Cariaco

Ecuador Offshore

On this hypothetical geological cross-section of the between the Nazca plate and the Amotape Mountains, crossing the Talara geographic basin (see next Canvas autotrace), which, in the Bally's sedimentary basins classification, corresponds to a forearc basins, i.e., to perisutural basins developed at the periphery of the Meso-Cenozoic megasuture, in association with a B-type (Benioff) and external to the volcanic arc. The Nazca oceanic plate plunges under the South America continental plate forming a Benioff subduction zones (B-type subduction) creating, in the overriding lithospheric plate, a forearc basin (the volcanic arc that is not visible on this cross-section is located tens of kilometers eastward) with its accretionary prism. Along this convergent margin there is, generally, a double Paleogene forearc basins (e.g. Manglare and Tumaco geographic basins) elongated parallel to the Nazca trench, being the inner mainly located in conventional offshore or in onshore). Following A. Noda and A. Myakaway (2017), the deformation of this accretionary forearc matches with the forearc basins single-wedge model, since the sediments are less shortened but they are tilted landward, for the reason that the outer arc highs move seaward with displacements of the thrusts faults in the accretionary wedges. In fact, the basin width is extended by this seaward movement of the outer-arc high, as well as, due to the landward migration of the depocenter. The subsidence of the forearc basin is, mainly, isostatic due to thickened wedge or due to a possible tectonic erosion beneath the basin at the level of the decollement surface.

On this Canvas autotrace of a seismic lines of the Ecuador offshore, located along the hypothetical geological cross-section (see previous plate), the asymmetrical vergence of the faults is, clearly, recognized, which allow to classify this forearc basin as single-wedge type (A. Noda and A. Myakaway (2017). The depocenter depicted on this tentative geological interpretation correspond to the outer Paleogene forearc basin of the Talara geographic basin.