Southeastern Section - 68th Annual Meeting - 2019

Paper No. 6-4
Presentation Time: 8:00 AM-12:00 PM


STREIB, Laura C., SPENCER, Brandon M., SWALLOM, Meredith L., LO, Edward, MCGLUE, Michael M., THIGPEN, J. Ryan, WOOLERY, Edward and BROWN, Summer J., Department of Earth and Environmental Sciences, University of Kentucky, Lexington, KY 40506

Measuring sediment volumes in lake basins using seismic data provides a means of estimating mass efflux as a response to tectonic and climatic forcing. Jackson Lake (WY) is amenable to studying variability in stratal development and the pace of sedimentation in a zone of crustal extension that has been modified by glacial activity over time scales that range from 102 to 104 yrs. Ancient sedimentation in Jackson Lake is likely constrained by the Pinedale glaciation (~30-13 ka). Jackson Dam was built on the lake in 1911 and in addition to increasing accommodation, provides a datum for sedimentation over the last ~100 years. We collected a grid of high-resolution CHIRP seismic profiles in Jackson Lake and used these data to identify key reflectors. Using the extant lake floor and acoustic basement reflectors, we generated a minimum isopach map of the post-Pinedale sediment package within the lake. In the deepest portions of the lake, total sediment thickness above acoustic basement exceeds 120 m, which would require a minimum sedimentation rate of 0.9 cm/yr since ~13 ka. To investigate sedimentation rates for Jackson Lake since dam emplacement, we identified a candidate reflector that may represent the transition experienced by the depositional system associated with the change in outflow. A literature review of 90 reservoirs suggests a mean sedimentation rate of ~2.1 cm/yr for these engineered lakes. Most reservoirs accumulate sediment at rates <1 cm/yr, and a few exceed 10 cm/yr. In the portion of Jackson Lake nearest to the dam, a possible “Dambrian” reflector lies ~13 m below the lake floor, suggesting a potential maximum sediment accumulation rate of 13 cm/year since the early 20th century. The spatial variability of sediment thickness suggests complex controls on sediment influx and accumulation; future acquisition of sediment cores and seismic data with greater depth-of-investigation will allow for more refined estimate of these rates.