塔里木盆地柯坪地区寒武系玉尔吐斯组沉积环境分析

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

塔里木盆地柯坪地区出露的寒武系底部玉尔吐斯组为层状硅质岩—黑色泥页岩—白云岩沉积组合。在露头实测的基础上,通过层序地层、岩石学、成烃生物组合及地球化学研究,剖析其沉积环境,为盆地内部早寒武世早期岩相古地理和烃源岩预测提供依据。玉尔吐斯组下部层状硅质岩与中部黑色泥页岩构成三级层序SQ1,受控于早寒武世早期海侵和上升流作用,准层序为退积式叠置;上部中薄层白云岩与肖尔布拉克组下部白云岩构成另一三级层序SQ2,是海退背景下进积型沉积组合。2个三级层序的沉积环境经历了浅水陆棚—深水陆棚—浅水陆棚的演变,其中SQ1黑色泥页岩段为深水陆棚缺氧环境沉积,是烃源岩发育的有利相带。

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.