酒泉盆地青西凹陷鸭西地区古地貌对沉积体系空间展布的控制作用

古地貌是控制盆地后期沉积相发育与分布的一个主要因素,通过研究古地貌可有效地预测富砂沉积体系的分布。以酒泉盆地青西凹陷鸭西地区下沟组形态较平缓的大型鼻状构造带为研究对象,综合运用测井、岩心、地震等资料分析下沟组3个三级层序发育时期沉积体系空间展布及变迁,利用平衡剖面技术将下沟组3个三级层序界面恢复到后期祁连山逆冲推覆构造变形前的沉积期原始空间分布状态,并分析各层序发育时期古地貌特征及演化,探讨了古地貌与沉积体系空间展布两者之间的耦合关系。研究结果表明,古地貌组合样式制约着不同时期层序的发育及沉积体系的展布,并提出了古地貌对沉积体系空间展布的控制模式。

CONTROL OF PALAEOGEOMORPHOLOGY ON SEDIMENTARY SYSTEM DISTRIBUTION: AN EXAMPLE FROM QINGXI DEPRESSION,JIUQUAN BASIN

Palaeogeomorphological units, such as paleo-bulges, paleo-sags and paleo-valleys, are critical in controlling the formation and development of sedimentary systems and sequences. Sediments move through paleo-valleys (usually structural slope-break zones) and are finally deposited in paleo-sags as fan deltas and/or turbidite fans. Therefore, palaeogeomorphology research can help reveal the spatial distribution of depression and deposition centers for predicting sand-rich sedimentary systems so as to benefit the exploration of oil and gas in petroliferous basins. Balanced cross section has been widely applied in recent years as an efficient tool for study of tectonic evolution. In this paper, we used the balanced cross section technique to reestablish the palaeogeomorphological framework, taking the nose-like structure in Xiagou Formation of Lower Cretaceous in Yaxi area, Qingxi sag as an example, where fan delta, lacustrine and gravity flow depositional systems are well developed. The influence of palaeogeomorphology on sedimentary system was discussed in details.