Facies analysis of a Bartonian-Aquitanian siliciclastic-carbonate system, Costa Rica

Costa Rican Eocene-Oligocene carbonate deposits have been known for more than a hundred years, however, there are few scientific contributions detailing the relation between facies analysis and regional basin evolution. Based on a detailed study in southern Costa Rica, a chronologic history of a Bartonian-Aquitanian sedimentary succession is proposed. The carbonate facies analysis allows for eight microfacies (MF1 to MF8) to be distinguish. The siliciclastic facies analysis permits identification of two main periods of sandstone deposition and one of shale formation. The mixed sandstone/carbonate succession exhibits three main periods of deposition: (1) Bartonian-lower Priabonian, represented by distal, relatively deep slope-to-basin environments. Deposits comprise thick accumulation of sandstones, calcareous breccias, and calciturbidites. This period terminates with a stratigraphic erosion surface; (2) Upper Priabonian-Rupelian, represented by more proximal, shallow to mid depth inner to middle ramp environments. Deposits are composed of peloidal/cortoidal grainstone, foraminiferal-algal rudstones, and rhodolith rudstones. This period terminates with a second stratigraphic erosion surface; (3) Chattian-Aquitanian, represented by proximal to distal, shallow to coastal and offshore environments. Deposits are composed of a mixed siliciclastic carbonate thin complex overlain by dark shale. The vertical and lateral facies changes permit a basin evolution model that is closely controlled by subsidence. Local tectonic uplift may have formed the first subaerial exposure surface. The second subaerial exposure surface may have been controlled by eustatic sea-level variations over relatively shallow water deposits. These results, the first-of-their-kind in the southern Costa Rican Fila Costena, could permit improvements of lateral regional correlations by bringing new lithostratigraphic layers of reference. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Costa Rican Eocene-Oligocene carbonate deposits have a long history but lack detailed scientific contributions on facies analysis and basin evolution. A study in southern Costa Rica identified a sedimentary succession from Bartonian to Aquitanian and proposed a chronologic history. The research results could improve regional correlation by introducing new lithostratigraphic layers of reference.