PALEOBOTANY OF THE GUATEMALA GROUP IN THE SAN SEBASTIAN FORMATION, PUERTO RICO: TAXONOMY OF PLANTS BASED IN LEAF PHYSIOGNOMY

Three paleobotanical sites were identified along the Guatemala River in San Sebastián, Puerto Rico. Rock samples and fossils from these sites were collected and properly curated. 19 specimens of fossil plant remains were examined, in detail, and classified based on their morphology, using the concept of leaf physiognomy. At least 15 different morphotypes of fossil leaves, of which one was classified as a Rhizophora sp. Herbivory signs and other leaf damage features were also reported in this study. In addition, pneumatophores roots were found in-situ in the upper site. These fossils were found in a typical sequence of rocks of a shallowing upward cycle, with flaser bedding and some marine content, such as shell fragments and marine vertebrate parts, indicative of coastal or near the coast depositional environments. Based in the geological setting and its fossil content, the paleoenvironmental implications of the Guatemala Group of the San Sebastián Fm. suggest an estuarine depositional environment with marine influence, typical of transgressive system tracts (TST) during the Oligocene. The given interpretation of the depositional environment at this locality is an intertidal estuarine area that developed into a mangrove environmental setting during the Oligocene, contrary to the previous pollen-based biogeographical models that present the San Sebastián Fm. as a highland.