ABSTRACT

There are four sources of information for constructing a sea level history, from Gulf of Mexico coasts: beach ridges, cheniers, sub-deltas, and barrier island nuclei.

Beach ridge plains around the Gulf of Mexico provide a detailed history of sea level rises and falls since 3,000-3,500 B.P. Dates for the initiation of Mississippi River sub-deltas, as well as southwestern Louisiana cheniers, confirm the rises and high sea levels, and dates for initiation of barrier islands (island nuclei) confirm some of the low stands. The beach ridge history is more complete and more detailed than any one of the other three; the latter three provide general support at important points, but the sequence of events and the details are best obtained from beach ridges.

Sub-delta history goes farther back in time than any of the others in this area. It can be checked against data from the very wide beach ridge plain at Jerup, northernmost Denmark, where an essentially complete sequence of ridges covers almost all of Holocene time. The Jerup history, obtained from topography, carbon-14 dates, and granulometry, matches the Gulf of Mexico beach ridge history very well, as well as dates of initiation of Mississippi River sub-deltas. The isostatic rebound that has been measured in the Jerup area has raised the ridges so that they are now available for study, but has been slow, compared with the local deposition rate, and has not affected the granulometry in any detectable way.

The most detailed history now available is compiled from beach ridge data, but the intent of the present paper is to show that there are other important coastal sources of information. They can provide support, corrections or complementary information for the beach ridge history, but their precision is not very great. For time intervals and localities where beach ridges are not available, or are not decipherable, these other sources may be useful.