济阳坳陷车镇凹陷古近系沙河街组深水沉积中的遗迹化石

Deep water trace fossils from the Shahejie Formation of Paleogene of Chezhen Sag in Jiyang Depression

通过岩心观察和标本鉴定,在济阳坳陷车镇凹陷古近系沙河街组沙一段深水沉积中识别出大量遗迹化石,包括Mermoides chezhenensis、Helminthopsis sp 、Gordia sp 、Helminthoidichnitessp 、Planolitesbeverlegensis、Neonereitesuniserialis和Planolites sp ,它们是无脊椎动物线虫、节肢动物、环节动物和腹足类等形成的牧食迹和进食迹。这些遗迹化石中的Neonereitesuniserialis为由一系列小球粒排成的蛇曲形痕迹,不分枝,长约7cm ,宽约2mm ,呈顶凸痕保存于灰色、深灰色页岩中。Mermoidesche zhenensis为微小简单、不规则弯曲的觅食拖迹,长1～3cm ,宽1～2mm ,近平行或略倾斜层面分布于灰色、深灰色薄层状泥岩中,内迹保存。根据遗迹化石的共生组合特征及沉积环境,可分出2个遗迹组合:Mermoidesche zhenensis遗迹组合和Neonereites uniserialis遗迹组合。Mer moidesche zhenensis遗迹组合丰度和分异度较高,组成分子有Mermoideschezhenensis、Helminthopsissp 、Gordiasp 、Helminthoidichnitessp 和Planolites beverlegensis,其中以Mermoides chezhenensis的大量出现为组合代表。该组合出现于灰色、深灰色泥岩中,反映了富氧的半深湖环境。Neonereites uniserialis遗迹组合组成分子为Neonereites

By means of observation on cores and identi fi cation of specimens,a lot of trace fossils including Mermoides chezhenensis, Helminthopsis sp.,Gordia sp.,Helminthoidichnites sp.,Planolite s beverlegen sis,Neonereites uniserialis and Planolites sp.,are discovered in deep w ater sediments in the Shahejie Formation of Paleogene in the Chezhen Sag,Jiyang Dep ression,Bohai Bay Basin.They are grazing trails and feeding trails produced by invertebrates such as annelids, arthropods,gastropods,and so on.Of these trace fossils,Neonereites uni serialis,with 7 cm in length and 2 mm in width,is a chain of knobs forming u nbranched meandering shape and is preserved in convex epirelief in gray-dark gray shales.Mermoides chezhenensis,which is simple,irregularly curving in sh ape,ranges from 1 to 3 cm in length and 1 to 2 mm in width.The trace is preser ved paral lelly or slightly obliquely in gray-dark gray thin-bedded mudstones.According to their palaeoecological and sedimentological features,these ichnofossils ca n be divided into two ichnoassemblages,namely,Mermoides chezhenensis ichno as semblage and Neonereites uniserialis ichnoassemblage.Mermoides chezhenens is ich noassemblage,which is characterized by the fully abundant Mermoides chezhenen sis ic hnospecies and commonly associated with Helminthopsis sp.,Gordia sp. ,Helmintho idichnites sp.,and Planolites beverlegensis,occurs in gray-dark gray t hin -bedded mudstones.The ichnoassemblage often has high ichnodiversity and abunda nce and represents highly oxygenated semi-deep lacustrine environments.Neonereit es uni serialis ichnoassemblage,consisting of ichnogenera Neonereites uniserialis an d Planolites sp.,develops in gray-dark gray shales and indicates semi-de ep t o deep dysoxic lacustrine environment.The Mermoides chezhenensis ichnoassem blage ha s similar characters as Mermia ichnofacies in composition,ichnodiversity an d a bundance of ichnoassemblage.The Neonereites uniserialis ichnoassemblage has lowe r ichnodiversity and abundance compared with the Mermia ichnofacies and the che mical characters of water represented by the trace assemblages are also differen t.The presen t continental trace fossil model is not complete,and there are still many ichn ofacies that have not been recognized and established.