Abstract

The Chiapas Foldbelt, Akal-Reforma “Horst”, and deepwater Campeche Foldbelt comprise Mesozoic through Middle Miocene strata separated in map view by the extensional NE-trending Macuspana (late Middle Miocene and younger) and Comalcalco (mainly Pliocene and younger) extensional troughs. During Middle Miocene NE-directed shortening within a greater “Chiapas-Akal-Reforma Foldbelt”, the continental “North Guatemalan backstop” served as a rigid, westward-pointing indenter into the more basinal and deformable foldbelt. The Chiapas Foldbelt was thrust against the southwestern flank of the backstop, while the Akal-Reforma trend shortened less intensely over a broader area and was allowed to bypass the backstop by dextral lateral ramping along the backstop’s northwest flank. By late Middle Miocene, the Akal-Reforma trend became gravitationally unstable under continued shortening, and the dextral lateral ramp collapsed transtensionally from the NW flank of the backstop, thus opening the Macuspana Basin. The detachment level appears to be at Callovian salt; subsequently, the Comalcalco Trough opened as a second surface extensional scar on salt, too, leaving the Akal-Reforma trend as a floating, rootless “horst” between the two detachment basins above salt. The NNW-directed extension within the two basins feeds into folds of the deepwater Campeche Foldbelt, whose age of NW-directed folding must primarily match the times of opening in the two troughs. However, folding related to that prior to the onset of extensional collapse occurs in some areas. The entire southern Gulf of Mexico petroleum system is contained with the structures noted, which were further buried and matured by younger overlap fill as extension continued, creating a world class petroleum exploration province.