Objective The Middle Cambrian gypsum−salt rocks in Tarim Basin are significance in deep oil and gas exploration, but the controlling factors on their formation and distribution are not clear. It is the goal of this paper to reveal the paleo−tectonic environment in the basin in Middle Cambrian and to figure out the controlling factors of the distribution of the gypsum−salt rocks.

Methods This study reexamined the well−logging data and determined the gypsum−salt rocks in wells drilling into the Cambrian and gypsum−salt rocks to stratum thickness ratios was obtained. The gypsum−salt distribution range was determined based on the seismic reflecting characteristics, reported sedimentary facies and salt structures. The Middle Cambrian gypsum−salt rocks thicknesses were got by that the gypsum−salt rocks to stratum thickness ratios timed the Middle Cambrian thickness. Finally, based on the seismic data and regional tectonic data, the structural characteristics and evolution of the paleohighlands controlling the gypsum−salt rocks were analyzed.

Results The Middle Cambrian gypsum salt rocks consisted of gypsum rock, salt rock, dolomite, limestone and mudstone, and distributed in a near circular area bounded by the Maigaiti slope, the southeast of the Madong structural belt, the east wing of Aman transitional belt, the west of Tabei uplift and Keping uplift. The thicknesses were big in center along the eastern Bachu uplift and western Tazhong uplift and thinned toward the margin. The boundary of the gypsum−salt lake was composed of fragments of various structural characteristics. The southwestern Tarim part was a Nanhua horst and a drape anticline from Sinian to Middle Cambrian. The Tanan part was a slope formed in Early Cambrian and was buried in Middle Cambrian. The Tazhong part was composed of Cambrian horst and differential subsidence from Sinian. The eastern Aman transitional belt was reefs depositing on the shoulder of the aulacogen in Early and Middle Cambrian. The Tabei part was related to differential thermal subsidence and the subsidence center was in the northern depression.

Conclusions The Nanhua rifting, Sinian−Cambrian differential subsidence, weak extension in Cambrian and the reef growth jointly controlled the gypsum−salt layer distribution in Middle Cambrian. These understandings both explained the distribution of the gypsum−salt rocks and helped to understand the tectonic evolution of the Tarim Basin in Sinian and Cambrian.