Characteristics And Taphonomy Of Aquatic Fauna In Jingangshan Layer, Yixian Formation, Western Liaoning

Western Liaoning is a typical area for studying Mesozoic strata and the Jehol Biota. Early Cretaceous Yixian Formation in Yixian Basin is an important strata for output Jehol Biota fossils. As the upper part of Yixian Formation, Jingangshan Layer produced fossils species rich, preserved beautifully, the combination is special as well. Based on the field studies in Jingangshan Layer, include sedimentary petrology and stratigraphic, this paper indicated the sedimentary facies is semi-deep lake facies.Jingangshan Layer produced aquatic organisms, including fishes(Yixianichthys), ostracoda(Ostracoda), conchostracans(Eosesthria), bivalves(Ferganococha、Sphaerium), insects(Ephemeropsis trisetalis), reptiles(Manchurochelys manchouensis、Yabeinosaurus tenuis). The surrounding rocks are gray-white tuffaceous shale and tuffaceous siltstone, have an obvious stratification. The fossils preserved completely, the fine structure clearly, without bioturbation phenomenon. This showed the hydrodynamic conditions of lake weakness.The fish fossils in Jingangshan Layer only one genus-Yixianichthys (Lycoptera muroii). Not only the morphological structure of Yixianchthys was difference to other Lycoptera, but also only located in Jingangshan-Zaocishan. This paper according to previous research, described morphological features in detail, contrast to L.davidi and L. sinensis. The most obvious features of Yixianchthys in field:the body was short spindle shape; the head wide and short,1/5 of the total length; the head height was less than body height.Based on the features of fossils preservation, the taphonomic type was proved origal place. The volcanic eruption resulting the death of cluster. The eruption gas spread rapidly led to aquatic environment changes, for examples, lack of oxygen, increased temperature, acidification of water and so on. Huge volcanic ash falled into water remains the bodies of biota sank to the lake bottom and buried fastly. What’s more, the clay minerals in volcanic ash could absorbed to bio-organic molecules, played a protective role on the bodies.