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 tapered 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.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018