Tectonic Evolution And Formation Mechanism Of Paleo-uplift In The Northeastern Sichuan Basin

In the northeastern part of the Sichuan Basin,there are two paleo-uplifts,the deep-seated Xuanhan-Dazhou paleo-uplift,and the shallow-seated Kaijiang paleo-uplift.The study of the tectonic evolution and formation mechanism of the paleo-uplift is helpful to the analysis of the deformation characteristics of the basin,and is of great significance to oil and gas exploration.In this paper,we use the drilling data,seismic data and geophysical data to analyze structures from the seismic profiles in the study area based on the fault-related folding theory.At the same time,we carefully trace the seismic horizon and analyze the tectonic evolution of each paleo-uplift since the Sinian period.And by using the balanced-cross section to characterize the tectonic evolution of each paleo-uplift,comprehensively explore the formation mechanism of each paleo-uplift,and finally discuss the controls upon hydrocarbon accumulation in the paleo-uplifts.This paper got to the following findings:1.Redefine the distribution of the paleo-uplifts.Xuanhan-Dazhou paleo-uplift:the core part is located in Xuanhan-Dazhou area and extend along south to north direction with an area of approximately 6300 km~2.Kaijiang paleo-uplift:the core part is located in Kaijing area and show an L-shaped uplift with an area of approximately9600 km~2.2.The Xuanhan-Dazhou paleo-uplift developed under the slippery layer of the Cambrian gypso-salt rock,which was formed by the differential uplift of the early basement.The overlying deposition of the Dengying Formation and the Lower Cambrian were developed.The four stages of the Xuanhan-Dazhou paleo-uplift evolution:(1)the early stage of the Late Sinian was the embryonic stage,(2)the later stage of the Late Sinian was the development stage,(3)the Early Cambrian was the declining stage,(4)the Caledonian period was the transformation stage.3.The Kaijiang paleo-uplift is a erosional paleo-uplift developed within the Cambrian gypsum salt rock slip layer and within the Leikoupo Formation.Controlled by the compressive stress from the Jiannan-Xuefeng structural belt and the closure of the Mian-Lue Ocean,there formed an L-type paleo-uplift.The four stages of the Kaijiang paleo-uplift evolution:(1)the deposition period of Jialingjiang Formation was the embryonic stage,(2)the deposition period of Leikoupo Formation was the development stage,(3)the deposition period of Xujiahe Formation was the declining stage,(4)the Yanshan-Himalayan period was the transformation stage.4.The Xuanhan-Dazhou paleo-uplift controls the development of two high-quality source rocks and two intra-platform reef flat reservoirs;As the Cambrian gypsum salt rock is widely developed,the main detachment layer in East Sichuan is formed.The structural deformation under the detachment layer is weak and stable,which has a large uplift background.During the peak stage of gas formation in Triassic,the Xuanhan-Dazhou area was at a high elevation,which was favorable for reservoirs forming.5.The Kaijiang paleo-uplift provided structural conditions for the formation of a large paleo structural-stratigraphic composite trap in the underlying Carboniferous Huanglong Formation,and controlled the secondary migration and early accumulation of hydrocarbon in the Huanglong Formation.