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