Rapid Adjustment of Submarine Channel Architecture To Changes In Sediment Supply

Abstract

Changes in sediment supply and caliber during the last ~130 ka have resulted in a complex architectural evolution of the Y channel system on the western Niger Delta slope. This evolution consists of four phases, each with documented or inferred changes in sediment supply. Phase 1 flows created wide (1,000 m), low-sinuosity (1.1) channel forms with lateral migration and little to no aggradation. During Phase 2, the Y channel system began to aggrade, creating more narrow (300 m) and sinuous (1.4) channel forms with many meander cutoffs. This system was abandoned at ~ 130 ka, perhaps related to rapid relative sea-level rise during MIS (Marine Isotope Stage) 5. Phase 3 flows were mud-rich and deposited sediment on the outer bends of the channel form, resulting in the narrowing (to 250 m), straightening (to a sinuosity of 1.22), and aggradation of the Y channel system. Renewed influx of sand into the Y channel system occurred with Phase 4 at ~ 50 ka, during MIS 3 sea-level fall. The onset of Phase 4 is marked by the initiation of the Y′ tributary channel, which re-established sand deposition in the Y channel system. Flows entering the Y channel from the Y′ channel were underfit, resulting in inner levee deposition that is most prevalent on outer banks, acting to further straighten (1.21) and narrow (to 200 m wide) the Y channel. The inner levees accumulated quickly as the flows sought equilibrium, with deposition rates > 200 cm/ky. Marked by the presence of the last sand bed, abandonment occurred at ~19 ka in the Y channel and ~15 ka in the Y′ channel and is likely related to progressive abandonment due to shelf-edge delta avulsion and/or progressive sea level rise associated with Melt Water Pulse 1-A. The muddy, 5-meter-thick Holocene layer has thickness variations that mimic those seen in the sandy part of Phase 4, suggesting that dilute, muddy flows continue to affect the modern Y channel system. This unique dataset allows us to unequivocally link changes in submarine channel architecture to variations in sediment supply and caliber. Changes in the updip sediment routing system (i.e. the channel "plumbing") are shown to have profound implications for submarine channel architecture and reservoir connectivity.

Facies architecture of submarine channel deposits on the western Niger Delta slope: Implications for grain‐size and density stratification in turbidity currents

“…Modern submarine channels are another valuable data source for interpreting density stratification because of the preserved geomorphology and the opportunity to sample recent stratigraphy. Sediment coring in modern submarine channels indicates that grain size and bed thickness decrease markedly with increasing height above the thalweg [ Hiscott et al ., ; Pirmez and Imran , ; Dennielou et al ., ; Babonneau et al ., ; Paull et al ., ; Kolla et al ., ; Migeon et al ., ; Jobe et al ., ]. Some studies have linked these trends in bed thickness [ Dennielou et al ., ] and grain size [ Migeon et al ., ] to turbidity current flow properties, including concentration and velocity profiles.…”

Integrating outcrop and subsurface data to assess the temporal evolution of a submarine channel–levee system

“…Notwithstanding this resolution difference, and mindful of the well-developed hierarchy in deepwater systems, such map view images provide a useful constraint on the geometries interpreted within C2. Figure 14 shows a horizon slice and cross section through Cenozoic slope deposits, offshore West Africa (Abreu et al, 2003;Armitage et al, 2012;Janocko et al, 2013;Jobe et al, 2015). The horizontal distance scales well with the distance across the Baviaans syncline, and the 25-ms (~25-m [82-ft]) vertical scale suggests that the channel features are only a little larger than the C2 channel complexes.…”

“…Older channels have thicker levees, higher sinuosity, and evidence of lateral stepping. A similarity between the Lucia Chica system (Maier et al, 2012), the Y channel (Jobe et al, 2015), and C2 is that lateral movement of channels was achieved through lateral stepping instead of lateral migration.…”

“…The architecture and evolution of deep-water channel systems has been of particular interest in both the hydrocarbon industry and academic study in recent years with detailed investigations using highresolution reflection seismic data sets (e.g., McHargue and Webb, 1986;Badalini et al, 2000;Babonneau et al, 2002Babonneau et al, , 2004Abreu et al, 2003;Deptuck et al, 2003Deptuck et al, , 2007Posamentier, 2003;Posamentier and Kolla, 2003;Schwenk et al, 2005;Mayall et al, 2006;Kolla, 2007;Cross et al, 2009;Catterall et al, 2010;Armitage et al, 2012;Jobe et al, 2015;Ortiz-Karpf et al, 2015) and seabed imaging techniques (e.g., Torres et al, 1997;Maier et al, 2011Maier et al, , 2013Covault et al, 2014), although these provide limited detailed information on subseismic-scale elements and the range and distribution of sedimentary facies. This gap has been addressed through the use of analogous systems at outcrops (Badescu et al, 2000;Blikeng and Fugelli, 2000;Campion et al, 2000;Clark and Gardiner, 2000;Gardner et al, 2003;Beaubouef, 2004;Pickering and Corregidor, 2005;Hodgson et al, 2011;Brunt et al, 2013b;Hubbard et al, 2014;Masalimova et al, 2016).…”

Development of cutoff-related knickpoints during early evolution of submarine channels

“…The HK model does not cover the full spectrum of submarine channel behavior. For example, turbidity currents that are not in equilibrium with their containing channel can deposit sediment closer to the outer bank (Kane et al, 2008;Jobe et al, 2015). Our goal here is to investigate the larger scale stratigraphic implications of relatively simple early sinuosity development that is coupled with incision.…”