Abstract

DENYER, Percy et al. Tranquerillas black shales: Peña Negra Formation of Middle Miocene, Costa Rica. Rev. Geol. Amér. Central [online]. 2024, n.70, pp.1-16. ISSN 0256-7024.  http://dx.doi.org/10.15517/rgac.2024.58434.

The occurrence of black shales and sandstones in the Candelaria basin, as well as in the Térraba, Tárcoles and Limón Sur basins has generated inconsistencies and errors in the stratigraphic interpretation, age and origin of these rocks. This is exemplified at the locality of Tranquerillas, where the Tranquerilla Member was associated with the Térraba Formation (Oligocene-Lower Miocene). Based on micropaleontological dating, this work clarifies a Middle Miocene age for this locality. This age and its origin in a shallow marine environment, high primary productivity and oxygen depletion, indicate that these lithologies are instead correlated with the Peña Negra Formation. These results have implications in the tectonic and cartographic model of the area, allowing a more simplified interpretation of the geology of the Tranquerillas locality. Additionally, the designation of these rocks under the member category is no longer necessary.

Keywords : Candelaria basin; Terraba Formation; Ciperoella anguliofficinalis; Orbulina suturalis; tectonic..

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