Deltaic Evolution During a Major Transgression
Timothy L. Eckard, Miles O. Hayes, Walter J. Sexton, 1986. "Deltaic Evolution During a Major Transgression", Southeastern United States: Third Annual Midyear Meeting, 1986, Raleigh, North Carolina, Daniel A. Textoris
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The sedimentary deposits of the Santee River deltam, South Carolina, consist of two primary facies: (1) a 13-m-thick Late Pleistocene-Holocene alluvial sequence composed of coarse-grained, fluvial, point-bar deposits; overlain by (2) a 7-m-thick fine-grained deltaic complex. During the Wisconsin low stand of sea level, the river incised a deep valley, which in response to the Holocene sea-level rise, aggraded with fluvial deposits. During active channel migration within the confines of the valley walls, multistage, stacked, point-bar and channel sands were deposited. A decrease in river gradient brought about by the continued rise in sea level resulted in widespread overbank deposition and eventual stabilization of the fluvial channels by 7,000-5,000 BP. Sea-level stabilization at about this same time period initiated constructional phases of delta formation.
A stratigraphic model for delta evolution has been constructed through analysis of 63 vibracores, 45 power augers, 30 gouge augers, and 12 radiocarbon dates. The alluvial sediments comprising the valley fill unit are composed of pebbly, coarsegrained sand deposited as fluvial, multistage, stacked, point-bar and channel deposits capped by a widespread, fining- upward, sandy clay unit representing floodplain deposition. The overlying deltaic complex is a gently inclined, seaward–thickening sediment body consisting of a lower delta plain and delta front facies. The lower delta plain deposits are composed primarily of organic-rich muds deposited in freshwater swamp and open bay environments. In a seaward direction, these deposits interfinger with estuarine sands and muds deposited in back–barrier–related environments of the delta front. The present delta front is in a destructive phase as the shoreline is advancing landward beyond reworked, abandoned deltaic deposits in water depths of 5-10 m. The facies complex of the Santee River delta should provide some insight into the stratigraphic nature of medium-to small-sized deltas deposited in a mixed energy setting during a major transgression.
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Southeastern United States–Guidebook is comprised of twelve field trips that were organized for the Third Annual Midyear Meeting held in Raleigh, North Carolina in 1986. The spectrum of geologic time represented in the Upper Precambrian, Lower Paleozoic, Mesozoic, Cenozoic and the very Recent. The geologic provinces are the Valley and Ridge, Blue Ridge Mountains, Piedmont, and the Coastal Plain. Besides North Carolina, trips include Virginia, South Carolina and West Virginia.