MAPPING THE ARCHITECTURE OF GLACIOFLUVIAL SEDIMENTS WITH 3-DIMENSIONAL GEORADAR

Three-dimensional (3-D) ground-penetrating radar (georadar) mapping of fers new opportunities for determining the geometries and facies of su rficial sedimentary units. To investigate the potential of this high-r esolution technique and at the same time study the architecture of Qua ternary glaciofluvial deposits, georadar data have been collected on a dense grid established across a sequence of braided-river gravels and sands in northeastern Switzerland, Results of this survey are strikin g 3-D images that provide many more details and much more reliable inf ormation on the heterogeneities of the shallow underground than are af forded by conventional georadar profile data, Continuous subhorizontal and oblique reflections can be traced throughout vertical sections an d horizontal slices of the georadar data block to a depth of similar t o 15 m. Clearly defined are the dominant flow direction of the ancient braided-river system, the boundaries between different sedimentary fa cies, and the level of the ground-water table, Trough-fill sediments a nd subhorizontal channel deposits observed on 7-m-high quarry walls ca n be followed confidently in the subsurface. The orientation, shape, a nd size of the troughs and the strike and dip of the cross-bedding are all well resolved.