山西兴县中奥陶统马家沟组五5亚段遗迹化石组合及其古环境意义

鄂尔多斯盆地东缘关家崖剖面奥陶系马家沟组五5亚段地层中保存大量无脊椎动物遗迹化石,可识别出居住迹、牧食迹、觅食迹三大类,共7个遗迹属、14个遗迹种,分别是Arenicolites isp.,Cylindricumisp.,Helminthopsis abeli,Helminthopsis isp.1,Helminthopsis isp.2,Lorenziniaisp.,Planolites isp.,Planolites beverleyensis,Planolites montanus,Teichichnus rectus,Thalassinoides isp.1,Thalassinoides isp.2,Thalassinoides isp.3,Thalassinoides isp.4。根据遗迹化石特征及其沉积环境,可划分3个遗迹组合:1、Helminthopsis-Planolites组合,该组合以觅食迹为主,部分为居住迹,出现在潮间带和潮下带;2、Thalassinoides-Teichichnus组合,该组合遗迹化石种类较单一,主要为觅食迹,分布于潮间带和潮上带;3、Thalassinoides-Helminthopsis组合,该组合出现在潮间带。基于遗迹化石组合的分布特点,提出山西兴县奥陶系马家沟组五5亚段的沉积环境模式。

CHARACTERISTICS OF PALEOENVIRONMENTAL EVOLUTION AND ICHNOCOENOSIS IN THE 55 SUBMEMBER OF THE MIDDLE ORDOVICIAN MAJIAGOU FORMATION, XINGXIAN, SHANXI

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.