滦平盆地西瓜园组中段厚层砾岩沉积特征及成因机制研究:来自滦页1井全井段连续取心的证据

为了探讨陆相断陷盆地厚层砾岩的沉积特征、成因机制和控制因素,寻找有利勘探目标,以滦平盆地西瓜园组中段厚层砾岩为研究对象,运用沉积学理论,结合测井、录井、岩心、薄片和测试结果,对厚层砾岩的岩相及岩相组合、沉积构造和电性进行分析。研究表明,西瓜园组中段厚层砾岩具有被黑色页岩包裹的特征,即顶、底部与黑色页岩突变接触。岩心中大量的黄铁矿和部分敏感元素指标反映了缺氧的强还原环境,表明其为深水环境中的砾岩体。基于不同成因,共识别出滑动、滑塌2种重力流类型。滑动沉积主要包括6种岩相、5种岩相组合,以主滑动面、次滑动面、高角度层理,以及层内小型正断层和逆断层为主要识别标志;滑塌沉积包括6种岩相、4种岩相组合,以滑动面、滑塌变形构造、包卷层理、泄水构造、变形砾以及部分原生层理(粒序层理)为主要识别标志。根据滑动面的发育位置、自然伽马曲线和声波曲线的幅度变化特征,可以划分出4期滑动沉积。西瓜园组时期滦平盆地的边缘坡折带、物源供给和一定的触发机制共同控制深水滑动、滑塌型重力流的形成,结合控制因素和沉积特征建立陆相断陷湖盆陡坡带滑动-滑塌型重力流的发育模式。

Sedimentary characteristics and genesis of thick conglomerate in the middle section of Xiguayuan Formation,Luanping Basin: Insight from a consecutive coring study of well LY1

In order to investigate the sedimentary characteristics, genetic mechanism and controlling factors of thick conglomerate in continental rift basins, and to find favorable exploration target, the thick conglomerate in the middle section of the Xiguayuanzu Formation, Luanping Basin, is taken as the research object. According to theory of sedimentation, combined with logging, core, thin sections and test data, the lithofacies, lithofacies assemblage, sedimentary structure, electrical property and magnetic susceptibility of the thick conglomerate were analyzed. The thick conglomerate appears to be wrapped by black shale, where, due to sudden deformation, contacts with black shale are made at the top and bottom of the conglomerate; whilst the occurrences of abundant pyrite and some sensitive elements in the core reflect a strong reductive environment under hypoxia, indicating the conglomerate is in a deep water environment. Based on the genetic differences, two types of gravity flow-slide and slump-were identified. The sliding deposition includes 6 lithofacies and 4 lithofacies assemblages, whose main identification marks are the main and secondary sliding surfaces, high angle bedding, small positive fault and reverse fault in the layer. The slumping deposition also includes 6 lithofacies and 4 lithofacies assemblages and the main identification marks include the sliding surface, collapse deformation structure, convolute bedding, water escape structure, deformed gravel and partial primary bedding (graded bedding). The sliding deposition process is further divided into four stages according to the development position of the sliding surface, the amplitude variation characteristics of the gamma-ray curve and the acoustic wave curve. In the period of the Xiguayuan Formation, the slope fold zone on the edge of the basin, the supply of material source and certain trigger mechanism in the basin jointly control the formation of the deep water slide-slump gravity flow. Combining this control mechanism with the results of lithofacies analysis, the development mode of slide-slump gravity flow in the lacustrine steep slope zone of continental rift basin could be established.