High-resolution seismic profiling reveals basin floor morphology, sedimentary processes, and shallow stratigraphy at Convict Lake (California, USA)

摘要

The sediments of glacial lakes in the eastern Sierra Nevada (California, USA) hold promise as archives of hydroclimatic and ecological changes, which has implications for understanding California's water supply. Here we present the initial results of a compressed high intensity radar pulse (CHIRP) seismic reflection survey of Convict Lake, a small, hydrologically open terminal moraine lake in the Sherwin Range of northeastern California. These 0.5-8.0 kHz CHIRP profiles represent the first acoustic images of the subsurface of Convict Lake. The sublacustrine geomorphology of Convict Lake is defined by a dominantly flat floored deepwater depocenter that reaches a maximum depth of-44 m. Seismic reflections over most of the depocenter are moderate amplitude, coherent, and continuous, consistent with hemipelagic sedimentation of silt-sized allochthonous particles and organic matter. The ice-sculpted lateral margins of the basin are steep and prone to mass wasting, as shown by discontinuous and chaotic reflections organized into convex lenses or irregular mounds on the lake floor. The southwestern axial margin is a sand-dominated deltaic ramp formed by the inflowing Convict Creek, whereas the northeastern axis is rocky littoral ramp that shoals toward the basin outlet and accumulates minimal lacustrine sediment. In areas unobscured by gas curtaining, the CHIRP data reveal an asymmetric basin fill that expands subtly to the southeast, reaching a maximum thickness of-19 m s two-way travel time. The basin fill consists of three seismic stratigraphic units. Onlap and truncation geometries separating the seismic units indicate that lake level changes likely played an important role in shaping the stratigraphy of Convict Lake. Seismic profiling at Convict Lake is the critical first step towards placing the lake and its depositional record into the late Quaternary environmental history of the Convict Creek Valley.