Seafloor Sediments & Resources from the Seafloor

1. Seafloor Sediments &Resources from the Seafloor Chapter 14, Sections 3 & 4

2. Seafloor Sediments • Most of the ocean floor is covered with sediment • Some sediment is deposited by turbidity currents • The rest of the sediment has slowly settled onto the seafloor from above • The sediment varies in thickness over the ocean floor • Ocean-floor sediments can be classified according to their origin into three broad categories: terrigenous sediments, biogenous sediments, and hydrogenous sediments

3. 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

4. Terrigenous Sediment

5. Biogenous Sediment • Biogenous Sediment – sediment that is biological in origin • Biogenous sediments consist of shells and skeletons of marine animals and algae • Calcareous Ooze – produced from the calcium carbonate shells of organisms • Calcareous ooze has the consistency of thick mud • Siliceous Ooze – composed primarily of diatoms—single-celled algae—and radiolarians—single-celled animals that have shells made out of silica

6. Biogenous Sediment

7. 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

8. Manganese Nodules

9. Distribution of Seafloor Sediments

10. Energy Resources • Oil and natural gas are the main energy products currently being obtained from the ocean floor • The ancient remains of microscopic organisms are the source of today’s deposits of oil and natural gas • The remains were buried and heated for millions of years to be transformed into oil and gas • Gas Hydrates – compact chemical structures of water and natural gas • Most oceanic gas hydrates are created when bacteria break down organic matter trapped in ocean-floor sediment • These bacteria produce methane gas along with small amounts of ethane and propane • Gas hydrates resemble chunks of ice, but will ignite when lit by a flame

11. Gas Hydrates

12. Other Resources • Other 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

13. Salt Deposits

14. 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)