Edad de las lavas del miembro los bambinos y sumario cronoestratigráfico de la Formación Barva, Costa Rica

Abstract

The age of Los Bambinos Member is established based on new geological observations, geology of drilled wells in the upper part of Barva volcano, and previous and a new radiometric ages. We also propose a new chro- nostratigraphy for Barva Formation (equivalent to Neo Barva volcano). The rocks underlying Tiribí Formation near the top of the volcano are stratigraphically correlationable to Colima Formation and are part of the Paleo Barva. Lavas from Bermúdez Member form several lava fields with a wide range of ages (270-40? ka). The pyroclastic deposits in stratovolcanoes like Barva are lesser in volume and are grouped diachronically, as it is the case of Carbonal Member, which in the upper part of the volcano can represent ages in the range 40-27.4 ka. Lavas of Los Bambinos Member are divided in two sub-members (Lower and Upper), and a lahar interbeded between the two sub-members yield an age of 27.4 ka. The whole member would have ages between 10-30 ka. The pyroclasts of Porrosatí Member could have ages <15 ka, according to ages of tephras overlying Los Bambinos lavas.