摘要
川东隔挡式褶皱由一系列北东走向的线性褶皱带组成,为典型的高陡背斜构造带。该区油气勘探目的层主要集中在中浅层石炭系,而且钻井主要位于构造核部,钻井深度相对较浅,由于地震资料对构造陡翼地层的反射资料显示品质较差,从而对该构造认识出现了多种解释结果。笔者应用断层相关褶皱理论,依据钻井资料标定,对川东褶皱带典型构造明月峡背斜构造的二维地震剖面测网及两条宽线二维地震剖面重新进行详细构造分析及解释。解释结果表明,如果假定地层厚度不变,明月峡构造样式可以认为是两个楔形构造垂向上叠合而成,发育两期构造。据此本文提出了明月峡背斜双楔形构造发育几何学模式图,分析了两期楔形构造垂向上叠加模式。根据已有的研究成果,地表变形是深部逆冲作用的结果,推测早期中浅层构造变形时间为中白垩世,晚期深层构造为晚新生代时期,而且晚期构造改造了早期构造。构造解释结果给出,剖面几何形态为浅层发育向东的反冲断层扩展褶皱,中深层分别以三叠系膏岩和志留系泥页岩为顶、底滑脱面的楔形构造,深层构造分别以志留系泥页岩和震旦系泥页岩为顶、底滑脱面的楔形构造。构造几何分析指出,深层楔形构造形成时间晚于中深层楔形构造,并改造了早期中深层楔形构造,从而出现了构造高点的向西偏移的现象。在平面分布上,明月峡背斜浅层高陡构造背斜东翼宽度从北向南逐渐变窄,深层楔形体楔形角度逐渐变大,构造缩短量相应增加。
Objectives:There are many high-steep anticlines with Northeast-striking to East—northeast-striking in the Eastern Sichuan Basin.There is uncertainty in the interpretation of the structural styles owing to most of the wells drilled in the area with the hydrocarbon accumulation of Carboniferous layers located in the high structural position,in which are relatively shallower and unrevealed deeper strata,and the quality of 2D seismic data is poor in the core and steep limb in the high-steep anticlines.Many researchers conclude that the high-steep anticlines are interpreted as the typical Jura-type folds,i.e,detachment folds.This paper has given a different idea in the Mingyuexia highsteep anticline Methods:In this study,we reanalyze the geometry of the Mingyuexia anticline based on the seismic data with the new wide-line two-dimensional seismic-reflection data.The horizons are calibrated by wells data and a 1∶20000 regional geological map,and our geometric models are built under fault-related fold theories and conservation of layer thickness.The deformation times are determined by previous apatite fission-track(AFT)and(U—Th)/He thermochronology studies.Results:Three major detachments are recognized regionally within the anticline:①a lower gypsum-bearing detachment mainly developed in the lower to middle Cambrian Longwangmiao Formation,the Gaotai Formation,and the Qiongzhusi Formation and②a dark-gray shale and mudstone layers of the middle detachment in the lower Silurian Longmaxi Formation,③an upper gypsum-bearing detachment mainly developed in the Lower Triassic Jialingjiang Formation and the Middle Triassic Leikoupou Formation.The a deep westward-thrusting lower wedgedshaped structure and a shallower westward-thrusting upper wedge structures have been identified based on the level of the wedge points with respect to layered Paleozoic—Mesozoic sedimentary rocks.The high-steep Mingyuexia anticline is interpreted to be the lower wedged-shaped structure superimposed with upper wedged-shaped structure.The upper wedge structure,which is commonly observed where thrust developed from the middle detachment of the Sinian mudstones and shale into an upper gypsum-bearing detachment of Lower Triassic Jialingjiang Formation.The lower wedge structure is commonly interpreted as thrusts developed from the gypsum-bearing detachment of Lower to middle Cambrian Longwangmiao and Gaotai Formations into the middle detachment of the Sinian mudstones and shale.We have proposed geometrical models for the development of two-stage vertical superimposed double wedging with multiple detachments.Previous apatite fission-track(AFT)and(U—Th)/He thermochronology studies by many researchers in the eastern Sichuan Basin areas have provided that the tectonic rapid uplift and denudation of the eastern Sichuan high-steep anticline’s belt suggest two age ranges:the Early Cretaceous and Neogene.Conclusions:We speculate that the upper wedged-shaped structure in the Silurian mudstone and shale developed in the early time,i.e,the Early Cretaceous and the lower wedge-shaped structure in the Sinian mudstones and shale,or Cambrian salt developed in the late time,i.e,the Neogene.The Mingyuexia anticline provides an excellent example of the lower wedge structure superposed vertically with the upper wedge structure in the Eastern Sichuan high-steep anticline’s belt.
作者
杨庚
陈竹新
王晓波
YANG Geng;CHEN Zhuxin;WANG Xiaobo(Research Institute of Petroleum Exploration and Development,PetroChina,Beijing,100083)
出处
《地质论评》
CAS
CSCD
北大核心
2021年第4期901-917,共17页
Geological Review
基金
中国石油重大科技专项(编号:2016E-0601,2019B-0503)
石油勘探开发研究院科学项目(编号:YJXK2019-1)的成果。
关键词
高陡构造
川东
明月峡背斜
多滑脱层
楔形构造
构造叠加
high and steep fault folding belt
east Sichuan
Mingyuexia anticline
detachment layers
wedged-shaped structure
structural superimposition
