摘要： 陆相深水重力流水道的类型细分及其沉积模式是制约其油气勘探开发的重要因素,但研究程度低。通过对鄂尔多斯盆地南缘瑶曲铁路桥剖面三叠系延长组实测、水道形态参数统计及岩相、粒度等分析,开展了湖相重力流水道的沉积特征、沉积过程及沉积模式研究。结果表明:(1)研究区内可识别出4期复合水道,主要为洪水重力流成因。根据其内部单一水道及单砂体形态特征、岩相组成,将其细分为沉积型和过渡型两类。(2)剖面下部2期复合水道为沉积型,以悬浮载荷成因岩相为主,常见块状净细砂岩、薄层泥岩岩相组合和鲍马序列岩相组合;上部2期复合水道为过渡型,岩相以底床载荷与悬浮载荷共存为特征,自下而上以交错层理细砂岩或叠瓦状泥砾细砂岩与含泥砾/泥岩撕裂屑块状细砂岩、平行层理粗粉砂岩及薄层泥岩的岩相组合为特征。(3)结合单一水道规模及其相互关系,建立了区内过渡、沉积型重力流水道的半定量沉积模式。过渡型水道内部侵蚀与沉积作用共存,单一水道宽度小、宽厚比低,呈透镜状,水道间切割性强,砂体横向稳定性较低,表现出不定向叠加、侧向拼接样式;沉积型水道内部由沉积作用主导,单一水道宽度较大、宽厚比较高,呈似板状—透镜状,砂体横向稳定性较高,表现出稳定的垂向加积样式。

关键词: 重力流水道, 岩相组合, 沉积型水道, 过渡型水道, 沉积模式, 延长组, 鄂尔多斯盆地

Abstract: The classification of lacustrine deep-water gravity flow channels and the sedimentary model are the key controls on hydrocarbon exploration and development. In this paper,depositional characteristics,sedimentary processes and sedimentary model are studied using section measurement of the Triassic Yanchang Formation of Yaoqu railway-bridge outcrop,morphological parameter statistics for single channel,lithofacies and grain-size analysis. This study shows that: (1)There are at least four sets of gravity flow composite channels,which were mainly triggered by flood events. According to the morphological characteristics,lithofacies composition of single channel,composite channels can be divided into depositional channels and transitional channels. (2)The two composite channels in the lower part of the section belong to depositional type with suspended load lithofacies association including massive clean fine sandstone,thin layered mudstone and the Bouma facies sequence. Besides,the two channels in the upper part of the studied section belong to transitional channel with mixed lithofacies of bed load and suspended load,which is characterized by vertical lithofacies association of cross-bedding fine sandstone or fine sandstone with imbricated mud clasts,massive fine sandstone containing ripped mud clasts,parallel bedding coarse siltstone and thin mudstone facies. (3)A semi-quantitative sedimentary model of transitional and depositional gravity channel is proposed by analyzing size and architecture of the single channels in the composite channel. Both erosional and depositional process occurred in the transitional channel. A single transitional channel shows a smaller width,lower ratio of width to thickness,lenticular shape,and strong erosional ability. The sand body shows a low stability in lateral and a stacking pattern of random superposition or lateral splicing. The depositional channel,showing plate-like and lenticular shape and dominated by sedimentation,has a bigger width,higher width to thickness ratio of single channels,higher lateral stability and the stacking pattern of stable vertical aggradation.

Key words: gravity flow channel, lithofacies associations, depositional channel, transitional channel, sedimentary model, Yanchang Formation, Ordos Basin

中图分类号: 

• TE122.2