Sedimentary characteristics and development model of Cambrian gypsum-salt rocks, Tarim Basin

Abstract

The Cambrian gypsum-salt rocks in the Tarim Basin are key geological elements to the pre-salt play typical marine evaporites, yet little attention has been paid to this set of evaporites. Based on a field survey, the latest 2D seismic interpretation and comprehensive analysis of sixteen exploratory wells, a study on the sedimentary characteristics of gypsum-salt rock was carried out in a progression of "point to line, and to plane", and a contour map of the Lower to Middle Cambrian cap rocks, gypsum-salt rocks and the sedimentary facies maps of the Awatag Formation were compiled. A development model of "dry and hot paleoclimate, continuous regression process, reef barrier background" of the Lower to Middle Cambrian gypsum-salt rocks was established. There are four sets of gypsum-salt rocks with four lithofacies combinations developed longitudinally and stably in the Wusongger and Awatag formations. The gypsum-salt rocks in the regression stage are featured by "inner salt, middle gypsum, outer red-layer", while those in the transgression stage are interbedded with gypsum, mudstone and dolomite. The average thickness of the Lower to Middle Cambrian cap rocks in the Tarim Basin is 245 m, and the average thickness of the gypsum-salt rocks is 167 m (340 m maximum), showing good sealing capacity. The arid-hot paleoclimate, continuous regression and reef and reef barrier provided favorable conditions for the development of thick gypsum-salt rocks in the Early to Middle Cambrian of the Tarim Basin. The paleoclimate and sea level change restricted the facies boundary between limited platform and evaporation platform, and made the Bachu Uplift and Awati Sag (the stable thickness of gypsum-salt rocks is over 300 m) become the salt accumulation center at that time.

Keywords

• gypsum-salt rocks
• sedimentary characteristics
• development model
• cambrian
• tarim basin