Lecture Thirty Two - Deep ocean sedimentary settings Flashcards
Who was the first to go to the bottom of the Mariana trench?
In 1960, Jacque Piccard and Lt. Don Walsh journeyed to the deepest part of the Mariana trench.
What drilling projects have been done in the Mariana trench?
1968 - Deep Sea Drilling Program (DSDP) - DSDP provided curtail data to support the seafloor spreading hypothesis and helped to prove the theory of plate tectonics. Vessel - Glomar Challenger.
1985 - Oceans Drilling Program (ODP) Joint Oceanographic Institutions for Deep Earth Sampling (KOIDES) on 110 expeditions to collect about 1000 deep sea cores from major geological features located in the ocean basins of the world.
2003 - Integrated Ocean Drilling Program (IODP; now ‘International ODP’).
What are the deep water sediment types?
Hemi-pelagic and pelagic oozes:
Long term suspension, in open ocean away from continents.
Volcanic ashes and mass flow deposits:
Important for estimating age of event (by measuring where layer of volt sediment is in the whole sedimentary rock).
Glacial marine sediments:
Mostly over South pole (some over North pole).
Mass flow clastics:
Turbidites, slumps/slides, debris flow deposits.
Short lived events.
Explain pelagic ooze sediments.
Calcareous oozes = Chalk.
Formes at depth shallower than the CCD.
Siliceous ooze = Chert.
Forms at depths deeper than the CCD.
Composed of more than 30% planktonic organism debris.
Zero current motion is required for sediments to settle.
Explain glacial marine sediments.
Glaciers have gravitational potential energy –> Slide downslope.
Iceburgs buoyantly support sediment as the float.
1) Particulate transport:
a) Ice rafting:
- Large volume of debris transported large distance (e.g. curium current around Antarctica).
- Melting icebergs leave isolated coasts and trails of debris.
b) Glaciers:
- High altitude and high latitudes.
- Erode bedrock.
- -> Large volume of debris.
- -> Clay to house sized.
- Sediment load.
- -> Top load = rock fall debris and dust on top.
- -> Bottom load = Plunked from bottom.
- -> Interior load = Transferred from bottom by upward, forward flow paths.
- High latitude glaciers deposit these sediments into lakes and oceans.
- -> Sedimentary deposits = till.
- -> Lithified = diamictite or tillite = matrix supported and very poorly sorted.
What is snow ball Earth?
A theory to try to explain the abundance of rocks of the same age all around the world which all indicate glacial and snow coverage.
Cryogenian glacial deposits (and their palaeolatitudes).
Explain the initiation of subsequent mass flows.
Mobilisation of volume of sediment from shallow to deep water by:
- Earth quakes.
- Volcanic eruptions.
- Major storms.
- (Mega-) river mouth floods.
- gravitational collapse on steep slopes.
- Once mobilised it keeps flowing for a long time/distance.
What are the critical angles for maintaining mass flows?
Grain flows = inertial, cohesion-less, granular flows).
Angle of repose ~30 degrees.
Debris flows = viscous flows of mud and debris).
Angle of repose ~ 4.5 degrees.
Turbidity currents = turbulent, cohesion-less density currents).
Angle of repose ~ 0.25-0.5 degrees.
In order of increasing viscosity and decreasing fluid content:
Turbidity current –> Liquified flow (turbidity current and debris flow). –> Grain flow –> Mud flow and debris flow.
Explain lateral changes in flows and deposits.
Mass flows evolve as they flow down slope and onto basin/abyssal plain.
Slide/slump –> Debris flow –> High conc turbidity currect –> Low conc turbidity current.
A channelized flow may also show transverse changes.
I.e. there can be differential distribution of sediments depending on the topography of the water bed.
What is the Bouma sequence?
Google it, I can’t be bothered putting in a crappy small picture that you can’t see.
Explain mass flow deposition in deep water settings.
Submarine fans at base of major marine slopes.
- Form at base f submarine canyon.
- Single sediment supply point.
- -> Controls fan morphology and sub environments.
Where can submarine fans be found?
Bengal fan coming out of the Ganges river in the Bay of Bengal.
Indus fan coming from the Indus river in the Arabian Sea.
How can submarine and terrestrial fans be differentiateD?
Consider: transport mechanisms. Medium. Magnitude. Topography. Resultant facies.
How can submarine facies be affected by tectonics?
Tectonic uplift at continental margins increases erosions rates in mountains.
This causes increased sediment flux to rivers and the shoreline zone.
If this sediment is fed into canyons then submarine fans are re-activated, and expand laterally (prograde).
E.g. Collisional event = lots of uplift and sediments are eroded from uplifted mountains and dumped into oceanic basins.
Form submarine fans.
Sediments spread out further and further over time, therefore fan is growing beyond its original parameters - spreading laterally from point source.
How could submarine fans be affected by sea level changes?
Sea level rise causes:
The shelf to drown as water depths increase.
the shore line zone to migrate landward (aka transgression), moving the point of sedimentary supply into the sea landward (e.g. river deltas.
Source point for sediments is being pushed further onto land therefore sediments have further to travel to get into fan
Cessation of sediment supply to canyons - submarine fans brome inactive.
Sea level fall causes:
The shoreline to move seaward (aka regression) onto the continental shelf edge.
Much of the shelf becomes exposed, subject to subaerial erosion.
Source sediments closer to fan, therefore erosions occurring closer to fan and fan therefore grows.
Large comes of sediment to be shed directly into canyons, submarine fans are reactivated and expand laterally (prograde).
