Multiple Pliocene-Quaternary Marine Highstands, Northeast Gulf Coastal Plain-Fallacies and Facts


  • Ervin G. Otvos


Beach and foredune ridges, sea level indicators, shore features, coastal scarps and lineaments, covered karst, strandplains, Silver Bluff shoreline.


Claims persist in the literature alleging multiple pre-Sangamonian Pleistocene, mid-Wisconsinan, middle and late Holocene marine highstands on the northeast Gulf coastal plain. These views, still encountered even in official publications are rooted in the assumed similarity between Atlantic and northeast Gulf coastal history. A critical re-examination of the evidence is based on detailed sedimentary, microfossil, and geomorphic data from hundreds of drillholes and field sampling. Sediment data were matched with basic diagnostic criteria of depositional facies.

Deposits and landforms that developed during the peak of Sangamonian transgression yielded the only evidence for higher-than-present Quaternary sea levels on the northeast Gulf. Pre-Sangamonian marine units are absent in the subsurface and not exposed in coastal plain surfaces. Post-Pliocene uplift and erosion had removed littoral and nearshore units from the northeast coastal plain. Upland ridges, mistaken for relict barriers, are elongated, high interfluves. Composed of alluvial deposits, they are bounded by semi parallel lineaments of apparently tectonic origin and incised by stream erosion. Combined with lineaments, rare covered karst depressions on a late Pleistocene alluvial plain provide the slight relief of subdued linear features that had been mistaken for relict barrier islands, associated with multiple Pleistocene highstands.

Claims for wide Holocene sea level oscillations and record highstands rest on the belief, unsupported by reliable sediment data, that the upper ridge lithosomes were essentially wave-built, intertidal and directly correlatable with sea level positions. However, the ridge morphology and dimensions clearly indicate the foredune origins of discussed Florida Gulf shore strandplain ridges. Cited texture parameters and sedimentary structure types also fail to lend independent diagnostic support to the intertidal origins of the highest beach ridge intervals. Wave-cut scarps and associated supratidal narrow terraces yield no independent proof for the postulated high eustatic Holocene sea levels.