鄂尔多斯盆地构造沉降特征及对盆地成因的启示

Tectonic subsidence characteristics of Ordos Basin and its enlightenment to basin genesis

构造沉降作为盆地成因研究中的重要组成部分,对其特征进行分析有助于盆地成因的解析。本次通过对鄂尔多斯盆地内5口典型探井的多期不整合所代表的的剥蚀厚度进行恢复,结合去压实矫正模型以及平均密度、平均古水深等参数的确定,较为精确地刻画出了鄂尔多斯盆地不同构造单元自早寒武世至今的构造沉降特征,同时结合裂谷盆地瞬时拉张模型、裂后热坳陷模型以及前陆盆地挠曲模型对构造沉降曲线进行了模拟,对盆地成因进行分析。鄂尔多斯盆地中寒武世—中生代末期主要由早古生代沉降旋回、二叠—三叠纪沉降旋回与侏罗—白垩纪沉降旋回组成。其中岩石圈热冷却作用引起的沉降贯穿全地质时期。早古生代沉降旋回中,中寒武世的加速沉降主要体现在盆地南部,沉降机制为岩石圈伸展减薄,中奥陶世马家期为全盆地尺度的加速沉降,沉降机制仍为岩石圈伸展减薄。二叠—三叠纪沉降旋回中,晚二叠世—早-中三叠世为该旋回的加速沉降期,该期加速沉降具有多幕裂陷的特征。侏罗—白垩纪沉降旋回中,中侏罗世盆地南部处于缓慢沉降期,沉降机制为岩石圈热冷却作用,晚侏罗世—早白垩世,除伊盟隆起,盆地整体处于加速沉降期,沉降机制为前陆盆地引起的挠曲沉降。

As an important part of basin genetic research,structural subsidence can explain the origin of the basin from one side.In this paper,the erosion thickness represented by multiple unconformities of five typical wells in Ordos Basin is restored,and the structural subsidence characteristics of different structural units in Ordos Basin since Early Cambrian are accurately described in combination with the determination of parameters such as decompressing correction model,average density and average paleowater depth.At the same time,combined with the simulation technology of rift basin,thermal depression basin and foreland basin,the structure subsidence curve is simulated and the origin of the basin is analyzed.The subsidence cycle from the Late Mesozoic to the Middle Cambrian in Ordos Basin is mainly composed of the Early Paleozoic sedimentation cycle,the Carboniferous to Triassic sedimentation cycle and the Jurassic Cretaceous sedimentation cycle.The subsidence caused by thermal cooling of lithosphere is through the whole geological period.In the Early Paleozoic subsidence cycle,the accelerated subsidence of the Middle Cambrian is mainly reflected in the south of the basin.The subsidence mechanism is the extension and thinning of the lithosphere,the whole basin scale accelerated subsidence of the Middle Ordovician Majiagou period,and the subsidence mechanism is still the extension and thinning of the lithosphere.In the Carboniferous to Triassic subsidence cycle,the period from Late Permian to early Middle Triassic is the accelerated subsidence period which has the characteristics of multi-stage rifting.In the Jurassic Cretaceous subsidence cycle,the southern part of the Middle Jurassic basin is in a slow subsidence period,and the subsidence mechanism is thermal cooling of the lithosphere.From Late Jurassic to Early Cretaceous,except the Yimeng uplift,the whole basin is in an accelerated subsidence period,and the subsidence mechanism is the flexure subsidence caused by the foreland basin.