JONES, PETER B., International Tectonic Consultants Ltd., Calgary, Alberta, Canada

ABSTRACT: Gravity Sliding, Thrusting, and Petroleum Traps in the Magdalena Basins and Cordillera Orientale, Colombia

Major gravity slides on flanks of mountain belts can be misinterpreted as tectonic thrusts. They occur as synclines ("fauteuils glissEs") striking sub-parallel to dip slopes of major uplifts, overlie low-angle listric thrusts which pass upslope into listric or bedding-parallel normal faults, and may be associated with gravity-driven buried thrust fronts.

The Nuevo Mondo syncline, underlain by the La Salinas thrust, and similar synclines along the east side of the Magdalena valley are interpreted as "fauteuils glissEs", whose occurrence at the edge of the Cordillera Orientale creates an illusion of westward thrusting. Minor faults, formerly interpreted as east-dipping reverse faults along the west edge of the Cordillera Orientale are too small to have uplifted the Cordillera or to be correlatable with the major thrusts beneath synclines. They are reinterpreted as major west-dipping lowangle normal faults which, along with major bedding-parallel faults, pass down-slope westward beneath the synclines and/or into blind imbricate thrust structures.

The Magdalena basins contain attractive east-verging tectonic thrust traps for hydrocarbons, and less attractive post-tectonic west-verging thrust traps formed by sliding down the east flank of the basin.

Interpretation of these structures as post-deformational features allows modeling of the Cordillera Orientale as an overthrust sheet about 10 km thick that moved over 160 km southeastward. Its ramp underlies the east flank of the Magdalena basins. Its buried thrust front marks the edge of the Llanos basin.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.