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Book Chapter

Evolution of the Magdalena Deepwater Fan in a Tectonically Active Setting, Offshore Colombia

By
Gloria A. Romero-Otero
Gloria A. Romero-Otero
Murphy Exploration and Production Corporation, 9805 Katy Fwy., Houston, Texas 77024, U.S.A. (e-mail: gloria_romero@murphyoilcorp.com)
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Roger M. Slatt
Roger M. Slatt
The University of Oklahoma, Conoco-Phillips School of Geology and Geophysics, 100 East Boyd, St. Suite 810, Norman, Oklahoma 73072, U.S.A. (e-mail: rslatt@ou.edu)
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Carlos Pirmez
Carlos Pirmez
Shell Petroleum Development Company of Nigeria Ltd., Plot 461, Constitution Avenue, Central Business District, Abuja, Nigeria (e-mail: carlos.pirmez@shell.com)
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Published:
January 01, 2015

Abstract

The slope morphologies of the Magdalena deepwater fan exhibit a series of channel-levee complexes (CLCs), recording the evolution of the Magdalena delta. Detailed morphological analysis of the seafloor expression of the channels and their lateral relationship allows the reconstruction of the history of Pleistocene fan development. The Magdalena deepwater fan was deposited on the northern offshore Colombia accretionary wedge (Caribbean Sea), initiated during the late Miocene. Fan evolution is closely related to the Magdalena River delta migration and reflects control by tectonic processes occurring from Pliocene to present. Major delta shifts toward the southwest (Canal del Dique) and northeast (Cienaga de Santa Marta region) create a submarine fan that migrated with the river, becoming younger toward the southwest. The main fan was abandoned during the Holocene, focusing deposition on the Barranquilla region to the northeast with modern active sedimentation. The depositional processes in the active fan area are mainly dominated by turbidity currents, alternating with slumps/debris flows that generated large mass transport deposits (MTDs). Eight river delta phases were identified, linked to the onshore geology and their corresponded submarine fan expression, which is characterized by the presence of CLCs and MTDs. Seven CLCs were studied using multi-beam bathymetry and seismic profiles. The CLCs showed a big variation of sinuosity and gradient throughout the slope. The higher sinuosity values were encountered at areas of high gradients, suggesting that the channels attempt to reestablish its equilibrium profile by increasing sinuosity as a response of changes in the slope.

Highly sinuous channels in the western fan suggest that sinuosity changes are controlled by changes on the slope associated with the deformation of the fold-and-thrust belt along the margin. In addition, channel’s forced migration, avulsions, convex-up profiles, and the presence of knickpoints (KPs) suggest ongoing deformation during western CLC deposition. Conversely, the northeastern section of the fan exhibits channel thalweg profiles with lower sinuosity values at deeper depths. Convex-up thalweg profiles in this area may represent disequilibrium profiles or post-abandonment deformation. Older CLCs are highly affected by degradational processes after the abandonment of the systems, increasing channel width and modifying levee walls. These processes should be considered when evaluating dimensions of buried deposits and reservoir quality prediction.

A sequence of KPs in the western fan seems to connect sediment flows from the shelf break downslope through a series of steps in the slope, culminating with lobate unconfined deposits. Upstream KP migration in slope steps as a response to deformation may represent a key process to explain the initiation of deepwater channel systems on the Magdalena Fan, as well as channel systems deposited on other tectonically active basins.

This study provides new understanding of the processes involved in the Magdalena deepwater fan and implications for channel systems characterization in areas with active deformation during deposition.

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Contents

AAPG Memoir

Petroleum Geology and Potential of the Colombian Caribbean Margin

Claudio Bartolini
Claudio Bartolini
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Paul Mann
Paul Mann
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American Association of Petroleum Geologists
Volume
108
ISBN electronic:
9781629812724
Publication date:
January 01, 2015

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