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 processes- uplifted 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.

Lithogenousor 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.

Richard W. Murray Water Encyclopedia

• 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 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 tochemical 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 of Earth Science

World Imagebank and (B) courtesy of Lisa Gardiner.

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 Foraminifera-calcareous 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

From J. Noyes El Camino College

Calcareous Ooze

Calcareous ooze

• The dominant deep ocean sediment in low latitudes above the CCD.

• Along the mid-ocean ridges, seamounts and other peaks

From J. Noyes El Camino College

Siliceous Ooze

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)

From J. Noyes El Camino College

Red Clay

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

• 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/videoplay?docid=-4514060660097791020 Marine Snow