MIDDLE HOLOCENE SEA-LEVEL AND EVOLUTION OF THE US GULF OF MEXICO COAST
Ongoing research is focused on testing the middle Holocene high sea level model through analysis of coastal landforms and deposits that may have formed during that key time period. First among these would be beach-ridge plains on the mainland central Texas coast, landward of Holocene barriers. Long considered to be part of the last interglacial shoreline, these Holocene beach-ridge plains attain elevations of 2.5-3 m, extend for 10s of kms along the mainland shore, and can be 1-3 kms in width. These mainland beach-ridge plains remain undated, but must have formed prior to development of the barrier chain, which severely limits fetch, and are therefore interpreted to represent maximum transgression during the middle Holocene, followed by sea-level fall to present elevations. We have also investigated Holocene shorelines along the Morgan Peninsula of the Alabama coast, to the east of Mississippi delta. Optical luminescence ages show that some beach-ridge sets are middle Holocene in age, ca. 6.7-4 ka, whereas others are late Holocene in age, ca. 3.5-2.5 ka. In aggregate, these data suggest that relative sea level was at, or very close to, present elevations since the middle Holocene along the Gulf of Mexico shoreline, both to the west and east of the subsiding Mississippi delta.