西藏东部三叠纪层序地层分析与对比

Correlation of Triassic Sequence Stratigraphy in Eastern Tibet

通过识别关键层序界面、体系域沉积的几何关系、迭置样式等特征 ,结合构造和地层综合标识 ,建立了西藏东部的江达 -昌都一带三叠系层序地层等时格架 .以江达岛弧盆地为例 ,厘定出1 0个层序界面 ,其中 6个 类界面和 4个 类界面 ;划分出 1 0个三级层序 ,其中 6个 类层序和 4个 类层序 .三叠纪层序共经历了 37Ma时间的演化 ,估算平均每个层序所占时限为3.7Ma,一般为 1～ 2 Ma,最长者约 1 0 Ma.初步总结了岛弧 -弧后盆地体系中的层序地层主控因素相互作用的规律 .认为岛弧区、弧后区与克拉通区的层序地层对比所反映的层序数量、结构与类型的较大差别 ,应是构造 -火山。

The Triassic marine sediments were predominated in Jiangda, Changdu, and eastern Tibet and accumulated respectively in Jiangda arc, Shengda back arc, and Changdu craton basins from east to west. The isotime grillwork for Triassic sequence stratigraphy was established. The recognized marks of boundaries were built by distinguishing the key sequence boundaries and geometric or superposed patterns of systematic traces. In Jiangda arc basin, for example, 10 sequence stratigraphic boundaries were discriminated with integrated marks of tectonics, in which 6 fall into class Ⅰ and 4 into class Ⅱ. 10 3rd order sequences were divided, in which 6 belong to class Ⅰ and 4 to class Ⅱ. These sequences were formed in 37Ma, averaged by 3.7Ma. The interaction of the main factors controlling the formation of sequence stratigraphy in arc and back arc basin systems was primarily summarized. Differences in quantity, structure, and type of sequences between the arc, back arc and craton area are thought to be the interactions of 3 factors, i.e. the tectono volcano activity, the sediment supply and the eustacy of sea level.