Huaxi Lower Triassic Daye Group Trace Fossils And Sedimentary Environment Research

Ichnology is a relatively new multidisciplinary research area concerning with biology, paleontology, and sedimentology. Studies of trace fossils can provide unique geological information to a wide range of geoscience.There are lots of trace fossils preserved in Daye Formation in Lower Triassic, which provide abundant research materials. Although the achievements of trace fossils study have been acquired, which mainly discussed the paleoenvironment, not emphasized on the palaeontology of trace fossils, ichnofabric and ichnofacies. A detailed study has been conducted to investigate ichnology of Daye Formation and sedimentary envrionment by analysized ichnofabrics and ichnofacies. Twenty ichnogenera and twenty-three ichnospecies have been described; among them, Circulichnis, Gyrochorte, Ophiomorpha, Planolites, Palaeophycus, Phycodes, Rhizocorallium, Undichna are first found in this area; Asterhaphe dangwuensis ichnogen. et ichnosp. nov., Polymacanopsis succincta ichnogen. et ichnosp. nov., Polymacanopsis snello ichnogen. et ichnosp. nov., Paleodictyon (Megadictyon) gigantus ichnogen. et ichnosp. nov. are new ichnogenera.Three ichnofabrics have been found in Daye Formation, including: Phycodes ichnofabric, Cosmorhaphe -Planolites ichnofabric and Thalassinoides-Phycodes ichnofabric. The ichnofacies of Daye Formation also have been found: Cruziana ichnofacies of the first and the third number, Zoophycos-Nereites ichnofacies of the second number. Based on trace ichnofabrics and ichnofacies, combined with analysis on sedimentary structures of host rocks, it is believed that the study area located the front line of deep water carbonate platform slope margin, in anoxia circumstances. Because of the special geomorphic condition of slope margin, Zoophycos-Nereites ichnofacies indicates the depth of water may be shallower than the nomal condition.