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RESSETAR, R., R. B. ALLEN, and C. A. ALFONSO, Earth Sciences and Resources Institute, University of South Carolina, Columbia; SC, L. SARMIENTO, Instituto Colombiano de Petroleos, Bucaramanga, Colombia; and C. RAMIREZ and F. LAVERDE, Hocol-Shell, Boca Grande, Cartagena, Colombia

ABSTRACT: Paleogene Depositional Patterns in the Magdalena Valley and Cordillera Oriental: Implications for Deformational Phases

The Paleogene rocks of the Magdalena Valley and the Cordillera Oriental of Colombia represent the synorogenic sedimentary fill of the ancestral Andean foreland basin. Although detailed correlation of the Paleogene is hampered by poor biostratigraphic control, recent field studies document variations between the Upper and Middle Magdalena Valleys in vertical facies succession and paleocurrent direction, suggesting independent depositional systems separated by the Girardot fold belt.

In the northern Upper Magdalena Valley, the Paleogene Gualanday Group lies unconformably to paraconformably on marine Upper Cretaceous and Paleocene rocks. Lower and upper conglomeratic units in the Gualanday Group grade eastward into finer grained fluvial sandstones in the western Cordillera Oriental. North of the Girardot belt, conglomerates occur only in the lower part of the Paleogene and grade northeastward into fluvial sandstones. These unconformably overlie rocks as old as Neocomian in a series of en echelon structures on the west flank of the Cordillera Oriental.

The structural trends and thickness of the Cretaceous here suggest inversion of the marine depocenter prior to Paleogene deposition. Previous reports of early Paleogene uplift of the Quetame Massif south of Bogota indicate that similar processes acted elsewhere in the Cordillera Oriental. These studies show that the Cordillera Oriental underwent at least one phase of uplift prior to the main inversion in the Neogene.

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