The Chang 7 interval of the Upper Triassic Yanchang Formation in the Ordos Basin represents a typical deep lacustrine depositional sequence. On the basis of field outcrops, cores, well logs, light/heavy mineral provenance analysis, and petrological studies, we evaluated the characteristics of deep-water gravity flow deposition of the Chang 7 interval and constructed a depositional model. The sediments mainly came from the northeast of the study area, and multiple sublacustrine fans were deposited in the center of the basin. Different from the deep-marine fan, the sublacustrine fan in the study area develops under the background of gentle slope without any erosional canyon between the fan and delta front. Gravity flow deposits in the study area can categorised into three groups: sand debris flow deposits, turbidity current deposits, and deep-water mudstone deposits. The main channel and branch channel are mainly developed with thick massive sandy debris sandstone, while the channel lateral margin and branch channel lateral margin are mainly developed with middle massive sandy debris sandstones and turbidite sandstones, which from bottom to top, the thickness of sand layer becomes thinner and the grain size becomes smaller. Thin mudstone is developed between channels; the lobe fringe includes sheet-like turbidite sandstones and deep lake mudstones. The widely distribute, good quality source rocks () developed in deep lacustrine have attained the peak stage of oil generation (). The superimposition of the sublacustrine fan sand bodies and the wide distribution of good quality source rocks favor the formation of large lithologic reservoirs characterized by source–reservoir integration, self-generation and self-storage, and near-source accumulation.

中文翻译：

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湖底扇的岩性特征及其对油气勘探的意义-以华北鄂尔多斯盆地东南部延长组长7层段为例

鄂尔多斯盆地上三叠统延长组的长7区间代表了典型的深湖相沉积序列。在野外露头，岩心，测井，轻/重矿物出处分析和岩石学研究的基础上，我们评价了Chang 7区间深水重力流沉积的特征，并构造了一个沉积模型。沉积物主要来自研究区的东北部，盆地中央沉积了多个湖底扇。与深海扇不同，研究区的湖底扇在缓坡的背景下发展，扇与三角洲前缘之间没有任何侵蚀性峡谷。研究区域中的重力流沉积物可分为三类：沙屑流沉积物，浊流流沉积物，和深水泥岩沉积物。主河道和支流道主要发育较厚的块状砂屑状砂岩，而河道侧缘和支流道侧缘主要发育有中型块状砂屑状砂岩和浊积砂岩，其自下而上，即砂层厚度变薄，晶粒尺寸变小。通道之间发育薄泥岩。裂片边缘包括片状浊质砂岩和深湖泥岩。分布广泛，质量优良的烃源岩（从下到上，砂层的厚度变薄，晶粒尺寸变小。通道之间发育薄泥岩。裂片边缘包括片状浊质砂岩和深湖泥岩。分布广泛，质量优良的烃源岩（从下到上，砂层的厚度变薄，晶粒尺寸变小。通道之间发育薄泥岩。裂片边缘包括片状浊质砂岩和深湖泥岩。分布广泛，质量优良的烃源岩（）在深湖相中发育的已达到产油的高峰期（）。湖底扇扇砂体的叠加和优质烃源岩的广泛分布，有利于形成大型的岩性油藏，其特征是源-储层整合，自生自储，近源成藏。