Quantitative Analysis of Downstream Fining Pattern in Fluvial Fans: A Case Study of the Dagele River, Qaidam Basin
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摘要: 【目的】为了建立定量的大型分支河流体系（河流扇）沉积物粒度递减模型，为预测沉积体系展布提供依据，服务智能油气勘探与开发。【方法】利用Google Earth、91卫图等地理信息软件，结合野外现场考察，对青海柴达木盆地大格勒河河流扇的河道形态和和沉积物粒度进行精细描述，使用imageJ等软件测量研究区砾石粒径，选择合适的方法拟合粒径递变曲线，总结砾石粒径的沿程变化规律。【结果】结果发现：大格勒河扇沉积物粒度整体以砾石为主，顶点最大砾石粒径可达90cm，从顶点向末端具有明显的递减特征；指数函数能够更好拟合河流扇沉积物的砾石粒径递变趋势，最大砾石粒径随距离变化的拟合函数为Dmax=90e-0.264x，平均砾石粒径随距离变化的拟合函数为D ?=7.04 e-0.11x；通过比较最大砾石粒径与平均砾石粒径的指数拟合模型，指出水力分选在沉积物粒径递减中的重要作用，同时认为以最大砾石粒径的沿程递减模型能够较好反映全分支河流体系（本研究段）的粒度变化趋势，由此建立了大格勒河分支河流体系沉积物递减模式。【结论】沉积物粒度变化与物源供给、水动力条件及沉积环境等因素有关，本研究为定量预测大型分支河流体系（河流扇）的相带变化和沉积体系规模提供了知识库信息。Abstract: [Objective] This study aims to establish a quantitative model of downstream grain size diminution in large-scale Distributive Fluvial Systems(fluvial fans) to provide a knowledge base for predicting the distribution of sedimentary systems in intelligent oil and gas exploration and development. [Methods] The study conducted detailed descriptions of channel morphology and sediment grain size in the Dagle fluvial fan of the Qaidam Basin, Qinghai. with using geographic information software such as Google Earth , 91 Wei Tu and ImageJ combined with field investigations. Appropriate methods were selected to fit the grain size variation curves, and the longitudinal changes in gravel size were summarized. [Results] The findings are as follows: The sediments grain size of the Dagle Fluvial Fan are generally coarse, dominated by gravels, with the maximum clast size reaching 90 cm at the apex,showing a clear diminishing trend from the apex to the distal end. Exponential functions better fit the trend of gravel size diminution in the fluvial fan. The fitting function for maximum clast size vs. distance is Dmax= 90e-0.264x, and for average clast size vs. distance is D ?= 7.04 e-0.11x. By comparing the exponential models of maximum and average clast sizes, the critical role of hydraulic sorting in grain size diminution is highlighted. The longitudinal decay model of maximum clast size is deemed effective in reflecting the grain size variation trends of the entire distributive fluvial system (within the studied area), leading to the establishment of a sediment diminution model for the Dagle Distributive Fluvial System.[Conclusions] Sediment grain size variations are close related to the source , the sediment supply, the hydrodynamic conditions, and the depositional environments etc. This study provides a knowledge base for quantitatively sedimentary facies prediction and depositional system scale estimation of large-scale Distributive Fluvial Systems.
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