Romero-Otero, Gloria, Roger Slatt, and Carlos Pirmez, 2015, Evolution of the Magdalena Deepwater Fan in a Tectonically Active Setting, Offshore Colombia, in C. Bartolini and P. Mann, eds., Petroleum geology and potential of the 24 Colombian Caribbean Margin: AAPG Memoir 108, p. 675–708. Evolution of the Magdalena Deepwater Fan in a Tectonically Active Setting, Offshore Colombia Gloria A. Romero-Otero Murphy Exploration and Production Corporation, 9805 Katy Fwy., Houston, Texas 77024, U.S.A. (e-mail: [email protected]) 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: [email protected]) Carlos Pirmez Shell Petroleum Development Company of Nigeria Ltd., Plot 461, Constitution Avenue, Central Business District, Abuja, Nigeria (e-mail: [email protected]) 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 morphologi- cal 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 encoun- tered at areas of high gradients, suggesting that the channels attempt to reestablish its equilib- rium profile by increasing sinuosity as a response of changes in the slope. Copyright ©2015 by The American Association of Petroleum Geologists. DOI:10.1306/13531953M1083656 675 13880_ch24_ptg01_675-708.indd 675 10/27/15 10:54 AM 676 ROMERO-OTERO ET AL 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 dis- equilibrium 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. INTRODUCTION and interpretation of its history. Seismic reflection data and detailed bathymetric coverage reveal the tempo- The Magdalena submarine fan is the main physi- ral and spatial evolution of the fan by examining the ographic feature comprising the present-day bathym- stratigraphic relationships between the various CLSs. etry of the modern seafloor morphology of offshore Based on the previous observations, the aims of this northwestern Colombia. It is one of the few deep-sea chapter are the following: fans with turbidity current activity today (Heezen, 1956; Munoz, 1966). The fan consists of a series of 1. To understand the evolution of the system from submarine channel–levee complexes (CLCs) and source to sink, by relating the evolution of the sub- mass transport deposits (MTDs), mainly formed marine fan to the Magdalena River drainage sys- by transport and deposition of sediments from the tem onshore, as outlined in previous studies. This Magdalena River, the main drainage system in Colom- approach allows for constraining the models for bia (Figure 1). The fan extends about 68,000 km2, with sedimentation–tectonic interactions and for plac- a volume of 180,000 km3 and extends to over 4000 m ing constraints on the timing of fan evolution. (13,123.3 ft) of water depth (Kolla and Buffler, 1984a, 2. To link the spatial and temporal evolution of the b; Wetzel, 1993; Reading and Richards, 1994). The sedimentary system to the patterns of tectonic de- Magdalena submarine fan forms a significant part of formation of the margin, including an analysis of the accretionary wedge complex formed by the col- the morphology of the various submarine CLSs, lision of the Caribbean and South American plates characterizing the thalweg profiles and variations (Duque-Caro, 1979; Breen, 1989). in sinuosity and gradient. Previous studies on the morphology and stratigra- 3. To study the effect of active deformation dur- phy of the Magdalena Fan (Kolla and Buffler, 1984a, b; ing the establishment of the channel systems and Ercilla et al., 2002a; Estrada et al., 2005a) showed that, post-abandonment, by characterizing the thalweg despite its active margin setting, the fan had features profiles, sinuosity, and slope changes. Most stud- that resemble the large fan systems encountered off ies of submarine fans are from passive margin set- major rivers on passive margins, such as sinuous tings. The Magdalena Fan is deposited in an active channel–levee systems (CLSs) and large MTDs. Previ- margin and reveals active deformation during the ous works by Hoover and Bebout (1985) and later by deposition of the channel systems, providing an Pirmez et al. (1990) addressed the link between migra- opportunity to study possible differences between tion of the Magdalena River course, regional tectonics, active and passive margin systems. and the deepwater fan deposits. 4. To discuss degradational processes to which the In this chapter we present new bathymetric and channels have been exposed after abandonment seismic data that complement previous studies and and the role of slope deformation on channel– allow for a more complete understanding of the fan levee morphology and knickpoint (KP) formation. 13880_ch24_ptg01_675-708.indd 676 10/27/15 10:54 AM Evolution of the Magdalena Deepwater Fan in a Tectonically Active Setting, Offshore Colombia 677 Figure 1. Bathymetry map of the Magdalena Fan, southern Caribbean Sea. Location of the channel– levee complexes (CLCs) and active fan. Canyons: U (unamed), S (Sabanilla), M (Magdalena), D (delta front gullies), SB (shelf break). Regional cross sections X–X' and Y–Y' are shown in Figure 6, and locations are shown in Figures 9B, 10B, 12A, 17A, and 19A. Multi-beam bathymetry—slope of the bathymetry. Cities of Cartagena, Luruaco, and Barranquilla are shown as a reference. Thalweg sections for these channels are depicted in Figure 7. 5 km (3.1 mi) GEOLogicaL SETTING offset in these two fault systems occurred during the last 10 Ma and is linked to the most important uplift The Magdalena submarine fan is an arcuate bathym- of the massif. The San Jacinto fold belt represents the etric feature, part of the accretionary wedge formed onshore portion of the accretionary complex com- by the subduction zone of the Caribbean–South posed of late Cretaceous to Pliocene sedimentary American plates (Duque-Caro, 1979; Kolla and Buffler, rocks. Deformation began during the early Paleogene 1984b; Breen, 1989). The Caribbean plate subducts and was reactivated during the late Miocene– Pliocene toward the east-southeast, at a low angle beneath the Andean compression (Ruiz et al., 2000). The Sinu South American plate and at a rate of 20 ± 2 mm/yr fold belt lies west of the San Jacinto fold belt and is (Trenkamp et al., 2002; Corredor, 2003). separated by the Sinu lineament (Duque-Caro, 1979) Sediment deposition along the Caribbean Mar- (Figure 2). Composed of Oligocene to Holocene sedi- gin of Colombia, and in the Magdalena Fan, began ments, the Sinu fold belt extends to the offshore area during late Cenozoic time (Kolla and Buffler, 1984b) represented by a series of imbricate structures, which (Figure 2). In the middle of the margin, the Magdalena become progressively younger toward the toe of the Fan forms a bathymetric bulge, separating