Download Lecture 7. Marine Sediments

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Lecture 8: Marine Sediments
What’s all that muck at the
bottom of the ocean, and what’s
it good for?
Marine Sediments are:
 Particles
of various sizes derived from
a variety of sources that are deposited
on the ocean floor
 A vast “library” recording geologic,
oceanographic and climatic conditions
 Remarkably complete compared to land
Where do these come from?
 Inputs
-------
are:
rivers
atmosphere
surface waters
volcanoes (both on land and submarine)
deep ocean water
outer space
Classifications
 By
Size
Clay -- Silt -- Sand -- Pebble -- Cobble
0.001 mm
1 mm
100 mm
 Effects of water velocity on transport:
rivers and near-shore vs open ocean
Sediment Transport
Figure 4-1
Fluid velocity
determines the
size of the
particles that
can be moved
Size Sorting
Classifications
 By
Origin
Biogenous
Terrigenous
Hydrogenous
Cosmogenous
Terrigenous sediments
(from land)
 Rivers
 Winds
(eolian)
 Glaciers (ice-rafted debris, IRD)
 Turbidites
 Sea level changes
River sediment loads (106 tons/yr)
Figure 4-9b
Glacial (Ice-rafted debris)
Figure 4-12a
Turbidites
 Rapidly-accumulated
terrestrial sediments
 Earthquake-triggered submarine avalanches
(turbidity currents)
 High velocity (~50 mph!), erosive events
 Good examples preserved on Mary’s Peak
Seafloor Features:
Continental Margins
Submarine canyons
(cut into the c. slope)
Abyssal
plain
Continental shelf
Continental rise
Abyssal
plain
Continental
slope
Turbidity Currents
(avalanches)
Sea Level Changes
Figure 4-3b
Biogenous sediments
(from living things)
 Calcareous
(CaCO3)
Foraminifera -- animals
Coccolithophores -- plants
 Siliceous (SiO2)
Radiolaria -- animals
Diatoms -- plants
mm = micron = millionth of a meter!
mm = micron = millionth of a meter!
mm = micron = millionth of a meter!
mm = micron = millionth of a meter!
Productivity = skeletons and
soft tissue
 Accumulation
depends on production
and preservation
 SiO2 is preserved everywhere
 CaCO3 is variable, depending on P, T,
pH
Carbonate Compensation Depth
Carbonate Compensation Depth
 The
depth at which carbonate input
from the surface waters is balanced by
dissolution in corrosive deep waters
 In today’s ocean this depth (CCD)
varies between 3 km (polar) and 5 km
(tropical)
 Thus, accumulation rates vary a lot!
Accumulation Rates for Oozes
 Productivity
– reproduction of planktonic organisms
 Preservation
– silica dissolves only very slowly
– calcium carbonate varies with depth
 Rates are variable: <1 to 15mm/1000 yr
Coastal waters are often highly productive, with
abundant planktonic organisms thriving in the
surface waters. Why then are biogenous oozes
rarely found nearshore??
Do biogenous sediments dissolve readily at
shallow depths on the continental shelf? NO
 Do plankton species in coastal waters lack
skeletons? NO
 Are planktonic organisms consumed by large
organisms, preventing deposition of
skeletons? NO

RIVERS!!!!

The large input of terrigenous
sediment to the continental margin
overwhelms the biogenous component
in the sediment. YES
Hydrogenous (from sea water)
 Metalliferous
sediments at spreading
ridges
 Manganese nodules
 Evaporites -- Salt deposits
baseball to bowling ball size!
Cosmogenous (from outer space)
 Meteorites
and comets
Sediment Accumulation
Figure 4-9a
Sediment Succession
Figure 4-17
Distribution of Marine Sediments
Figure 4-16a
Global Ocean Drilling
Ocean Drilling
 International
program
(20 nations; began 1968)
 2-month cruises
 Deepest hole: 2 km
But, new vessel will drill
to >6km!