Abstract

Oligocene and Miocene-age carbonates were studied in outcrop and from the subsurface along the southern margin of the hydrocarbon-rich Macuspana Basin and Chiapas fold belt. A multi-disciplinary approach integrating biostratigraphy, sedimentology, 3D seismic data, and sequence stratigraphic concepts allowed establishment of a regional geologic model for use in hydrocarbon exploration.

During the Oligocene lowstand, a deep-water ramp was deposited towards the basin center in the east. Drowning of this ramp in the basal Miocene resulted in a westward shift in deposition up the paleoslope. The Miocene-age Macuspana Limestone Formation (100 to 400 meters thick) consists of three, 3rd -order sequences (Caliza-I – Caliza-III). Cycle-base marine shales contain distinctive planktonic foraminifer assemblages, which allow age determination of these maximum flooding surfaces.

Five biofacies based on foraminifer distributions, and twelve environmentally significant lithofacies are recognized. Carbonate deposition changed from the initial steepening of the gentle ramp (Caliza-I) into a rimmed shelf with a lagoon (Caliza-III). Basinward progradation was, in part, a response to forced regression.

Deeper water, basin and outer ramp facies show no evidence of debris flows or turbidites. Barrier reefs were not observed; instead, mud-rich, biostromal patch reefs are present on the inner ramp that developed during ramp highstand systems tract.

Syn-sedimentary tectonism related to shale movement affected the internal architecture of the ramp. Positive areas were sites of reef development and high-energy grainstone deposition.

Three potential reservoirs are identified with fracture and matrix porosity: 1) Upper Oligocene ramp; 2) Caliza-I; and, 3) Caliza-III. Caliza-II appears to lack reservoir potential.