Transcript Marine Sediments

Marine Sediments
CBGS
2011
More than 50% of all rocks exposed on the surface of
the continents are sedimentary rock of marine origin.
They were deposited when :
1. sea level was higher - 250 million year old fossils from
shale beds in the Tetons, Wyoming
2. Land was uplifted by tectonic processesuplifted coral reefs around Mt. Skukum caldera, Yukon
There are 4 main sources of marine sediments:
• Lithogenous- sediments from land sources
• Biogenous- these sediments are derived from the
skeletal remains of marine organisms
• Hydrogenous- form as a result of chemical
reactions taking place in the water or at the
sediment-water interface
• Cosmogenous- these sediments have their origins
in outer space- they are dust, spherules and
chondrules, and meteorites.
Lithogenous
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or Terrestrial
Lithic - refers to rock or continental origin
including:
River discharge, coastal erosion and
landslides
Volcanic eruptions (ash to rock sized)
Turbidity currents (submarine canyons
/continental slope)
Glacial & Iceburg debris
Aeolian (wind) transported sediments
They compose roughly 75% of marine sediments
Rivers deposit massive amounts of sediment, mostly along
continental margins,
Ejecta from volcanic eruptions can vary in size
from ash and dust to house size boulders
Turbidity
currents can
carry fine
sediment from
the continental
slope to edges
of the deep
ocean basin
Icebergs can form where
glaciers run into the sea.
• Any rocks or
sedimentary material
that has imbedded in
the bottom of the ice
sheet will drop out onto
the sea floor as the
iceberg melts at sea.
African dust
storms
(Aeolian (wind)
Transport)
• Carry fine silts
and clays far out
over the open
ocean and
deposit as
abyssal clays
in the deep sea.
• Wind-swept desert sands
not only produce a
cooling effect due to
deflection of incoming
solar radiation, but they
also deposit sand, silt
and dust on the ocean
surface and ultimately on
the ocean floor. (Shown
here is a dust storm over
the Red Sea.) Through
mineralogical and
chemical analysis,
scientists can recreate
historical patterns in
climate and geological
Richard W. Murray Water Encyclopedia
development.
Cosmogenous Sediments
• Make up only a
small % of total
marine sediment.
• Constant
bombardment by
‘space dust’
contributes a
small proportion
all over the globe
Major impacts can cause
localized sediment
structure (tektities)
Hydrogenous sediments
(Precipitation of dissolved materials
directly from seawater due to
chemical reactions)
• Key Mineral Resources
• Manganese nodules and crusts- abundant
baseball sized nodules composed of Mn, Fe, Cu,
Co, and Ni. Found only in very deep ocean
environment where other sediments accumulate
slowly. Formation is a mystery (onion-like layers).
• Massive Sulfides- (Iron, Nickel, copper, zinc, silver)
- found at ocean floor hydrothermal vents
Hydrogenous sediments (cont…)
• Phosphorites- deposits as the mineral,
apatite, in shallow to mid-depths on
continental shelf/slope. They grow
downward into the sediment using
remineralized excess phosphorous from
bacteria.
• Evaporites- form from evaporation of
seawater, (Gypsum, Halite, other Salts)
Hydrogenous sediments (cont…)
• Oolites – sedimentary rocks made of
spherical ooids (concentric layers of
CaCO3)
Ooids- shaped
spheres with
onion like
layers form
from CaCO3
• Whiting- patches of
cloudy seawater
saturated with
aragonite needles
which lead to ooid
formation
The Bahama
Banks are
composed
of calcium
carbonate
ooid sands
and
aragonite
needle
muds.
These are
biological
deserts
because the
sands are
constantly
shifting.
Biogenous Sediments
• Macroscopic shells and skeletons of
CaCO3 (Shells, corals)
• Microscopic shells of CaCO3
(coccolithophores and foraminiferans for
calcareous ‘ooze’)
• Microscopic shells of SiO2 (Diatoms
and radiolarians form siliceous ‘ooze’)
Stromatolites are possibly the most
ancient biological rocks on earth
• They are layered accretionary
structures formed in shallow water by
the trapping, binding, and cementation
of sedimentary grains by biofilms of
microorganisms, especially
cyanobacteria (commonly known as
blue-green algae).
• The earliest stromatolite of confirmed
microbial origin dates to 2,724 million
years ago.
• Stromatolites are a major constituent
of the fossil record for about the first 3.5
billion years of life on earth, with their
abundance peaking about 1,250 million
years ago.
Biogenous Sediments
• Macroscopic shells and skeletons of
CaCO3 (Shells, corals)
• Microscopic shells of CaCO3
(coccolithophores and foraminiferans for
calcareous ‘ooze’)
• Microscopic shells of SiO2 (Diatoms
and radiolarians form siliceous ‘ooze’)
Biogenous deposits are those which result
from living things.
• Massive reefs are created
by hermatypic reef building
corals who secrete calcium
carbonate (CaCO3) from
the water. In conjunction
with a symbiotic alga,
Zooxanthellae , which lives
in their tissues.
• In warm, tropical oceans, like that shown in (A), large numbers of corals and
other marine animals and plants make skeletons out of calcite and other
carbonate minerals. These skeletons and carbonate mud make a rock called
limestone like the one shown in (B) from San Salvador Island in the
Bahamas. This limestone was a coral reef living under a shallow sea about
120,000 years agoA) Abi Howe, American Geological Institute, courtesy
Calcareous Ooze
• Composed predominantly of CaCO3 shells of
Foraminiferans and Coccolithophores
• These plankton are dominant in warm surface
waters
• They compose 48% of deep ocean sediments
Coccolithophores and Foraminiferacalcareous tests
Coccolithophores can
bloom over massive areas
• Coccolithophore species
Emiliania huxleyi can
overproduce in blooms
and often sheds excess
coccoliths, these tiny
particles act like sequins
in the water and are very
reflective, they make the
sea surface “glitter”.
Carbonate Compensation Depth
• At depths of >4,500m, the
dissolved CO2 concentration
is so high it causes CaCO3 to
dissolve. As a result,
calcareous shells are not
found below ~5,000m.
• The depth where carbonate
supply is equal to the rate of
dissolution is the Carbonate
Compensation Depth.
• This occurs around 6000m in
Atlantic and 3500-4000 m in
parts of the Pacific.
Siliceous Ooze
• Composed predominantly of SiO2 shells
of Diatoms and Radiolarians
• These plankton are dominant in cold
surface waters or areas of upwelling
near equatorial landmasses
• They compose 14% of deep ocean
sediments
Diatoms and Radiolarians- glass frustules
3 types of sediment cover most of the
deep ocean floor:
• Abyssal clay- covers most of the deep ocean floor,
accumulates at <1mm/1000yr. Source is continent
and cosmogenic, carried by ocean currents and
aeolian transport.
• Oozes- must be composed of >30% biogenic
material (tiny skeletons of plants and animals) mixed
with clay.
Rate of deposition of oozes depends on:
– Productivity of area
– Destruction by chemical dissolution
– Physical dilution- mixing with other sediments
Sedimentary processes in the open ocean
Calcareous Ooze
From J. Noyes El Camino College
Calcareous ooze
• The dominant deep ocean sediment in
low latitudes above the CCD.
• Along the mid-ocean ridges, seamounts
and other peaks
Siliceous Ooze
From J. Noyes El Camino College
Siliceous Ooze
• The dominant deep ocean sediment in
high latitude regions, below the CCD
and surface current divergences near
the equator (where cold water is
upwelling)
Red Clay
From J. Noyes El Camino College
Abyssal Clays
• Dominant in deep ocean basins in areas
where oozes are absent
• Especially below CCD in warmer
oceans
Global Distribution of Marine Sediment Types
Diagram illustrating
the ocean’s
biological pump.
(1) Carbon dioxide is
fixed by
photosynthesis,
(2) this organic
matter sinks into
deeper waters,
(3) bacterial decay
releases carbon
dioxide and other
nutrients, making
them available to
be used again by
phytoplankton,
until
(4) ultimately
deposition locks
away the carbon in
ocean sediments.
The depth of the CCD varies as a function of the
chemical composition of the seawater and its
temperature. Furthermore, it is not constant over time,
having been globally much shallower in the Cretaceous
through to Eocene.
If the atmospheric concentration of carbon dioxide
continues to increase, the CCD can be expected to rise,
along with the ocean's acidity.
CaCO3(s) + H2O + CO2 → Ca2+(aq) + 2HCO3-(aq).
CO2 Concentration in the
Atmosphere is increasing
Carbon is stored in several
pools on Earth
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Atmospheric Carbon CO2- 720 Gt
Seawater Carbonate System 37400 Gt
Terrestrial Biosphere 800 Gt
Dead Terrestrial Biomass 1200 Gt
Marine Biosphere 2 Gt
Dead Marine Biomass 1000 Gt
1 Gt=1015 grams (1015 = 1 million billion)
• To maintain current ocean pH, fluxes must be
balanced CO2 in=CO2 out, not currently the case
In Terms of
Climate Change
and CO2 cycles,
ocean
sediments are
by far the most
significant
carbon sink on
Earth. What
happens when
we start to
liberate that
stored carbon?
• Up to one half of the CO2 released by burning
fossil fuels over the past 200 years has been
absorbed by world's oceans.
• This has lowered its pH by 0.1
• Seawater is mildly alkaline with a "natural" pH
of about 8.2
• The IPCC forecasts that ocean pH will fall by
"between 0.14 and 0.35 units over the 21st
Century, adding to the present decrease of 0.1
units since pre-industrial times"
Acidification affects Corals
http://video.google.com/videop
lay?docid=4514060660097791020
Marine Snow