Early Paleogene Isolation of the Gulf of Mexico from the World’s Oceans

Joshua H. Rosenfeld¹ and Jon F. Blickwede^2
1 Yax Balam, Inc, Granbury, TX
² Unocal Corporation, Sugar Land, TX

Deep paleocanyons in the western Gulf of Mexico, thick sands in the deep Gulf, salt in the Veracruz Basin and a major unconformity in deep water near the mouth of the Gulf suggest that sea level dropped significantly during the Late Paleocene-Early Eocene. We relate these features to an evaporative drawdown when the Gulf's connection to the world ocean was blocked by the collision of Cuba with the Yucatán and Florida-Bahamas blocks. Sea level fell as the evaporation rate far exceeded additions from rainfall and fluvial runoff.

The Upper Paleocene-Lower Eocene Wilcox Formation is a submarine fan complex more than 1.5 km thick that blankets a vast area of the western and central deepwater Gulf. We surmise that this anomalously thick, relatively uniform sand accumulation contains recycled Lower Wilcox shelf sands deposited in the deep basin during the lowstand.

We explain the unconformity between Yucatán and Florida, represented by Pleistocene sediments overlying Cenomanian limestones at DSDP Site 535, as the result of erosion when the oceanic connection was re-established.

A variety of local explanations have been invoked to explain these and other manifestations of the proposed drawdown; however, a single mechanism linked to a widely accepted plate tectonic model (the Cuba-Bahamas collision) can account for this variety of hitherto unrelated geological phenomena.