nepheloid transport vs gravity flows gravity flows and sea level narrow, steep shelves receive much sed different type of gravity flow mass and chemical transport important RECENT OBSERVATIONS OF GRAVITY FLOWS IN SUBMARINE CANYONS C. Nittrouer, P. Puig, A. Ogston T., B. Mullenbach, J. Walsh, T. Drexler, A. DeGeest, G. Kineke, S. Kuehl
IMPORTANCE OF MODERN CANYONS To document modern sediment fluxes to the deep ocean To understand mechanisms of lowstand sedimentation SOME RECENT STUDY AREAS Narrow shelf:Eel canyon (northern California) No shelf:Sepik canyon (northern Papua New Guinea) Cold water:Cap Creus canyon (northeastern Spain)
41 o 00’ 40 o 50’ 40 o 40’ 124 o 40’ 124 o 30’ Eel River Drainage Basin ~9000 km 2 Study Area 0 m Elevation California Eel margin
S 60
from Traykovski et al., 2000 mid-shelf gravity-flow processes
Signals of Episodic Sedimentation on the Eel Shelf
Normalized 210 Pb dpm/(g clay) 10 depth (cm) % Clay content 7 Be dpm/g 2610 ND Larry entrance Eel River sediment is quickly deposited in the Canyon
0 cm Core 1Core 2Core 3 A B 90m Core 1 Core 2 Core Water depth (m) A B Distance along transect (m) tripod 124 o 27.83’27.50’ 40 o 39.5’ 39.33’ Larry thalweg A Channelized sediment transport and deposition Formed by gravity-driven sediment flows
sand silt clay A B C D E 60cm Sand, silt and clay content (%) Total Pb-210 activity (dpm/g) Non-steady-state profiles in thalwegs Cs-137 Multiple seasonal deposits are preserved
MT160B Jul 98 MT450 Jul cm cm Depth (cm) 1 10 Total Pb-210 activity (dpm/g) 1 10 Total Pb-210 activity (dpm/g) Moe 160 m Moe 450 m Evidence of sediment removal over decadal time scales
PNG Study Areas
SEPIK CANYON narrow shelf (<5 km) and…
April 1999 Courtesy of Gail Kineke
Plume bifurcates ~15% sed mass as surface plume ~85% sed mass as bottom plume Courtesy of Gail Kineke
Kadovar Island Bam Island Blupblup Island Wei Island 4 o 30’ S 144 o 30’ E Sepik River 500 m 1000 m 10 km 100 m Accumulation Rate (cm/yr) Kuehl et al. 2000
KC16 Pb210
KC16 Th234
Gravity-flow Deposition
Primary sediment source for Gulf of Lions is Rhone River
Some sediment reaches submarine canyons on the continental slope
(courtesy of Orange et al.) Cap Creus Canyon
Courtesy of Amy DeGeest Sediment accumulation rates ~mm/y
Along-marginAlong-margin Shelf-to-canyonShelf-to-canyon Winter Winter EuroSTRATAFORM Monitoring Courtesy of Pere Puig
Durrieu de Madron et al., Prog. Oceanogr. (2005) & Heussner et al., Mar. Geol. (2006) 10 February 1995 Lacaze-Duthiers Canyon Long-term Monitoring Courtesy of Pere Puig
Courtesy of Pere Puig
Time series recorded at 500 m water depth ( mab) Courtesy of Pere Puig Coarse sediment also observed to be transported
Adapted from Fohrmann et al., J. Phys. Oceanogr. (1998) Mixing Neutral density level INLs Heat flux Courtesy of Pere Puig Dense shelf water cascades down continental slope
(courtesy of Orange et al.) Cap Creus Canyon
750 m Courtesy of Pere Puig Deep-towed side-scan sonar survey
Courtesy of Pere Puig Furrow orientation controlled by bottom currents
Deposition during weak flows Erosion during strong flows Flood, Geological Society of America Bulletin (1983) Cap de Creus Canyon sedimentary furrows Maximum width = 50 m Wavelength = 100 m Maximum height = 10 m Type 1C Erosive Courtesy of Pere Puig Sedimentary Furrow Formation
CONCLUSIONS Much sediment can enter submarine canyons today especially on collision margins Canyon heads commonly are located in shallow depths fluvial/estuarine processes (turbidity max) surface gravity waves (liquefaction, resuspension) shelf water masses intercepted Turbid water transported into canyon head regularly sed gravity flows (fluid mud, hyperpycnal flows) cold-water gravity flows also observed Autosuspending gravity flows occur less frequently turbidity currents flush canyon heads?