I. Classification

A. By Origin

1. Terrigenous - erosional products (also volcanics)

2. Biogenous - critter shells

3. Hydrogenous - in situ precipitation, alteration/weathering

4. Cosmogenous - extraterrestrial

B. By Size

1. Gravel (pebbles, cobbles) = > 2mm

2. Sand = 62 µm - 2 mm

3. Silt = 4 - 62 µm

4. Clay = < 4 µm

C. By Constituents

1. Pelagic sediments - open ocean, fine grained

a. clays & biogenic oozes

2. Hemipelagic - continental margin, coarser grained

b. muds

II. Terrigenous Sediments

A. Transported to Ocean By:

1. Rivers - presently trapped on shelf, during glacials deposited at shelf edge

2. Glaciers - high latitudes only

3. Wind - definitely aeolian principally off deserts (see deep sea clay below)

B. Results in Thickest Sediments at Continental Margins

C. Transport Downslope by Gravity Once in Ocean

1. Slumps & Slides

2. Sediment Gravity Flows

a. debris flows

b. grain flows | - decreasing viscosity

c. fluidized sediment flows

d. turbidity currents

3. Turbidity Currents

a. proposed in the 1930's

b. laboratory experiments in the 1940's

i. head, neck, body, tail

c. deep-sea evidence in the 1950's

i. sand in deep-sea cores

ii. effects of 1929 Grand Banks & 1966 Solomon Sea earthquakes

d. Bouma Sequence - depositional product of a turbidity current (turbidite)

i. subdivided into several distinct layers designated A to E from top to bottom

D. Submarine Canyons

1. Mostly incised into the continental slope

2. Major conduit of sediment to the deep ocean

3. Controversial origin

a. subaerial erosion - only at canyon heads on shelves

i. except for Mediterranean

b. turbidity currents - during glacials

c. tidal currents - during interglacials

i. Georges Banks - plenty of sand in axis, cutting active

ii. Hudson Canyon - only mud, cutting inactive

E. Deep Sea Fans

1. Depositional setting for turbidites

2. Morphology

a. upper - inner

i. leveed channel with sand & conglomerates

ii. overbank mud

b. middle - proximal

i. several suprafans with channels not as well developed

ii. ideal Bouma sequences developed

iii. only one suprafan actively depositing at one time

c. lower - outer- distal

3. Abyssal Cones

a. big fans associated with major rivers

b. Amazon Cone

i. meandering channels

ii. overlapping suprafans on middle fan

c. Bengal Cone

i. several episodes of turbidite deposition separated by intervals of more biogenous, pelagic deposition

F. Continental Rises

1. Winnowing & redeposition of turbidites parallel to depth contours

a. contourites - cross lamination of sand & silt

2. Development of large sediment waves

G. Abyssal Plains

1. Elongate features

2. Sediment transport (turbidites) parallel to long axis

H. Hemipelagic Sediments

1. Characteristic of the continental slope & rise

2. Muds carried across shelf by wave & tide energy as slightly dense plumes

a. extend out from slope at depth where denser water is encountered

3. Relatively fast sedimentation rate - pore water O2 is used up quickly

a. hemipelagic mud is generally gray or green from the presence of sulfides or magnetite

I. Deep Sea Clay

1. Composition

a. Illite - middle latitude continental physical & chemical weathering

b. Montmorillonite - oceanic volcanic weathering

c. Chlorite - high latitude continental physical weathering

d. Kaolinite - low latitude continental chemical weathering

2. Most likely transported by wind

3. Very slow sedimentation rate - significant oxidation (at least now)

a. deep sea clay is red or brown from the presence of hematite

III. Biogenous Sediments

A. Types

1. Calcareous (carbonate)

a. foraminiferal -> amoeba-like protozoan

b. nannofossil (coccolith) -> algae

c. pteropods -> planktonic gastropods (aragonitic shells)

2. Siliceous (opalline SiO2)

a. radiolarian -> amoeba-like protozoan

b. diatom -> algae

c. silicoflagellates -> algae

B. Controls on Distribution

1. Productivity

a. nutrient poor = calcareous

b. moderate to high productivity = siliceous

i. SiO2 is undersaturated in surface water

ii. siliceous tests carry SiO2 into nutrient rich deep water

iii. organisms with siliceous tests will only be abundant where SiO2 & nutrients are returned to the surface quickly

c. siliceous oozes abundant at high latitudes (vigourous vertical mixing) & along the equatorial Pacific (upwelling)

2. Dilution

a. although biological productivity is highest along continental margins, so are terrigenous sedimentation rates

b. biogenous is diluted by more abundant terrigenous

3. Dissolution

a. CaCO3 is undersaturated at depth in the open ocean

i. solubility increases with increasing pressure, decreasing temperature, & decreasing salinity

b. CaCO3 is absent at great depth - below the Calcite Compensation Depth (CCD)

i. deeper than 5500-5000 m in the Atlantic

ii. deeper than 5000-4500 m in the Indian

iii. deeper than 4500-4000 m in the Pacific

c. dissolution of CaCO3 starts above the CCD at the lysocline

d. CaCO3 is abundant in sediments lying above the CCD

i. MOR

ii. seamounts, aseismic ridges

e. CaCO3 is generally not well preserved at continental margins either

i. decay of abundant organic matter generates CO2 which makes the water more acidic

ii. however, the abundant productivity along the equatorial Pacific results in a local deepening of the CCD to the seafloor here

4. note - calcareous oozes convert first to chalk & then to limestone during diagenesis, while siliceous oozes convert to porcellenite & then to chert

C. Plate Stratigraphy

1. That the relatively young crust of the MOR is generally above the CCD, but older crust subsides below the CCD results in a distinct vertical sedimentary section:

a. carbonate sediments (or metalliferous sediments) immediately overlie layer 2 basalts

b. these calcareous sediments are in turn overlain by pelagic clay or by interbedded pelagic clay & siliceous sediment

c. for sections overlying very old oceanic crust, the pelagic clay/siliceous sediment may be overlain by abyssal plain turbidites or continetal rise muds or volcanic sediments

IV. Hydrogenous Sediments

A. Ferro-manganese Nodules

1. Iron & manganese = 30-45%

2. Nickle, copper, & cobalt = 1-3%

3. Variation in composition geographically:

a. nickle & copper -> in silica-rich areas

b. cobalt -> in pelagic areas

4. Nodules grow concentrically about some nucleus

a. biogenic sediment grains are often incorporated into nodules

b. nodules can coalesce to pavements

5. Rate of formation

a. 1-4 mm/MILLION years

i. can be faster - WWII bomb fragments off southern California often are coated with thick crusts that formed at 1-4 mm/yr

6. Paradox of formation

a. nodules grow at 1 mm/my, but the slowest sedimentation rates are 3 orders of magnitude greater (>1 meter/my)

b. thus nodules form only because they aren't buried

c. several ways to prevent burial:

i. non-deposition/erosion of sediments because of bottom currents

ii. animals keep at the surface

7. Nodules are abundant in the pelagic clay-rich areas of the Pacific, on the lower flanks of the MOR in the Atlantic, & on the west side of the Atlantic where bottom current velocities are high

B. Hydrothermal Sediments

1. Formed at MOR crests from circulation of seawater through the crust

2. Occur as Fe/Mn oxide-rich (fast spreading), Fe sulfide-rich (intermediate spreading), & Mn oxide-rich (slow spreading) basal sediments

3. Progressive dilution of primary, hi-T, reduced solution by seawater

V. Cosmogenous Sediments

A. Extraterrestrial

B. Micrometeorites = microtektites = glassy

1. 30 µm to 1 mm in size

2. Morphology

a. generally smooth, either aerodynamic or irregular

b. sometimes rough from solution

3. Disseminated throughout sediment column in very low abundances (0.00002 mm/ky)

C. Found in greater concentrations adjacent to tektite strewn fields in North America, Africa, & Australasia

1. Tektites - 2-4 cm in diameter

2. Known to be extraterrestrial by composition

3. association of tektites & microtektites is based on location, age, general morphology, petrography, physical properties, & chemical composition

4. Also a Czechoslovakian tektite strewn field with no marine equivalent

D. Marine microtektite strewn fields

1. 20-40 cm thick layers

2. 10-100 microtektites per 8 cm3 (cube 2 cm on a side)

3. Thickness indicates degree of reworking by bioturbation

4. Ages

a. 700,000 for Australasian

b. 1.1 ma for Ivory Coast

c. 35 ma for North American

5. Implication of ages

a. Australasian coincides with Bruhnes-Matayama magnetic polarity reversal

b. Ivory Coast is associated with Jaramillo magnetic polarity reversal, although somewhat older

c. Suggested by Glass & Heezen (1966) that the magnetic polarity reversal was caused by meteorite impact

VI. Miscellaneous Sediment Types

A. Windblown (Eolian) non-volcanic

1. Off deserts in subtropics

a. dry - dust not removed by rain

b. trade winds - persistent wind direction

2. Mixed up to jet stream & upper troposphere

a. 2 week residence time, transported thousands of km

3. Components

a. quartz: 2 - 10 µm: 30 degrees N & S - coincides with deserts

i. really apparent in Pacific - no turbidites

ii. most useful - continental source only & lasts longer because more resistant to dissolution

b. opal phytoliths

c. freshwater diatoms

4. Paleoclimatology

a. dry zones expand - more phytoliths & diatoms

b. only good off Sahara for past 1 ma - warmer & wetter previously

B. Windblown volcanic

1. Tephra = volcanic glass or ash: < 2 mm

2. Distribution determined by prevailing wind directions (see Fig. 3-4)

C. Glacial-marine

1. Mostly from ice-rafting (either icebergs or sea ice)

2. Distribution

a. Southern hemisphere - as much as 2000 km from Antarctica

b. Northern hemisphere - mostly in northern North Atlantic & Arctic

D. Black shales

1. Called SAPROPELS (sapro = Greek for putrid, decaying organic matter)

2. Organic rich - 5-20%; also contain abundant pyrite

3. Formed under anoxic conditions - no O2 to oxidize organic matter

4. Two ways to get anoxic conditions

a. reduce vertical mixing

b. expand O2 minimum layer

5. Black Sea, Orca Basin - reduced vertical mixing

6. Upper continental slope - O2 minimum (see Fig. 9-20)

a. O2 content 5-8 ml/l in upper 500 m - photosynthesis

b. O2 content 0-3 ml/l from 500 to 1000 m - respiration

c. O2 content 3-5 ml/l > 1000 m - deep circulation

7. Ancient examples

a. Eastern Mediterranean - low salinity cap - vertical mixing stopped

b. early Atlantic - expanded O2 minimum layer (note - absolute Corg decreased during black shale deposition)

VII. Sedimentation Rates

A. Terrigenous

1. Shelf: 5-10 cm/ky (50-100 m/ma)

2. Slope: 5-100 cm/ky (50-1000 m/ma), but no net accumulation (erosional setting)

3. Rise: 5-100 cm/ky (50-1000 m/ma)

4. Abyssal plains: 5-10 cm/ky (50-100 m/ma) - turbidites

1-10 mm/ky (1-10 m/ma) - hemipelagic

5. Deep sea clays: <1 mm/ky (<1 m/ma)

B. Biogenous

1. CaCO3: 1-3 cm/ky (10-30 m/ma)

2. SiO2: 1-5 mm/ky (1-5 m/ma)

C. Hydrogenous

1. Nodules: 1-4 mm/MA

2. Metalliferous sediments: 20 cm/MA?

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