鄂尔多斯盆地志丹-富县地区三叠系延长组长8油层组风暴沉积特征及意义

根据露头勘查和岩心观察描述,系统分析了鄂尔多斯盆地志丹-富县地区延长组长8油层组风暴沉积的特征及沉积模式。分析表明,风暴岩的岩性以细砂岩和泥质粉砂岩为主,缺乏粗粒沉积,沉积构造主要包括截切构造、"V"字形泥砾、泥岩撕裂屑、冲刷面、丘状和洼状交错层理、浪成沙纹层理、波状交错层理、准同生变形构造等。风暴沉积序列在垂向上具备"似鲍马序列"的特征,自下而上可划分为底面侵蚀构造段（A段）、平行层理段（B段）、丘状和洼状交错层理段（C段）、浪成沙纹层理段（D段）、波状层理段（E段）和泥岩段（F段）。沉积序列主要包括5种类型,其中Ⅰ型的层理构造（A段-F段）发育齐全,Ⅱ型缺失丘状和洼状层理段、Ⅲ型缺失平行层理段、Ⅳ型缺失底面侵蚀构造和平行层理段、Ⅴ型仅发育浪成沙纹层理、波状层理段和泥岩层段。志丹-富县地区半深湖相的主要物源来自其NE方位的三角洲前缘沉积,根据风暴岩的沉积特征和搬运距离,可将志丹-富县地区发育的风暴岩划分为近源型和远源型2种类型。风暴岩的发现完善了志丹-富县地区沉积体系和沉积演化的认识,并可为古纬度与古环境的恢复、地层的划分与对比提供依据,拓展志丹-富县地区延长组油气勘探的新思路。

Sedimentary characteristics and significances of storm deposition in Chang-8 oil layer of Triassic Yanchang Formation,Zhidan-Fuxian area,Ordos Basin

According to the outcrop survey and core observation, this study systematically analyzes the sedimentary characteristics and storm deposition model in Chang-8 oil layer, Yanchang Formation, Zhidan-Fuxian area, Ordos Basin. The analysis shows that the lithologies of tempestites are dominated by fine sandstone and argillaceous siltstone, and there are lacks of coarse grain sediments. The sedimentary structures of storm deposition mainly include the truncated structure, V-shaped mud-gravel, mudstone tearing debris, flushing surface, hummocky and swaley cross bedding, wave-ripple lamination, wavy cross bedding, penecontemporaneous structure, and etc. The storm deposition sequence has the characteristics of "Bouma-like sequence" in the vertical direction, which can be divided into five segments:the basal erosion structure (segment A), the parallel bedding (segment B), the hummocky and swaley cross bedding (segment C), wave-ripple lamination (segment D), wavy cross bedding (segment E) and mudstone (segment F) from bottom to top. The sedimentary sequences mainly consist of five types, thereinto type Ⅰ fully develops bedding structure (from segment A to segment F), type Ⅱ lacks the hummocky and swaley cross bedding, type Ⅲ lacks the parallel bedding, type Ⅳ lacks the basal erosion structure and parallel bedding, and type Ⅴ only develops wave-ripple lamination, wavy cross bedding and mudstone. The main provenance of the semi-deep lacustrine sediments in Zhidan-Fuxian area is derived from the northeast delta front. According to the sedimentary characteristics and transport distances of tempestite, the storm deposition developed in Zhidan-Fuxian area can be divided into proximal type and distal type. The discovery of storm deposition improves the understanding of sedimentary system in Zhidan-Fuxian area, provides a basis for the paleo-latitude and paleo-environment reconstruction and the stratigraphic division and correlation, develops a new idea for oil and gas exploration in Yanchang Formation, Zhidan-Fuxian area.