Keynote Presentation: Imaging Crustal Constraints on the early evolution of the Gulf of Mexico with 2D and 3D Seismic Data: how realistic are comparisons to the South Atlantic?

Abstract

We present a significantly updated history of Mesozoic tectonic and plate boundary evolution of western Pangea that embraces the two primary stages (1 and 2; Pindell, 2010) of the Gulf of Mexico’s (GoM) evolution. The history embraces: 1) a revised Equatorial Atlantic closure reconstruction that provides more initial space across the paleo-GoM (Pindell et al., 2019b); 2) the Bajocian depositional age of salt in the Gulf of Mexico (A. Pulham, 2017 unpublished; Pindell et al. 2019a; Peel, 2019); 3) structural and stratigraphic observations in 2D and 3D seismic data that portray the basinward-younging character of rifting beneath GoM salt ; 4) the Pemex aeromagnetic map of the Gulf of Mexico and its margins that indicates a two-pole history of seafloor spreading in the GoM (Pindell et al., 2016); 5) field observations and laboratory analyses of Triassic-Jurassic sections (e.g., detrital zircon) on samples in Mexico and Guatemala (Molina-Garza et al., 2019 in press; this volume); and 6) a critical re-examination of northern Andean paleo-reconstructions (Dewey and Pindell, 1985; 1986), which is southern Mexico’s conjugate margin. The implications of the work are substantial for the GoM, including 1) a possible Bathonian onset of seafloor spreading and deep-water deposition, 2) an age span for the “Norphlet window” (Godo, 2017) that is 8 m.y. longer than currently believed, 3) a more protracted period (Bathonian-Oxfordian) of marginal marine transgression than previously thought, and 4) 8 m.y. of additional time for rift- and seafloor spreading-related heat to dissipate prior to Oxfordian-Tithonian source rock deposition (Pindell et al., 2019b), ensuring preservation of source potential for Cenozoic burial maturation. The synthesis also exhibits various seismic observations including: 1) possible inner, syn-rift SDR sets in the offshore margins of Campeche and northwest Florida (Pindell et al., 2011); 2) the circum-GoM basement step or step-up to the oceanic crust (Pindell, 2002; Pindell and Kennan, 2007; Barker and Mukherjee, 2011; Hudec et al., 2013); 3) the circum-GoM step-up trough (Pindell et al., 2011) or outer marginal trough (Pindell et al. 2014; Rowan, 2018); 4) the North Yucatán salt slide onto oceanic crust (Horn et al., 2015; Hudec and Norton, 2019); 5) the structural character of the East Mexico transform margin (Pindell, 1985) that now appears to pass into the onshore Veracruz Basin (Pindell et al., 2016); 6) sag sections along north western Florida (Pindell et al., 2011) and northern Campeche (Horn et al., 2015); 7) the planar nature of most of the base-salt unconformity (Pindell et al., 2011; 2014; Hudec and Norton, 2013; Horn et al., 2015). Seismic and other data suggest that rifting in the GoM was locally magma rich, locally arc-related (Molina et al., this volume), but that margin breakup was magma poor, demonstrating a temporal variability in magma supply during margin development such that margins should not be classified merely as magma-rich or magma-poor. In addition, we examine the enigmatic thin but very deep salt occurrences along northern Yucatán and northwest Florida (paleo-eastern GoM) to make a case for the probability of deep-water salt deposition there (e.g., Anati, 1993; Roveri et al., 2014; Lugli et al., 2015). If this suggestion is eventually accepted, we would acknowledge that much of the GoM was likely never completely filled with salt to sea level, and that an air-filled depression below global sea level during rift and sag time might best explain the GoM’s history of salt deposition. This, in turn, leads to reduced appeal for the concept of outer marginal collapse (Pindell et al., 2014). The looser fit afforded by the revised Equatorial Atlantic reconstruction removes the need to employ the hypothetical Mojave-Sonora Megashear (Anderson and Schmidt, 1983) during the syn-rift stage. Instead, a model of Basin and Range style sinistral transtension of the eastern Mexican continental lithosphere, which had been the site of Permian anatexis due most likely to crustal over thickening during the Alleghanian Orogeny, seems a better means of emplacing the Mexican continental crust into the “Colombia overlap position” in Pangean reconstructions, driven by oblique subduction along the Pacific margin. This updated model for the syn-rift phase (GoM Stage 1) is portrayed in a series of new plate reconstructions, which continues through the drift phase (Stage 2) and into the medial Cretaceous. Although many new observations are explained by this revised tectonic model, we identify new and remaining questions that must be addressed. The pre-salt history outlined here for the GoM can be used as a framework for considering in the GoM various elements of the pre-salt petroleum system of the better-documented South Atlantic salt basins. Similarities and differences are highlighted.

AAPG Datapages/Search and Discovery Article #90369 © 2020 AAPG Hedberg Conference, Geology and Hydrocarbon Potential of the Circum-Gulf of Mexico Pre-salt Section, Mexico City, Mexico, February 4-6, 2020