1 facies: turbidites i. introduction ii. the bouma sequence iii. types

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 and submarine canyons of passive margins.

3 Introduction Bouma (1962) 1st described turbidites; studied deepwater sediments 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. Gorgoglione Flysch, Miocene (5-23 MYA), S. Italy

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

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 the speed of sound (~380 mph)!http://faculty.gg.uwyo.edu/heller/sed_video_downloads.htm

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

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

8 Introduction 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) (Heezen and 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) (Heezen and Ewing, 1952; Fine et al., 2005). - Definitive proof of turbidity flows. - Large and powerful: slope failure area = 20,000 km 2 ; displaced material = 200 km 3

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

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

20 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. Bouma, 1962

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

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

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

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

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

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

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

28 Types Silt turbidites (Stowe and Piper, 1984). - Silt turbidites can have A-F divisions. - Sequences often incomplete. - Often are the distal edge of a sandier turbidite unit. - Often several 100s 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 Types Mud turbidites Stowe and Piper, 1984

31 Types 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 much more common. Arctic seamount

32 Types Stowe and Piper, 1984 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 nannofossils go with fine silt and clay. - Carbonate may not form flocs like clay- rich materials, so upper units do not have intricate layering like lithogenous turbidites.

33 Types 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 turbidite flows. Sinclair and Tomasso, 2002

34 Types Baffin Bay New 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: facies models, 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: facies models, 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.

1 facies: turbidites i. introduction ii. the bouma sequence iii. types

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