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垂向叠置形成。低密度浊流沉积中大部分为中—薄层的正粒序砂岩垂向叠置而成，部分泥质含量较高，表现出砂泥互层的特征。混合事件层主要由下部干净的块状细砂岩与上部富含变形泥岩撕裂屑的砂质泥岩或泥质砂岩成对组合形成，其成因为浊流流动过程中侵蚀泥质基底，黏土物质或泥质碎屑的混入导致浊流向泥质碎屑流转化，最终形成下部浊流沉积上部泥质碎屑流沉积的混合事件层。相近位置不同深度不同类型的深水重力流沉积垂向叠置，指示了复杂多变的重力流流体演化过程。对重力流沉积类型的准确认识，能进一步促进对深水重力流流体转化过程的理解，明确深水重力流沉积分布，为鄂尔多斯盆地深水重力流沉积及常规与非常规油气勘探与开发提供理论指导。

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.