AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Two-Phase, Full-Fit, Triassic-Mesozoic Reconstruction of the Gulf of Mexico Basin, Its Continental Margins and Twin Salt Basins

Abstract

For decades, the kinematic opening of the Gulf of Mexico (GOM) and the tectonic evolution of its hydrocarbon-rich, continental margins have remained controversial. A breakthrough in our understanding of the GOM came with the 2014 release of satellite-derived gravity data that provided evidence for counterclockwise rotation of the Yucatan block along an arcuate, late Jurassic-age seafloor spreading system. The amount of Triassic-Jurassic continental extension that occurred during the Triassic and early Jurassic remains a poorly understood question due to the difficulty in mapping and quantifying the amount of crustal thinning of its deeply-buried and salt-covered continental margins. This study addresses the earlier, pre-oceanic spreading history of the GOM with a new crustal thickness map for the entire GOM and its surrounding margins based on integration of: 1) depth to basement compilation of previous seismic refraction and well data; and 2) estimation of Moho depths from 3D gravity inversion. Our new map shows crustal thickness variations that are consistent with available seismic refraction and reflection constraints from the last six decades. Oceanic crust in the central GOM has an average thickness of 6 km with a range from 3-12 km. Our model shows a 600 km-wide zone of stretched continental crust with average thickness of 20 km in the North American margin whereas over Yucatan margin stretched crust is shown over a much narrower, 200-km-wide zone. Using an areal balancing method along with crustal thickness information, we fully restored the stretched continental crust of the conjugate margins to its pre-rift thickness. From various early opening scenarios examined, continental rifting most likely occurred initially in a NW-SE direction prior to the late Jurassic, counterclockwise rotation phase of GOM opening. On the basis of gravity inversion, we also estimated the total salt thickness in the main salt basins of the GOM. With an average thickness of 4 km, salt reaches a maximum of 8 km in thickness over the Louann salt basin. In the Campeche salt basin, salt thickness is 2 km on average. These estimates are comparable with observations from ~50 exploration wells that penetrated thick salt within the Louann salt basin. Using the most likely early opening scenario we propose a full-fit restoration of the Yucatan block and North American plate prior to the first phase of rifting and a later reconstruction of a single, GOM salt basin.