Pelagic Environments
Importance of pelagic environments
• Most common depositional environments on the planet
• Play a crucial role in the carbon cycle on intermediate to long
timescales
• Repository for natural resources
• Excellent record of evolution
• Excellent record of paleoclimate
Sediments lying on underwater rock (basement)
Seismic survey of the North Atlantic Ocean. Garrison, 4th Ed., Fig. 4.26
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Marine sediments are deposited in layers
The oldest sediments are laid down first and then covered by younger sediments
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Recovering Marine Sediments
Coring:
Various systems collect a ~1-50 meter long cylindrical tube of sediment from the seafloor .
Drilling: Specially designed ships
sediment
can recover 1000's of
Top: Sediment cores. A. Jennings
Colorado, Boulder)
photographer. Courtesy of NOAA.
Bottom: Drillship JOIDES
meters of
(Univ. of
Resolution. J. Ortiz, photographer.
Piston Cores
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Collects a tube of sediment from the sea floor
Layers of sediment are analyzed for their characteristics
The tube falls through the water. As it is driven into the ocean floor, a hydraulic piston pulls
sediment into the tube
Garrison 4th Ed., Fig. 5.15b-e
DSDP and the Glomar Challenger
Dynamic Positioning
Sedimentology - core description
Giant Piston Coring: The Calypso Coring system
•Ten Metric ton core
• Kevlar Line
• Up to 75 m long barrel
• Winch with 30 tons of pull
photos: Left,
working deck of
the French research
vessel, Marion
Dufresne with the
Calypso core ready
to deploy. Right,
Laminated
sediments from
Guymas basin.
Turbidite facies model of Bouma
Turbidity currents on the slope and rise
Turbidity currents of the
Grand Banks Earthquake
Turbidity currents at work:
Submarine Canyons
Turbidity
currents at work:
Submarine fans
Interlayering of
• Turbidites
• Mud layers
• Debris flows
Bottom currents
and contourites
on the
continental rise
North Atlantic
Bottom currents
Deep sea giant mudwaves
Composition of Marine Sediments
• Terrigenous
• Clay, silt, sand, rare pebbles, etc.
• Hydrothermal (authigenic)
• Calcium carbonate
• Foraminifera, Coccolithophorida
• Amorphous Silica (opal)
• Diatoms, Radiolara
• Red Clay (deep sea clay)
Distribution of marine sediments
Dropstones and
Ice Rafted Debris (IRD)
Metaliferous sedimengs form in Hydrothermal
zones
Radiolaria,
Forminifera, and
Coccolithophorida
Controls on marine sediment distribution and
preservation
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Distance from coast
Water depth
Water chemistry
Settling and reworking
Faunal and floral distribution
Tectonics
Carbonate dissolution increases with
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Decreasing [CO3=] ion
Decreasing temperature
Increasing pressure
Increasing water flow
Increasing bottom water CO2
Increasing organic matter concentration
Silica vs. Carbonate
Preservation
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Silica is undersaturated everywhere in the ocean but particularly in surface water.
Carbonate ion is undersaturated in deep water.
This results in inverse preservation patterns for Silica and Carbonate in marine environments
Production and water depth influence sediment
type
Bathymetry and plate motion