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Terrigenous Sediment Terrigenous Sediment – sediment that originates on land Terrigenous sediments consist primarily of mineral grains that were eroded from continental shelf and continental rocks and transported to the ocean Larger particles (gravel and sand) settle rapidly near shore Finer particles (clay) may take years to settle on the ocean floor and may be carried thousands of kilometers by the ocean’s currents On continental shelves, the terrigenous sediment is the thickest
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Seafloor Sediments &Resources from the Seafloor
Chapter 14, Sections 3 & 4
Seafloor SedimentsMost of the ocean floor is covered with sedimentSome sediment is deposited by turbidity currentsThe rest of the sediment has slowly settled onto
the seafloor from aboveThe sediment varies in thickness over the ocean
floorOcean-floor sediments can be classified
according to their origin into three broad categories: terrigenous sediments, biogenous sediments, and hydrogenous sediments
Terrigenous Sediment
Terrigenous Sediment – sediment that originates on land
Terrigenous sediments consist primarily of mineral grains that were eroded from continental shelf and continental rocks and transported to the ocean
Larger particles (gravel and sand) settle rapidly near shore
Finer particles (clay) may take years to settle on the ocean floor and may be carried thousands of kilometers by the ocean’s currents
On continental shelves, the terrigenous sediment is the thickest
Terrigenous Sediment
Biogenous SedimentBiogenous Sediment – sediment that is
biological in originBiogenous sediments consist of shells and
skeletons of marine animals and algaeCalcareous Ooze – produced from the calcium
carbonate shells of organismsCalcareous ooze has the consistency of thick
mudSiliceous Ooze – composed primarily of
diatoms—single-celled algae—and radiolarians—single-celled animals that have shells made out of silica
Biogenous Sediment
Hydrogenous Sediment
Hydrogenous sediment consists of minerals that crystallize directly from ocean water through various chemical reactions
These make up only a small portion of the ocean’s sediments
Manganese nodules are hard lumps of metals which precipitate around grains of sand
Calcium carbonates form by precipitation directly from ocean water in warm climates
Evaporites (salts) form where evaporation rates are high and there is restricted open-ocean circulation
Manganese Nodules
Distribution of Seafloor Sediments
Energy ResourcesOil and natural gas are the main energy products currently
being obtained from the ocean floorThe ancient remains of microscopic organisms are the
source of today’s deposits of oil and natural gasThe remains were buried and heated for millions of years to
be transformed into oil and gasGas Hydrates – compact chemical structures of water and
natural gasMost oceanic gas hydrates are created when bacteria break
down organic matter trapped in ocean-floor sedimentThese bacteria produce methane gas along with small
amounts of ethane and propaneGas hydrates resemble chunks of ice, but will ignite when lit
by a flame
Gas Hydrates
Other ResourcesOther major resources from the ocean floor include
sand and gravel, evaporative salts, and manganese nodules
Sand and gravel from offshore are used for landfill, to fill in recreational beaches, and to make concrete; many high economic value minerals can also be found in these deposits (diamonds, gold, platinum, etc.)
Manganese Nodules – hard lumps of manganese and other metals that precipitate around a smaller object
The manganese nodules also contain many minerals which have high economic value (iron, copper, nickel, cobalt, etc.)
When seawater evaporates, the salts increase in concentration until they no longer remain dissolved and precipitate out to form salt deposits
Salt Deposits
Assignment
Read Chapter 14, Section 3 (pg. 407-409)Do Section 14.3 Assessment #1-6 (pg. 409)Read Chapter 14, Section 4 (pg. 410-413)Do Section 14.4 Assessment #1-8 (pg. 413)
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