sediments
Biogenous
Biologically precipitated from dissolve components in seawater
Lower actual concentration
faster the solid will dissolve
Three factors control distribution of biogenous oozes in world oceans
1: Production of particles 2: Destruction of particles 3: Dilution by other sediment types
Continental shelf sediments
-On passive margins majority of neritic sediments are terrigenous. -Exact nature depends on geology of river drainage basins and coastal areas. -On active margins majority of neritic sediments are volcanic -Highly variable chemical, physical, geological, biological conditions produce highly variable sediment deposits -typical accumulation rates > 10-100 cm/kyr -Wave action suspends particles in shallow continental shelf waters, and particles are moved by currents -Modern sediments currently being deposited
Continental slope sediments
-Primarily Hemipelagic sediments -less variable than shelf sediments -mixtures of land derived (terrigenous or volcanic) and calcaeous biogenous particles -accumulation rates 1-10 cm/kyr
Why?
-The only chemical, biological, geological and physical history we have of the oceans over the last 200 million years is contained in marine sediments -More ancient information is contained in sedimentary rocks on land, but more difficult to interpret because of alteration by geological processes
Continental rise sediments
-Three different types of deposits -Background hemipelagic sediments -Particle by particle accumulation -Very similar to slope sediments, but usually more biogenous material -Accumulation rates 1-10 cm/kyr
Three different classification schemes that will help us interpret sedimentary record
1: partical size (important because physical transport processes are size dependent) 2: Depositional environment (where in the oceans are sediments found?) 3: Source (what processes make and transport sediments?)
Two types of weathering
1:Physical weathering 2:Chemical weathering
Lysocline is ______ km in atlantic and _______km in pacific
3-4 1-3
for spherical particles what happens to area/volume ratio as particles get smaller?
AREA = 4πR2 = 3 VOLUME 4/3πR3 R
Given these particle settling data, would you expect smallest sediment particles to be on sea floor very close to where they enter or are produced within the surface ocean?
Actual distribution patterns of modern sediments indicate almost all particles, large and small, are found very close to where they enter or are produced in the surface ocean EX: Siliceous sediments are only found under zones of high biological productivity
PArent rock
Andesite + granite
OOZE
Any pelagic sediment deposit that has more then 30% of a biogenous component
Why is it surprising that Greenland produces more glacial sediments than Antarctica?
Arctic ocean has different type of ice rafted sediment deposits. North American and Asian river ice contains sediments that are washed into Artcic ocean in spring. Also, rivers in north America and Asia bring sediments to ocean during summers and deposits them on wide, shallow continental shelves. Winter sea ice formation in shallow waters incorporates sediments into ice sea ice is transported by winds and ocean currents when ice melts, sediments drop Better sorted than glacial marine sediments, but still not very well sorted.
What would be an example of a well-sorted deposit with large average sizes?
Beach sand
Sediment classification by soure
Biogenous Lithogenous(terrigenous) Hydrogenous (Authogenous) Cosmogenous
What two things is dissolved material a source for?
Biogenous and hydrogenous particles
Paleoceanography
Branch of marine geology that deals with interpretation of the sediment record found in the oceans
What impact would ocean acidification have?
CCD will get shallower and shallower Increase in acid dissolution rate shifts up
What does the distribution pattern correlate with?
Calcareous sediment distribution patterns not controlled by primary productivity, but by water depths.
Most significant sediment type in the open ocean?
Calcareous sediments
If rain rate > dissolution rate
Calcite will accumulate, even though water is undersaturated, because it is buried before it can dissolve
Manganese nodules
Can be found in continetal margin areas and even in fresh water, but they are fundamentally different from deep ocean nodules. Composed of mostly iron and manganese oxides, with variable amounts of trace metals (chemically related to metalliferous sediments) typically found in openocean on surface of aeolian and hydrogenous clays and siliceous oozes, but rarely on calcite oozes.
Saturated
Cannot dissolve anymore solute All solute is dissolved Adding more solute will result in undesolved particles
When and how were relict sands depositd across continental shelves?
Characteristic of rising sea level. Sea level higher today by 100 meters than 15000 years ago. As sea level rises, high energy beach environments migrate across what used to be coastal plain
Montmorillonite, secondary mineral produced by chemical weathering of basalts, Two sources....
Continental basalt's (lithogenous), and submarine basalt's (hydrogenous), can be dominate clay mineral. Primarily hydrogenous, except river input from montmorillonite-rich soils in india
Chemical weathering
Decomposition of minerals through chemical reactions Requires liquid water, high temperatures, acid solutions
CCD (calcite compensation depth )
Depth at which rain rate equals dissolution rate
dissolution rate
Dissolution rate= f[(equil) - (actual)]
Do you see anything wrong with the nodules being on sediment surface?
Even faster nodules grow much more slowly than sediments accumulate
when do siliceous particles end up preserved in the sediments?
Eventually pore waters (interstitial waters) become saturated and not further dissolution occurs. Globally 2% of siliceous particles end up preserved in the sediments, but only under the highest productivity surface waters.
what happens after glaciers move across land, scraping and picking up rocks (1-2% by volume)?
Eventually they reach the sea, for floating ice shelves, and ultimately break off to form icebergs
What would you expect sediment size distribution to look like for these deposits?
Extremely poorly sorted, with everything from finest clays to huge, house-sized boulders
Physical weathering (mechanical weathering)
Fragmentaton of rocks by temperature changes, freezing water, organisms, glaciers, rivers, etc. Produces primary minerals, those that are present in the parent rock
Where are greatest dissolution rates?
Greatest rates are deepest water column
supersaturation
Heating a saturated solution til you can dissolve more solution then cooling it down again without any precipitants
Chlorite, Never dominant (<30%), Primary mineral released by physical weathering, easily destroyed, and found in great concentrations in .......
High latitudes and dry climates such as Arabian sea and off eastern Australia
Where would modern ice rafted deposits be found?
High latitudes, where there is a lot of ice EX: glacial marine sediments are one type of ice rafted sediments, found primarily around Greenland and Antarctica, where extensive glaciers are found.
Why is CCD deepest in equatorial waters?
High productivity region with higher calcite rain rates
Large, well sorted particles are usually indicative of what?
High turbulent energy environment
After it forms icebergs?
Icebergs move with ocean currents and melt, releasing their sediment loads
How can solid inorganic calcareous and siliceous particles be destroyed?
Inorganic dissolution
Hydrogenous (Authogenous)
Inorganically precipitated from dissolved components in seawater, or secondary minerals produced by chemical weathering of submarine basalts
ICP
Ion concentration product= [Ca2+]act[CO3^2-]act
Where on earths surface would chemical weathering rates be highest? lowest?
Ions are leached into solution and secondary minerals, not found in the parent rock are formed
First sediments to accumulate on top of new ocean crust basalt's
Iron (III)oxide and Manganese (IV)oxide rich sediments found as thin (few tens of meters) basal layer above sea floor basalts
Lysocline (saturation horizon)
Is thermodynamic boundary, supersaturated above and undersaturated below
Why is calcite next to accumulate?
It is shallow water
Clay minerals
Kaolinite Chlorite Illite Montmorillonite
Kaolinite, Rarely dominant, secondary mineral produced by intense chemical weathering, highest concentrations at.......
Low latitudes Aeolian transport from Sahara, Aeolian transport from Australia
Small, poorly sorted sediments are usually indicative of what?
Low turbulent energy environment (protected shallow water, deep water)
Phosphorate nodules
Made from mineral called apatite, which is fundamentally a calcium phosphate. Phosphorites can occur as nodules, pebbles, and slabs, with growth rate of 0.1-1 cm/kyr
Small (clay size) radioactive dust particles produced at atmospheric thermonuclear bomb testing in 1950s and 1960s should have taken 50 years to reach the deep ocean sediments, but were observed there in less than two years. How can we explain this?
Much faster transport Most small sediment particles reach the sea floor much faster than expected based on their sizes because of biological activity in the surface ocean
How can this be explained?
Much slower currents Much faster vertical transport
What would be an example of a poorly-sorted deposit with small average sizes?
Mud flats
Illite is most abundant clay mineral in oceans and found abundant in
North pacific Aeolian, North atlantic rivers, and around antarctica glaciers
Most surface ocean areas have low rates of primary production because.....
Of nutrient limitation (N, P, Si)
how do they stay on the surface?
One hypothesis is that disturbance of sediments by foraging benthic organisms is enough to keep sediments from accumulating on nodules (compare to shaking a cat liter box wit clumping liter)
Wind (aeolian) transport
Only significant transport of lithogenous material to open ocean
do benthic organisms eat fecal pellets?
Organic matter in fecal pellet membranes and within pellets is source of food for benthic organisms, so the pellets are quickly broken down once they reach sea floor, so we normally see just individual particles
Sand
PHI -1 to 4 Very course Course Medium Fine very fine
Colloid
PHI 12
Silt
PHI 4 to 8 Course Medium Fine Very fine
Clay
PHI 8 to 12 Course Medium Fine Very fine
Gravel
PHI size -8 to -1 Boulder Cobble Pebble Granule
What controls settling velocities?
Particle settling velocities depend on particle densities and particle sizes. Since particle densities are pretty uniform in wide variety of marine sediment particles (2.5-3.0 g/cm3) and particle sizes vary over many orders of magnitude, particle sizes are dominant factor controlling sediment velocities.
Quartz
Pure crystalline SiO2 Primary mineral in felsic rocks Very resistant to weathering
Why is a logarithmic scale used?
Range of particle sizes covers many orders of magnitude (compare to PH scale for acids) sediments from unique source typically show a log normal size distribution
Production
Rates of primary production by autotrophs in the surface ocean control rain rates of biogenous particles to sea floor, even for particles produced by heterotrophs
Cosmogenous
Remains of meteorites
Lysocline
Saturation horizon
Where might dilution by other sediment types be important?
Significant in continental margin areas, where terrigenous particles can accumulate much faster than biogenous particles
Wentworth Phi scale
Size classification used for marine sediments
Palegic sediments
Slow particle by particle accumulation of sediments Average accumulation rates 0.1-1 cm/kyr
Why much higher currents necessary to erode consolidated muds than unconsolidated?
Small sediment particles actually held together by london forces (dispersion forces)
Lithogenous (terrigenous)
Solid particles transported from land to the oceans
Ocean Basins
Temporary resting place for almost all solid materials free to move around on earths surface
What is different about calcite saturation state than silica saturation state?
Top part of ocean is supersaturated, so no dissolution.
Equatorial open ocean upwelling zones
Trade winds at the Equator blow surface water both north and south, allowing upwelling of deeper water.
What does the internal structure of the nodules look like
Tree rings with alternating dark and light bands
Why is there a decrease in siz as a function of distance offshore?
Turbulent energy of environment decreases offshore direction as water gets deeper. Modern mud's can be found close to shore in low energy environments. Relict sands exposed in many places on outer shelf
Hydrogenous sediments
Two production mechanisms Direct inorganic precipitation of particles from seawater Submarine chemical weathering of fresh ridge basalts
What are london forces?
Type of intermolecular force that holds non-polar substances together
Fecal pellets
Undigested organic matter and inorganic matter is packaged inside organic membrane and excreted. These fecal pellets are larger than individual particles they contain and settle at much faster rate, since settling speeds depend on particle sizes. They are a major transport mechanism of sediments from surface oceans to sea floor
Sediment particle settling velocities
Very important physical characteristic of sediment particles, since settling velocities are involved in the control of distribution patterns
Lithogenous sediment particles are derived from.....
Weathering of continental rocks (igneous, sedimentary, and metamorphic)
What are forces that act on particles moving downward in the ocean?
Weight, Buoyancy, and friction Weight and buoyancy depend on volume of particle, while friction depends on area
Large particles
Well sorted
Relict
a thing that has survived from an earlier period or in a primitive form.
Undersaturation
all solute in it is dissolved It has the ability to dissolve more solute
CCD is kinetic boundary
below which no calcite accumulates
Weathering refers to what?
destruction of the parent rock
Use size distribution to infer.......
direction of movement of bottom water
Pelagic sediments
found in open ocean EX: Pelagic (red) clays, Calcareous ooze, and siliceous ooze
Neritic sediments
found mostly on continental shelf
Hemipelagic sediments
found mostly on continental slope and rise EX: calcareous muds, terrigenous muds, volcanogenic muds
CCD is always deeper than lysoclin
from 200 meters to 1500 meters
Do you have dissolution above the lysocline?
no
Reason siliceous sediments not found in shallow waters because....
of extreme undersaturation
Why are ocean basins only a temperary resting place
plate tectonic processes recycle entire sea floor every 200 million years study of marine sediments very important branch of marine geology
Small particles
poorly sorted
Contourites
sediments eroded by deep ocean contour currents and deposited downstream from erosion site Found mainly on western sides of ocean basins, typically at base on continental slope
Solid biogenic silica dissolves in water to produce.....
silicic acid, very weak acid
Dissolution occurs only below _________
the lysocline
Areas of higher than normal primary production only occur........
where nutrients are added to euphotic zone
Wentworth PHI formula
φ= -log2 [diameter(mm)] [diameter(mm)] =2-φ