札达盆地构造旋回层及其地质意义

TECTONIC CYCLOTHEMS IN THE ZANDA BASIN AND ITS SIGNIFICANCE

札达盆地位于青藏高原南西部 ,其北东和南西侧分别为阿依拉日居和波林断裂系所限。在盆地内沉积了一套上新世 -更新世地层 ,从下至上可分四段 ,上部为湖相泥岩段 ,下部三段代表了三个构造沉积旋回 ,它们有类似的沉积特征 ,即 :每段下部为辫状河沉积的砾岩层 ,中部主要为曲流河沉积的砂岩层 ,并逐渐过渡到上部湖相泥岩。旋回沉积特征和地层变形反映了本区从上新世以来处于挤压状态 ,并有强烈垂向运动 ,为青藏高原在近几个百万年来持续隆升提供了依据。

The Zanda basin, bounded by the Ayila Ri'gyu and Boling faults in the northeast and southwest respectively, is located in the southwest of the Tibetan plateau. There developed a suite of Pliocene to Pleistocene strata, which can be, from bottom to top, divided into four members: A, B, C and D. The first three members, representing three large tectonic cyclothems, have similar sedimentary features. Their lower parts are composed of conglomerates deposited in braided river, the sandstones of middle parts deposited in meandering river, and the upper parts being lacustrine mudstones with minor thin sandstones. The member D is a suite of lacustrine mudstone. Cyclothemic characteristics, penecontemporaneous and subsequent deformation reflect that this area was compressed, from Pliocene, by the regional stress, and uplifted strongly. What mentioned above provided strong support for the Tibetan uplifting in the recent several million years.