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AAPG ACE 2018

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Tectonic Controls on Along-Strike Variations in the Bathymetry, Width, and Structural Style of the Mexican Ridges Deepwater, Fold-Thrust Belt, Western Gulf of Mexico

Abstract

The Mexican Ridges fold-belt (MRFB) of the western Gulf of Mexico (GOM) is a 600-km-long, deepwater, passive margin fold-belt along the continental margin of Mexico formed by Miocene to Recent linked extensional-contractional, gravity-driven system detached on Eocene and Oligocene shale horizons. We have used a 20,000 km grid of 2D industry seismic data tied to 15 wells to map horizons ranging in age from a mid-Cretaceous carbonate surface to the seafloor. This mapping has defined two, structural provinces of the MRFB with differing characteristics: the 150-200 km-wide and 250 km-long Northern Mexican Ridges extending from the Perdido deepwater foldbelt to offshore Tampico, and the 100-200 km-wide and 390 km-long Southern Mexican Ridges extending from offshore Tampico, past the Jalapa Uplift and southward to its Previous HittaperedTop termination near Veracruz. Structurally, both segments consist of symmetric detachment folds and break-thrust detachment folds. However, the southernmost part of the SMR exhibits much longer wavelength folds and a complete absence of up-dip, normal faults along the shelf margin. Instead, the SMR exhibits broad folds on the shelf and slope. We measured the dip of the underlying, seaward-dipping top Cretaceous carbonate surface present in both the northern and southern provinces. Measured angles of slope along the northern MRFB display steeper dips (> 6.7°) compared to the central (5.2-6.3°) and most of the southern ridges south of the Talapa uplift (4-6.5°). Steeper slopes in the northern MRFB correspond with the greatest widths of the entire wider run-off, however this is likely due to the presence of salt rather than slope angle. When examining the southernmost part of the MRFB with the shortest run-off width, there is a sharp increase in slope dip (to 7.9-8.2°) corresponding to the Jalapa uplift which represents the orthogonal intersection of the Miocene to Recent Trans-Mexican Volcanic belt (TMVB) with the MRFB. The impinging TMVB is also expressed by a change in slope morphology from wider, flatter, more variable slopes in the northern and majority of the southern segment compared to the southernmost, TMVB-influenced segment. Identified differences in fold-thrust style and spacing controlled by these factors will influence potential trapping mechanisms for hydrocarbons and affect migration routes from source kitchen areas based on their position.