The Georgia Embayment continental shelf: Stratigraphy of a submergence

Abstract

Forty vibracores taken across the continental shelf and in proposed drilling lease areas of the southeast Georgia Embayment are used to document the unconsolidated shelf-sediment cover. The Holocene-Pleistocene sediment veneer is thin, generally less than 4 m thick. Lagoon sediments deposited during the last regression (shelf emergence) or the Holocene transgression (shelf submergence) occur in patches on the inner and central shelf. Because essentially only late Pleistocene and Holocene mollusk shells are present in the shelf-sediment cover, it is believed that most of the carbonate fraction was removed by subaerial leaching during low sea-level stands aided by mechanical abrasion and biological degradation during the regressive-transgressive cycle. During each transgression or submergence, the surficial sand sheet is recharged with a new biogenic carbonate fraction along with the addition of small amounts of clastic sediments derived from “overrun” estuaries and erosion of underlying Tertiary sediments. The stratigraphy based on the vibracores supports the concept of cross-shelf migration of the shore face—barrier island systems in response to rising sea level. Sedimentologic and paleontologic analyses also indicate that extensive in-place mixing of shelf sediments may have occurred, an important factor to consider in evaluation of the fate of particulate pollutants. The establishment of the time frame of such mixing should be given high priority in future studies.