鄂尔多斯盆地上三叠统延长组长7段深水重力流沉积类型

以鄂尔多斯盆地上三叠统延长组长7段取芯段为主要研究对象,以详细的岩芯观察为基础,以Z43井为例,研究鄂尔多斯盆地延长组长7段深水重力流沉积类型及其特征.研究结果表明,研究区主要发育砂质碎屑流沉积、低密度浊流沉积及混合事件层三种沉积类型.砂质碎屑流沉积整体呈块状,岩性为中—细砂岩,内部可见多个接触面,为多套砂质碎屑流沉积...

Sedimentation Types of Deep-water Gravity Flow,Chang7 Member,Upper Triassic Yanchang Formation,Ordos Basin

The deep-water gravity-flow deposits in the Chang7 member of the Upper Triassic Yanchang Formation,Ordos Basin,were the object of this study.The types and characteristics of deep-water gravity-flow deposits were determined by detailed analysis of a drill core from well Z43.The results suggest that sandy debris-flow deposits(debrites),low-density turbidity current deposits and hybrid event beds were developed in the region penetrated by well Z43.Most of the sandy debrites were featured by structureless medium-to fine-grained sandstone.Several amalgamation surfaces were observed,indicating different stages of vertical stacking of the deposits.Low-density turbidity current deposits were characteried by vertical stacking of medium-to thinly bedded sandstone having normal grading.The upper part of this sandstone featured a high mud content with clear sandstone/mudstone interbedding.Hybrid event beds were primarily characterized by a bipartite structure,of which the lower part is clean structureless finegrained sandstone and the upper part is sandy mudstone or muddy sandstone with deformed mud clasts.The argillaceous base may indicate erosion by the turbidity current that caused an increase in the clay content of the current.The presence of mud clasts and/or clay content may have been the key element driving flow transformation from low-density turbidity current to muddy debris flow.This transformation resulted in the event beds that are characteristically observed as muddy debrite to low-density turbidite couplets.The fact that several types of deep-water gravity-flow deposits appear at the same location indicating a complicated gravity flow evolution process.An accurate recognition of gravity-flow types might contribute to understanding the flow transformation and the distribution of their deposits.This advancement could provide theoretical guidance on deep-water gravity-flow deposits and conventional and unconventional oil and gas exploration and development in the Ordos Basin.