摘要
全球志留纪苔藓动物群的面貌和研究程度远不及奥陶纪和其他地质时期,原因有两方面:1.受沉积环境的制约。苔藓动物群通常发现于大陆棚区近岸带的灰岩和页岩中,由于保存在页岩中的苔藓虫受后期造岩作用挤压和地下水的淋滤,使苔藓虫钙质骨骼很难完整地保存并供切片详细研究其硬体组织。所以在页岩中能够发现的仅仅是一些苔藓虫骨骼的印痕。尤其兰多维列世早期是全球海进时期,从已研究的典型剖面如英国的Wales,Bohemia,Scandinavia西部等多以页岩和砂岩为主,在这样沉积环境中不利于苔藓动物群的发生和生长。2.
In general features and extent of researches, the global Silurian bryozoan faunas appear to be far behind as compared with those of the Ordovician and other geological periods. There are two reasons for this. One is the restriction of sedimentary environments. As everyone knows, bryozoan faunas are generally discovered from the limestone and shale since the bryozoans preserved in shales were subject to compression through lithogeneous process and eluviation of underground water stages, their calcareous skeletons could hardly be preserved for making detailed thin-section observations on their skeleton. This is why what can be discovered from the shale are simply some imprints of bryozoan skeletons. The early Llandovery is one of the periods of global transgressions. Judged from the typical faces (such as Wales of Britain, Bohemia, western Scandinavia, etc.), they are mostly dominated by shale and sandstone. Such sedimentary environments are unfavourable for the occurrence and growth of bryozoan faunas. The other reason is the attenuation in the evolution of the bryozoan fauna itself. The Ordovician was an important stage for the occurrence and multiplication of Early Palaeozoic bryozoan faunas, and also a stage in which the Trepostomata became flourishing. After entering into the Silurian, due to the alteration in ecological environments, it was rather difficult for the bryozoan fauna with an inclination for benthonic ecological environments. This caused the rapid decline and extinction of the Trepostomata which were common in Ordovician. In addition, there were very few new genera or groups appearing at this time. For this reason, the features of the Llandovery bryozoan fauna still remain unclear up to now. Although the Llandovery bryozoan fauna has already been discovered from many areas such as Britain, Norway, Sweden, Estonia, the Anticosti Island of Canada, etc., it has not been systematically studied in detail so far. On the other hand, although there have been fragmentary reports on the bryozoan faunas of s
出处
《古生物学报》
CAS
CSCD
北大核心
1990年第5期601-611,共11页
Acta Palaeontologica Sinica
基金
国家自然科学基金4870090项目资助
为中英志留系研究项目的阶段成果之十四