羌塘盆地雁石坪地区侏罗纪沉积物特征与沉积环境

The Jurassic sediments and their depositional environments in the Yanshiping region of the Qiangtang Basin, northern Xizang

关键词:  羌塘盆地  雁石坪地区  侏罗纪  沉积物特征  沉积环境

Key words:  Qiangtang Basin  Yanshiping region  Jurassic  sediment characteristics  depositional environment

摘要:

藏北羌塘盆地地层出露以海相三叠系、侏罗系为主。盆内侏罗系为海相、海陆交互相沉积,具"三砂夹二灰"的特征。侏罗系分布广泛、层系连续、发育完整、化石丰富。羌塘盆地雁石坪地区位于青藏公路旁,露头较好,许多地质工作者前来考察研究。本文所涉及的区域是雁石坪地区向斜南翼,主要为中侏罗统夏里组、上侏罗统索瓦组。夏里组以碎屑岩沉积为主,广泛发育紫红、暗紫色泥岩与灰绿色粉砂岩、细砂岩不等厚互层;索瓦组以灰岩为主,层理发育、化石丰富,这些都是各种环境条件的记录。通过野外实测剖面,采集大量的样品以及室内的分析,结合沉积岩特征,借助相标志,初步分析夏里组为潮坪沉积环境,索瓦组为碳酸盐缓坡环境,为恢复重建古沉积环境——岩相古地理提供依据。

Abstract:

The marine Triassic and Jurassic strata crop out over a wide range of scales in the Qiangtang Basin, northern Xizang. The Jurassic strata composed of alternating marine-continental sediments are characterized by widespread occurrence, laterally persistent strata and abundant fossils. The Middle Jurassic Xiali Formation and Upper Jurassic Suowa Formation are laid down on the southern flank of the Yanshiping geosyncline studied herein. The former contains prevailing clastic rocks including purplish red and/or dark purple mudstones and grayish green siltstones and fine sandstones; the latter is dominated by limestones and contains well-developed beddings and abundant fossils. The integration of field investigation and indoor studies has disclosed that the Xiali Formation is located in a tidal-flat environment whereas the Suowa Formation in a carbonate ramp environment.