Control of slope-pattern on the deposition of fan-delta systems: a case study of the Upper Karamay Formation, Junggar Basin

IF 1.8 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Mingxuan Gao, Xinghe Yu, Shunli Li, Wenmiao Zhang, Songhao Hu, Menglu Zhang
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Abstract

The Mesozoic fan deltas in the north-west margin of the Junggar Basin, as important petroleum reservoirs, exhibited complex facies change and internal structures with strong heterogeneity which were controlled by the transformation of slope-patterns, bringing great challenges to the study of sedimentary characteristics. The Upper Karamay Formation at north-west margin of the Junggar Basin was the objective in this paper which attempts to clarify the mechanism of sedimentary response and sand-body distribution of fan delta systems under the control of slope-pattern change. Based on a data set of cores, well logs and seismic, two types of slope-pattern were identified in the study area, which include steep-to-gentle in the south and gentle-to-steep in the north. The control of difference slope-patterns on the sand-body distribution was clarified based on the analysis of the sedimentary dynamics, facies characteristics, and depositional evolution of the fan deltas. The study shows that the transport mechanism of sediments on the steep-slope was dominated by debris flows, developing coarse-grained, thick-bedded lobes with poor structural maturity of clasts. On the gentle-slope, the deposition was dominated by hyperconcentrated-traction currents, forming relatively fine-grained, thin-bedded lobes with increased sandy matrix. The sand-bodies show frequent bar-channel transformation and channel down-cutting under the steep slope setting, which exhibit migration of isolated river channels on the gentle slopes. Under the steep-to-gentle pattern, the coase-grained sediments were mainly accumulated at slope toe, generally developed equiaxial lobes. However, the coarse-grained clasts were preserved both at proximal and distal lobes on the gentle-to-steep slopes, showing obvious lateral extension of the fan delta. The slope patterns controlled sedimentary respond rates of the fan deltas during lake level change. By comparing the modern cases of fan systems worldwide, the control of slope patterns on deposition of coarse-grained fans was clarified, providing insight into hydrocarbon exploration on basin margins.

斜坡形态对扇三角洲系统沉积的控制:准噶尔盆地上卡拉麦地层案例研究
准噶尔盆地西北缘中生代扇三角洲作为重要的石油储层,在斜坡形态转换的控制下,表现出复杂的层位变化和具有强烈异质性的内部结构,给沉积特征研究带来了巨大挑战。本文以准噶尔盆地西北缘上克拉玛依地层为研究对象,试图阐明在斜坡形态变化控制下扇形三角洲系统的沉积响应机制和砂体分布。根据岩心、测井记录和地震资料,研究区确定了两种坡度模式,即南部由陡变缓,北部由缓变陡;其中,南部坡度最大,北部坡度最小。在分析扇三角洲的沉积动力学、岩相特征和沉积演化的基础上,明确了不同斜坡形态对砂体分布的控制作用。研究表明,陡坡沉积物的运移机制以泥石流为主,形成粗粒、厚层、碎屑结构成熟度差的裂片。在缓坡上,沉积则以超集中牵引流为主,形成相对细粒、薄层的裂片,砂质基质增多。在陡坡环境下,砂体经常出现条状河道转换和河道下切,在缓坡上则表现为孤立河道的迁移。在由陡变缓的模式下,胶粒沉积物主要堆积在坡脚,一般发育等轴裂片。然而,在由缓到陡的斜坡上,粗粒碎屑岩在近端和远端裂片处均有保留,显示出明显的扇三角洲横向延伸。坡度模式控制着扇三角洲在湖面变化过程中的沉积响应速度。通过比较全球扇形系统的现代案例,阐明了斜坡模式对粗粒扇形沉积的控制,为盆地边缘的油气勘探提供了启示。
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来源期刊
Frontiers of Earth Science
Frontiers of Earth Science GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
3.50
自引率
5.00%
发文量
627
期刊介绍: Frontiers of Earth Science publishes original, peer-reviewed, theoretical and experimental frontier research papers as well as significant review articles of more general interest to earth scientists. The journal features articles dealing with observations, patterns, processes, and modeling of both innerspheres (including deep crust, mantle, and core) and outerspheres (including atmosphere, hydrosphere, and biosphere) of the earth. Its aim is to promote communication and share knowledge among the international earth science communities
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