论文部分内容阅读
叶肢介是一种淡水甲壳类动物,个体不大,一般在几毫米到两厘米之间,软体有点像虾,具有很多附肢,雌雄异体,外裹一对几丁质壳瓣,形似蚌壳,但不如后者的钙质壳那么厚实坚硬。叶肢介从泥盆纪开始出现,中生代时其演化中心从欧洲迁移到了东亚,白垩纪它们的分异和演化达到顶峰,到了新生代则进入衰亡阶段。叶肢介化石一般出现在陆相地层中,由于它数量多、演化快、分布广泛,近年来已成为中国和邻近地区中生代非海相生物地层划分和对比研究的重要手段之一。中国大陆白垩系主要是陆相沉积,按古地理和生物地理区系,早白垩世可以划分为西南湖群和东北、东南、西北两个大区,前者出现的是直线叶肢介(Orthestheria)动物群,后者则是东方叶肢介(Eosestheria)和延吉叶肢介(Yanjiestheria)动物群;晚白垩世在西南湖群出现的是华美叶肢介(Aglestheria)动物群,在东北松花湖水系出现的是真瘤模叶肢介(Euestherites)动物群,在华中和东南沿海云梦泽水系出现的是薄壳叶肢介(Tenuestheria)动物群。链叶肢介(Halysestheria)是联系它们相互对比的共同分子;晚白垩世早期的线叶肢介(Nemestheria)动物群则在上述3个区系都有分布,甚至在西北喀什地区的塞诺曼期海陆交互相沉积和美国德克萨斯州同期海相地层的陆相夹层中都有发现的记录,它是将中国陆相白垩系与国际海相标准划分联系起来的重要证据。关于中国白垩纪的叶肢介动物群和有关陆相地层的划分对比,产东方叶肢介的义县组以前放在上侏罗统顶部或做为侏罗系-白垩系过渡层处理,这次按全国地层表将东方叶肢介群归入早白垩世。
Leaf extremity is a freshwater crustacean, not individual, usually between a few millimeters to two centimeters, the software is a bit like shrimp, with many appendages, dioecious, the outer shell of a pair of chitin shell, shaped like mussels Shell, but not as thick as the calcium shell of the latter. Leaf veins began to appear from the Devonian. During the Mesozoic era, their evolution centers migrated from Europe to East Asia. Their differentiation and evolution peaked in the Cretaceous, and reached the stage of decline in the Cenozoic. Because of its large number, rapid evolution and wide distribution, leaf-exoduomet fossils usually appear in terrestrial strata. In recent years, foliar mesotrons have become one of the important means to divide and contrast the Mesozoic non-marine biostratigraphy in China and its adjacent areas. The Cretaceous in mainland China is mainly continental facies. According to the palaeogeography and biogeography fauna, the Early Cretaceous can be divided into two groups: southwest lake group and northeast, southeast and northwest regions. The former appears Orthestheria, Fauna, while the latter is the Eosestheria and Yanjiestheria fauna. The Late Cretaceous appeared in the Southwest Lake Group is the gorgeous Aglestheria fauna, Emerging from the Eumindacean faunal flora, the Tenuestheria fauna appears in the Yunmengze water system in central and southeastern China. The Halysestheria is a common molecule that associates them with each other. In the early Late Cretaceous, the Nemestheria fauna distributed in the above three floristic regions. Even in the Norman region of Kashi Prefecture in the northwest China, It is found in the marine intercontinental facies sedimentary facies and continental facies interlaminar strata in the same period of Texas in the United States. It is an important evidence linking the terrestrial continental Cretaceous in China to the international maritime standard division. Regarding the division of the Cretaceous leaf-limbs and related terrestrial formations in China, the Yixian Formation, which produces eastern leaf-limbs, was previously placed on the top of the Upper Jurassic or treated as a Jurassic-Cretaceous transitional layer, which According to the national stratigraphic table, the Eastern Yexu Group was classified as Early Cretaceous.