Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Shortening Gradients and Structural Styles in the Eastern Cordillera of Colombia. Implications for the Petroleum Systems of the Cordillera and Adjacent Foothills
(1) Ecopetrol-ICP, Piedecuesta, Colombia.
(2) VEX, Ecopetrol, Bogotá, Colombia.
(3) Namson Consulting Inc., San Clemente, CA.
(4) Geologia, Universidad Nacional de Colombia, Bogotá, Colombia.
(5) Geologia, Universitat Autònoma de Barcelona, Bellaterra, Spain.
(6) Geology and Geophysics, Utah University, Salt Lake City, UT.
During the 1990s, in the Northern Andes the most popular shortening estimates for the Colombian Eastern Cordillera and adjacent foothills ranged from more than 100 km to ca. 200 km (Dengo & Covey, 1993; Roeder and Chamberlain, 1995). In those cases most of the values came from the assumption of a ubiquitous presence of fault-related folds with ramp-flat geometries and long flat segments at multiple scales. In this work we present 5 new structural cross sections of the Eastern Cordillera with much more conservative values, a minimum of 55 km and a maximum of 80 km, depicting a shortening gradient from S to N. We build these sections based on a more than 15 years of extensive seismic interpretation experience of the authors in the Eastern Cordillera and other analogues (Teixell et al., 2003; Teson and Teixel., 2006), a wealth of subsurface data, microtectonic field work and mapping (e.g., Julivert, 1970; Kammer, 1996; Mora et al., 2006; Mora et al., 2010) as well as an analysis of rock mechanics in relationship to structural styles (e.g., Nemcok et al., 2005). We find that these various lines of evidence make unlikely the ubiquitous presence of fault-related folds. Direct observation shows that these are restricted to the foothill areas, and well data shows much lower shortening than previously thought for these kinds of structures. In contrast, the internal parts of the orogen appear to be dominated by either detachment folds or well-documented basement-involved buckling. Fragile deformation appears to be concentrated via footwall shortcuts or inversion faults. In addition, an evident shortening gradient is documented from south to north. A higher degree of overthrusting and alloctonous hangingwall blocks appear to condition a confined petroleum system to the north, whereas less shortening by faulting and more authoctonous folded blocks appear to favor water recharge and eventually make easier oil leakage in presence of active kitchens in the southern areas. This pattern coincides with the low rate of discoveries in the southern Magdalena and Llanos foothills versus the behavior of both foothills to the north.