鄂尔多斯盆地南部长7段深水沉积特征及沉积模式

鄂尔多斯盆地南部延长组深水沉积砂体的成因类型及沉积模式研究具有较大的争议,而且只用一种成因模式去解释深水沉积系统有一定的局限性。依据对鄂尔多斯盆地南部延长组长7段的野外剖面的观测及部分岩芯观察,基于沉积学相标志分析,对盆地延长组长7段深水沉积砂体特征及沉积模式进行了详细研究,取得了以下认识:首先,划分了研究区深水沉积砂体成因类型,包括风暴岩、滑动岩、滑塌岩、砂质碎屑流沉积及浊流沉积,总结了各类型深水沉积体的识别标志;其次,将研究区深水沉积体系划分为水道化的风暴沉积体系和无水道发育的滑移-滑塌沉积体系;风暴沉积体系划分为水道化风暴岩、水道侧缘及风暴浊积岩朵叶体,为风暴侵蚀成因;滑移-滑塌体系可以分为滑动岩、滑塌岩、碎屑流舌状体、远源浊流沉积,为地震、火山或风暴活动触发三角洲前缘坡折带沉积物失稳滑塌形成。综合砂体成因类型和沉积模式,可以更加直观地研究湖盆深水区沉积物组合及分布规律,为湖盆深水区油气勘探提供理论支撑。

Sedimentary characteristics and sedimentary model of deep waterdeposits of Late Triassic Chang 7 Member in southern Ordos Basin

It has been controversially debated on genetic types and sedimentary models of deep-water sandstones of the Yanchang Formation exposing in the southern of Ordos Basin. It is limited to interpret deep-water system using only one sedimentary model. Based on the detailed observation of field outcrop and core, and analysis of sedimentary facies markers, the sedimentary characteristics and sedimentary model of deep water deposits of the Late Triassic Chang 7 member in the southern Ordos Basin were studied in detail in this paper. The conclusions can be drawn as followings. Firstly, five types of deep-water deposits are identified: slides, slumps, sandy debris flows, turbidity currents and tempestite, and the identification marks of them are summarized. Secondly, the deep-water sedimentary systems in this studied district are divided into channelized tempestite sedimentary system and unchannelized slip-slump sedimentary system. The tempestite sedimentary system can be subdivided into channelized tempestite, channel lateral margin and leafy turbidite, which were mainly caused by storm erosion and were distributed between wave storm base and normal wave base. The slip-slump sedimentary system consists of four parts:slide rock, slump rock, debris flow lobe and sheeted turbidite, occurring at deep water where slope is steep and provenance is sufficient. They could be formed by the collapse of sediments in the delta front slope that triggered by earthquakes, volcanism or storm event. This study shows that analysis by combining facies models with types of gravity flow deposits can directly reveal the sedimentary characteristics and genetic models of lacustrine deep-water deposits,and provide theoretical prediction for oil and gas exploration in deep-water environments.