西昆仑山前侏罗-白垩系分布特征及其控制因素

Distribution Characteristics and Controlling Factors of Jurassic-Cretaceous in the Front of West Kunlun Mountains

中生界侏罗-白垩系在西昆仑山北缘大量出露,但是山前覆盖区钻井揭示其分布较为有限且不连续.通过大量野外地质调查,厘定了西昆仑山前侏罗-白垩系与上、下地层的接触关系,认为研究区的侏罗-白垩系与下伏地层为角度不整合接触,与上覆新生代为平行不整合接触,内部为整合或平行不整合接触,与邻区有明显的区别.确定了侏罗-白垩系在地球物理资料中的识别标准,并通过大量的地球物理和钻井资料的标定、解释,圈定了侏罗-白垩系的分布范围,总结了其厚度变化趋势;认为三叠纪末挤压变形残留的古地形对侏罗-白垩系的分布起到了控制作用,新近纪以来的挤压变形则对侏罗-白垩系的分布起到改造作用.研究成果对解剖西昆仑山前的中、新生代的演化历史,指导该地区的油气勘探具有重要参考价值.

Jurassic Cretaceous strata are widespread in outcrops of northern margin of West Kunlun Mountains. However, drilling data indicate that they are sparsely and discontinuously distributed in the foreland overlaid regions. To determine the contact relations between the JurassicCretaceous and overlaying and underlying strata, and their distribution and thickness variation, new data of field geologic investigation and interpretation of seismic profiles are presented, which suggest that the Jurassic-Cretaceous strata overlay the beneath sequences in an angular unconformity and contact with the overlaying sediments in a parallel unconformity, while within the Jurassic-Cretaceous sequence they contact with each other in conformity or parallel unconformity. These contact relations show totally different features compared to those of adjacent regions. Based on these contact relations, we establish structural interpretation models. The structural interpretation of seismic profiles and subsequent strata distribution and thickness variation indicate that compression event in End Triassic and its remnant paleo-tectonotopography has controlled occurrence and thickness of Jurassic-Cretaceous strata, while compression since Neogene has reconstructed their distribution and thickness patterns. The study results provide significant constraints for the Mesozoic-Cenozoic evolution of piedmont fold and thrust belt in tho front of West Kunlun Mountains and petroleum exploration in this region.