细粒冲积扇沉积特征研究——以酒西盆地老君庙构造带古近系白杨河组为例

Sedimentary Characteristics of Fine-grained Alluvial Fan: A Case Study of the Paleogene Baiyanghe Formation in Laojunmiao Structural Belt,Jiuxi Basin

利用研究区丰富的岩心、测井及地震资料,分析了玉门油田老君庙构造带古近系白杨河组M及L-M层的沉积特征,确定了沉积相类型,明确了其沉积相分布样式,并在此基础上探讨细粒冲积扇的主控因素。研究表明：研究区目的层发育以砂岩沉积为主的细粒冲积扇沉积,M层自下而上发育扇根和扇中亚相,L-M层发育扇缘亚相,粒径向上变细,整体为一退积型冲积扇。冲积扇在平面上呈伸长扇形,宽度为5~10 km,长为10~15 km,厚度为15~25 m,冲积扇的根部发育下切河道,宽度为2~4 km,受地势的影响,顺物源砂体呈厚度薄、分布范围广的分布特征。细粒冲积扇的形成及沉积特征是气候、物源和古地形等因素共同控制的结果,山间河道出山口后开阔的地势为冲积扇提供了有利的地形,白垩系泥岩和砂岩作为母岩以及山间河道出山口前平缓的地势影响了细粒冲积扇的粒度,同时干热环境加剧了母岩的风化程度,三种因素综合导致研究区形成了细粒冲积扇。

Based on abundant core, logging and seismic data, this paper mainly analyzed the sedimentary types and characteristics of the Paleogene M reservoir in Laojunmiao structural belt, and further discussed the distribution characteristics, as well as their main controlling factors. The result shows that M reservoir develops fine-grained alluvial fan,which contains upper fan, mid fan and lower fan deposits, with size-decreasing grains in a complete retrograding sedimentary sequence. The deposit displays fan-shape in plane view and convex-shape in cross section. And an incised valley is developed in the root of fan-shaped deposits. The width of individual fan varies from 5 km to 10 km,with the length from 12 km to 15 km and thickness from 15 m to 25 m.The width of incised valley ranges from 2 km to 4 km, with incised depth from 20 m to 25 m.Sandbodies display thinner thickness and wider distribution in the longitudinal direction, which is affected by the landform. The formation of the fine-grained alluvial fan in the study area is controlled by three factors, including geomorphology, source rocks and climate. Open topography at the toe of mountain provides an open landform for the generation of alluvial fan, which, together with the fine-grained clastic sediments from the paleo-weathering crust of Cretaceous mudstone and sandstone, are the main factors controlling the generation of the fine-grained alluvial fan. Hot and dry climate intensifies the weathering process of the source rocks.