Giant submarine canyons: Is size any clue to their importance in the rock record?

Abstract

INTRODUCTIONSubmarine canyons continued to be a major area of interest for Francis P. Shepard throughout his career. His Submarine Geology textbooks, which were revised over the years, devoted substantial space to a review of the world's canyons that were known at the time; these reviews were a standard resource for several decades of marine geologists (e.g., Shepard, 1973). Shepard and his coworkers observed that canyon size was not directly related to the size of the rivers that fed them. In fact, many major canyons were not fed directly from rivers but fed from littoral drift transport of beach sediment, for example, the La Jolla Canyon (Shepard, 1973;Shepard and Dill, 1966). As our ability to map the deep-sea floor has improved since Shepard's pioneering work, it has become clear that the size of submarine canyons also shows no simple relation to the size of the turbidite systemssubmarine fans, abyssal plains, slope basin deposits, etc.-fed through the canyons. ABSTRACTSubmarine canyons are the most important conduits for funneling sediment from continents to oceans. Submarine canyons, however, are zones of sediment bypassing, and little sediment accumulates in the canyon until it ceases to be an active conduit. To understand the potential importance in the rock record of any given submarine canyon, it is necessary to understand sediment-transport processes in, as well as knowledge of, deep-sea turbidite and related deposits that moved through the canyons. There is no straightforward correlation between the final volume of the sedimentary deposits and size of the associated submarine canyons. Comparison of selected modern submarine canyons together with their deposits emphasizes the wide range of scale differences between canyons and their impact on the rock record.Three of the largest submarine canyons in the world are incised into the Beringian (North American) margin of the Bering Sea. Zhemchug Canyon has the largest cross-section at the shelf break and greatest volume of incision of slope and shelf. The Bering Canyon, which is farther south in the Bering Sea, is first in length and total area. In contrast, the largest submarine fans-e.g., Bengal, Indus, and Amazon-have substantially smaller, delta-front submarine canyons that feed them; their submarine drainage areas are one-third to less than one-tenth the area of Bering Canyon. Some very large deep-sea channels and turbidite deposits are not even associated with a significant submarine canyon; examples include Horizon Channel in the northeast Pacific and Laurentian Fan Valley in the North Atlantic. Available data suggest that the size of turbidity currents (as determined by volume of sediment transported to the basins) is also not a reliable indicator of submarine canyon size.

Quantitative bounds on morphodynamics and implications for reading the sedimentary record

“…The width of the Bengal fan is about 1,000 km and to estimate the cross-sectional area we need a depth scale of sediment transport. We used the depth of the submarine canyon 54 , Swatch of No Ground (B1 km), as an upper bound on the depth scale of sediment transport through the system. Assuming depth scales of 10-100 m yields a sediment velocity scale of 1-10 m yr À 1 .…”

Connections Between Fluvial To Shallow Marine Environments and Submarine Canyons: Implications For Sediment Transfer To Deep Water

“…Examination of Quaternary systems, however, shows that all major submarine fans are fed by submarine canyons (Normark and Carlson 2003). Published examples where canyons feed submarine fans, or fed them during the last glacial period, include the Amazon (Damuth and Kumar 1975), the Mississippi (Normark et al 1986;Weimer 1989), the Zaire (Babonneau et al 2002), the Bengal (Weber et al 1997), the Rhone (Droz and Bellaiche 1985), the Indus (Prins et al 2000), the Nile .…”

“…Normark and Carlson (2003) observed that the ratio of canyon area to the area of their associated fans ranges from 0.15% to 17% with an average of 4%. To further examine this issue, we calculated canyon volume for the Bengal Fan ''Swatch of No Ground,'' the Danube, and the Monterey canyons, where we had adequate bathymetric data and river-discharge data.…”

“…With improved technology for imaging the sea floor, and the deployment of current monitors and sediment traps in some submarine canyons, the scale and distribution of these canyons has become better defined and their role as conduits for transferring sediment from terrestrial sources into the deep basin has become better understood (e.g., Piper and Savoye 1993;Khripounoff et al 2003;Paull et al 2003;Smith, et al 2005;Oliveira et al 2007;Harris and Whiteway 2011). Indeed, as observed by Normark and Carlson (2003), every major submarine fan in the world is fed by a submarine canyon.…”

Rapid Adjustment of Submarine Channel Architecture To Changes In Sediment Supply

“…The development of large entrenched submarine channel systems (i.e., valleys) like the Y channel system has been linked both to high sediment supply (Normark and Carlson, 2003) and to baselevel changes (McHargue et al, 2011;Sylvester et al, 2011Sylvester et al, , 2012. Cross-sectional area (CSA) is also a good proxy for sediment supply and flux.…”