Ichnofabrics And Their Sedimentary Significance From The Jialingjiang Formation In Longmendong Section, Mount Emei, Sichuan Province, China

Through the detailed study on lithologic types and associations, sedimentary structures , sedimentary sequences and trace fossils of Jialingjiang Formation in Emei area, the author recognizes that Jialingjiang Formation in Emei area is deposited in an estuary-tidal flat sedimentary system. Five sedimentary subfacies of the estuary, the Sebkha, the intertidal flat, the restricted subtidal flat and the restricted lagoon are proposed.The trace fossils mainly occur in intertidal and subtidal zone. Based on the trace fossils morphological characteristics and their tiering distribution, five types of ichnofabrics are recognized. In the member 1 of the Jialingjiang Formation, Arenicolites ichnofabric and Palaeophycus ichnofabric, representing intertidal sand flat and mud flat respectively, occur in loose, soft clastic substrates. Arenicolites ichnofabric corresponds to the rapid deposition period, while Palaeophycus ichnofabric to the low deposition. Planolites ichnofabric represents a soft carbonate substrate subenvironments transitional from an intertidal carbonate flat to a restricted lagoon. Thalassinoides and Rhizocorallium ichnofabrics, mainly occurring in the Member 3 of the Jialingjiang Formation, are formed in firm carbonate substrates within a coastal carbonate flat and restricted lagoon environment with unstable energy and sea leavel change, and locally displaying storm depositions and restricted lagoon depositions.By means of the semi-quantitative analysis on the ichnofabrics in the Jialingjiang Formation in the study area, the following phenomenon that trace makers in this area are commonly small and the biotubation index is lower compared to that after Early Triassic, is unveiled in the early Early Triassic: The output of trace fossils is probably mainly dominated by the physical process.