Paleocene-Eocene Boundary Sea Level Drawdown of the Gulf of Mexico

Abstract

Rosenfeld and Pindell (2002, 2003) hypothesized that late Paleocene-early Eocene docking of the northward migrating Caribbean Plate blocked the 200 km-wide deep water strait between the Florida/Bahamas Block and Yucatan, thereby isolating the Gulf of Mexico from the world ocean. Within several thousand years, net evaporation of the Gulf lowered its level by about 2,000 meters, and producing a land bridge across the eastern Gulf that encompassed Yucatan, Florida, Cuba, and the Bahamas. Isolation of the Gulf was enhanced by isostatic uplift of the basin’s margins as sea level dropped. After some 1 million years of isolation, reconnection with the world ocean and energetic refill of the basin eroded a deep thalweg between Florida and Cuba. This relatively brief drawdown explains many phenomena unique to this period of Gulf history, including: -The excavation of deep canyons across contemporary continental shelves and slopes: e.g., Yoakum, St. Landry, Chicontepec/Bejuco-La Laja paleocanyons, and canyons and sinkholes on the lower carbonate continental slopes of western Florida and northern Yucatan. -Subaerial bitumen seeps sandwiched among bathyal strata in Chicontepec tributary canyons. -The sudden deposition, and equally sudden cessation of a widespread, thick, high net sand blanket in the deep Gulf Basin. -A regional unconformity across the eastern deep Gulf basin. The proposed drawdown is coeval with the worldwide Paleocene-Eocene thermal maximum (PETM) that may have been triggered by the release of voluminous methane from destabilized hydrates and breached conventional reservoirs by removal of the water overburden resulting in nearly instantaneous over-pressuring during the Gulf low stand. The drawdown also profoundly affected the petroleum geology of the Gulf of Mexico, most obviously by deposition of the basal Wilcox “Whopper Sand” in U.S. and Mexican waters. Further petroleum ramifications include porosity enhancement by leaching and fresh water infiltration of a) reefal carbonates of the Golden Lane Atoll, b) deep-water carbonate detritus reservoirs in the Poza Rica Trend and c) the Campeche Sound K/T breccias.

AAPG Datapages/Search and Discovery Article #90330©2018 AAPG Hedberg: Geology of Middle America – the Gulf of Mexico, Yucatan, Caribbean, Grenada and Tobago Basins and Their Margins “Integration of the geology of the area from the southern onshore of North America to the northern onshore of South America”, Siguenza, Guadalajara, Spain, July 2-5, 2018