藏南吉隆盆地中新世—早更新世沉积演化

Late Miocene-Early Pleistocene sedimentary evolution in Gyirong Basin,southern Tibet

位于喜马拉雅北麓的吉隆盆地中新统旦增竹康组,为冲积扇-辫状河沉积。沃马组沉积演化自下而上依次为扇三角洲-滨浅湖-扇三角洲,总体上表现为进积-退积-进积的沉积旋回。沃马剖面在10～7.4Ma期间,古流向主体为SEE向;7.4～1.67Ma,古水流方向主体为SWW向,说明7.4Ma以后,吉隆盆地古地理格局发生显著变化,古地势由原来的西高东低转变为后期的东高西低。根据沉积学、磁性地层学、年代学等方面的研究资料,将10Ma以来吉隆盆地的湖盆演化大致划分为3个阶段:10～7.4Ma,湖盆裂陷形成期;7.4～3.6Ma,湖盆扩展与稳定发展期;3.6～1.67Ma,湖盆萎缩消亡期,代表了盆地周围喜山的3次隆升期,即10～7.4Ma、7.4～3.6Ma和3.6～1.67Ma,其中3.6～1.67Ma为强烈隆升期。

The Gyrong Basin was located in the northern piedmont of the Himalayas. Sedimentary facies in Miocene Danzengzhukang Fom^ation of the basin are composed from the bottom upwards of alluvial fan-braided river. The Orma Formation consists of delta fa- cies-lacustrine thcies-delta facies from bottom to top, which represents a progradation-regradation-progradation sequence. The pale- ocurrent reflected in Orma section was mainly in SEE direction in 10--7.4Ma, and was in SWW direction in 7.4-1.67Ma. These data imply that the paleogeographic framework of Gyrong Basin changed drastically and its topography changed from high in the west and low in the east into high in the east and low in the west after 7.4Ma. Based on the sedimentary, magnetostratigraphic and chronologic data available, the authors hold that Gyrong Basin has experienced three evolutionary stages since 10Ma： 10-7.4Ma was the stage of rift and formation; 7.4-3.6Ma was the stage of expansion and steady development, an 3.6-1.67Ma was the stage of withering and ex- tinction. These three stages represented the three uphft period of the Himalays, which included 10-7.4Ma, 7.4-3.6Ma and 3.6- 1.67Ma, and the Himalayas was strongly uplifted during 3.6-1.67Ma.