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Thick-Skinned Style and Timing of Convergent Tectonics in Northwestern South America and Implications for Petroleum Exploration

Sanchez, Carlos J.*1; Mann, Paul 1
(1) Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX.

Previous interpretations of surficial structures of northwestern South America are thin-skinned; infer a major thrust detachment at a depth of 8 km; and propose that most thrusting occurred as a single Late Miocene to recent pulse of uplift and shortening accompanying the so-called Andean orogeny. In this study we use subsurface data including 3500 km of seismic reflection data tied to 16 wells from a 11,800 km2 area covering the Cesar and Rancheria basins of northern Colombia to construct three, 40 to 90-km-long structural transects. Observations include: 1) dip and amount of displacement of major thrust faults observed on seismic reflection lines; 2) timing of major thrust-related events as inferred from syn-thrusting sedimentary wedges and angular unconformities. Our results show: 1) measured dips on major thrust faults varies from 30 to 45° indicative of a thick-skinned structural style likely related to inversion of preexisting normal faults; displacements vary from 1 to 7 km with northwestward transport; 2) wedging and unconformities show three major periods of shortening that include: a) a Paleocene-early Eocene event that produced eastward-dipping Cretaceous and Paleocene strata beneath a major angular unconformity that increases its erosional hiatus in a westward direction; b) an Oligocene-early Miocene event accompanying the topographic uplift and erosion of the Sierra Perija; and c) a Pliocene-Pleistocene event marked by wedging in the Cesar-Rancheria basin; 3) the style of faulting is mainly thrusting although a component of strike-slip motion is indicated by the linearity of fault traces especially in the Sierra de Perija. Three regional transects are balanced using 2D Move and show shortening amounts ranging from 10-15 km. We propose that the initial Paleocene shortening phase is related to accretion of the Great Arc of the Caribbean; the Oligocene phase is a fault inversion driven by shallow subduction of the Caribbean plate; the Plio-Pleistocene phase is related to collision of the Panama arc. Structural traps for hydrocarbons are formed during all three shortening events and all structures are underlain by excellent Late Cretaceous source rocks of La Luna type. The presence of Paleocene coals now exposed at the surface indicates a complex interplay of subsidence and uplift that accompanied the three convergent phases.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California