Sediments
The continental shelves are covered by terrigenous sediments; that is, those derived from erosion of the continents. However, little of the sediment is from current rivers; some 60-70% of the sediment on the world's shelves is relict sediment, deposited during the last ice age, when sea level was 100–120 m lower than it is now.
Sediments usually become increasingly fine with distance from the coast; sand is limited to shallow, wave-agitated waters, while silt and clays are deposited in quieter, deep water far offshore. These shelf sediments accumulate at an average rate of 30 cm/1000 years, with a range from 15–40 cm. Though slow by human standards, this rate is much faster than that for deep-sea pelagic sediments.
Read more about this topic: Continental Shelf
Famous quotes containing the word sediments:
“People who, out of an inborn moderation, leave every glass standing only half-emptied refuse to admit that everything in the world has its sediments and dregs.”
—Friedrich Nietzsche (1844–1900)