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Restoring the Late Jurassic, Conjugate Margins of the Gulf of Mexico: Recent Progress and Remaining Problems

Abstract

The Gulf of Mexico (GOM) petroleum system is one of the most productive “super basins" in the world. Yet, the 10-15-km-thick sedimentary and evaporitic infill has impeded detailed imaging of the deeper, continental and oceanic GOM. The lack of a regional, observational data base made it difficult to define the rifted margins, to constrain the timing of the Triassic-Jurassic opening phases, and to define the precise directions of GOM opening. In 2014, the publication of high-resolution satellite images of the GOM improved the mapping of the global marine gravity field by a factor of two to four and revealed the presence of a single, deeply-buried, extinct spreading ridge of inferred late Jurassic age within the deep, central GOM. The arcuate, spreading ridge is about 1000 km long, extends from the southwest GOM in Mexico to the southeast GOM near Cuba, and is comprised of long fracture zones and short, orthogonal spreading ridges typical of a slowly spreading, ridge system. The new gravity images also reveal the location and shapes of the conjugate, edges of thinned, continental crust along the Yucatan and Florida margins in areas of the eastern and south-central GOM that are not obscured by thick salt. Previous plate models had provided the overall plate framework for this crescentic-shaped area of oceanic crust as a result of late Jurassic, counterclockwise rotation of the Yucatan Peninsula - but the resolution of the new gravity maps of the fracture zones and shapes of the continent-ocean boundaries now allow for more precise reconstruction of the two GOM conjugate margins. With the new gravity images, the origin of several, basic, GOM features are clarified: 1) the late Jurassic oceanic crust of the deep, central GOM opened in a roughly, north-south and highly arcuate direction as shown by the well mapped, system of curvilinear fracture zones and orthogonal spreading ridges; 2) the crescentic area of oceanic crust neatly separated the Louann and Campeche salt provinces; 3) the Louann and Campeche salt was originally deposited on rifted, continental crust prior the formation of the oceanic area; and 4) localized areas of salt overlying oceanic crust only occurred as the result of Cretaceous and Cenozoic, gravity-related salt remobilization. To illustrate and support these observations, we first use the orientations of the oceanic fracture zones to define a single Euler pole in western Cuba that describes the opening of the oceanic area. We then remove the area of oceanic crust to restore the mapped edges of the Yucatan-Florida, continental margins. We then validate features seen on the satellite gravity images with overlays of gravity and magnetic maps along with mapping based on 117,000 km of seismic reflection data for the Yucatan-Florida conjugate margin. These integrated data constrain the locations of three regional arches or “ pinning points" on the two conjugate margins that are roughly orthogonal to the marg