From Strike-Slip Depositional Setting to Fold and Thrust Belt: Tertiary to Recent Structural and Sedimentary Development of a Forearc Basin (Terraba Basin, Southern Costa Rica)

Hannelore E. Krawinkel and Justus J. Krawinkel

The present day Terraba belt represents part of the inverted forearc area of the Costa Rican island arc system. Geographically this tectonostratigraphic unit corresponds to the Fila Costena. An approximately 3500 m thick sequence of deformed early Tertiary to Pleistocene sedimentary and volcanic rocks reveals three stages of basin development: (1) a transpressional depositional setting (latest Cretaceous to Eocene), (2) a transtensive margin depositional setting (Oligocene to lower Miocene), (3) a transpressional depositional setting (middle Miocene to Recent). During the latest Cretaceous to Eocene strong transpressional uplift of ridges leads to the formation of shallow marine carbonates. Rapid drowning of these carbonate platforms along major lineaments marks the begin ing of the transtensive regime, which resulted in small, elongated, deep strike-slip basins that were filled with 2 km of siliciclastic turbidites. Strong uplift and contemporaneous extension can be interpreted as phenomena caused by the subduction of buoyant Pacific crust related to the Galapagos Gore during the middle Miocene. Unroofing processes driven by gravitational mass movements provided accumulation space between rotating blocks on both flanks of the uplifting Cordillera de Talamanca. These half graben like structures subsequently were filled by shallow marine to terrestrial sedimentary sequences bounded by regional unconformites.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California