Abstract
The outcroping stratigraphic sequence of the following quadrangles is shown: Belén, Carrillo Norte, Matapalo and Punta Gorda. We mapped the following geologic units: The Nicoya Ophiolitic Complex is constituted by basalts, radiolarites and the Potrero Intrusive, which is composed by gabros, diabases and plagiogranites. Probably, the origen of the Potrero Intrusive is related to a hot spot.
The sedimentary cover begins with hemipelagic rocks of the Sabana Grande Formation, which are overlied by neritic and talud deposits of the Barbudal Formation, Rivas (or Curú) Formation and Brito (or Descartes) Formation. These units belong to the Upper Cretaceous and Paleogene.
The lgnimbrites of the Liberia and Bagaces Formations are covering the ophiolitic rocks and/or the sedimentary rocks in the north of the are.
The alluviall Quaternary deposits are showing recent tectonic movement, which is confirmed by abrasion terraces uplifted in several locations on the shoreline.