TRACE FOSSILS OF THE UPPER TRIASSIC BAYANHARSHAN GROUP IN THE QUMARLEB-ZHIDOI AREA, SOUTHERN QINGHAI
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Abstract:
Trace fossils from the upper pant of the Bayanharshan Group (Upper Triassic) in Qumarleb-Zhidoi area, Southern Qinghai Province, have been systematically gathered for the first time, they comprise 54 ichnospecies in 33 ichnogenera. The main ichnogenera include Arthrophycus,Asterichnus,Chondrites,Circulichnis,Cosmorhaphe, Didymaulichnus, Helminthoida,Helminthopsis,Megagrapton,Neonereites,Nereites,Palaeophycus,Palaeodictyon,Pelecypodichnus,Phycodes,Phycosiphon,Planolites,Xiangquanheichnus,Zoophycos and so on. According to the morphology, ethnology and water depth, the studied trace fossils include two ichno-assemblages: one formed before turbidity flows, such as Cosmorhaphe,Helminthopsis,Helminthoida,Megagrapton,Palaeodictyon etc., and the other emplaced after the turbidity event, such as Chondrites,Neonereites,Palaeophycus,Phycosiphon,Planolites,Zoophycos, etc. Both of these assemblages are typical representatives of the bathyal-abyssal Nereites ichnofacies, which therefore would indicate that the Late Triassic pant of the Bayanharshan Group of the studied area was formed in a flysch facies with abundant turbidity currents.
