Abstract:

An unconformity analysis method is provided to study the basement paleo-uplift of Bachu-Markit area, Tarim basin. On the basis of regional tectonic and sedimentary evolution of previous research, we divided the Precambrian top surface to angle unconformity, nonconformity, overlap unconformity and parallel unconformity through the recognition of well data and seismic data. The four types of unconformity reflect rift, basement paleo-uplift, slope and depression, respectively. Furthermore, the distribution of unconformity has a gradual transition pattern, which is arrangement from nonconformity, overlap unconformity to conformity. We consider that the north boundary of basement paleo-uplift is Tumuxiuke fault zone and that the south boundary is possibly Tiekelike zone. Therefore, it could be affirmed that the main part of paleo-uplift is located in Markit area and the southern Bachu area; that the slope of paleo-uplift is distributed in present southwestern Tarim depression and the northern Bachu area. The tectonic evolution of basement paleo-uplift can be divided into 3 stages, which are gentle Precambrian archicontinent stage, final Precambrian uplifting stage and Early-Middle Cambrian subsidence stage. As a whole, the paleo-uplift is gentle at the south and steep at the north in Precambrian; while it is contrary in Early-Middle Cambrian, which controls the strata development and distribution of Nanhuaian-Sinian and Early-Middle Cambrian.

Key words: unconformity, Precambrian, paleo-uplift, Bachu-Markit area, Tarim basin