1. I. Introduction II. The Bouma Sequence III. Types
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: 2005
Augustine 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 ½ the speed
of sound (~380 mph)!

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
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 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. DEM – Hueneme Canyon, CA (off Ventura, CA coast)
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).

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
● 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.
Piper and Normark, 1983

19. 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.
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
ceases and C where traction
transport is important.
Bouma, 1962

22. 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.
Bouma, 1962

23. 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.
Bouma, 1962

24. Bouma Sequence ● Division E: E3: Un-graded muds; just
floc settling (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
laminae amid mud layers
(two cannot be cleanly
separated); same mechanism as in D ( turbulence, variable
concentrations).
Bouma, 1962

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

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

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, bioturbation restricted
to bed tops.
● compositional, textural or other features indicating deposits
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 100’s m thick, have low
concentrations (~2500 mg/l) and
move down slope at 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
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 ● 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.
Stowe and Piper, 1984

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. ● Baffin Bay New Zealand
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, 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, Deep-water fine-grained sediments: facies models,
In: Fine-Grained Sediments: Deep-Water Processes and Facies, p , ed. Stow,
D.A.V., Piper, D.J.W., Geological Society, Oxford: Blackwell.

36. Bibliography
Bouma, A.H., Sedimentology of some flysch deposits: Amsterdam, Elsevier, 168 p.
**Fine, I.V., A.B. Rabinovich, B.D. Bornhold, R.E. Thomson, E.A. Kulikov, The
Grand Banks landslide-generated tsunami of November 18, 1929: preliminary
analysis and numerical modeling, Marine Geology, 215:
Hampton, M., The role of subaqueous debris flows in generating turbidity
currents, Journal of Sedimentary Petrology, 42:
Heezen, B.C., M. Ewing, Turbidity currents and submarine slumps and the 1929
Grand Banks earthquake. American Journal of Science, 250:
McGregor, B.A., Bennett, R.H., 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, Sur submarine slide, Monterey Fan, central
California, Sedimentology, 35:
Piper, D.J.W., W.R. Normark, 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:
**Piper, D.J.W., W.R. Normark, Turbidite depositional patterns and flow
characteristics, Navy Submarine Fan, California Borderland, Sedimentology, 30: 681-
694.
Sinclair, H.D., M. Tomasso, Depositional evolution of confined turbidite basins, J.
of Sedimentary Research, 72(4):
**Stow, D.A.V., D.J.W.Piper, Deep-water fine-grained sediments: facies models,
In: Fine-Grained Sediments: Deep-Water Processes and Facies, p , ed. Stow,
D.A.V., Piper, D.J.W., Geological Society, Oxford: Blackwell.