ALLEN, R. B., C. A. ALFONSO, R. RESSETAR, and A. SALAZAR, Earth Sciences and Resources Institute, University of South Carolina, Columbia, SC, I. BALLESTEROS, E. CARDOZO, F. LAVERDE, and C. RAMIREZ, Hocol-Shell, Boca Grande, Cartagena, Colombia, J. M. MORENO, Universidad Nacional de Colombia, Bogota, Colombia, J. RUBIANO and L. SARMIENTO, Instituto Colombiano de Petroleos, Bucaramanga, Colombia.

ABSTRACT: The Cretaceous Stratigraphy of the Western Cordillera Oriental, Colombia

During 1987 and 1988, a major field project sponsored by Tenneco was undertaken along the west flank of the Cordillera Oriental of Colombia between Alpujarra (between the Neiva and Girardot Sub-Basins) and the Middle Magdalena Basin (Cimitarra area). An important result of this study was the documentation of pronounced regional variation in the age, thickness, and facies of the Cretaceous section.

The maximum thickness estimated was 7 km for the Bogota-Villeta section, with ages as old as Berriasian. This section can be divided into 4 or 5 depositional sequences.

A clastic source to the west or southwest is indicated for the lower sequence 1 (and 2?), an eastern source dominated sequences 3 and 4, and eastern and western sources supplied the upper sequence. Toward the north, the section thins to an estimated 3-5 km but still ranges in age throughout the Cretaceous. Southward, on the other hand, the Cretaceous thins to about 2 km and is restricted to Aptian-Albian and younger ages.

The variations in ages, facies, and thickness are consistent with recent models of the evolution of the Cretaceous basin. During the Neocomian, the Bogota area formed the main depocenter of the basin and was characterized by restricted facies and turbidites, suggesting steep, possibly faulted basin margins. Facies to the north, near the Middle Magdalena Basin, indicate shallower water, possibly a platform. By the end of the Early Cretaceous, expansion of the marine basin out of the central Cordillera Oriental and regionally more constant facies indicate the onset of dominantly thermal subsidence. The end of the Cretaceous was marked by regression and asymmetric clastic input from east and west of the basin.

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