Facies: Turbidites

1. Facies: Turbidites I. Introduction II. The Bouma Sequence III. Types

2. Introduction ● What is a turbidity current? - Sediment-laden water moving rapidly down-slope (gravity current). - Current moves due to high density + slope + gravity. - Occur in lakes and oceans; often triggered by slumping or earthquakes. - Cause both extensive and severe erosion and deposition. - Occur in submarine trenches, active margin slopes and slopes andsubmarine canyons of passive margins.

3. Introduction ●Bouma (1962) 1st described turbidites; studied deepwatersediments and found fining-up intervals within shales. ●Odd, no mechanism known to carry and deposit coarse sediments to abyssal depths. ●Turbidites = classic hosts for metal lode deposits; near Victoria, Australia, 2,600+ tons of gold extracted from reef deposits hosted in shale sequences from thick Cambrian-Ordovician turbidites. GorgoglioneFlysch, Miocene (5-23 MYA), S. Italy

4. Introduction El Palmar, Guatemala: 1989 ●Analogues: lahars, mud slides and nueeardenteform deposits similar to turbidites. Augustine Volcano, AK: 1986 La Conchita, Mexico: 2005

5. Introduction ●What is a turbidity current? - A vicious cycle… ● Slope , current speed . ● Flow speed , turbulence . ● Turbulence , current draws up more sediment. ● More sediment = increased current density. ● density = speed. ● Can travel at ½ the speed of sound (~380 mph)! http://faculty.gg.uwyo.edu/heller/sed_video_downloads.htm

6. Introduction Fine et al., 2005 ●Grand Banks earthquake (1929) (Heezenand Ewing, 1952; Fine et al., 2005). - M 7.2 earthquake occurs on southern edge of Grand Banks, ~280 km south of Newfoundland.

7. Introduction Fine et al., 2005 ●Grand Banks earthquake (1929) (Fine et al., 2005). - Fine et al. (2005) presented numerical model results of tsunami.

8. Introduction Fine et al., 2005 ●Grand Banks earthquake (1929) (Fine et al., 2005). - Slope failure  tsunami killing 27 in Newfoundland; seen on U.S. E. coast, the Azores and Portugal. Fine et al., 2005

9. Introduction ●Grand Banks earthquake (1929) (Heezenand Ewing, 1952; Fine et al., 2005). - N. America to Europe telegraph cables on slope and rise south of Newfoundland broken (orderly), none on shelf damaged. Fine et al., 2005

10. Introduction ●Grand Banks earthquake (1929) (Heezenand Ewing, 1952; Fine et al., 2005). - Definitive proof of turbidity flows. - Large and powerful: slope failure area = 20,000 km2; displaced material = 200 km3

11. Introduction ● CONTINUUM RULES in nature: Slumps  Debris flows  Dilute turbidity currents  Tidally-driven nepheloid layers (Stow and Piper, 1984).

12. Introduction ●Where do we find turbidity flows? - Slopes where sediment type / consolidation allows slumping; any natural conduits (submarine canyons). - West coast of U.S. DEM – Hueneme Canyon, CA (off Ventura, CA coast)

13. Introduction ● Where do we find turbidity flows? - West coast of U.S.: Monterey Bay Canyon

14. Introduction ● Where do we find turbidity flows? - U.S. East coast, Hudson Canyon - Other major submarine canyons ● Congo Canyon: Africa ● Amazon Canyon: S. America ● Ganges Canyon: Bangladesh ● Indus Canyon: India ● La Jolla Canyon: N. America

15. Introduction ● What initiates turbidity flows? - Seismics: slump and turbidity current of Grand Banks, 1929. - Any process causing slumps and debris flows can initiate turbidity currents (Hampton, 1972; Normarkand Gutmacher, 1988). - Slope failures depend on geotechnical properties. - Instability often associated with rapidly accumulating sediments (low shear strength and under-consolidated).

16. Introduction ● What initiates turbidity flows? - Example: Baltimore Canyon region; slumps of Pleistocene sediment on upper slope (McGregor and Bennett, 1979).

17. Introduction ● What initiates turbidity flows? - Failure occurs when shear stress > shear strength. - At static conditions, overburden imposes a shear stress in down slope direction. - Middle - lower slope and upper rise have finer sediment than upper slope; lower sediments have 1. higher compressibility; and 2. water content > liquid limit. - Remolding transforms sediment into a thick, viscous slurry; since shear strength increases slowly with depth, some slope and rise sediments are under-consolidated.

18. Introduction Piper and Normark, 1983 ● How frequently do they occur (Piper and Normark, 1982, 1983)? - Turbidity flows occur as a function of: ● Frequency / strength of seismic events. ● Rate / type of sediment accumulation. ● Setting and sediment geotechnical properties.

19. Bouma, 1962 Bouma Sequence ●Bouma Sequence (Bouma, 1962) describes classic set of beds laid down by turbidity currents (medium grained type, usually found on slope or rise). ● Sequence divided into 5 distinct beds labeled A – E, (A at bottom and E at top). ● In reality, some beds may be absent – Bouma describes ideal sequence.

20. Bouma, 1962 Bouma Sequence ●Division A: - Rapid deposition from concentrated suspension. - Sorting inhibited; grains entrapped when transport ceases. - Massive texture. - Medium – coarse grains. - Poor or no grading. - Sharp, scoured base.

21. Bouma, 1962 Bouma Sequence ●Division B: - Graded. - Parallel lamination. - Medium grain size. - Transition between A where transport abruptly ceases and C where traction transport is important.

22. Bouma, 1962 Bouma Sequence ●Division C: - Graded; cross-laminations (ripples) during traction transport. - B and C: same texture, different structure; both contain particles that settled as individuals (not flocs). - Sediment often re- suspended as traction load = fines expelled and resulting sediment has < mud than that deposited by simple settling.

23. Bouma, 1962 Bouma Sequence ●Division D: - Silts. - Finely graded, parallel- laminated, sorted silt and mud intervals. - Decreased turbulence, so mud is deposited intermittently (fluctuating concentrations) and flocs mature into aggregates.

24. Bouma, 1962 Bouma Sequence ●Division E: E3: Un-graded muds; just flocsettling (no particles remain that are big enough to settle except as flocs). E2: Graded muds with silt lenses; texturally similar to E1, structurally different. E1: Thin, irregular, silt laminaeamid mud layers (two cannot be cleanly separated); same mechanism as in D ( turbulence, variable concentrations).

25. Bouma, 1962 Bouma Sequence ●Division F: - Resumption of pelagic sedimentation.

26. Lacustrine turbidite, WA USA Bouma Sequence ●Resumed sedimentation ●Division E:Massive/graded muds. ●Division D:Upper lllaminae. ●Division C: Ripples, wavy or convoluted laminae. ●Division B: Plane lllaminae.

27. Types ●Fine grained turbidites (Stowe and Piper, 1984). - Widespread in deep sea and volumetrically important. - Distinguished from other deep sea facies by: ● regular vertical sequence of structures and grading. ● structures indicating rapid deposition, bioturbationrestricted to bed tops. ● compositional, textural or other features indicating deposits are exotic to depositional environment.

28. Types ●Silt turbidites (Stowe and Piper, 1984). - Silt turbiditescan have A-F divisions. - Sequences often incomplete. - Often are the distal edge of a sandier turbidite unit. - Often several 100’s m thick, have low concentrations (~2500 mg/l) and move down slope at 10 - 20 cm/s. Stowe and Piper, 1984

29. Types ●Mud turbidites (Stowe and Piper, 1984). - Characteristic features are subtle, can be easily missed. - Mud turbidites have D-F including T0-T8 subdivisions of E division. - Textural / compositional grading is common; upward increase of mica, OM, clays and upward decrease in heavy minerals, quartz and forams; often coincides with color change. - Mud turbidites can be thick (cm - m).

30. Stowe and Piper, 1984 Stowe and Piper, 1984 Types ●Mud turbidites

31. Types Arctic seamount ●Biogenic turbidites (Stowe and Piper, 1984). - Biogenic pelagic sediments are widespread (open ocean and shelves) where terrigenous inputs are reduced. - Areas of relief or tectonic activity (ridges, seamounts) = re- sedimentation of pelagic oozes by slumping, debris flows and turbidity currents. - While both siliceous and carbonate types are known, carbonate types are muchmore common.

32. Types ●Biogenic turbidites (Stowe and Piper, 1984). - Often finer grained than pelagic host sediment so E/F unit shows reverse grading due to bioturbation. - Fractionation of components; forams go with coarse silt and diatoms and nannofossilsgo withfine silt and clay. - Carbonate may not form flocs like clay- rich materials, soupper unitsdo not have intricatelayering like lithogenous turbidites. Stowe and Piper, 1984

33. Types Sinclair and Tomasso, 2002 ●Disorganized turbidites (Stowe and Piper, 1984). - Chaotic distributions of poorly defined sequences. - Found inter-bedded between well defined turbidites or alone. - Can result from turbidite “ponding” in restricted basins or from repetitive turbiditeflows.

34. Types ●Baffin BayNew Zealand

35. Facies: Turbidites ●Readings for contourites and glacio-marine: **Maldonado, A., A. Barnolas, F. Bohoyo, J. Galindo-Zaldivar, J. Hernandez-Molina, F. Lobo, J. Rodriguez-Fernandez, L. Somoza, J.T. Vazquez, 2003. Contourite deposits in the central Scotia Sea: the importance of the Antarctic Circumpolar Current and the Weddell Gyre flows. Palaeogeography, Palaeoclimatology, Palaeoecology, 198: 187- 221. **Stow, D.A.V., D.J.W. Piper, 1984. Deep-water fine-grained sediments: faciesmodels, In: Fine-Grained Sediments: Deep-Water Processes and Facies, p. 611-646, ed. Stow, D.A.V., Piper, D.J.W., Geological Society, Oxford: Blackwell.

36. Bibliography Bouma, A.H., 1962. Sedimentology of some flysch deposits: Amsterdam, Elsevier, 168 p. **Fine, I.V., A.B. Rabinovich, B.D. Bornhold, R.E. Thomson, E.A. Kulikov, 2005. The Grand Banks landslide-generated tsunami of November 18, 1929: preliminary analysis and numerical modeling, Marine Geology, 215: 45-57. Hampton, M., 1972. The role of subaqueous debris flows in generating turbidity currents, Journal of Sedimentary Petrology, 42: 775-793. Heezen, B.C., M. Ewing, 1952. Turbidity currents and submarine slumps and the 1929 Grand Banks earthquake. American Journal of Science, 250: 849-873. McGregor, B.A., Bennett, R.H., 1979. Mass movement of sediment on the continental slope and rise seaward of the Baltimore Canyon Trough. Marine Geology, 33: 163- 174.

37. Bibliography II Normark, W.R., C.E. Gutmacher, 1988. Sur submarine slide, Monterey Fan, central California, Sedimentology, 35: 629-647. Piper, D.J.W., W.R. Normark, 1982. Effects of the 1929 Grand Banks earthquake on the continental slope of eastern Canada, Current Research, Part B, Geological Survey of Canada, Paper 82-1B: 147-151. **Piper, D.J.W., W.R. Normark, 1983. Turbidite depositional patterns and flow characteristics, Navy Submarine Fan, California Borderland, Sedimentology, 30: 681- 694. Sinclair, H.D., M. Tomasso, 2002. Depositional evolution of confined turbidite basins, J. of Sedimentary Research, 72(4): 451-456. **Stow, D.A.V., D.J.W.Piper, 1984. Deep-water fine-grained sediments: faciesmodels, In: Fine-Grained Sediments: Deep-Water Processes and Facies, p. 611-646, ed. Stow, D.A.V., Piper, D.J.W., Geological Society, Oxford: Blackwell.