CHARACTERISTICS OF PALEOENVIRONMENTAL EVOLUTION AND ICHNOCOENOSIS IN THE 55 SUBMEMBER OF THE MIDDLE ORDOVICIAN MAJIAGOU FORMATION, XINGXIAN, SHANXI
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Abstract:
A large number of invertebrate fossils are preserved in the stratum of the 55 Submember of Ordovician Majiagou Formation in the Guanjiaya section, eastern margin of Ordos Basin, identified types of domichnia, fodinichnia and grazing traces, 8 ichnogenera and 15 ichnospecies, Arenicolites isp., Cylindricum isp., Helminthopsis abeli, Helminthopsis isp. 1, Helminthopsis isp. 2, Lorenzinia isp. , Planolites isp., Planolites beverleyensis, Planolites montanus, Teichichnus rectus, Thalassinoides isp.1, Thalassinoides isp.2, Thalassinoides isp.3, Thalassinoides isp.4. Three trace fossil assemblages under different sedimentary environments have been recognized as follows: 1) Helminthopsis-Planolites trace fossil assemblages mainly consists of fodinichnia and domichnia from intertidal and subtidal zone; 2) Thalassinoides-Teichichnus trace fossil assemblages, its trace fossils are relatively simple mainly consists of fodinichnia from intertidal and supratidal zone; 3) Thalassinoides-Helminthopsis trace fossil assemblages from intertidal zone. Based on the distribution characteristics of the trace fossil assemblages, the sedimentary environment model of the submember 55 of Middle Ordovician Majiagou Formation in the eastern margin of Ordos Basin was proposed.
