Sedimentation in a Piedmont Reservoir: Evidence from Brown’s Cove, Lake Wylie, North Carolina

摘要

Sedimentation in Brown’s Cove of Lake Wylie, North Carolina, can be reconstructed from historical records, cores, heavy mineral analysis, geochemical analysis, and ~(210)Pb data. The sedimentology and sequence stratigraphy of the cores document changing sedimentary provenance, processes, and rates. Brown’s Cove was flooded in 1924, resulting in a transgressive sequence composed dominantly of suspension load deposited between 1924 and 1983. Based on air photos and cores, distributary channels on Beaverdam Creek delta supplied sediment to prograding, coarseningupward delta lobes composed of turbidites grading up to traction load deposits. In 1983, a delta lobe began prograding into Brown’s Cove and was abandoned ca. 1993, leading to compaction, subsidence, and a second transgression. Another distributary avulsed to the site ca. 2003, resulting in a second prograding delta lobe. Prior to flooding of Brown’s Cove, mafic-rich fluvial sediments from the southern part of the watershed were a large component of the sediment. Between 1983 and 1993, felsic-rich sediments from the recently clear-cut northern part of the watershed dominated. The youngest sediments are mafic-rich and likely due to extensive land clearances in the southern part of the watershed that began in 2004. Three methods of estimating sedimentation rates for the main part of Brown’s Cove provide comparable results of ～1 cm/yr averaged over the full period of record. This estimate can be refined to ～0.6 cm/yr for the interval 1924–2003, and ～1.8 cm/yr for the interval 2003–2008. Higher rates of sedimentation (～7 cm/yr) occur where delta lobes actively prograde.