THE TRACE FOSSIL ASSOCIATIONS OF EARLYORDOVICIAN IN THE EASTERN SIDE OF KANGDIANOLDLAND AND THEIR FACIES-INDICATING SIGNIFICANCE

Abstract: A clastic rock association is developed in Lower Ordovician in the eastern side ofKangdian oldland, with trace fossils very abundant.The relation between trace fossil associa-tions and sedimentary facies is the central topic to be dealt with in this paper. Thirteen tracefossils are described in the paper, among which there are six new ichnosp.Cruziana regularianov. ichnosp.，C. dimorphiconis nov. ichnosp.，Dimorphichnus ebianensis nov. ichnosp.，D.reticularis nov.ichnosp., Cvlindricum ovatus nov.ichnosn., etc. According to our researches, the area of trace fossils can be divided into the easternpart and the wastern part by a line from Weiyuan, through Yiliang, to Xuanwei. In littoralzone of the western, the trace fossils of Scoyenia, Skolithos and Gruziana occuredalternately, which indicate that the water body of the littoral environment was shallower,and the sea level changed violently(the cyclic change of the supratidal, intertidal andsubtidal) to Meitan age. In the eastern part, such as Guiyang, Hezhang, the trace fossilswere mainly occured in the Meitan age. The abundant trace fossils of Skolithos were occuredin the prolittoral fades of the sedimentary sequence of the sandy progradationad shore in ear-1y Meitan age; the abundant trace fossils of Cruziana were occured in the sandstone and theshale occurring in the Limestone of late Meitan age in Guiyang, which indicate a subtitalmid and high-energy littoral environment, that is to say a linear sandy ridge controlled bytidal current. As a result that the trace fossils associations formed and influenced by the changes oftime and space of water body envisoument，it has the important facios-indicating signifi-cance.