摘要
由于缺乏有效的古温标,对鄂尔多斯盆地中-上元古界—下古生界热演化程度一直以来了解十分有限。本文通过对盆地内20余口钻井中-上元古界—下古生界开展自生伊利石结晶度和伊蒙混层系统性测试,试图从新的角度分析盆地中-上元古界—奥陶系热演化程度及分布规律。结果表明:盆地不同部位伊利石结晶度与深度关系存在明显的差异,整体具有随深度增大而减小的趋势,主要受控于古埋深及古地温梯度。盆地沉积盖层伊利石结晶度普遍大于0.25,未达到绿片岩相浅变质阶段;盆地下古生界奥陶系伊利石结晶度大于0.42,表明处于成岩演化阶段;寒武系样品结晶度略小于奥陶系,整体处于成岩带中-晚期到极低级变质作用阶段;中元古界伊利石结晶度相对更低,对应热演化程度更高。此外,我们对比了伊利石结晶度和等效镜质体反射率分别恢复的地层最大古地温结果,两者在误差范围内基本一致,表明这一方法对研究我国古老地层热演化程度具有明显的可行性。
The understanding of the thermal evolution degree of the Middle-Upper Proterozoic-Lower Paleozoic in the Ordos Basin has always been limited due to the lack of effective paleotemperature scales.This article conducts systematic tests on the crystallinity of authigenic illite and the I/S mixed-layer in the Middle-Upper Proterozoic-Lower Paleozoic in over 20 drilling wells in the basin,attempting to analyze the degree of thermal evolution from a new perspective.The data suggest that there are notable variations in the correlation between crystallinity and depth of illite across different regions of the basin,with a general tendency for the correlation to decrease with depth,primarily influenced by burial depth and paleogeothermal gradients.The illite crystallinity in the sedimentary rocks of the basin is generally greater than 0.25,an indication that it is not yet in the greenschist facies shallow metamorphic stage.The crystallinity of illite in the Lower Paleozoic Ordovician of the basin is greater than 0.42,indicating that it is in the stage of diagenetic evolution.The Cambrian samples have slightly lower crystallinity than Ordovician,placing them in the middle to late stage of metamorphism in the diagenetic belt.Similarly,a higher degree of thermal evolution is indicated by the relatively low illite crystallinity in the Middle Proterozoic.Furthermore,we compared the maximum paleogeothermal results obtained from illite crystallinity and equivalent vitrinite reflectance,and found that they were consistent within the error range.These results indicate that this method is highly feasible for studying the thermal evolution of ancient strata in China.
作者
范立勇
祁凯
刘新社
任战利
李进步
邢光远
张才利
崔军平
Fan Liyong;Qi Kai;Liu Xinshe;Ren Zhani;Li Jinbu(Exploration and Development Research Institute of PetroChina Changqing Oilfield Company,Xi'an 710018;National Engineering Laboratory for Exploration and Development of Low-Permeability Oil&Gas Fields,Xi'an 710018;Department of Geology,Northwest University,Xi'an 710069;State Key Laboratory of Continental Dynamics,Northwest University,Xi'an 710069)
出处
《地质科学》
CAS
CSCD
北大核心
2024年第3期673-682,共10页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
长庆油田重大专项“鄂尔多斯盆地中元古界—奥陶系构造沉积演化、成源机制及勘探新领域研究”(编号:ZDZX2021)资助。
