Evolution of the Magdalena Linked Delta-Submarine Fan in a Tectonically Active Setting, Offshore Colombia

Abstract

Abstract

The Magdalena deepwater slope fan exhibits a series of channel–levee complexes (CLCs), recording the evolution of the fan as well as the Magdalena delta. Reconstruction of the linked delta-submarine fan system was derived from detailed seafloor morphological analysis (based on multi-beam bathymetry and seismic profiles). The Magdalena deepwater fan was initiated during the late Miocene, reflecting the tectonic control on the slope processes from Pliocene to present. Major delta shifts toward the southwest (Canal del Dique) and northeast (Cienaga de Santa Marta region) created 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 with modern active sedimentation. 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 their corresponding submarine fan expression, which is characterized by the presence of CLCs and MTDs. CLCs show a big variation of sinuosity and gradient throughout the slope. High sinuosity values were encountered at areas of high gradients, suggesting increase in channel sinuosity as an attempt to reestablish its equilibrium profile.

Western fan, highly sinuous channels are associated with the fold-and-thrust belt deformation along the margin. Channel's forced migration, avulsions, convex-up profiles, and presence of knickpoints, suggest ongoing tectonic deformation during western CLC deposition. Conversely, the northeastern section of the fan exhibits channel 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 abandonment, increasing channel width and modifying levee walls. Upstream knickpoint 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 in 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.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016