Structure Of The Offshore Sinu Accretionary Wedge. Northern Colombia

The Sinu Accretionary Wedge is located along the northern Colombia Caribbean margin an is partially exposed onshore (Lower Magdalena valley and San Jacinto mountains) and offshore extending from Uraba to the offshore Santa Marta area and joints the northern accretionary wedge of Venezuela in the north. The Offshore and younger part of the prism is much wider and develope than the inner " starved " onshore part. The Proto-Magdalena, Plato and other sedimentary systems contributed to a high sediment supply triggered by the surrection of the Central and Eastern Andean Cordillera since Upper Miocene time, when the offshore part of the prism developed. The offshore Sinu accretionary wedge illustrates the effect of strong lateral (i. e. along strike) variations of syn-tectonic sediments on the structural style of the prism. The thickness of syn-sedimentary strata is huge along the Proto-Magdalena delta (Offshore Cartagena area) which results in a blanketing effect of the deformation (i. e. false image of non-deformed strata). Along strike variations of sediment supply induce lateral changes of the critical taper angle. To re-equilibrate and reach a more stable profile (lower than the critical angle) the wedge collapses through normal faulting and toe-thrusting (i. e. thrusts that accommodate rear extension). Gravitationally induced toe-thrusts are superimposed to pre-existing thrust imbricates related to compression. This complex structure becomes more complicated by the presence of a ductile level of overpressure Oligocene shale that rise as shale ridges. Listric normal faults, toe-thrusts and shale ridges control fore-arc basins like the San Bernardo basin (SW from Cartagena). The present day structure of the offshore Sinu accretionary wedge is the result of NW-vergent compressional imbricates related to the B-subduction process overprinted by extensional and compressional gravitational structures.