268 / 2022-03-31 22:44:22

软沉积物变形构造特征及地质意义--以鄂尔多斯盆地陇东地区延长组长7为例

软沉积物变形构造，滑塌沉积，砂质碎屑流，长7油层组，鄂尔多斯盆地

Soft sediment deformation structures are regarded as typical geological records preserved in strata. Their main classification, basic characteristics, triggering mechanisms and formation mechanisms have been a hot and difficult issue. According to detailed observation and description of 344 m cores in 20 typical wells, the soft sediment deformation structures are characterized by various types, multiscale, multi-cause and wide distribution, which are widely developed in Triassic Chang 7 Oil-member, Longdong area, the Southwest Ordos Basin. Based on morphological characteristics and formation mechanisms, the soft sediment deformation structures are divided into three categories: soft sediment lateral disturbance deformation, soft sediment vertical load deformation and soft sediment non-directional invasion deformation. There are mainly composed of 7 types of soft sediment deformation structures were recognized, including slump deformation, liquefied curled deformation structures, torn mud intraclasts, liquefaction sandstone dikes, sandy ball-pillow structures, flame structures and load casts, et al.

Soft sediment deformation structures are widely developed in Chang 7 oil-member, there are more soft-sediment deformation structures in Chang 7₂ submember than Chang 7₁ submember, and Chang 7₃ submember is very few. Spatially, slump deformation and liquefaction sandstone dikes are developed in the west of the study area; there are a large number of soft sediment deformation structures, which were controlled by lateral disturbance and vertical heavy load, in the middle of the study area, such as slump deformation, liquefied curled deformation structures, torn mud intraclasts, sandy ball-pillow structures, flame structures and load casts, et al. With the increase of transportation distance, torn mud intraclasts,  flame structures and load casts were gradually increase.

The soft sedimentary deformation structures, such as lump deformation and liquefied curled deformation structures, are geological responses to sliding or slumping activity. These phenomenon indicates the obvious topographic slope changes and regional slope break belt in the study area. Plant debris in massive sandstone and mudstone and tuff interlayer in the strata of soft sediment deformation structure reveal the geological events such as seismicity, volcanism and seasonal floods. As shown by the core data, massive structures and torn mud intraclasts are developed in the study area, which indicates the sandy debrites deposits. Meanwhile, flame structures and load casts are the geological result of the turbidite deposit. And the sandy debris flow deposits, turbidities and soft sediments are generally associated with deformation structures. These structures  comprehensively reflect the development of deep-water gravity flow sedimentary system.

In summary, the regional slope break zone triggered by geological events such as seismic activity, volcanic activity and seasonal flood tends to form gravity flow sedimentary sand body deposits.  And the gravity flow sedimentary is the indicator for a favorable zone for high-quality deep water reservoirs.