Origin and Distribution of Marine Sediments Whats all

Origin and Distribution of Marine Sediments 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

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

Classifications FBy Size Clay -- Silt -- Sand -- Pebble -- Cobble 0. 001 mm 100 mm F Effects of water velocity on transport: rivers and near-shore vs open ocean

Sediment Transport Ø 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

River sediment loads (units 106 tons/yr)

Glacial (Ice-rafted debris)

Turbidites u. Rapidly-accumulated terrestrial sediments u. Earthquake-triggered submarine avalanches u. High velocity (~50 mph!), erosive events u. Good examples preserved on Mary’s Peak

Turbidites (submarine avalanches)

Sea Level Changes

Biogenous sediments (from living things) FCalcareous (Ca. CO 3) Foraminifera -- animals Coccolithophores -- plants FSiliceous (Si. O 2) Radiolaria -- animals Diatoms -- plants

mm = micron = millionth of a meter!

Productivity = skeletons and soft tissue u. Accumulation depends on production and preservation u. Si. O 2 is preserved everywhere u. Ca. CO 3 is variable, depending on P, T, p. H

Carbonate Compensation Depth

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!

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