Ocean Sediments

TYPES AND DISTRIBUTION

Ocean Sediments

Ocean Sediments

Sediment: Defined as particles of organic or inorganic matter that accumulates in an unconsolidated form.

Sources of Ocean Sediments Terrigenous: (lithogenous) 45% of all ocean floor sediments.

From weathering and erosion of rocks on continents and islands. Biogenous: 55% of ocean floor sediments

From siliceous and calcareous producing organisms that extract these compounds from the ocean water.

Hydrogenous: <1% of all ocean floor sediments From direct precipitation of sediment or minerals from seawater.

Cosmogenous: Extremely small amounts From atmosphere, meteorites, and dust

Atlantic Vs. Pacific

Atlantic has twice the sediment cover of pacific. Why?

1.) Trenches: make it difficult for sediment to accumulate.

2.) Size: Hard to get terrigenous sediments to mid-Pacific

3.) Rivers: Atlantic has more rivers emptying sediment into it.

Thickness of Ocean Floor Sediments

Terrigenous Sediment—Turbidites

Hydrogenous Sediment—Manganese nodules

Biogenous Sediment—calcareous ooze

Distribution of Marine Sediments

Neritic: Coastal sediments derived from the continents that accumulate on continental shelves. Carried out to oceans by rivers and streams Sorting: Coarser grains like sand deposited near coast

and finer sediments like silt and clay deposited farther out on shelf.

Turbidity currents can disrupt sorting. Typical deposition occurs at a rate of 20 cm per 1,000

years. Though at the mouths of major rivers (i.e. The Nile,

Mississippi) can have rates of 8 meters per year!75% of all sediments by volume but only 20% by area. (thick but not widespread)

Sorting on continental shelf

Neritic sediment after Hurricane Irene

Shelf Sediments By Latitude

Carbonate Shelves

Carbonate (limestone) is deposited in warm, shallow,tropical seas with limited sediment input from rivers.

Pelagic: Deep water sediment of the slope, rise, and deep ocean basin (abyssal plain, mid-ocean ridges, seamounts) and are primarily biogenous.

Thickness is highly variable from place to place and ocean to ocean. Turbidties Clays: 38% of deep ocean sediments. Terrigenous origin (from the

continent). Settle slowly because they are small (1 mm per 1,000 years).

Ooze: a deep-ocean sediment composed of at least 30% of biogenous material. Organisms include single-celled, drifting, plantlike organisms and the single

celled animals that feed on them. Shells of silica (quartz) or calcium carbonate (calcite) When they die, their shells settle to the floor and combine with

terrigenous silts and clays to form ooze. Accumulates at 1-6 cm/1,000 years

4 types of clays

1.) Chlorite: high latitude clay due to low chemical weathering. (North and South Pacific and Atlantic)

2.) Kaolinite: Warmer latitudes. Formed from lots of chemical weathering. (tropics)

3.) Illite: Most widespread but dominant in Northern Hemisphere.

4.) Montmorillonite: Ash from volcanoes (Pacific mostly).