Abstract: Variations in Structural Style and Kinematics of the Medina Block of Colombia
Roberto Linares, Mark Rowan, Tomas Villamil
The Medina area is located in the Llanos foothills of the Eastern Cordillera, 100 km southwest of the giant Cusiana discovery. We illustrate a variety of fault/fold styles using both a regional, balanced cross section that traverses the entire Cordillera and a detailed, three-dimensional interpretation of the Medina block derived from surface, seismic, and well data. The Eastern Cordillera represents a Triassic/Jurassic rift that evolved into a passive margin and that was subsequently inverted during Tertiary compression. Reactivation of the old basement rift blocks resulted in both thick- and thin-skinned structures that are interpreted as part of the same tectonic event, rather than as separate phases.
Paleozoic basement exposed in the hanging wall of the Tesalia Fault, west of the Medina block, represents the footwall of the west-dipping Mesozoic normal fault reactivated during shortening. The Tesalia Fault is a footwall shortcut that branched off from the normal fault at depth. In the hanging wall of the old normal fault, the structural style is dominated by detachment folds within Cretaceous, shale-rich strata; folding may have been caused by buttressing against the basement footwall to the East.
The Medina block itself, located to the East in the footwall of the Tesalia Fault, is characterized by a different structural style. The Medina anticline is a large, fault-bend fold flanked on both sides by broad synclines. The western syncline forms the eastern flank of a duplex in the footwall of the Tesalia Fault. These thin-skinned geometries are attributed to the higher proportion of sandstone in this area, located between the old basement footwall and the craton to the East.
AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela