CGRG Bibliography of Canadian Geomorphology
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Author : Smith, D.G.; and Jol, H.M.
Date : 1992.
Title : GPR results used to infer depositional processes of coastal spits in large lakes
Publication : Fourth International Conference on Ground Penetrating Radar, June 8-13, 1992, Rovaniemi, Finland. Edited by Paulie Hanninen and Sini Autio. Special paper - Geological Survey of Finland, 16, 1992
Issue :
Page(s) : 169-177
Abstract
Ground penetrating radar (GPR) field experiments were carried out on two coastal spits located in Lake Athabasca, northeast Alberta, Canada, and former Pleistocene Lake Bonneville, Utah State, U.S.A. To determine depositional processes of the spits from radar profiles, we first identified radar facies (reflection patterns) which correspond with sedimentary facies and structures. Next, we interpreted processes using the geomorphic associations between facies and process. The objective was to test present ideas regarding the origin of spits, then if necessary revise depositional models for exploration sedimentologists in the oil industry. The current practice in the oil industry is to classify all subsurface stratigraphic units having thick, inclined strata of sandstone and conglomerate as deltas. A pulse EKKO IV radar system was used with 50 and 100 MHz antennae, GPR transects were carried out along level beaches or were corrected for topography.GPR surveys indicate that both spits formed by progradation of sediment supplied by wave-induced longshore transport. In deeper water at the spit end sediment is avalanched downslope as foreset beds. Sometimes slope angle of foreset facies is reduced by waves from 25 degrees to as low as 2 degrees. Individual, long, continuous reflections of foresets (bedding planes) often have signoidal-to- shingled patterns, interpreted as major sedimentary surfaces, deposited by rare, high magnitude, storm waves and currents. Besides slight changes in sediment grain size at bedding planes, prominent GPR reflections may be partially attributed to the tight packing of the individual sediment particles. Very difficult penetration by bivracoring of spit sediments adds support to this suggestion. The GPR data and interpretation partially agree with the depositional model proposed by Nielsen et al. (1988). The loss of signal return from below the inclined strata isattributed to a lithofacies change from sand to mud or diamicton, or GPR is unable to penetrate to the lowest part of the foreset beds.
Bibliography of Canadian Geomorphology