeophycus ichnofabric is observed at the bottom of the point bar of fluvial deposits with very high energy. Arenicolites ichnofabric is preserved in the point bar and Skolithos ichnofabrics in the transitional environment from the point bar to the embankment in fluvial deposits. And the last two ichnofabrics are both preserved in the natural levee deposits with lower energy.
