Sedimentary Basins of Costa Rica: Late Mesozoic-Cenozoic Evolution and Hydrocarbon Potential

Abstract

The Upper Cretaceous/Cenozoic basins of Costa Rica are underlain by oceanic crust and located along the western margin of the Caribbean Plate. A primitive intraoceanic arc formed along the western margin of the Caribbean Plate since Albian time, with associated anoxic pelagic sedimentation. This arc marked the beginning of subduction of the Pacific Plate in this region and of the first elements of the land bridge joining North and South America. Continued subduction of the Pacific Plate from Campanian until the present created a convergent marginal tectonic setting with, from southwest to northeast, a trench, an outer arc, a forearc region, a volcanic arc, and a backarc region. Localized platforms of shallow water carbonates, overlain by extensive cyclical turbidite systems, characterized the sediments of most of the basins up to the Eocene, when a major tectonic compressive event affected the area. Also about this time, a major sinistral east-west fault system (Costa Rica TranscurrentFaultZone) divided the region into north and south segments, and transtensional or pull apart basins developed along the fault system. During this pre-Miocene time, the north segment was emergent and subject to erosion, whereas in the south segment sedimentation continued. From Miocene on, shallow marine deposition was widespread in both segments. In the north segment, extension in the backarc region created a structural depression filled with Neogene sediments. The south segment experienced compressional tectonics due to north-directed movement of the Panama block. Later, in the Pleistocene, northeasterly-directed shallow subduction of the thick Cocos Ridge resulted in additional thrusting and the development of a foreland basin.

Organic-rich, deep-water, thermally mature source rocks occur in several basins with high TOC (total organic content) values and adequate maturation levels. Potential carbonate reservoirs in some of these basins include shallow water carbonates, rudistic reef buildups, and grainstone accumulations. Potential clastic reservoirs include turbidite sandstones, regressive deltaic deposits, and near-shore porous sandstones. Potential petroleum traps are diverse and numerous in all of the basins. Seismic and stratigraphie well data recently acquired and interpreted in a joint RECOPE-PCIAC (Petro-Canada International Assistance Corporation) program added significantly to the understanding of the Costa Rican basins.