The Guanling Biota—A unique “Fossillagerstatte” in the world

Abstract: The Guanling biota is characterized by the occurrence of numerous well-preserved Late Triassic(Carnian) marine reptiles and crinoids with ammonoids, bivalves, conodonts, brachiopods, elasmobranch ichthyoliths and a few fossil fishes and plants. Such a rich, diversified and perfectly preserved paleontological assemblage is rarely encountered in the world and can be called, therefore, a unique Late Triassic“Fossillagerst?覿tte”in the world. Preliminary study indicates that the principal marine reptiles are ichthyosaurs: Qianichthyosaurus zhoui Li (1999), Cymbospondylus asiaticus Li et You (2002), Panjiangsaurus epicharis Chen et Cheng gen. et sp. nov., thalattosaurs: Anshunsaurus huangguoshuensis (Liu, 1999), Xinpusaurus suni (Yin et al., 2000), X. bamaolinensis sp. nov. Cheng et Liu, placodonts: Sinocymodus xinpuensis Li (2000) and some new unidentified taxa. The crinoids are dominated by Traumatocrinus hsui (Mu) (? =T. caudes (Dittmar,1866), ? =T. guanlingensis Yu et al. 2000) revised in the present paper. New discovery of Traumatocrinus attaching drifting wood fossils by anastomosing or articulated rootlets indicates that the taxa of crinoids are widespread in the world, depending on its pseudo-planktonic living style. Associated fossils comprise conodonts of the Metapolygnathus nodosus Zone redefined by Chen (in press), ammonoids of the Trachyceras multituberculatum Zone, bivalves of the Halobia-“Daonella” bifurcatus Assemblage Zone, brachiopods, Koninckina guizhouensis, K. zhengfengensis, and newly discovered fossil fishes, Asialepidotus sp. nov., shark scales and teeth, plants, Equisetites arenaceus, Ctenozamites sarrani etc. Comprehensive analysis of the above-mentioned various kinds of fossil suggests that the age of the Guanling biota should be Late Triassic early-middle Carnian. Detailed investigation and systematic exploration indicate that the Guanling biota is distributed mainly in the interval of 5-11 m above the base of the Lower Member of the Xiaowa Formation (former “Wayao Formation”) around Huangtutang, Xiaowa, Maowa, Bamaoling of Xinpu Township and Baiyan of Gangwu Township, Guanling County, covering an area of about 200 km2. Combined tectono-paleogeographic and eco-, sequence- and chemo-stratigraphic studies indicate that this rare biota was probably formed and developed in a particular “asylum” situated in the NW corner of the active shelf margin close to the relatively stagnated Nanpanjiang intracontinental rift basin. This basin was surrounded by the Sichuan-Yunnan-Guizhou-Guangxi old land on three sides during the earliest Late Triassic transgression, following the Middle Triassic Ladinian global regression. The anoxic and salted events, caused by subsequent Early-Middle Carnian maximum transgression and sedimentary organic surplus stockpiling, were probably the main causes for the mass extinction of this biota and formation of well-preserved taphococenosis.