Seafloor Sediments &
Resources from the Seafloor
Chapter 14, Sections 3 & 4
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
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 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
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 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
Gas Hydrates
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
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)