新疆北天山地区侏罗系齐古组陆相遗迹化石及古环境意义

Terrestrial trace fossils of Jurassic Qigu Formation in northern Tianshan area and their paleoenvironmental significance

探讨新疆北天山地区侏罗系齐古组陆相沉积中新发现的遗迹化石与沉积环境的关系。基于野外实测剖面,通过遗迹学和沉积学研究的技术方法,对遗迹化石及其赋存层位的岩性和沉积构造特征进行了精细描述。结果显示,塔西河剖面齐古组的遗迹化石为(内生迹)Cylindricum,Palaeophycus,Planolites;(表生迹)Sellaulichnus。这些遗迹化石赋存于紫红色泥岩与杂色(或黄绿色)泥质粉砂岩中,见小型交错层理和滑塌构造;红沟剖面齐古组仅见(表生迹)Circulichnis,赋存于紫红色中-厚层状砂岩中,见平行层理和雨痕构造。这些遗迹化石表明该区在中-晚侏罗世存在一个以蠕虫类、腹足类或节肢类动物为主的底栖生态系统,该系统内的生物具有在沉积底质上居住、觅食和爬行等生物习性。造迹生物在沉积物表层及半内栖层内的生物行为,表明沉积底质可能为充氧-富氧环境,相对简单的生物行为反映了其生活的底栖生态系统面临着沉积环境的压力。结合遗迹化石赋存层位的沉积学特征,认为北天山地区齐古组可能为富氧的曲流河沉积。

Based on the field measured section,the trace fossils and their hosting layers and lithology in the Jurassic Qigu Formation terrestrial deposits in the northern Tianshan area of Xinjiang are studied by means of ichnology and sedimentology in order to discuss the relationship between the trace fossils and sedimentary environment.The results show that the trace fossils of the Qigu Formation in the Taxihe section consist of Cylindricum,Palaeophycus,Planolites and epichnia Sellaulichnus.These fossils occur in purple mudstone and variegated color(or yellow-green)argillaceous siltstone,with small cross-bedding and slump structures.Epichnia Circulichnis can only be found in the Qigu Formation in Honggou section,which occurs in the purplish red medium-thick bedded sandstone with parallel bedding and rain marks.The characteristics of these trace fossils indicate that there was a benthic ecosystem dominated by worms,gastropods or arthropods in the middle to late Jurassic,and the organisms in this system had the habit of living,foraging and crawling on the sedimentary sediments.The biological behavior of trace organisms in the surface near surface layers of sediments indicates that the sedimentary bottom may be an oxygen-rich environment,and the relatively simple biological behavior reflects that the ecosystem in which they live is under the pressure of the sedimentary environment.The sedimentary characteristics of the occurrence horizon of trace fossils suggest that Jurassic Qigu Formation in the northern Tianshan area may be an oxygen-rich meanded-river deposit.