Abstract

This paper presents the data derived from the geological mapping of the Paraíso sheet (3445-IV23), 1:10.000 scale, located within the Central Valley of Costa Rica, together with the most relevant structural and hydrogeological aspects. In general, the existence of a rocky basement associated with the Pacacua Formation of the Upper Miocene, discordantly overlain by materials from the Irazú paleovolcano, related to the Paraíso Formation of the Middle Pleistocene and to the Reventado Formation of the Upper Pleistocene was determined. Due to the climatic conditions and to the composition of the volcanic materials the unit El Rincón Laterite Bed has been developed, which appears in the greater part of the sheet. The above materials are overlaid discordantly by the Upper Pleistocene Alluvial Deposits and by the Lacustrine Deposits, whereas the Current Alluvial Deposits overlap discordantly to the previous materials due to changes in the base level of the rivers produced by the active tectonics in the region. According to morphological observations, a structural model with an axis of N-S orientation stresses, consisting of E-W orientation inverse faults, with shear faults associated with NE-SW and NW-SE orientation is proposed. The hydrogeological model is formed by two aquifers associated with lava flows, with intermediate capacity and affected by the effects of tectonic activity in the sector E of the quadrangle.

Keywords: Paraíso; Pacacua; Irazú; Reventado; Cartago; active tectonic; aluvial; facies; Istarú