华南奥陶、志留纪腕足动物群的更替兼论奥陶纪末冰川活动的影响

地史时期大规模的生物群更替与全球大环境的灾难性变化密切相关 ,尽管这种更替在性质、延续时间及等级上各个时期不尽相同。奥陶、志留纪腕足动物群的更替提供了一个重要的实例。全球广布的晚奥陶世较深水叶月贝动物群 ( Foliomena Fauna)和其后浅、凉水的赫南特贝动物群 ( H irnantia Fauna)的灭绝 ,均受控于当时的冈瓦纳大陆冰川活动及其影响效应。志留纪早期 ,以正形贝目和扭月贝目占主导地位的晚奥陶世动物群被一大批新类型 (如无洞贝目、五房贝亚目和石燕目 )所替代 ,组成典型的志留纪动物群。

ORDOVICIAN-SILURIAN BRACHIOPOD FAUNA TURNOVER IN SOUTH CHINA

Biotic turnover was related to global environmentalchangesduring the geologic history.Turnover of the Ordovician and Silurian brachiopod faunas in South China afforded an importantexample.The firstphase of the Late Ordovician mass extinction ( such as the elimination of the deeper water Foliomena fauna at the end of mid- Ashgill) strongly related to substantialfalling temperatures,falling sea- level,and a fundamentalchange in oceanic circulation/chemistry. The second phase of the extinction again related to a rise of oceanic temperature and a sharp rise of sea- level with onlap and spread of bottom water anoxia which caused the demise of the shallow and cool/cold water H irnantia fauna atlater Hirnantian,latest Ashgill.The two phases were coincided with the start of the then Gondwana continental glaciation and its melting respectively.The Ordovician brachiopod faunas dominated by Orthida and Strophomenida were replaced by a new phase of the typical Silurian brachiopod faunascharacterized by predominance of atrypoids,pentameroids,and eospiriferids in the earlier Silurian.