A Study On The Fossils And Environment Of The Late Permian Changxing Grottoes In The Northeastern Sichuan Basin

The Dalong formation in Northeast Sichuan Province during Changhsingian exposed superbly and characterized by sand argillaceous limestone and siliceous shale, with well-preserved and abundant bioturbation structures.These structure disturbances through out most of the Dalong formation, for the study of Late Permian Basin phase biological propagation characteristics of living, The individual behavior of biological, sediment properties change and the ability of biology to adapt on the sedimentary environment, which provide the corresponding materials and can help us to understand the characteristics of the ecological evolution of the Late Permian and analysis the causes of mass extinctions before the P/T biological extinction. However, Analysis of ichnofabric must combine with sedimentological characteristics, on the Dalong formation remains of species identification and trace fossils from the ecological habits of bioturbation intensity classification, quantitative assessment. Focusing on the study of ichnofabrics and lithofacies of the whole depsitional profiles, especially discuss the ichnological data, inluding that identication of ichnofossils and ichnofabrics, degree and depth of bioturbation, ichnodiversity, styles of tiering.five aspects of results are chiefly obtained as follows:(1) Based on the sedimentary characteristics of the study area, the Dalong formation is divided into3sections of10layers, and identify the2kinds ofsedimentary facies of4types of lithofacies associations;(2) Eight ichnogenus and thirteen ichnospecies have been identified and a lot of blurry biogenic sedimentary structures in Dalong Formation, the tracing behavior4species;(3) In Dalong group identified6ichnofabrics, namely Palaeophycus tubularis ichnofabric deep-sea basin phase, Palaeophycus heberti, Chondrites type-B ichnofabric and Treptichnus bifurcus ichnofabric, Planolites montanus ichnofabric and Palaeophycus striatus ichnofabric. The evolution of ichnofabric indicates the changes of sedimentary environment:from the deep sea basin in thesiliceous shale deposits to deep water shelf environment with sand and argillaceous carbonate sediments, response of Late Permian in deep water environment in the colonial state.(4) Dalong formation from bottom to top, ichnofabrics have certain regularity:Biological disturbance of the trend:the middle strong, up and down gradually turn weak; ichnofabric between class type is from type of Simple-class to type of heritage is a single but shallow stratum, and finally the transition to the simple shallow in the class type; deposition of sediment is a process from water saturated soft bottom to the soup to the variation of consolidation of hard bottom sediment; The development process of trace fossils from the boundary is clear to the development of thick lining to the final development of no lining These rules indicate that the process of in faunal bioturbation intensity changes in the vertical direction in the basin of phase transformation changed the sedimentary characteristics of sediment, but also led to the biological behavior changes.(5) The environmental factors controlling the Dalong formation ichnocoenosis mainly turbidity current event insertion, sedimentary environment and the ecological environment evolution, the aggregation state of trace making organisms (abundance and diversity), tracing behavior (disturbance, disturbance depth, class type, characteristics of sediment) and death (hypoxia) produced an important influence.