Chapter 4 The Sea Floor and Its Sediments

CO 4

4.1 Measuring the Depths

Methods for measuring depths:Hand line and wire marked with fathoms, with a lead weight on the endEcho sounder, or depth recorderLaser airborne depth sounder (LADS)Satellites

Boxed Reading: Bathymetrics

Lead line vs. multibeam sound systemsSide-scan sonar systemSwath bathymetry

Fig. 4.3

Side – Scan Sonar Box Fig. 1, pg. 102 Box Fig. 2, pg. 103

4.2 Bathymetry of the Sea FloorContinental margin

Continental shelfContinental shelf breakContinental slopeContinental rise

Ocean basin floorAbyssal plainAbyssal hillsSeamountsGuyotsFringing reefsBarrier reefs

Ridges, rises, and trenchesPlate tectonics

Fig. 4.1

Fig. 4.12

Fig. 4.16

Fig. 4.7

World wide Continental ShelvesFig. 4.11

Fig. 4.6

Field Notes: Giant Hawaiian Landslides

Giant landslides Blocks or rock: 30 km x 5 km x 2 km

Frequency of occurrenceSeveral per million years

Posed important hazardScientific research

Identifying the causesPredicting the next giant landslide

Box Fig. 1, pg. 108

4.3 SedimentsParticle size

ClassificationHorizontal transport and sorting

LocationClassification: neritic or pelagic

Rates of depositProcesses and variability

Source and chemistryLithogenous sedimentsBiogenous sedimentsHydrogenous sedimentsCosmogenous sediments

Sediments: SourcesLithogenous sediments – Come from rocks,

erosion, examples: sand, boulders, gravel, siltBiogenous sediments- comes from organisms’

remains. Diatomaceous (diatoms) chalk.Hydrogenous sediments- precipitate out of water.

Manganese nodulesCosmogenous sediments – Comes from space

Meteorites, comet dust, etc.

4.3 Sediments, continuedPatterns of deposit on the sea floor

Processes and patternsClimatic variations are recorded in layered sediments

Formation of rockSedimentary rockMetamorphic rock

Sampling methodsDredges, grab samplers, a corer, and acoustic profiling

Sediments as historical recordsDistribution and isotopic composition of skeletal remains

4.4 Seabed ResourcesSand and gravel

Sand and gravel, calcium oxide, calcium carbonate, tin, iron, platinum, gold, and diamonds (currently mined)

PhosphoritePhosphate fertilizer (not currently mined)

Sulfur (no longer mined)Coal (currently mined)Oil and gas (currently extracted)Gas hydrates (not mined)

Methane and water

4.4 Seabed Resources, continued

Manganese nodulesManganese, copper, nickel, and cobalt (not currently mined)

Sulfide mineral deposits (not currently mined)Relatively little is known about these deposits to determine their economic importance

Laws and treaties200-mile economic zonesInternational treaties

SummaryMethods for measuring ocean depthBathymetric features

Continental shelf, slope, and riseOcean basin floorSeamounts and barrier reef formation

Sediment classification Size, location, origin, and chemistry

Biogenous sedimentsSiliceous and calcareous sedimentsCarbonate compensation depth (CCD)

Sediment sampling methodsCalcareous biogenous sediment cores

Used to study climate change

GEN – to make or create, comes from, the beginning or source