Three Dimensional Geologic Framework Modeling from Drill Hole Data of Yangwu Proluvial-Alluvial Fan Deposits in Yuanping Depression of Xinding Basin, Shanxi Province, North China: A Case Study Using GMS 6.0

摘要

The Yangwu proluvial-alluvial fan is a broad fan-shaped deposit consisting of infilled with up to 200 m of Quaternary sediment and belongs to the arid and semiarid region. The sedimentary architecture, the distribution of lithofacies and of architectural elements in such heterogeneous deposits is of fundamental importance for the analysis of groundwater flow. Modeling focused on a spatial representation of the distribution of sediments of complex proluvial-alluvial deposits which form the porous water-bearing aquifer systems. This geologic framework model is the first of its kind for the area and was assembled using digital geologic map data, lithologic contour line maps and borehole information from 62 bore holes from a 317.76 km2 area combined using Geographic Information System (GIS) and the TINs code and SOLID code in Groundwater modeling system (GMS 6.0) to form a volumetric, lithologic three-dimensional geologic model. Lithologic data were reduced to a limited suite of descriptors based on geologic knowledge of the basin and distributed in 3D space using interpolation methods. Lithologic variations are related to different depositional environments within the basin, related to periods of sediment input and river level changes which include proluvial piedmont fan, alluvial fan, channel, basin axis and lacustrine deposits. The resulting three-dimensional geologic model contains three lithostratigraphic units; Pliocene bedrock (N) and Quaternary proluvial-alluvial deposits (Q1+N, Q2 and Q3) which consist of seven lithofacies: coarse sand, medium to coarse sand, medium to fine sand, sabulous sand, silty sand, clayey soil, clay units. The sequence is complex with abrupt changes in lithology occurring over short distances with unconsolidated alternating and interfingering sand, silt and clay reflecting a variety of sedimentary depositional environments. Comparisons of the computed model to geologic cross-sections indicate that this methodology produced a model that supports the conceptual model of the subsurface. The three-dimensional geologic framework model is useful for visualizing subsurface sediment distributions and geometries and will be used not only to better constrain the Quaternary depositional history of the region, but also to identify and delineate major aquifers and aquitards, which is an important step for understanding ground water flow system.