长江源各拉丹冬地区上三叠统结扎群双壳类组合与古环境

PALEOECOLOGICAL ENVIRONMENT AND ASSEMBLAGE OF FOSSIL BIVALVES FROM THE UPPER TRASSIC JIEZA GROUP IN THE HEADWATERS OF THE YANGTZE RIVER

在长江源各拉丹冬地区雀莫错一带上三叠统结扎群采获大量双壳类化石,根据产出层位,建立了Quemocuomegalodon orientus-Neomegalodon boeckhi、Halobia superbescens-Halobia disperseinsecta、Amonotis togtonheensis-Cardium(Tulongocardium)xizangensis3个组合.这一生物组合反映的地质时代为诺利期,依据双壳类化石的外部形态和内部构造特征及围岩岩石化学分析,说明垂向上双壳类生活的结扎群具浅—深—浅的古地理变化特征,为区域上地层对比及生物生存环境提供了基础资料.

There has been little research in the northern headwaters of the Yangtze River in the past years. Fossil bivalves assemblages of Triassic age were not known. Near Quemocuo of the northern side of Yangtze River source, a large number of fossil bivalves have been found in the Upper Triassic JieZa Group, and on the basis of location, three assemblages are known： Quemocuomegalodon orientus-Neomegalodon boeckh, Halobia superbescens - H. disperseinsecta, Amonotis togtonheensis-Cardium （Tulongocardium） xizangensis. They are considered as Norian in age. From analysis of the paleoecologic characteristics and lithochemical and trace element contents we believe the environment changed with high to low to high sea levels. The bivalves provide an important reference material for comparison to adjacent areas.