SEDIMENTARY AND STRUCTURAL RESPONSE OF RIGHT-LATERAL TRANSPRESSION ASSOCIATED WITH OBLIQUE CONVERGENCE ALONG CARIBBEAN-SOUTH AMERICAN PLATE MARGIN, NORTHERN COLOMBIA

The objective of this study is to assess structural styles and kinematic evolution in the Cesar-Rancheria basin (CRB), located on the northwestern South America. Integrated methods include: 1) subsurface mapping of key horizons using 2D seismic tied to well data, 2) surface geologic mapping and remote sensing analyses, 3) interpretations of crustal structure from gravity modeling, 4) construction of serial structural cross sections, which are balanced to the Upper Mesozoic, 5) interpretation of recent surficial deformation from analysis of stream channel morphologies. Growth strata and unconformities show three major periods of NW-SE crustal shortening: 1) an Upper Cretaceous-early Eocene event that produced east-dipping Cretaceous and Paleocene strata beneath a major unconformity that increases in erosional hiatus from east to west and is interpreted as initial accretion of the Great Arc of the Caribbean; 2) an Oligocene-early Miocene event accompanying inversion, topographic uplift, and erosion of the eastern edge of the basin (Sierra de Perija); we interpret this as shallow subduction of the Caribbean plate following Great Arc collision; and 3) a Pliocene-Pleistocene event marked by out of sequence faulting of the recent deposits of the CRB possibly driven by far-field collision of the Panama arc. Structural cross section balancing indicate shortening amounts ranging from ~10 km in the north where the CRB is most narrow to ~20 km in the south where the basin is widest. The locus of the Cenozoic deformation moved eastward through time as shown by the migration in the same direction of Upper Cretaceous to early Eocene depocenters, as well as the westward migration of the Miocene depocenters induced by the Sierra de Perija uplift. Evidence of transpressive component and some degree of strain partitioning related to the vicinity of an oblique convergent plate margin are: 1) More than one trend of faults and a possible right-stepping en-echelon relay arrangement among different fault segments, 2) the CRB being limited by two significant transcurrent systems with opposite sense of motion, 3) linearity of some active fault traces indicating a component of strike-slip motion.