摘要
为了明确不同类型深水碎屑流沉积特征及其成因，以鄂尔多斯盆地三叠系延长组7段深水重力流沉积为研究对象，综合测录井资料、岩心观察分析、薄片分析和定量统计，分析碎屑流沉积特征、总结沉积序列和探讨成因机制。研究表明：研究区的深水碎屑流主要发育砂质碎屑流、泥质碎屑流和泥流3种类型。砂质碎屑流沉积以块状砂岩最为常见，漂浮状泥质碎屑发育，单层厚度分布在0.24~1.10 m，平均厚度为0.55 m。泥质碎屑流沉积包含孤立块状沉积和与下伏块状砂岩成对产出两种类型，前者内部大量发育漂浮状泥岩撕裂屑及软沉积物变形构造，后者富含漂浮状泥质碎屑与砂质团块，单层厚度分布在0.21~1.29 m，平均厚度为0.60 m。泥流沉积包含孤立块状沉积和与下伏块状砂岩成对产出两种类型，前者整体为泥质砂岩或砂质泥岩，后者内部可见漂浮状成层排列的毫米级泥质碎片，单层厚度分布在0.20~0.60 m，平均厚度为0.30 m。高浓度砂质沉积物或泥质沉积物搬运过程中环境水体卷入导致的流体转化是形成砂质碎屑流、孤立块状泥质碎屑流和泥流沉积的主要原因。与下部块状砂岩相伴生的泥质碎屑流沉积多为流体侵蚀成因或砂体液化成因；与下部块状砂岩相伴生的泥流沉积包含流体减速膨胀导致的流体转化和碎屑颗粒的差异沉降等成因。
Abstract
The deep-water gravity flow deposits in the 7 member of the Triassic Yanchang Formation (Chang 7 Member), Ordos Basin, are taken as the main research object to investigate the sedimentary characteristics and genesis of different types of subaqueous debris flow deposits.An integration of log data, core observation and analysis, thin section analysis and quantitative statistics, is applied to discuss the features, sedimentary sequences and genetic mechanisms of debris flow deposits.The results show that the deep-water debris flows in the study area mainly consists of 3 types, that is sandy debris flow, muddy debris flow and muddy flow.Deposits of the first type feature massive sandstone with floating argillaceous debris and a single layer thickness of 0.24 m to 1.10 m, averaging 0.55 m.Those of the second type occur either in isolated massive deposition or in massive argillaceous deposition paired with the underlying massive sandstone: the former is rich in floating mudstone tearing debris and deformation structures of soft sediments, while the latter is rich in floating muddy debris and sandy agglomerates with a single layer thickness ranging from 0.21 m to 1.29 m, averaging 0.60 m.The occurrence of the third type resembles the first type, while its former is composed of sandy mudstone or argillaceous sandstone, and its latter has floating argillaceous chips of millimeter scale in laminar, with a single layer thickness ranging from 0.20 m to 0.60 m, averaging 0.30 m.The flow transformation caused by the involvement of environmental water body in the process of high-concentration sandy or muddy sediment transport, is the main reason for the formation of sandy debris flow deposits, isolated massive muddy debris flow deposits, and mud flow deposits.The muddy debris flow deposits paired with the underlying massive sandstone is mainly caused by flow erosion or sand body liquefaction; and the mud flow deposits paired with the underlying massive sandstone may be caused by flow transformation resulted from deceleration and expansion, and differential settlement of clastic particles.
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