Organismos de un arrecife fósil (Oligoceno Superior-Mioceno Inferior), del Caribe de Costa Rica

Abstract

This paper describes the fossils, materials and paleoenvironmental conditions found in some outcrops near the town of Jesús María, Turrialba, Costa Rica. The rock materials (reefal limestone, sandstones and conglomerates) are associated to the Punta Pelada Formation of Upper Oligocene to Lower Miocene age. Outcrops are of reduced extent and are unevenly distributed, hence they are considered as patch reefs developed by environmental energy fluctuations, sea level changes and clastic sedimentation from sources on small islands acting together in narrow platforms. The structural and environmental characteristics where fossil communities developed were derived from the analysis of 460 samples containing 36 species. The reefs represent low diversity communities comprising four coral species (three of them reef builders), 31 mollusks species (21 gastropods: a new species, 14 carnivores, three herbivores and three of uncertain feeding habits; 10 bivalves species: five endobenthic and five epibenthic); algae (at least three groups represented); sea urchins; foraminifers; crabs. The evenness index is low, mainly regarding the Scleractinian corals, where Antiguastrea cellulosa predominates (80% of the recognized forms). The fossil assemblage suggests that the communities developed in shallow marine environments (50-80 m depth), affected by sea level changes, strong marine currents and clastic imput from nearby small islands.