Paper No. 4
Presentation Time: 8:00 AM-12:00 PM
DELTA ARCHITECTURE IN BROWN'S COVE, LAKE WYLIE, NC: MODERN ANALOG FOR LEGACY SEDIMENTS
The lower reaches of Beaverdam Creek, a tributary to the Catawba River, were flooded in 1924 when the Lake Wylie dam was constructed, thereby forming the ~9 hectare Brown’s Cove. The cove has been a site of sedimentation for more than 85 years and the rate of sedimentation has accelerated over the last decade in response to urbanization within the 1100 hectare Beaverdam Creek watershed. The history and nature of sedimentation is the focus of this study. The architecture of the deltaic and lacustrine deposits has been documented using comparative bathymetric maps, 40 cores, 34 probes, and ground penetrating radar. Six recurring facies have been identified from the cores that record progradation of several avulsing, stacked, coarse grained delta lobes into organic-rich lacustrine muds. We used floating 400 and 100 MHz antennas and a GSSI SIR 3000 controller to conduct 38 linear profiles across the cove. Also, we collected five 400 MHz GPR surveys on the delta top during low stands as continuations of the floating surveys. GPR surveys were calibrated with sediment cores to derive accurate sediment package thicknesses. The saprolite/sediment interface in GPR profiles is marked by differences in reflection properties with stronger, somewhat higher frequencies in the sediment cover and weaker, diffuse, and lower frequency returns in the sub-sediment basement rather than a sharp, singular reflector. 400 MHz lines provided high definition facies boundaries within sediment packages as well as sediment/water interface features such as runnels that formed during lowstands in the lake, and relict inclusions like stumps in the sediment column. The combined core and GPR data permit the construction of a depositional model for the deltaic and lacustrine sediments in Brown’s Cove that documents the architecture and overall volume of the deposits. Information derived from this study may be useful for interpreting the physical processes and depositional environments of legacy sediments from former impoundments.