Abstract: Evolution of the Shoreline of the Georgia Bight: A Model for Shoreline Embayments
Miles O. Hayes
The embayed 1205 km of shoreline between Cape Hatteras, North Carolina, and Cape Canaveral, Florida, known as the Georgia Bight, serves as an excellent model for similar embayed paleoshorelines in the rock record because of the abundance of detailed studies that have been conducted on the Holocene sediments in the area. The bight, which flanks the coastal plain on the trailing edge of the North American plate, is downwarping slowly and is bordered by two northwest-southeast-oriented tectonic highs: the Cape Fear arch on the north and the Ocala uplift on the south. This tectonic regime has apparently been in existence since the late Paleocene.
Analysis of the geomorphology and sedimentology of the shoreline of the Georgia Bight by compartment shows a systematic change of the coastal depositional systems around the bight. Long barrier islands averaging 38 km in length that are morphologically wave dominated and stratigraphically retrograding compose greater than 50% of the shoreline of the outer edges of the bight. Over 50% of the shoreline at the head of the bight is composed of short (approximately 8 km), mixed-energy, stratigraphically prograding barrier islands that show downdrift offsets and drumstick configurations in plain view.
Tidal inlets, which increase markedly in abundance toward the head of the bight because the tidal range increases to more than 3 m in that area, play several important roles in the evolution of the barrier islands. The inlets have a major influence on erosional/depositional patterns of the islands as a result of their migrationary and sediment-storage characteristics. At the head of the bight, over 70% of the available Holocene sand is stored in large ebb-tidal deltas that serve as sediment sources and/or sinks for the barrier islands over time.
AAPG Search and Discovery Article #90985©1994-1995 AAPG Distinguished Lecture