Paper No. 1
Presentation Time: 8:10 AM
THE ENDURING MYTHS OF HOLOCENE HIGHSTANDS AND STILLSTANDS, GULF OF MEXICO: CONTRASTS WITH A RECENTLY REVISED SEA-LEVEL CURVE
While record high sea-levels are globally documented in the equatorial zone, proposed mid and late Holocene highstands, +2-to-+3 m MSL, associated transgressive-regressive cycles along the northern Gulf, and multimillennial stillstands cited in TX and LA lack credible evidence. These claims originated on the Texas coast and inner shelf, in the New Orleans Pine Island barrier complex, in shore scarps, and mainland and island barrier strandplains on the NW and W Florida coast. Assumed post-6.5 ka highstands, abrupt sea-level drops, and oscillations were based on coastal ridge and scarp elevations, washover fans, and various other features. These include postulated but unproven major erosional unconformities of regional extent. Sangamon-age Ingleside barrier sectors on the Texas coast were arbitrarily reinterpreted with dubious luminescence dates and other data as having been formed during a hypothetical mid-Holocene highstand and regressive phase. Cat Island, marsh-stranded south Hancock barrier islands, MS, and Morgan-Perdido strandplain dune ridges, AL-FL, reliably dated c. 4.6 (4.2)-to-2.2 ka, accumulated at -2 to- -0.5 m sea-levels during decelerating rise that stayed below the present level. Submerging the lowest dune ridges, Gulf waters drowned inter-ridge swales in various barriers. Dune summit elevations were not closely constrained by the associated Gulf level. The highest dune ridges rise 3-4 m above present MSL. As late Holocene Louisiana cheniers and W Florida island strandplains illustrate, if temporarily raised by distant storms even wave-built beach ridges may aggrade significantly above coeval sea-levels. Instead of their assumed mid-to-late Holocene ages, scarps often may be storm- and/or slope erosion-related sub-modern features. Inconsistent old luminescence dates often complicate strandplain age identification. Utilizing numerous NW and NE Gulf intertidal peat dates, a new Gulf curve (J. Coast. Res., 20: 695) compares well with sea-level curves of south Florida, Yucatan, and west Atlantic islands. Unlike the 1970 Nelson-Bray Gulf curve, it does not reflect a major early Holocene sea-level decline either.