| 鄂尔多斯盆地三水河剖面上三叠统块状砂岩的异重流成因——来自岩石结构的证据 |
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| 引用本文： | 张国栋,鲜本忠,晁储志,宋德邻,刘建平,于硕,王馨冉,晏奇.鄂尔多斯盆地三水河剖面上三叠统块状砂岩的异重流成因——来自岩石结构的证据[J].沉积学报,2019,37(5):934-944. |
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| 作者姓名： | 张国栋 鲜本忠 晁储志 宋德邻 刘建平 于硕 王馨冉 晏奇 |
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| 作者单位： | 中国石油大学(北京)地球科学学院,北京,102249;中国石油大学(北京)地球科学学院,北京 102249;油气资源与探测国家重点实验室,北京 102249 |
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| 基金项目： | 国家自然科学基金项目（41872113，41372117，41702104）；国家科技重大专项（2017ZX05009-002，2016ZX05026-007） |
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| 摘 要： | 由于储层质量好、非均质性弱、成藏条件优越，深水沉积中的块状砂岩常常成为油气勘探开发的重要目标。相对具有各种交错层理等沉积构造的其他砂岩而言，块状砂岩的成因判识难度更大。因此，对块状砂岩成因机制的研究，直接影响了其沉积过程的认识，制约了其沉积模式、储层预测地质模型的重建。针对鄂尔多斯盆地南部旬邑县三水河剖面中发育的晚三叠世中层—巨厚层块状砂岩，利用高密度岩石样品的岩石薄片和激光粒度分析，对块状砂岩的粒度组成、粒度参数及其垂向变化特征进行研究。结果表明: 1）块状砂岩为长石岩屑质极细砂—细砂岩，内部偶含漂浮状灰黑色、红褐色泥砾，底部发育球枕、沟模等沉积构造；2）块状砂岩之间及其与交错层理砂岩层之间夹薄层—极薄层灰黑色泥岩、油页岩，二者间突变接触常见；3）岩石薄片中碎屑颗粒分选差，呈棱角—次棱角状，成分及结构成熟度中等偏低；4）粒度组成上，跳跃组分与悬浮组分各占50%左右，显示底床载荷与悬浮载荷同时存在且贡献相当；5）其偏度与浊流沉积相似，但其分选略差于浊流沉积，与三角洲沉积相差更远；6）垂向上，块状砂岩内部存在多期分米级复合韵律，厚度范围为10~30 cm。综合研究区地质背景、沉积构造、微观显微结构、粒度组成及其搬运过程、沉积分异解释结果，认为该剖面块状砂岩为洪水成因的异重流沉积。该研究丰富了对深水块状砂岩成因的理解，深化了异重流沉积块状砂岩结构特征的认识，同时也为异重流沉积的判识提供了依据。
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| 关 键 词： | 块状砂岩 异重流 深水沉积 粒度分析 鄂尔多斯盆地 |
| 收稿时间： | 2018-09-06 |
Flood-generated Massive Sandstones of the Sanshuihe Outcrop in the Triassic Ordos Basin: Evidence from sedimentary textural characteristics |
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| Institution: | 1.College of Geosciences, China University of Petroleum (Beijing), Beijing 102249, China;2.State Key Laboratory of Petroleum Resources and Prospecting, Beijing 102249, China |
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| Abstract: | Deep-water massive sandstones are a significant target for hydrocarbon exploration because of their good reservoir quality,weak heterogeneity and well accumulation conditions. Sedimentary process identification for massive sandstones is more difficult than for cross bedded sandstones. Therefore,the study of the genesis of massive sandstones directly affects the understanding of their sedimentary process,and restricts reconstruction both of their sedimentary model and of their reservoir predictive geological model. In this study,the grain composition,grain size parameters and their vertical changes in massive sandstone were examined using thin sections and laser particle size analysis of high-density rock samples of Late Triassic medium-bed and very-thick-bed sandstones in the Sanshuihe outcrop in Xunyi county,southern Ordos Basin. The study showed the following. (1)The massive sandstones are fine to very fine feldspathic sandstones containing floating gray-black and red-brown muddy clasts,with ball-and-pillow structures and groove casts. (2)The massive sandstone and the overlying and underlying massive sandstones and cross-bedded sandstone layers contain thin to very thin layers of gray-black mudstones and oil shale,commonly with abrupt contacts between the massive sandstone and mudstone/oil shale. (3)Thin section analyses indicated that the massive sandstones are poorly sorted,angular to sub-angular,and of lower-to-medium maturity in composition and structure. (4)In terms of particle size composition,the jump component and suspended component each account for about 50%,indicating that the bed load and the suspended load are both present and contribute equally. (5)The skewness of each component is similar to that of turbidites,but their sorting is slightly worse,and is far worse than in delta deposits. (6)In the vertical direction,there are multi-period decimeter-level compound rhythms in the massive sandstone,with thicknesses ranging from 10 to 30 cm. The geological background,sedimentary and microscopic structures,grain size composition,handling process and sedimentary differentiation throughout the study area all suggest that the massive sandstones are deposits from flood-induced hyperpycnal flows. This study adds to the understanding of the genesis of deep-water massive sandstones and the structure of hyperpycnally formed massive sandstones, and provides a guide for the identification of hyperpycnal flow deposits. |
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