Shell concentrations of Early Silurian virgianid brachiopods in northern Guizhou: Temporal and spatial distribution and tempestite formation

作     者：LI Yue RONG JiaYu 

作者机构：Nanjing Institute of Geology and Palaeontology Chinese Academy of Sciences Nanjing 210008 China State Key Laboratory of Palaeobiology and Stratigraphy Nanjing Institute of Geology and Palaeontology Chinese Academy of Sciences Nanjing 210008 China 

出 版 物：《Chinese Science Bulletin》 (Chin. Sci. Bull.)

年 卷 期：2007年第52卷第12期

页      面：1680-1691页

核心收录：

学科分类：070903[理学-古生物学与地层学(含：古人类学)] 0709[理学-地质学] 07[理学] 

基　　金：Supported by Chinese Academy of Sciences (Grant Nos. KZCX3-SW-149 and KZCX2-YW-122) the National Natural Science Foundation of China (Grant Nos. 40572069 and 40532009) 

主　　题：风暴岩 早志留纪 古生物学 腕足类动物 时空分布 贵州北部 

摘      要：Shell beds in the uppermost Xiangshuyuan Formation and its coeval Upper Shihniulan Formation (Lower Silurian), northern Guizhou, SW China, are interpreted as tempestites occurring on the Upper Yangtze Platform. The shells are dominated by two endemic and transient virgianid (brachiopod) taxa, Paraconchidium shiqianensis and Virgianella glabera, which vary in relative abundance and deposited as fragments of valves with cemented micrite that differs from the surrounding sediment, demonstrat- ing that the shells were not originally preserved in growth positions. The thicknesses of individual shell layers vary from ten centimeters to more than four meters. Shells had been strongly stirred up by high-energy currents, mainly caused by ocean storm events and probably related to the profile of the geographic shape of the coastline. Fragmentation of shells, in particular, their thinning anterior parts of ventral and dorsal valves are more intensive. The benthic assemblages are from lower BA2 to upper BA3 in depth, assigned to near shoal belt in geographic background. Breakage and stacking density are of the indexes of proximal and distal transportations. Northern Guizhou was located within the lower latitudes of the Southern Hemisphere during the Silurian time, and obviously affected the depth of the virgianid inhabitation. Most of these shells were disturbed repeatedly by surges. It is inferred that on average, several ten thousand years of growth of shells were required for development of shell layers, followed by storm disruption.