石油与天然气地质 ›› 2025, Vol. 46 ›› Issue (5): 1522-1535.doi: 10.11743/ogg20250509

• 原摘要 • 上一篇    

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

吴吉泽(), 李华(), 何幼斌, 姜纯伟, 何一鸣, 姚凤南, 张显坤   

  1. 长江大学 地球科学学院,湖北 武汉 430100
  • 收稿日期:2025-04-07 修回日期:2025-05-08 出版日期:2025-10-30 发布日期:2025-10-29
  • 通讯作者: 李华 E-mail:2651144729@qq.com;501026@yangtzeu.edu.cn
  • 第一作者简介:吴吉泽(2000—),男,硕士研究生,深水沉积学。E‑mail: 2651144729@qq.com
  • 基金项目:
    国家自然科学基金项目(42272113);国家自然科学基金项目(42272115)

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

Jize WU(), Hua LI(), Youbin HE, Chunwei JIANG, Yiming HE, Fengnan YAO, Xiankun ZHANG   

  1. School of Geosciences,Yangtze University,Wuhan,Hubei 430100,China
  • Received:2025-04-07 Revised:2025-05-08 Online:2025-10-30 Published:2025-10-29
  • Contact: Hua LI E-mail:2651144729@qq.com;501026@yangtzeu.edu.cn

摘要:

为了明确等深流与重力流交互作用下的沉积特征、形成过程及主控因素,对研究区进行了岩性、古水流和粒度分析。研究区发育6种岩相及4种沉积类型:①粉砂质泥(页)岩相,属于深水原地沉积;②块状层理砾屑灰岩相,为碎屑流沉积;③粒序层理砂岩相,为浊流沉积;④波状层理砂岩相、透镜状层理砂岩相和双向交错层理砂岩相,为等深流改造重力流沉积。改造砂沉积具有5个特征:①分选系数更好(0.63 ~ 0.70)、次棱角状-次圆状,具有多个粒度次总体;②古水流方向为NW向和NE向,沿斜坡向下的浊流方向为NW向,等深流平行斜坡运动方向为NE向;③概率累积曲线可为一段式、两段式和三段式,具重力流和牵引流沉积特征;④沉积物由底部到顶部粒度变细,为正递变层理,层内部发育冲刷面、顶部多被侵蚀;⑤沉积构造丰富多样,以波状层理、透镜状层理和双向交错层理较为典型。研究区从下至上依次发育改造砂沉积、浊流沉积、改造砂沉积和碎屑流沉积。浊流顺斜坡向NW向运动,等深流大致呈NE向平行于斜坡运动。当浊流能量强于等深流时,以浊流沉积为主;当浊流能量弱于等深流时,等深流可对原始沉积物(浊流沉积等)进行搬运、改造和再沉积,从而形成改造砂。改造砂孔隙度为7.56%,渗透率为2.10 × 10-3 µm2;浊流沉积砂孔隙度为2.42%,渗透率为1.74 × 10-3 µm2。改造砂相比浊流沉积储集性能更好。深水原地沉积内发育较好的烃源岩,与改造砂互层沉积形成了有利于油气富集和保存的生-储-盖组合。

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

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.

Key words: gravity flow, contour current, reworked sands, turbidites, Yingtaogou Formation, Ordovician, Ordos Basin

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