Early Paleogene Isolation of the Gulf of Mexico from the World’s Oceans? Implications for Hydrocarbon Exploration and Eustasy
Joshua Rosenfeld, James Pindell, 2003. "Early Paleogene Isolation of the Gulf of Mexico from the World’s Oceans? Implications for Hydrocarbon Exploration and Eustasy", The Circum-Gulf of Mexico and the Caribbean: Hydrocarbon Habitats, Basin Formation and Plate Tectonics, Claudio Bartolini, Richard T. Buffler, Jon F. Blickwede
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Deeply incised and backfilled paleocanyons in early Paleogene shelf strata along the western and northern Gulf of Mexico margin attest to large relative sea-level fluctuations, but they predate the accepted age for onset of Cenozoic continental glaciation. Using Pleistocene canyons as a crude yardstick, the scale of these paleocanyons suggests relative sea-level changes at least as large as Pleistocene fluctuations. Therefore, we speculate that water level in the Gulf of Mexico was drawn down while the Gulf was isolated from the world’s oceans during the late Paleocene/early Eocene interval. We suggest that the cause for isolation was the progressive collision of the Cuban arc with the Yucatan and Bahamas carbonate platforms, which temporarily closed off the southeastern Gulf of Mexico. In Miocene Mediterranean and Holocene Black Sea examples of marine-basin isolation, evaporation greatly exceeded rainfall and runoff, and our examination of the Gulf of Mexico case suggests that water level may have dropped below the level of the world’s oceans at least once by several hundred meters, and possibly much more.
Implications for geology and hydrocarbon exploration in the Gulf may include:
bypass of enormous quantities of coarse detritus into the deep basin
seaward collapse of exposed clastic shelf margins
triggering and/or acceleration of salt evacuation (basinward “squeegee” effect of slumping sediments)
release of gas hydrates from sediments under shallower and warmer water, thereby contributing to the ˜100,000-year-long worldwide Paleocene/Eocene boundary heating event
development of secondary porosity in both platform and deep-water carbonate sections by dissolution and phreatic diagenesis, e.g., in the Golden Lane/Poza Rica area of Mexico
hypersalinity and possible sea-bottom stagnation with source-rock deposition in areas that remained marine
deposition of fine-grained condensed sections (seal and source rock) during flooding period(s) when connection with the world’s oceans was reestablished, creating stratigraphic traps at canyon flanks and turbidite reservoirs in the canyons.
Recognition that early Paleogene relative sea-level changes seen in the Gulf may pertain to basin isolation is grounds for treating “eustatic” curves derived for or from the Gulf with suspicion. In addition, catastrophic basinward transfer and collapse of mass near the shelf edges would have caused isostatic unloading (rebound) of shelf margins that was proportional to the mass transfer. In the case of a discreet slumping event, such as the Lavaca “Megaslump” event of south Texas, this effect may have caused uplift of several to a few tens of meters of footwall areas within about 100 km from the slump. Larger downslope movements such as those related to the collective Wilcox fault province would have caused far larger isostatic rebounds on the shelf, perhaps in excess of 100 m if sedimentation did not keep pace with faulting.
A body of circumstantial evidence continues to grow in support of this hypothesis; its potential implications, both academic and commercial, merit further investigation. Integration of information from Cuba, Mexico, the United States, and the Bahamas will be required to fully test the hypothesis.
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The Circum-Gulf of Mexico and the Caribbean: Hydrocarbon Habitats, Basin Formation and Plate Tectonics
The Circum-Gulf of Mexico and the Caribbean has long been one of the world's most important petroleum provinces, as well as one of the world's most geologically complex regions. These two characteristics have resulted in an extensive amount of ongoing research by both industry and academia. AAPG Memoir 79, The Circum-Gulf of Mexico and the Caribbean, is the first volume in more than a decade to document such a wide range of research on the geology of this vast area. Of the total 44 papers, roughly two-thirds pertain to the Gulf of Mexico, with an emphasis on the Mexican portion of the basin, and to the petroliferous areas of the southern Caribbean, including Colombia, Venezuela, Cuba, and Trinidad and Tobago. The remaining papers relate to the Antilles and Central America, as well as a series of papers that address region-wide topics such as plate tectonic evolution. A significant number of papers were contributed by authors from national oil companies and universities from within the region.