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ABSTRACT: Gloria Mosaic of the Magdalena Deep-Sea Fan, Northern Colombian Convergent Margin

C. Pirmez, N. A. Breen, R. D. Flood, S. O'Connell, R. D. Jacobi, J. W. Ladd, G. Westbrook, J. V. Franco, M. Garzon, F. A. Arias-Isaza

We imaged the Magdalena deep-sea fan and adjacent fold belt on the northern Colombian continental margin using GLORIA long-range side-scan sonar, water gun and air gun single-channel seismic reflection, and 3.5 kHz profiling. East and west away from the fan, the deformed belt comprises a series of folds and thrusts that die out toward the fan. Folds seaward of the deformed wedge are buried by flat fan sediments. However, we also observed deformation of recently deposited sediments. Folding within the coastal region of Colombia is part of the convergent margin deformation and might lead to drainage redirection on land and, subsequently, on the fan. These observations indicate a complex spatial and temporal interaction between sedimentation and deformation.

The deep-sea fan shows a series of meandering channel-levee systems and large-scale mass-flow deposits. Older channel systems to the west are presently disconnected from major river systems and appear to be related to older courses of the Magdalena River. These older channels, in part, are buried by mass flows. The river was redirected to the east during the late Pleistocene. Offshore the present river mouth, large-scale mass flow deposits are associated with canyons where cable breaks have been recorded.

Bottom-simulating reflectors (gas hydrates?) are observed throughout the deformed belt and on the upper fan. Mud volcanoes and diapirs are recognized mostly in the actively deforming region east of the fan.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990