Reading Material

See class website

“Sediments”, from “Oceanography”M.G. Gross, Prentice-Hall

Classification of marine sediments

Lithogenic – from disintegration of rock on landaeolian, FLUVIAL, and glacial sources

Biogenic – organic precipitation of dissolved components dominated by single-celled plants and animals (create oozes) calcium carbonate (limestone) = calcareous silicon dioxide (opal) = siliceous

Authigenic – inorganic precipitation of dissolved components seawater becomes supersaturated with regard to some

chemicals

Cosmogenic – from outside Earth meteorites, usually very small (tektites)

Distribution of Marine Sediments

Lithogenic sedimentdominates near continents (shelf, slope, rise)because source from landglacial at high latitudes, fluvial at all latitudes

Biogenic sedimentdominates away from lithogenic sediments, usually away from

continents(exception: calcareous sediment can dominate shallow low-latitude

areas)

calcareous sediment (foraminifera) found on flanks of mid-ocean ridges

because it dissolves in water >4000 m deep

siliceous sediment found where nutrient supply is greatnutrients stimulate marine productivity (diatoms, radiolarians)

Authigenic sediment and red claydominates away from continents, in water depths >4000 m, not

high prodbecause they are overwhelmed everywhere else by lithogenic and

biogenic

Deep-sea sediments

Trailing-Edge Margin

Sea-Level Change

Time scales of ~10,000 years

Sea level fluctuates due to climate change

Cold periodsmore precipitation as snow (not rain)more snow remains for multiple years, ice sheets form miles thickevaporation continues from oceans, but return as runoff reducedcold temperatures cause sea water to contractsea level drops

Warm periodsless precipitation as snowglaciers meltwarm temperatures cause sea water to expandsea level rises

Likely Cause of Natural Climatic Changes

Cyclical variations in orbital and rotational factors

Holocene sea-level changeConstructing sea-level curves

indicator of sea level, not transported(e.g., oyster beds, marsh peats)

age dates,14C good for Holocene

stable land surface

108 years

106 yearsPleistocene

104 yearsLast high-stand

106 yearsbroad fall in sl

Holocene eustatic sea-level rise

LGM = Last Glacial Maximum130 m lower, 18-20 kybprose rapidly until ~7 kybp

Step-wise rise in sea leveldue to pulses of meltwater

Flooded river valley on the continental shelf – in the Gulf of Papua (between Australia and New Guinea)

This valley might have been flooded quickly by step-wise sea-level rise

This is a bathymetric chart, cool colors are deep, warm colors are shallow

~35 m deep

~65 m deep

“Local” sea-level rise

Puget Sound

Tectonic Uplift

Deltasubsidence

Last ~7000 years

Past Century

The future

Holocene Rise in Sea Level

Cold period (ice age) ends ~20,000 years ago

Sea level stood ~130 m below present sea levelat edge of continental shelf (shelf break)

Global sea level rose quickly (~10 mm/y) until ~7000 years ago

Rate of global (eustatic) rise has been slow (~2 mm/y) since then

Sea-level change along any particular coast depends also upon land movement

plate tectonicssediment consolidation (e.g., deltas sink)glacial rebound (weight of glaciers removed, land rises)

Continental-Margin Sedimentation during Low Sea Level

Rivers and glaciers cross continental shelf to shelf break

Much sediment supplied at top of steep slopecreates unstable sediment

Large storms or earthquakes trigger underwater landslides

Slurry of sediment moves down continental slopeknown as “turbidity currents” and “debris flows”

Erodes seabed on continental slopeforms submarine canyons

Deposits sediment on continental rise and abyssal plainscreates layers known as “turbidites”

Trailing-Edge Margin

Turbidity Current and resulting

Turbidite

1929 Grand Banks turbidity current