Marine Sedimentation

What is it and where does it come from?

Table 5-1, p. 103

Bottom of the Ocean Floor (Antarctica)

How do we know/How do we get it?

Ice samples

River inputs (sedimentation)

Atmospheric Inputs

Dust input

• Based upon water depth, the ocean environment can be divided into:

– the shelf• shallow and near a terrigenous source

– the deep ocean basin• deep and far from a terrigenous source

Shelf Sedimentation

• Shelf sedimentation is strongly controlled by:– Tides– Waves– Currents

• Their influence decreases with water depth.

• Shoreline turbulence prevents small particles from settling in the shallow water.

• Particle size decreases seaward for recent sediments.

• Geologic controls of continental shelf sedimentation must be considered in terms of a time frame.

• For a time frame up to:

– 1000 years, waves, currents and tides control sedimentation.

– 1,000,000 years, sea level lowered by glaciation controls sedimentation and cause rivers to deposit their sediments at the shelf edge and onto the upper continental slope.

– 100,000,000 years, plate tectonics determines the type of margin that develops and controls sedimentation.

4-2 Sedimentation in the Ocean

What’s in there?

• Forams

• Coccoliths

• Radiolarians (and other Protozoans)

• Diatoms and other Phytoplankton (shells)

• Fecal Pellets and “Dead” things (marine snow)

Major pelagic sediments in the ocean are red clay and biogenic oozes.

“Marine Snow”

Foraminifera

Diatoms

Foram

Coccolith

Radiolarians

Diatoms

Fecal Pellet

What do you get?

…What geologic structures? and where?

100 mya - Lithified Coccolith Cliffs (Dover, England)

Fig. 5-12, p. 111

Global Deep-Sea Deposits

Sedimentation Rates

If influx of terrigenous sediment is low and the water is warm, carbonate sediments and reefs will dominate.

Distribution of Carbonate Shelves

• Deep-sea Sedimentation has two main sources of sediment:

– External – terrigenous material from the land

– Internal – biogenous and hydrogenous from the sea.

Deep-Sea Sedimentation