GPR stratigraphy used to infer transgressive deposition of spits and a barrier, Lake Bonneville, Stockton, Utah, USA

Abstract

Abstract Ground penetrating radar (GPR) stratigraphic profiles of the classic cross-valley barrier and associated spits of Late Pleistocene Lake Bonneville, near Stockton, Utah, are used to infer transgressive depositional style and internal sedimentary structures. From onlapping patterns of radar reflections, which mimic subsurface stratigraphy, we reconstruct the following depositional sequence and style: (1) at the north end of the Rush Valley, the barrier formed by vertical accretion while keeping pace with hydro-isostatic-forced basin subsidence and/or slow lake-level rise; (2) a reorientation of the longshore transport pathway, induced by continued basin subsidence and/or a lake-level rise, produced a spit that prograded 2.5 km southwestward into Rush Valley. The NW-dipping radar reflections from the spit onlap SE-dipping reflections from the back-barrier, indicating that this spit was deposited after the barrier; (3) a final rise in lake level and/or basin subsidence again reoriented longshore transport and deposited the smaller upper spit. Radar reflections from the upper spit onlap the proximal eastern margin of the Stockton spit. This upper spit is the final landform deposited during the Bonneville highstand. The depositional sequence inferred from radar stratigraphy agrees with the transgressive hypothesis formulated in 1890 by G. K. Gilbert.