Chapter 4: Marine Sediments

what is the origin of the word sediments

sedimentum = settling, mainly of eroded particles, fragments of dust, dirt, debris

what is suspension settling

sediments settle out of water and accumulate on ocean floor

what do marine sediments provide?

a record of earth history, important resources, and they have origins from many sources.

what clues do marine sediments provide about earth’s history

organism distribution

ocean floor movements,

ocean circulation patterns

climate change

global extinction events

do mountains contain ocean sediments?

yes, tall mountains contain marine fossils because sediments lithify into sedimentary rock.

what are the types of sediments?

lithogenous, biogenous, cosmogenous, and hydrogenous

how is sediment collected

early exploration used dredges with bucket like devices.

modern exploration uses cores to get sediment columns, and rotary drilling which collects deep ocean sediment cores

what is the national science foundation

NSF formed Joint Oceanographic Institutions for Deep Earth Sampling (JOIDES) in 1963.

what institutions does JOIDES include

Scripps Institution of Oceanography

Rosenstiel School of Atmospheric and Oceanic Studies \n Lamont-Doherty Earth Observatory of Columbia \n University \n Woods Hole Oceanographic Institution

What is the deep sea drilling project

DSDP was initiated in 1966 on Glomar Challenger drilling ship. Core collection in deep water up to 6000 m (3.7 miles)

what did DSDP confirm

existence of sea floor sprading,

ocean floor age,

sediment thickness,

magnetic polarity reversals

when did the DSDP become the ocean drilling project

DSDP became ODP in 1985. JOIDES resolution replaced Glomar Challenger. Drilling rig to conduct rotary drilling up to 2100 m (6900 ft). drilled > 2000 holes.

What is the integrated ocean drilling program

IODP replaced ODP in 2003, can drill up to 7000 m (23k ft) into sea floor. Chikyu- new exploration vessel in 2007. Expedition to japan trench after 2011 earthquake.

paleoceanography

study of how ocean atm, and land interactions have produced changes in ocean chemistry, circulation, biology and climate.

what do marine sediments provide

marine sediments provide clues to past environmental conditions. cores of sediment collected from sea floor.

what can oceanographers learn about environmental conditions from sediment cores

timing of major extinctions

global climate change

plate movements

historical info about earth’s geology and biology

lithogenous sediments

composed of fragments of pre existing rock material, that originates on continents or islands from erosion, volcanic eruptions, or blown dust. also terrigenous sediments

biogenous sediments

composed of hard remains of dead marine organisms

hydrogenous sediments

composed of material that is dissolved in water and precipitates to form deposits.

cosmogenous sediments

composed of material of extra terrestrial origin

how do lithogenous sediments form

eroded rock fragments from land. reflect composition of rock from which it was derived. produced by weathering (water, temp changes, chemical effects).

how are small lithogenous particles transported

carried to ocean by streams, wind, glaciers, gravity. greatest quantity around continental margins. deposited in bays and lagoons. beach deposits along shoreline. can be carried beyond continental margin to deep ocean basin

lithogenous transport mechanisms

streams, wind, glaciers, gravity

where are coarser sediments?

closer to shore, finer are further.

what is the main mineral in sediments?

quartz, SiO2. it is one of the most abundant and chemically stable minerals in the Earth’s crust. it is resistant to abrasion, and as a result it can be transported large distances and deposited far from the source.

what is the wentworth scale of grain size for sediments

boulder, cobble, pebble, granule, sand, silt, clay

what does texture indicate about environmental energy

high energy (strong wave action) conditions predominate close to shore, large particles. Low energy conditions predominate in deep ocean basins = small particles.

neritic sediment

shallow water deposits, close to land, mainly lithogenous, deposited quickly, coarse grained.

pelagic sediment

deeper water deposits, finer grained sediments, deposited slowly

beach deposits

wave deposited quartz rich sands

continental shelf deposits

relict sediments

turbidite deposits

graded bedding

glacial deposits

high latitude continental shelf, forming by ice rafting around Antarctica and greenland.

what are pelagic deposits made of

volcanic ash, wind blown dust, fine material.

abyssal clay

70% of clay sized particles from continents. Red clay oxidized iron. abundant if other sediments absent

two types of biogenous sediment

macroscopic: visible, shells, bones, teeth , microscopic: tiny shells or tests, biogenous ooze, algae and protozoans

two most common chemicals in biogenous sediment

Calcium carbonate, silica.

diatoms

photosynthetic algae, silica, perforated for passage of substances.

radiolarians

single celled protozoans, long spikes. tests are shells of microscopic organisms.

diatomaceous earth

siliceous ooze lithifies into this.

foraminiferans and coccolithophores

nannoplanktons, photosynthetic algae.

rock chalk

formed in cretaceous period, lithified coccolith rich ooze. like white cliffs of S England (dover)

calcareous ooze

protozoans, coccoliths, and other calcareous secreting organisms

distribution of biogenous sediments

productivity: # of organisms in surface water above floor, destruction: skeletal remains (tests) dissolve in seawater at depth, dilution: deposition of other sediments decreases percentage of biogenous sediments

neritic deposits

lithogenous sediment, some biogenous. Carbonate deposits like limestone. fossil shells

stromalites

lobate structures consisting of fine layers of carbonate forming in warm shallow ocean with high salinity. cyanobacteria produce these deposits.

calcite compensation depth (CCD)

depth where CaCO3 dissolves easiest.

lysocline

depth at which a significant amount of CaCO3 begins to dissolve rapidly

where are high concentrations of calcareous ooze

along mid ocean ridge, little is found in deep ocean basins below CCD

environmental conditions for oozes

siliceous: cool, high latitudes. Calcareous: warm, low latitudes, dissolves below CCD.

hydrogenous sediments

precipitate out of a solution, formed when solids left behind after water evaporates.

precipitates

occur when salts or minerals precipitate directly from seawater, at mid ocean ridges . Examples: manganese nodules, phosphates, carbonates, metal sulfides

manganese nodules

slow accumulation rates, discovered in 1872 by HMS challenger, commercial uses. origin and formation is unresolved. unsure why they’re not buried by seafloor sediments. central object for nucleation (teeth, bone, rock, coral)

metal sulfides

Iron, nickel, copper, zinc, silver, associated with hydrothermal vents

evaporites

minerals that form when seawater evaporates. restricted open ocean circulation, high evaoporation rates. Mediterranean

cosmogenous sediments

microscopic spherules, macroscopic meteor debris.

tektites

molten space dust

are marine sediments mixed

yes, lithogenous and biogenous sediment rarely occur as absolutely pure deposits that do not contian other types of sediment

where is pelagic and neritic sediment distributed

neritic is near shore, covers 1/4 of sea floor. coarse grained deposits dominate continental margins (lithogenous)

pelagic is deep ocean basin: 3/4 of sea floor, biogenous

what is the most dominant sediment worldwide

calcareous ooze 45%,

abyssal clay 38%

siliceous ooze 8%

energy resources from sediments

petroleum: ancient remains of microscopic organisms. 95% of economic value of oceanic nonliving resources. >30% of world’s offshore resources.

gas hydrates

clathrates: high pressures squeeze chilled water and gas into ice like solid. methane hydrates most common