石油与天然气地质2025，Vol.46Issue(5)：1522-1535,14.DOI:10.11743/ogg20250509
鄂尔多斯盆地西缘奥陶系樱桃沟组等深流-重力流交互作用沉积特征及形成机理
Characteristics and mechanisms of deposition under joint action of contour current and gravity flow in the Ordovician Yingtaogou Formation along the western margin of the Ordos Basin
摘要
Abstract
Based on the analyses of lithologies,paleocurrents,and grain sizes,we investigate the characteristics,formation processes,and controlling factors of deposition under the joint action of contour current and gravity flow.The results indicate the presence of six lithofacies and corresponding four types of sedimentary origins in the study area:(1)silty mudstone(shale)facies,indicative of deep-water autochthonous deposits;(2)calcirudite facies with massive bedding,representing debris flow deposits(debrites);(3)sandstone facies with graded bedding,reflecting turbidity current deposits(turbidites);and(4)sandstone facies with wavy bedding,lenticular bedding,and bi-directional cross-bedding,corresponding to the contour current-reworked gravity flow deposits(also referred to as reworked sands).Among these sedimentary types,the reworked sands exhibit five distinct characteristics.First,the reworked sands exhibit favorable sorting coefficients ranging from 0.63 to 0.70,sub-angular to sub-rounded morphologies,and multiple grain-size subpopulations.Second,paleocurrents moved in the NW and NE directions.Specifically,the turbidity currents moved in the NW direction downward along slopes,while the contour currents moved in the NE direction parallel to slopes.Third,the cumulative probability curves of grain sizes present a pattern of one to three segments,suggesting the characteristics of gravity flow and traction current deposits.Fourth,the grain sizes of sediment decrease gradually from bottom to top,forming normally graded bedding,with scour surfaces developed within layers and erosion extensively occurring at the top.Fifth,a variety of sedimentary structures are identified,typified by wavy bedding,lenticular bedding,and bi-directional cross-bedding.From the bottom up,the study area exhibits sedimentary types of reworked sands,turbidites,reworked sands,and debrites sequentially.In this area,turbidity currents moved in the NW direction northwestward along slopes,while contour currents moved northeastward roughly parallel to slopes.In the case where the turbidity currents have higher energy than the contour currents,turbidites predominate.While when they are equal in strength,the contour currents could transport,modify,and redeposit original sediment(e.g.,turbidites),leading to the formation of reworked sands.The reworked sands exhibit a porosity of 7.56％and a permeability of 2.1 × 10-3 μm2.In contrast,the turbidites display a porosity of 2.42％and a permeability of 1.74 × 10-3 μm2.Therefore,the reworked sands deliver more favorable reservoir performance than the turbidites.The deep-water autochthonous deposits exhibit favorable source rocks.These deposits are interbedded with reworked sands,forming a source rock-reservoir-cap rock assemblage that facilitates hydrocarbon accumulation and preservation.关键词
重力流/等深流/改造砂沉积/浊流沉积/樱桃沟组/奥陶系/鄂尔多斯盆地Key words
gravity flow/contour current/reworked sands/turbidites/Yingtaogou Formation/Ordovician/Ordos Basin分类
能源科技引用本文复制引用
吴吉泽,李华,何幼斌,姜纯伟,何一鸣,姚凤南,张显坤..鄂尔多斯盆地西缘奥陶系樱桃沟组等深流-重力流交互作用沉积特征及形成机理[J].石油与天然气地质,2025,46(5):1522-1535,14.基金项目
国家自然科学基金项目(42272113,42272115). （42272113,42272115）
