Characteristics and Mechanism of Thick Sandbody of Yanchang Formation at the Centre of Ordos Basin
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摘要: 晚三叠世延长组长6、长7油层组沉积期鄂尔多斯盆地湖盆中部深水区稳定发育厚层砂岩，局部地区连续厚度可达上百米。在盆地西南沉积体系，巨型砂带北西—南东向平行于相带界线展布，与三角洲前缘砂体呈现出“断根”的现象；在东北沉积体系，砂带围绕三角洲呈群状、带状分布。厚层砂体成因复杂，总体上可称作深水重力流—牵引流沉积复合体，包括滑塌砂体、砂质碎屑流砂体、浊积砂体、三角洲砂体及底流改造砂体5种成因类型，其中以重力流沉积组合为主，但白豹及其北部主要为三角洲沉积夹重力流沉积。不同成因的砂体纵向叠加，横向复合连片形成了稳定分布、规模宏大的砂带。厚层砂体的形成、展布方向、分布范围主要受控于沉积物的供给速率、湖盆底形及构造活动等因素。Abstract: Thick sandbody are widely and stably developed at the depositional period of Chang6 and Chang7 oil bearing formation in late Triassic in the centre of Ordos basin. The thickness surpass one hundred metres uninterruptedly in some areas. The large scale sand belt, formed in deep lake, stretches along the facies boundary and isolates itself from delta front sandbody in the southwest sedimentary system, while the sand belt or lobes encircle the delta front in the northeast sedimentary system. The thick sandbody was resulted from gravity flow and deep water tractive current and can be divided into five types, i.e. slump, sandy debrite, turbidite, delta sandbody and underflow transforming sandbody. Among them, deposition of gravity flow is the dominant sedimentary type; However, thick sanbody in Baibao area and its north area belong to delta deposition and sandy debrite, with deposition of gravity flow. The stable distribution of thick sandbody is controlled by the factors as supply rate of sediment, bottom shape of basin and tectonic activity.
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Key words:
- thick sandbody /
- gravity flow /
- deepwater tractive current /
- Ordos Basin /
- basin centre /
- Yanchang Formation
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