SEDIMENTARY RECORD OF THE CRETACEOUS–PALEOCENE ARC–CONTINENT COLLISION IN THE NORTHWESTERN COLOMBIAN ANDES: INSIGHTS FROM STRATIGRAPHIC AND PROVENANCE CONSTRAINTS

Abstract The collision of intra-oceanic arcs with continental margins is a primary factor controlling the evolution, modification, and growth of continental crust. Syn- to post-collisional basins are formed on both the oceanic and continental sides of an accretionary orogen as a consequence of tectonic activity, which preserve the associated erosional and exhumation record of the colliding element. During the late Cretaceous–Paleogene, the evolution of the northern Colombian Andes was shaped by an oceanic arc-continent collision as a result of the interaction between the Caribbean and South American plates. The timing and stratigraphic record of the collision have mostly been reconstructed from foreland and hinterland basins. In this contribution, we present the results of an integrated stratigraphic, paleontological, and provenance study of Upper Cretaceous sedimentary sequences accumulated on the oceanic side, to the west of the collisional event. Our results suggest that clastic rocks mainly accumulated in short depositional systems in deep marine settings. Two stratigraphic units can be distinguished: A volcanoclastic unit, composed of dark gray siliceous mudrocks interlayed with thick to medium volcanic-rich sandstone layers, accumulated in a slope? and submarine fan. A siliciclastic unit (Urrao Member) composed of dark gray mudrocks, and thin to thick, fine- to medium-grained feldspathic litharenites and lithic arkoses accumulated in the lobes and splays of submarine fans. Polymictic conglomerates and sandstones associated with submarine channels and levees are less common and can be used as stratigraphic markers. The Urrao Member was mostly sourced from igneous, sedimentary, and metamorphic Cretaceous and older rocks forming the continental paleo-margin that was being rapidly exhumed as suggested in previous works. Zircon crystal morphology and depositional ages suggest volcanism simultaneous with sedimentation. The maximum depositional U-Pb ages of zircons and poorly preserved macro- and microfossils (mollusks and calcareous microfossils) suggest a Coniacian and Campanian–Maastrichtian age for the volcanoclastic and siliciclastic units, respectively; nevertheless, regional paleontological and geochronological data indicate that marine siliciclastic sedimentation continued into the Paleocene. These new data suggest that the late Cretaceous–Paleocene interaction of the Caribbean and South American plates did not trigger considerable and long-lasting uplift/erosion of the colliding oceanic domain and that magmatism was active during collision.