Río Hatillo FormationThe Río Hatillo Formation is a geologic formation in Dominican Republic. It preserves bivalve, echinoid, gastropod and ammonite fossils dating back to the Early Albian period.DescriptionRío Hatillo Formation comprises a basal conglomerate, sandstones and calcareous sandstones, covered by a massive biogenic limestone. The formation was probably deposited in a shallow, near-shore environment as part of the Cretaceous Volcanic Arc sections.