康滇古陆东侧早奥陶世遗迹化且合及其指相意义

THE TRACE FOSSIL ASSOCIATIONS OF EARLY ORDOVICIAN IN THE EASTERN SIDE OF KANGDIAN OLDLAND AND THEIR FACIES-INDICATING SIGNIFICANCE

康滇古陆东侧的下奥陶统,发育有一套碎屑岩相岩石组合,遗迹化石丰富,其组合与沉积相的关系密切,起到了极好的指相佐证。遗迹化石组合有三个特点:1、Cruziana产出层位由西向东升高,具穿时性,越过了整个早奥陶世;2、Cruziana分布较广,而Skolithos较局限;3、Cruziana与Skolithos在时间上交替出现,而在贵州赫章县则只有Skolithos相。

A clastic rock association is developed in Lower Ordovician in the eastern side of Kangdian oldland, with trace fossils very abundant.The relation between trace fossil associations and sedimentary facies is the central topic to be dealt with in this paper. Thirteen trace fossils are described in the paper, among which there are six new ichnosp.Cruziana regularia nov. ichnosp., C. dimorphiconis nov. ichnosp., Dimorphichnus ebianensis nov. ichnosp. , D.reticularis nov.ichnosp., Cylindricum ovatus nov.ichnosp., etc. According to our researches, the area of trace fossils can be divided into the eastern part and the wastern part by a line from Weiyuan, through Yiliang, to Xuanwei. In littoral zone of the western, the trace fossils of Scoyenia, Skolithos and Cruziana occured alternately, 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 and subtidal) to Meitan age. In the eastern part, such as Guiyang, Hezhang, the trace fossils were mainly occured in the Meitan age. The abundant trace fossils of Skolithos were occured in the prolittoral facies of the sedimentary sequence of the sandy progradationad shore in early Meitan age; the abundant trace fossils of Cruziana were occured in the sandstone and the shale occurring in the Limestone of late Meitan age in Guiyang, which indicate a subtital mid and high-energy littoral environment, that is to say a linear sandy ridge controlled by tidal current. As a result that the trace fossils associations formed and influenced by the changes of time and space of water body envisoument , it has the important facios-indicating significance.