Sedimentsin the

Oceans

sediment - matter that has been deposited by some natural process

smaller – easier for currents to movelarger – harder for currents to move

Sediment Sizes

large

small

marine sediments classified as:oceanic (pelagic) –

• found in open ocean• further away fromland

neritic – • found in watersabove continental margins • closer to land - coastal

sediment types*terrigenous - derived from land

*biogenous - derived from plants and animals

hydrogenous (authigenic) – form from chemical reactions in the ocean

cosmogenous - from outer space

*most common

derived from landrock fragmentsvolcanic ashblown dust

broken down by weathering (erosion)

Terrigenous Sediment

sources:•rivers - biggest contributors•glaciers•wind blown dust•coastal erosion•volcanic debris•groundwater

Terrigenous Sediment

turbidite – like an underwater landslide – carries terrigenous sediment down cont. slope

Terrigenous Sediment

Terrigenous Sedimentdust from the Sahara Desert

Biogenous Sediment

• derived from plants and animals• mostly shells, some bones

Biogenous Sediment

ooze – very fine sediments at least 30% biogenous in origin

• found in deep sea off continental margins• build up very slowly• two main types:

calcareous ooze and siliceous ooze

Biogenous SedimentCalcareous Ooze• made of calcium carbonate (CaCO3) - chalky• dissolves in very deep waters• includes: foraminifera (like ameba w/ shell)

coccolithophores (algae w/ shell)

pteropods (small drifting snails)

foraminifera coccolithophores pteropods

Coccolithophores and a coccolithiphore bloom near

England

Biogenous Sediment

The White Cliffs of Dovermade of calcareous ooze – basically chalk

Biogenous Sediment

Siliceous Ooze• made of silicon (glass)• deeper than calcareous oozes and polar

regions• includes: diatoms (algae)

radiolaria (like ameba w/ shell)diatoms radiolaria

Hydrogenous Sediment

• also called authigenic sediments• form from chemical reactions in the ocean• very small percentage of ocean sediments

Hydrogenous Sediment

Manganese Nodules:• golf ball size chunks of manganese and iron• found in deep sea• thought would be economically valuable one day

Hydrogenous Sediment

Phosphorites:• like manganese nodules, but mostly phosphorus• may be important some day for fertilizer

Hydrogenous Sediment

Hydrothermal Vents:• like underwater hot springs at mid-ocean ridges• form metal sulfides

Hydrogenous Sediment

Evaporites:• salts that precipitate (form solid) as water evaporates from an isolated arm of the ocean

Cosmogenous Sediment

from outer space• found in trace amounts – least common• examples:

dust from outer spacemeteorite debrismicrotektites – crustal material that exits earth’s atmosphere during meteor impact and then falls back to earth – melts forming glassy teardrops

Where types of sediment are found:

sediments can be:well sorted – all one sizepoorly sorted – many sizes together

affects:amount of water between sediment grainsoxygen leveltypes of organisms that can live there