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

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.、Helminthoidichnites sp.、Planolites beverlegensis、Neonereites uniserialis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Neonereites uniserialis为由一系列小球粒排成的蛇曲形痕迹，不分枝,长约7 cm，宽约2 mm，呈顶凸痕保存于灰色、深灰色页岩中。Mermoides chezhenensis为微小简单、不规则弯曲的觅食拖迹，长1~3 cm，宽1~2 mm，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，可分出两个遗迹组合：Mermoides chezhenensis遗迹组合和Neonereites uniserialis遗迹组合。Mermoides chezhenensis遗迹组合丰度和分异度较高，组成分子有Mermoides chezhenensis、Helminthopsis sp.、Gordia sp.、Helminthoidichnites sp. 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 uniserialis和Planolites sp.。该组合分布于灰色、深灰色页岩中，反映了贫氧的半深湖-深湖沉积环境。Mermoides chezhenensis遗迹组合与Mermia遗迹相相比，其化石组成、丰度及分异度基本相似。但Neonereites uniserialis遗迹组合与Mermia遗迹相在化石组成、丰度及分异度等方面存在很大差异，所反映的水体化学性质也不相同。因此，目前所建立的陆相遗迹相模式还不完善，尚有许多遗迹相未被识别和建立。

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

By means of observation of cores and identification of specimens, a lot of trace fossils including Mermoides chezhenensis, Helminthopsis sp., Gordia sp., Helminthoidichnites sp., Planolites beverlegensis, Neonereites uniserialis and Planolites sp., are discovered in deep water sediments in the Shahejie Formation of Paleogene in Chezhen Sag, Jiyang Depression of Bohai Bay Basin. They are grazing trails and feeding trails produced by invertebrates such as annelids, arthropods, gastropods, and so forth. Of these trace fossils, Neonereites uniserialis, with 7 cm in length and 2 mm in width, is a chain of knobs forming unbranched meandering shape and is preserved in convex epirelief in gray, dark gray shales. Mermoides chezhenensis, which is simple, irregularly curving in shape, ranges from 1 to 3 cm in length and 1 to 2 mm in width. The trace is preserved parallelly or slightly obliquely in gray, dark gray thin-bedded mudstones. According to their palaeoecological and sedimentological features, these ichnofossils can be divided into two ichnoassemblages, namely, Mermoides chezhenensis Ichnoassemblage and Neonereites uniserialis Ichnoassemblage. Mermoides chezhenensis Ichnoassemblage, which is characterized by the fully abundant Mermoides chezhenensis ichnospecies and commonly associated with Helminthopsis sp., Gordia sp., Helminthoidichnites sp., and Planolites beverlegensis, occurs in gray, dark gray thin- bedded mudstones. The Ichnoassemblage often has high ichnodiversity and abundance and represents highly oxygenated semi-deep lacustrine sediments. Neonereites uniserialis Ichnoassemblage, consisting of ichnogenera Neonereites uniserialis and Planolites sp., develops in gray, dark gray shales and indicates semi-deep to deep dysoxic lacustrine environment. The Mermoides chezhenensis Ichnoassemblage has similar characters as Mermia ichnofacies in composition, ichnodiversity and abundance of ichnoassemblage. The Neonereites uniserialis Ichnoassemblage has lower ichnodiversity and abundance compared with the Mermia ichnofacies and the chemical characters of water represented by the trace assemblages are also different. The present continental trace fossil model is not complete, and there are still many ichnofacies that haven’t been recognized and established.