PROVENANCE OF OLIGOCENE CONGLOMERATES AND ASSOCIATED SANDSTONES FROM THE SIAMANÁFORMATION, SERRANÍADE JARARA, GUAJIRA, COLOMBIA: IMPLICATIONS FOR OLIGOCENE CARIBBEAN-SOUTH AMERICAN TECTONICS

Analyses of composition and sedimentological attributes of conglomerate clasts together with petrographical and heavy mineral analyses and detrital geochronology from sandstones of the Oligocene Siamaná Formation in the Serranía de Jarara, are presented in order to reconstruct de provenance of this sedimentary sequence and contribute to the knowledge of the tectonosedimentary evolution of the Guajira Peninsula and the Caribbean. The results indicate that the source areas are proximal and are located to the southeast. The presence of plutonic igneous and mediumto Lowgrade metamorphic rocks, as well as highpressure metamorphic rocks, indicate that the lithostratigraphic units (Parashi Stock and Jarara Formation) of the Serranía de Jarara and an unidentified unit to the southeast, are the main rock sources. The heavy minerals and the detrital zircon distribution with peaks at approximately 50 Ma, 207Ma, 245 Ma, 463 Ma, 963 Ma and 1044 Ma, confirm that this is the source area. The extremely proximate sources and the rapid burying of the basin, which is evident due to the presence of marine sediments that overlie this sequence, indicate that this siliciclastic unit is related to the initial phases of a pullapart basin. This basin was probably formed as a result of the movement of the Caribbean plate towards the east. The origin of the highpressure clasts is unknown, and is possibly linked to a tectonic mélange. The U-Pb ages of approximately 50 Ma and the presence of fragments from the Parashi Stock, suggest exhumation during the Eocene and Upper Oligocene, possibly linked to the formation of the basin.