华北地台南部中寒武世徐庄组遗迹化石及其沉积环境

MIDDLE CAMBRIAN HSUCHUANGIAN TRACE FOSSILS FROM SOUTHERN NORTH CHINA PLATFORM AND THEIR SEDIMENTOLOGICAL SIGNIFICANCE

华北地台南部中寒武世徐庄组为一套以砂、页岩和灰岩为主的碎屑和碳酸盐沉积,下部以碎屑沉积为主,上部主要是碳酸盐岩,与上覆地层张夏组和下伏地层毛庄组均为整合接触。徐庄组内除了含有三叶虫实体化石外,还含有大量的遗迹化石,这些遗迹化石主要是产在下部的碎屑岩中。关于徐庄组顶、底界线,我们采用卢衍豪等(1953)的划分方案,下部以Hsuchuangia带为底界,上部以Bailiella带为顶界。本文所研究的遗迹化石分别采自山东张夏、汶南,江苏徐州和河南鲁山的中寒武世徐庄组。通过遗迹化石的研究,我们在徐庄组建立了Cruziana barbata-Rusophycus ramellensis遗迹群落,结合三叶虫实体化石,相分析等,探讨了徐庄组的沉积环境。

A great quantity of trace fossils have been discovered from the Middle Cambrian Hsuchuang Formation in Shandong, Jiangsu and Henan in China, including: the predominant Cruziana and Rusophycus (trilobite traces), together with Arenicolites, Bifungites, Didymaulichnus, Diplichnites, Monocraterion, Monornorphichnus, Neonereites, Palaeophycus, Parallehelcura ichnogen, nov. Phycodes, Plagiogmus, Planolites, Scolicia, Treptichnus and Zoophycos.Based on the principles of palaeoecology and sedimentology, the ichnocoenosis Cruziana barbataRusophycus ramellensis is established, including a new ichnogenus and 3 ichnospecies with a discussion on the sedimentary environments of the Hsuchuang Formation. This study comes to the conclusion that: 1. The ichnocoenosis Cruziana barbata-Rusophycus ramellensis reflects traces created by benthos which were distributed in the southern part of the North China Platform in Early Hsuchuang times of Middle Cambrian, mainly confined to the shallow marine muddy shelf environment; 2. The southern part of the North China Platform was under a turbulent shalloW marine environment but laterally rather stable in Middle Cambrian Hsuchuang times.Description of New Iehnotaxa Monomorphichnus henanensis iehnosp, nov. (P1. Ⅱ, fig. 7)Name: Derived from its type locality——Henan province.Description: A trace fossil preserved on the sole of siltstone beds, with 15—20 ridges, which are 1.5—4cm long, and 0.5cm apart, parallel or subparallel. Discussion: The new species usually with more than 15 ridges differs from its type species M. bilinearis.Oeeurrenee: Hsuchuang Formation, Middle Cambrian, Lushan, Henan.Parallehelcura iehnogen, nov.Name: From Latin Paralle, parallel and Helo, trail.Description: Two groups of parallel ridges, with three in each group; middle ridge coarser than both lateral ridges.Type Iehnospeeies: Parallehelcuria trilineata.Occurrence: Hsuchuang Formation, Middle Cambrian, Lushan, Henan.P. trilineatus iehnogen, et iehnosp, nov. (P1. Ⅱ, fig. 4)Name: From Latin Trilinea, three scratches.Description: Two groups of parallel ridges, with three in each group; ridges 8cm long, and 0.1—0.2cm apart.Occurrence: Ibid.Rusophyeus unilobus iehnosp, nov. (P1. Ⅲ, figs. 4—6)Name: From Latin Uni, single; and Lobos, lobe.Description: A trace fossil preserved on the sole of siltstone beds, representing a single lobe resting trace; scratches radial and fan-shaped, in 7--8 bundles, with at least 3 scratches in each bundle.Oeeurrenee: Hsuchuang Formation, Middle Cambrian, Lushan, Henan.