Contractional Growth Faulting in the Mexican Ridges, Gulf of Mexico

Abstract

The Mexican Ridges fold belt is a Neogene contractional system located on the western continental slope of the Gulf of Mexico Basin. This contractional system formed in response to gravitational slide processes affecting continental shelf deposits along 500 km (311 mi) of the Quetzalcoatl extensional system. Numerous north-south–oriented contractional growth faults are developed mainly above a thick detachment zone consisting of Paleogene argillaceous strata. The main structural style of these fold geometries corresponds to classical detachment folds and detachment folds with late-stage reverse faults. The detachment folds are generally symmetrical, although some folds are asymmetric with eastward vergence in the dominant shortening direction of the fold belt. The contractional folds range in length from 20 to 120 km (12.4 to 74 mi) with amplitudes between 6 and 15 km (3.7 and 9.3 mi) and are important hydrocarbon exploration prospects. Some examples from the Mexican Ridges indicate that contractional folding belt initiated during the middle Miocene and that the most recent folds are forming in the central and eastern part of the fold belt. Generally, the youngest and highest amplitude folds are found toward the center of the basin. The growth folds are analyzed on the basis of their stratigraphic relationship to syntectonic sedimentation, which displays different geometries as a consequence of fault movement. Converging seismic reflection geometries are common toward the fold crests and may appear as thinning sets or onlaping above an unconformable surface and are characteristics of fault kinematics and fault activity. In this study, we use growth strata to determinate (1) structural styles of the folds based and their kinematics and (2) the age of contractional deformation. These geological characteristics allow an evaluation of elements such as timing, possible migration pathways, and geological risks of exploration prospects.