Investigating the formation and evolution of coarse-grained deposits in modern lakes and the relevant controlling conditions is indispensable to the prediction of reservoir sandbodies, disaster prediction, and limnological research. The source-to-sink system of coarse-grained deposits in Lake Chenghai, a deep, scarped Late Quaternary lake, was investigated in this study based on 62 outcrops, Advanced Land Observing Satellite (ALOS) digital elevation model (DEM) data, and regional geological survey data. The findings include the following: (1) the source areas of coarse-grained deposits in Lake Chenghai were lithologically classified into carbonate source areas, basaltic source areas and siliciclastic source areas, and were geomorphically categorized as scarp type or confluence type. Subaqueous colluvial aprons have formed downstream of the carbonate source areas and scarp-type basaltic source areas, while Gilbert-type deltas have formed downstream of siliciclastic source areas and confluence-type basaltic source areas. (2) The formation and evolution of coarse-grained deposits are controlled by the sediment flux that evolves in synchrony with the geomorphic evolution of the source areas and the sink regimes. Scarps represent the initial landform of the source areas. Source material rolls off or slides down scarps or forms small-scale debris flows before entering the lake. The source material initially formed subaqueous colluvial apron (synonymous with subaqueous fans) where sufficient space was present to accommodate sediments and the basement angle exceeded than the natural angle of repose. As weathering and denudation have progressed, the initial scarps have transformed into confluence-type slopes, and the source material has formed medium- and large-scale debris flows that have entered the lake, resulting in an increase in sediment flux. Consequently, the subaqueous colluvial aprons have rapidly grown and developed subaerial deposits, which have evolved into larger-scale Gilbert-type deltas that overlie the initial aprons. (3) The morphology and distribution of coarse-grained deposits vary in response to differences in quantity and composition of materials from different source areas, which resulting from different rates of weathering and denudation and different sediment input regimes. Firstly, the size and surface slope angle of a subaqueous colluvial apron from a carbonate source are smaller than those of a subaqueous colluvial apron of basaltic origin. Secondly, a Gilbert-type delta from a basaltic source features a greater slope angle and a thicker topset than does a Gilbert-type delta of siliciclastic origin, and the latter exhibits a longer foreset and a thicker bottomset than in the former. Thirdly, the sizes of subaqueous colluvial aprons are not strongly correlated with the sizes of the source areas, while the sizes of Gilbert-type deltas are.

为探讨陆相断陷湖盆陡坡带构造活动控制下水下粗碎屑岩沉积特征、搬运机制及其演化规律,以滦平断陷盆地陡坡带下白垩统西瓜园组为研究对象,采用无人机倾斜摄影、实测剖面、砾石定向性定量表征等技术方法 ,从沉积背景、岩相类型、沉积单元及相序特征等方面开展野外露头解剖工作.滦平盆地西瓜园组沉积时期,近岸水下扇沉积于构造沉降速率大、湖平面上升、深水、古地貌陡峭环境,洪水携带粗碎屑沉积沿陡坡带入湖,底部发育与地震活动相关的砾质碎屑流,伴随发育滑动-滑塌沉积,上部发育高密度浊流.随着沉积物不断供给,斜坡坡度逐渐减小;随着粗碎屑沉积搬运距离不断增加,砂砾质碎屑流中砾石表现出明显定向性,高密度浊流所占厚度比例增加;末端以低密度浊流为主.扇三角洲沉积于构造沉降速率相对较低、水深相对较浅、古地貌相对平缓的环境,发育相对成熟的供源体系,汇水系统长度较长,扇三角洲前缘粗碎屑岩由碎屑流向高密度浊流、牵引流、低密度浊流转换.

杭锦旗地区是鄂尔多斯盆地致密气勘探的重点研究区域,其下石盒子组以岩屑砂岩为主,属于典型的特低孔-特低渗透储层.根据岩石铸体薄片观察、阴极发光、扫描电镜、毛管压力测试和黏土矿物X射线衍射等分析结果,结合孔渗数据,研究鄂尔多斯盆地北部杭锦旗地区下石盒子组致密砂岩储层的主要成岩作用类型及其特征,建立成岩演化序列并分析其对孔隙发育的影响,进而构建孔隙度演化定量模型.结果表明:研究区下石盒子组发育以次生孔隙-微裂缝为主要储集空间的致密砂岩储层,其成岩作用类型多样,主要有压实作用、胶结作用、交代作用和溶蚀作用;其中,压实作用是造成原生孔隙大量损失的主要因素,导致储层孔隙度减少约20.25％;胶结作用破坏储层物性,早期和晚期胶结作用导致储层孔隙度分别减少约5.58％ 和6.06％;溶蚀作用形成次生孔隙,使储层孔隙度增加约5.20％.

鄂尔多斯盆地杭锦旗地区具有良好的致密气勘探潜力,下石盒子组是杭锦旗地区的主力产气层段.储层岩石类型以岩屑砂岩和岩屑质石英砂岩为主.根据偏光显微镜下铸体薄片观察以及扫描电镜、高压压汞、粘土矿物X-衍射、阴极发光等分析测试手段的应用,结合相关孔渗数据对鄂尔多斯盆地北部杭锦旗地区下石盒子组储层的岩石学特征及储层物性特征进行了研究,明确了岩屑颗粒的发育特征及其对储层物性的影响.结果表明:下石盒子组储层粒度较粗,主要为粗粒及中-粗粒砂岩;岩屑平均含量高达40％.研究区储层埋藏较深,成岩作用改造强烈,压实作用强,原生孔隙绝大部分被改造充填,次生孔隙为主要的储集空间.储层岩屑类型发育多样,根据岩屑对储层物性的影响,将其整体划分为减孔型岩屑、增孔型岩屑、保孔型岩屑3类.减孔型岩屑较发育会使粒间次生溶孔大量减少且自身难以溶蚀,因而破坏储层的物性,其中以高含量的千枚岩岩屑对储层物性影响最为显著;增孔型岩屑的发育则对储层物性有着明显的改善效应,其可以保存部分粒间孔,还易发生内部溶蚀,改善储层物性,其中以高含量的变质石英岩屑对储层物性影响最为显著;保孔型岩屑本身抗压实能力较强且多数较难溶蚀,可以保护原有孔隙却不能通过自身溶蚀改善储层物性,通常与增孔类岩屑同时发育,该类岩屑与物性呈间接性正相关关系.