RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute.
CO - CODEN: IGABBY
AN - ACCESSION NUMBER: 1991-044786
UD - UPDATE CODE: 1991
Registro 3975 de 5614 - GeoRef Disc 3: 1985-1992
BK - BOOK TITLE: Structural geology of the Ortega region, upper Magdalena Valley, Colombia.
BA - BOOK AUTHORS: Allen-George-D
CP - COUNTRY OF PUBLICATION: United-States
PY - PUBLICATION YEAR: 1989
DG - DEGREE GRANTED: Master's
DI - DEGREE GRANTING INSTITUTION: Baylor University. Waco, TX, United States.
LA - LANGUAGE: English
AB - ABSTRACT: Convergent plate motion of the South American, Nazca, and Caribbean plates coincides with northwest southeast compressional stress in the three Cordilleran ranges of the Colombian Andes. Foreland and overthrust style fold-thrust belts characterize the Upper Magdalena Valley, and the Ortega region within the Andes. Convergent dip-slip transport on basement-cored, first-order fold-thrusts coincides with detachment folding. Structure at the Ortega Field consists of convergent, third-order fold-thrusts, with internal decollement. Tight flexural-slip folds imbricate and tectonically thicken upward on the west-verging Ortega Anticline. The buried, east-vergent Salado Anticline acts as a buttress to westward propagation at Ortega, but retreats along strike to allow the Porvenir Anticline to develop a low, broad, fault-bend fold geometry. To the south, the Sortija-La Calera Fold Belt converges with the Cucuana Fold-Thrust. Compressive stress is distributed within the Sortija-La Calera structure as cross-crestal folding and thrusting (Sortija Anticline), and as opposite-verging backthrusting and folding (Tetuan Anticline). To the west, the basement-cored Vergel and Calarma fold-thrusts converge and coincide with tight, steep to overturned folding in the Chiquinima Syncline. Five orders of fold-thrusts, from regional basement-involved to small-scale anticlines, have evolved from Oligocene to Pliocene time in the Ortega region. The Ortega, Porvenir, and Sortija-La Calera structures are considered third-order structures. Third-order structures shorten the entire Cretaceous sequence, and may detach within the Jurassic-Triassic Payande Group. Typically preserved in the footwall of basement-cored, second-order fold-thrusts like the Cucuana Fold-Thrust, the third-order structures are significant as oil and gas traps. East-verging fold-thrusts, accommodating crustal shortening focused in the Central Cordillera, occurred during Eocene to Oligocene time. From late Oligocene to Pliocene time, east-verging first-order fold-thrusts propagated farther and farther east of the Ortega region. As the eastward tectonic transport continued, east-dipping second-order backthrusts propagated west across the Ortega region. The latest phase of deformation thus proceeded east to west within the Ortega region. In cross-section, all orders of structure exhibit components of fault-bend and flexural-slip fold geometry. Fault-bend and flexural-slip geometry coincides with bedding-parallel anisotropy.