Sedimentary characteristics and depositional environment of Yuertusi Formation in Keping area, Tarim Basin

The Lower Cambrian Yuertusi Formation in the Keping area of the Tarim Basin consists of bedded cherts, black shales and dolostones. Its sedimentary environment was studied based on sequence stratigraphy, lithology, hydrocarbon-forming organisms and geochemical features of outcrops, which provided evidences for the prediction of lithofacies palaeogeography and source rock during the Early Cambrian. The lower bedded cherts and middle black shales formed one third-order sequence SQ1, which was controlled by transgression and upwelling in the Early Cambrian and represented a regressive cycle. The upper thin-middle bedded dolostones of Yuertusi Formation and the lower thick dolostones of Xiaoerbulake Formation formed another third-order sequence SQ2, which represented a transgressive cycle. The sedimentary environment of these two sequences evolved from shallow to deep and then again to shallow shelves. The black shales of SQ1 represented an anoxic sedimentary environment of deep shelf, which was favorable for source rock development.