西藏仲巴县穷果北部日喀则弧前盆地地层再认识

通过对区内发育完好并保留下来的白垩纪—始新世地层的研究,海相白垩纪日喀则群自下而上可划分为昂仁组、帕达那组、曲贝亚组;古新世—始新世错江顶群包括下部曲下组和上部加拉孜组,整合覆于错江顶群之上的“如角藏布砂砾岩”为弧前盆地封盆粗碎屑岩。日喀则群与错江顶群在沉积学、地层古生物学及构造地质学诸方面的差异揭示了两群之间,更确切地说,曲贝亚组与曲下组之间呈不整合接触,该不整合形成于坎潘期—马斯特里赫特期与丹尼期之间。该区日喀则弧前盆地完整的地层序列全面再现了印度板块向欧亚板块俯冲过程,两板块的碰撞和新特提斯洋的彻底关闭发生在弧前盆地封盆粗碎屑岩沉积结束以后,这比原来认识的要晚些。

New understanding of stratum of Xigaze forearc basin in the north of Qiongguo area,Zhongba,Tibet

Located in the west of Xigaze forearc basin, the Cretaceous to Eocene stratigrphic sequence reserved grows in the Zhongba region along the north bank of the Yarlung Zangbo Suture Zone. The marine Cretaceous Xigaze Gr. could be subdivided in ascending order into the Angren Fm., Padana Fm. and Qubeiya Fm. Pale-ocene Eocene Cuojiangding Gr. inclouds Quxia Fm. and Jialazi Fm.. "Rujiaozangbu psepholite"—the confining coarse clastic rock of Xigaze forearc basin, is concordant on the Cuojiangding Gr.. Four differences in sedimentology,stratig raphic palaeontology and structural geology show that there exists a nonconformity between Xigaze Gr.and Cuojiangding Gr..Speaking concretely, this nonconformity existed between Qubeiya Fm.and Quxia Fm..The nonconformity was formed between Campanian-maast richtianand danian.The whole stratigrphic sequence of Xigaze for earc basin in this region reappear the course of strong underthrust between India plate and Eurasian plate fully.The main collision between India plate and Eurasian plate took place after "Rujiaozangbu psepho lite" had been deposited,the time of collision between the two plates is later than primary under standing's.