TECTONOSTRATIGRAPHIC STUDY OF THE SOUTH SINU PLATFORM, URABA GULF, COLOMBIA

The Uraba Gulf displays a tectonic setting that combines features of an extinct subduction zone at the foothills of the Western Cordillera of Colombia and the geology of the Caribbean. This region is thus a mandatory reference for comparing tectonic styles between the Colombian West and the South Caribbean margin, and is of paramount interest in understanding the accretion of the Panama arc to the South American plate. The evidences of active tectonics are registered in sedimentary Neogene rocks (Miocene-Pliocene), which are folded and border the continental margin and belong to the Atrato river lower basin, a typical progradant deltaic system with proximal facies separated by unconformities. As consequence of Caribbean-South America collision the basin evolved in an elliptical fold system which show 2 main trends (N-S) and (N20E). A tectono-stratigraphic reconstruction based on recent interpretation of regional seismic lines across the Sinú belt suggests that its elliptical (or doubly plunging) synclines represent sites of enhanced subsidence, as deduced by growth strata identified within the Oligocene-Miocene siliciclastic sequences. Mud volcanoes occur 1) as individual edifices along synclinal axes, or 2), as diffuse manifestations along marginal faults that limit elliptical synclines. Fragments of hydrothermal breccia within major edifices attest to an explosive activity. The overlapping of folds evidences a regional field stress rotation which syn-sedimentary evolution is registered on the angular unconformities of Middle- Miocene and Pliocene –Upper Miocene, the interpretation of these relationships allows to define a current margin with younger syncline structures perpendicular to Caribbean-South America convergence establishing that here is a link between the growth of volcanic edifices and the subsidence of small-scaled basins that prefigured the formation of elliptical synclines.