The Yucatan Platform bisects the NW-SE Sierra de Chiapas fold belt of SE Mexico at right angles. The outcropping Sierra de Chiapas involves Mesozoic platform carbonates, but its northwestern subsurface continuation involves mostly Mesozoic basinal and slope facies sediments in the Villahermosa folds and their offshore continuation, the Sonda de Campeche folds. The main decollement level for the folds is a middle Jurassic evaporite sequence. The pre-salt "basement" of the area is poorly defined but estimated to dip from about a depth of 6 km to the north (Campeche offshore) to 13 km in the south (Sierra de Chiapas). The fold belt was formed during upper Miocene time and is characterized by bivergent NW-SE striking folds. The amount of shortening is estimated to be in the order of 45 km to 65 km. In the onshore and offshore subsurface the folded belt is orthogonally superposed by a late Neogene growth fault system which soles out near the base of the Neogene. This growth fault system developed on the continental slope and intercepted salt diapirs that probably emanated from the core of deep-seated folds. Much of the salt accumulated farther north in the large allochthonous mass of the Campeche salt domes.