Sedimentary characteristics of turbidite of Chang 7 member in southwestern Ordos Basin
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摘要:
根据野外露头、岩心观察及粒度分析, 对鄂尔多斯盆地西南部延长组长7段浊积岩的沉积特征进行了研究。结果表明, 浊积岩主要为岩屑长石砂岩, 以次棱角状为主, 成分成熟度及结构成熟度较低; 粒度分布上具有典型的浊流沉积的特征, 发育粒序层理、包卷层理、沟模、槽模、重荷模、滑塌变形等沉积构造; 常见的鲍马序列层序组合有AB型、ABC型、ADE型、AE型。研究区浊积扇可分为上扇、中扇、下扇亚相及主沟道、辫状沟道等相应的沉积微相, 上扇、中扇分布范围较广, 是浊积扇的主体。在古地理演化过程中, 长73浊积岩体规模较小, 长72-长71湖侵作用减弱, 深湖线收缩, 浊积岩逐渐发育, 在华池-庆城一带连片展布; 湖盆地形、物源供给及构造运动是影响浊积岩发育及分布的重要原因。
Abstract:Based on outcrops, cores and grain size analyses, the authors studied systematically sedimentary characteristics of turbidite of Chang 7 member in southwestern Ordos Basin. The results show that turbidites are sub-angular lithic feldspar sandstone with low compositional maturity and textural maturity. The turbidites exhibit typical turbidite particle size distribution. The sedimentary structures include graded bedding, flute cast, delve mold, gravity cast and collapse, and the common Bouma of turbidite sequences includes AB, ABC, ADE and AE. Hackberry facies can be divided into three sedimentary subfacies, i.e., the upper fan, mid fan, outer fan as well as relative sedimentary microfacies such as main groove and braided groove, and the upper fan and mid fan are main bodies of the turbidite with a wide distribution range. During the evolution of paleogeography, turbidites were small during Chang 73 stage of Chang 7 member. With the weakening of lake invasion and the retreat of the deep lake line, turbidites were developed gradually from Chang72-Chang71 and were distributed along Huachi-Qingcheng-Heshui area. Topography of the lake basin, source supply and tectogenesis seem to have been the important factors influencing formation and distribution of turbidites.
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Keywords:
- southwestern Ordos Basin /
- Chang 7 menber /
- turbidite /
- sedimentary characteristics
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致谢: 本文写作及绘图得到西安石文软件公司魏颖的大力帮助，审稿专家的建设性修改意见对本文水平的提高具有重要作用，在此一并致以衷心的感谢。
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图 2 鄂尔多斯盆地西南部浊积岩粒度概率统计
Figure 2. Cumulative granularity diagram for turbidites of southwestern Ordos Basin
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图 4 研究区常见浊积岩鲍马序列组合
a—Z164井，1694.8m，长72；b—B211井，2162.2m，长71；c—H95井，2752.8m，长71；d—Y33井，1689.6m，长72
Figure 4. Bouma sequence assemblage of the study area in Ordos Basin
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图 5 鄂尔多斯盆地CH77井长7油层组岩性岩相柱状图
Figure 5. Lithology and sedimentary facies of Chang 7 interval in Well CH77 in Ordos Basin
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图 6 鄂尔多斯盆地西南部长7油层组沉积相及浊积岩展布
Figure 6. Sedimentary facies and turbidite distribution of Chang 7 interval in southwestern Ordos Basin
表 1 鄂尔多斯盆地西南部延长组湖底扇浊积岩相特征
Table 1 Depositional characteristics of Yanchang Formation lake bed fan turbidites in southwestern Ordos Basin
相 亚相 微相 单层砂厚/cm 浊积岩类型 发育位置 湖底扇 上扇 主沟道 > 100 泥砾砂岩、中砂岩、细砂岩、粉细砂岩具AB、AB序列和A、A、A、A序列 深湖线附近，湖底扇刚进人深湖的区域 溢岸沉积 < 1 细砂岩、粉砂岩、泥质粉砂岩、粉砂质泥岩组成BCDE和CDE序列典型浊积岩 中扇 辫状沟道 > 30 泥质细砂岩、细砂岩、粉细砂岩，粒序层理、冲刷构造和液体逃逸构造发育，具AB、AB序列和A、A、A、A序列 湖底扇向深湖的推进过稈中，上扇与深湖平原的过渡区 沟间 < 1 序层理、砂纹层理、波状层理，具BCDE和CDE序列典型 中心席 10〜30 细-粉砂岩、粉砂岩、泥质粉砂岩、粉砂质泥岩和泥岩不等厚互层，具ABCDE、BCDE和CDE序列典型浊积岩 外扇 末梢席 1〜10 粉砂岩、泥质粉砂岩、粉砂质泥岩和喑色泥岩不等厚互层，具CDE和DE序列的层状典型浊积岩 湖底扇最外缘的湖底平原 
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