Cenozoic Structural, Deformational, and Erosional Events Observed Along a 400-km Long, Onshore-to-Offshore Regional Transect Across Northwestern South America

Abstract

The complex Jurassic to recent tectonic evolution of northwestern South America (NSA) controlled the regional structure and formation of differing basin types. We integrate offshore and onshore 2D seismic profiles, gravity, and magnetic grids to identify the main Cenozoic deformational stages, associated structures and syn-tectonic basinal deposits. Two different provinces are crossed by a 400-km-long regional, onshore-to-offshore, structural transect: (1) The offshore South Caribbean deformed belt (SCDB) and (2) the onshore Cesar-Rancheria basin (CRB). The SCDB is a 100-km-wide, late Cenozoic, 5–18 km thick, sedimentary accretionary prism formed by subduction of the Caribbean plate beneath northern South America. Key relationships seen on the offshore part of the transect include: (1) onlapping stratal termination of an Oligocene-Miocene sequence above the subducting Caribbean plate that we interpret as a flexure produced by the initial subduction of the Caribbean plate; and (2) Plio-Pleistocene growth strata in piggyback basins overlying the prism interpreted as filled from the erosion of the uplifted Santa Marta massif (SMM), and from the deposition of the Magdalena submarine fan.

Key relationships seen on the onshore part of the transect crossing the SSM to the west and the Sierra de Perija to the east include two northwest-southeast shortening events: (1) An early-middle Eocene event that produced east-dipping Cretaceous and Paleocene strata beneath a major unconformity that increases in erosional hiatus from east to west. This shortening and overlying unconformity are interpreted as the result of collision of the Caribbean arc with South America. (2) A late Miocene–Pliocene event with major exhumation of the eastern CRB, where recent deposits are faulted as a result of the Late Miocene to Recent Panama arc collision. The most recent shortening event recorded in the CRB initiated the erosional event observed to the northwest in the filled, offshore piggyback basins. Faster Pliocene-Pleistocene deformation rates in the SCDB, may indicate accelerated convergence between Caribbean and South America and are possibly linked to the collision of the Panama arc.

AAPG Datapages/Search and Discovery Article #90219 © 2015 GCAGS, Houston, Texas, September 20-22, 2015