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)