Piping coarse-grained sediment to a deep water fan through a shelf-edge delta bypass channel: Tank experiments

Abstract

[1] It is now generally accepted that deltas that prograde to the shelf edge are able to transport coarse sediment to deep water either with or without sea level changes. However, it is still unclear how feeder rivers behave differently in the shelf-edge delta case to rivers found in a delta that progrades over the shelf. A series of nine shelf-edge delta experiments are presented to investigate the lateral mobility of the feeder channel at the shelf edge and the associated deep water depositional system under a range of sediment supply rates and shelf-front depths. In the experiments, constant sediment supply from an upstream point source under static sea level led the fluviodeltaic system to prograde over the shallow shelf surface and advance beyond the shelf edge into deep water. The feeder river of the fluviodeltaic system became a bypass system once the toe of the delta front reached the shelf edge. After the delta front was perched at the shelf edge, a submarine fan developed in deep water although remaining disconnected from the delta. In this bypass stage, no regional avulsion or lateral migration of the feeder river occurred and all sediment from the upstream source bypassed the river, delta front, and shelf-front slope. The duration of the bypass stage is proportional to shelf-front depth and inversely proportional to sediment discharge. The combined duration of the shelf-transit phase of the fluviodeltaic system and the bypass phase is the characteristic time scale for the continental margin to "anneal" transgression-inducing perturbation due to high-frequency and/or high-amplitude relative sea level rise. The sequential evolution in the experiment compares favorably to the Eocene Sobrarbe Formation, a shelf-edge delta in Spain, although natural variations are noted. This comparison justifies the application of concepts proposed herein to natural systems and provides insight into interpreting processes from ancient shelf-edge delta systems.

Shelf-edge trajectories and stratal stacking patterns: Their sequence-stratigraphic significance and relation to styles of deep-water sedimentation and amount of deep-water sandstone

“…First, enhanced differential sedimentation on the shelf (high A s ∕A b ) could have served as a metaphorical sieve of coarsegrained sediment because there was significant accommodation in the shelfal depositional environments (e.g., fluvial-deltaic systems), leaving predominantly relatively fine-grained strata to accumulate in the deep-water region, such as the mud-rich strata associated with steeply rising shelf-edge trajectories. Second, enhanced differential sedimentation on the basin-floor areas (low to negative A s ∕A b ) serves to pipe coarse-grained sediment directly to the basin floor (Kim et al, 2013), resulting in a coarse-grained submarine fan such as the Red River submarine fan in the downdip of flat to slightly falling shelf-edge trajectories (Tables 2, 4). Third, enhanced differential sedimentation on the shelf (high A s ∕A b ) increases the relief of the clinoforms (high R c ), thereby increasing the angle and instability of the shelf resulting in large-scale mud-rich masswasting processes and resultant large amounts of MTDs, which is evident in deep-water strata in front of steeply rising trajectories (Tables 2, 4).…”

Mid to late Holocene geomorphological and sedimentological evolution of the fluvial–tidal zone

“…To begin answering these two questions, we will relate the mid-Holocene to present geomorphic evolution of the LCR to the experimental results of Kim et al (2013) who investigated the morphodynamics of shelf-edge deltas. For clarity, we are not herein suggesting that the mid to late Holocene LCR system was/is a shelf-edge delta.…”

“…Building on the results of Clarke et al (2010), the physical experiments of Kim et al (2013) employed a constant upstream sediment feed rate and steady base-level elevation, and found that under these steady boundary conditions deltas that prograde to a shelf-edge (where there exists a steep gradient in water depth/accommodation between the toe of the delta and the basin floor) cannot completely fill this space immediately via submarine fan sedimentation ( Fig. 6.5).…”

“…This steep accommodation gradient forces the delta to abandon multiple active distributary channels in favor of a single, active, nonmigrating feeder channel that "entrenches" and effectively bypasses all supplied sediment instantaneously to the basin floor ( Fig. Thus, this geomorphic condition circumvents the deposition of deltaic foreset, and shelf-slope sediments (Kim et al, 2013), and allows basin water to transgress up-dip into the "entrenched" feeder channel (Fig. Thus, this geomorphic condition circumvents the deposition of deltaic foreset, and shelf-slope sediments (Kim et al, 2013), and allows basin water to transgress up-dip into the "entrenched" feeder channel (Fig.…”

Coupling Between Shelf-Edge Architecture and Submarine-Fan Growth Style In A Supply-Dominated Margin

“…However, researchers have argued conceptually (Burgess and Hovius 1998) and have demonstrated with ancient datasets that rising and high sea-level stand can also produce deepwater fans in high-sediment-supply basins Steel 2006, 2009;Covault et al 2007;Covault and Graham 2010;Kim et al 2013). The behavior and process regime of shelf-edge deltas (sediment feeder to deep water) in high-sediment-supply basins is also now known to impact the presence and volume of deep-water fans (Dixon et al 2012).…”