Chronostratigraphy and tectonic deformation of the North Ecuadorian-South Colombian offshore Manglares forearc basin

Forearc basins in convergent margins contain a nearly continuous record of sedimentation and deformation. Their chronostratigraphy reflects the manner in which the basin accommodates loads and vertical and horizontal motion caused by eustasy, tectonics and sedimentation during plate convergence. Along the North Ecuador and South Colombia (NESC) Margin (1 degrees-3.5 degrees N), thick Cenozoic sedimentary sequences accumulated over blocks of oceanic basement that accreted between the Late Cretaceous and Early Cenozoic, thus forming the onshore Borbon and Tumaco Basins and the offshore Pacific Frontal Basin. Based on morphology and seismic data analysis, the NESC forearc basin. named Manglares Basin, consists of five acoustic units of sedimentary nature (Units A-E) separated by unconformities (U1-U5), resting over the interpreted oceanic basement (Unit F). By integrating these data with regionally-compiled chronostratigraphic charts of the onshore Borbon and Tumaco Basins and the geology of Gorgona Island, we propose a model for the tectonic and stratigraphic evolution for the Manglares Basin and its oceanic basement. This model shows that (1) unconformity U5 between units F and E marks a tectonic phase that may correlate with the accretion of the oceanic basement of the Manglares Basin to the Northern Andes, possibly between the Late Cretaceous and Paleocene. (2) A marked change in seismic facies between Units E and D, associated with major tectonic unconformity U4 is compatible with the Incaic compressive phase that affected the Andes during the Late Eocene-Early Oligocene. (3) This tectonic phase likely peaked during the Latest Oligocene-Earliest Miocene (U3) and later during the Middle Miocene (U2). (4) The regional Middle Miocene erosion period (U2) marked a change in the tectono-sedimentary evolution of the forearc basin. Compressive deformation ceased in the southern margin segment, which underwent long-term basin subsidence, while compression and uplift increased in the central and northern segments. (C) 2008 Elsevier B.V. All rights reserved.