Origin and Distribution of Marine Sediments What’s all that squishy muck at the bottom of the ocean? What can we learn from it? What’s all that squishy muck at the bottom of the ocean? What can we learn from it?

Marine Sediments are: FParticles of various sizes derived from a variety of sources that are deposited on the ocean floor FA vast “library” recording geologic, oceanographic and climatic conditions FRemarkably complete compared to land FParticles of various sizes derived from a variety of sources that are deposited on the ocean floor FA vast “library” recording geologic, oceanographic and climatic conditions FRemarkably complete compared to land

Where do these come from? FInputs are: -- rivers -- atmosphere -- surface waters -- volcanoes (both on land and submarine) -- deep ocean water -- outer space

Classifications FBy Size Clay -- Silt -- Sand -- Pebble -- Cobble mm 1 mm 100 mm F Effects of water velocity on transport: rivers and near-shore vs open ocean FBy Size Clay -- Silt -- Sand -- Pebble -- Cobble mm 1 mm 100 mm F Effects of water velocity on transport: rivers and near-shore vs open ocean

Sediment Transport  Fluid velocity determines the size of the particles that can be moved

Size Sorting

Classifications FBy Origin Terrigenous -- from land Biogenous -- from life in the oceans Hydrogenous -- precipitated from water Cosmogenous -- extraterrestrial

Terrigenous sediments (from land) FRivers FWinds (eolian) FGlaciers (ice-rafted debris, IRD) FTurbidites FSea level changes FRivers FWinds (eolian) FGlaciers (ice-rafted debris, IRD) FTurbidites FSea level changes

River sediment loads ( units 10 6 tons/yr )

Glacial (Ice-rafted debris)

Turbidites uRapidly-accumulated terrestrial sediments uEarthquake-triggered submarine avalanches uHigh velocity (~50 mph!), erosive events uGood examples preserved on Mary’s Peak uRapidly-accumulated terrestrial sediments uEarthquake-triggered submarine avalanches uHigh velocity (~50 mph!), erosive events uGood examples preserved on Mary’s Peak

Turbidites (submarine avalanches)

Sea Level Changes

Biogenous sediments (from living things) FCalcareous (CaCO 3 ) Foraminifera -- animals Coccolithophores -- plants FSiliceous (SiO 2 ) Radiolaria -- animals Diatoms -- plants FCalcareous (CaCO 3 ) Foraminifera -- animals Coccolithophores -- plants FSiliceous (SiO 2 ) Radiolaria -- animals Diatoms -- plants

 m = micron = millionth of a meter!

Productivity = skeletons and soft tissue uAccumulation depends on production and preservation uSiO 2 is preserved everywhere uCaCO 3 is variable, depending on P, T, pH uAccumulation depends on production and preservation uSiO 2 is preserved everywhere uCaCO 3 is variable, depending on P, T, pH

Carbonate Compensation Depth

FThe depth at which carbonate input from the surface waters is balanced by dissolution in corrosive deep waters FIn today’s ocean this depth (CCD) varies between 3 km (polar) and 5 km (tropical) FThus, accumulation rates vary a lot! FThe depth at which carbonate input from the surface waters is balanced by dissolution in corrosive deep waters FIn today’s ocean this depth (CCD) varies between 3 km (polar) and 5 km (tropical) FThus, accumulation rates vary a lot!

Accumulation Rates for Oozes FProductivity  reproduction of planktonic organisms FPreservation  silica dissolves only very slowly  calcium carbonate varies with depth FRates are variable: <1 to 15mm/1000 yr FProductivity  reproduction of planktonic organisms FPreservation  silica dissolves only very slowly  calcium carbonate varies with depth FRates are variable: <1 to 15mm/1000 yr

Coastal waters are often highly productive, with abundant planktonic organisms thriving in the surface waters. Why then are biogenous oozes rarely found nearshore??

the large input of terrigenous sediment to the continental margin overwhelms the biogenous component in the sediment.

Hydrogenous (from sea water) FMetalliferous sediments at spreading ridges -- “black smokers” FManganese nodules FEvaporites -- Salt deposits FMetalliferous sediments at spreading ridges -- “black smokers” FManganese nodules FEvaporites -- Salt deposits

baseball to bowling ball size!

Cosmogenous (from outer space) FMeteorites and comets

Sediment Accumulation

Sediment succession

Distribution of Marine Sediments