The Sea The Sea Floor and Floor and

Its Its SedimentsSediments

An Introduction to the World’s Oceans Sverdrup et al. - Chapter Four - 8th Ed.

Bathymetry How deep is that water

anyway?

Sounding techniques Line or cable – “rock-on-a-rope”

Echo Sounding

Multibeam Systems – swath image

Satellite Altimetry

Measuring the Depths – Measuring the Depths – BathymetryBathymetry

a study in a study in technological evolution.technological evolution.Methods for measuring depths:

Hand line and wire marked with fathoms, with a lead weight on the end – “Rock on a Rope” Posidonius 85 B.C. made soundings fathoms = 6 feet (arm span) greased piano wire & cannonball

Echo sounder, or depth recorder Meteor – 1925 German vessel – echo sounding GLORIA – sidescan sonar “fish” - multibeam

Laser airborne depth sounder (LADS) limited depth – turbidity matters

Satellites Gravity bumps and valleys

Historic “Soundings” Posidonius – 85B.C. – “rock on a rope”

– 2km

Sir James Clark Ross – 1818 – 4.893 km

HMS Challenger – 1870’s – “steam powered” rock on a rope - 492 bottom soundings – confirmed Maury’s discovery of the Mid-Atlantic Ridge

Echo Sounding and

its disadvantage

Echo Sounding and

its disadvantage

Fig. 4.1

Box Fig. 1.

Box Fig. 2, pg. 103

U. S. Navy satellite Geosat

How a “Gravity” survey works.

How a “Gravity” survey works.

Fig. 4.3

Bathymetry of the Sea Floor

Continental margin Continental shelf

Submarine canyons

Continental shelf break

Continental slope

Continental rise Turbidites

Abyssal fans

Bathymetry of the Sea Floor Ocean basin floor

Abyssal plain Abyssal hills Seamounts Guyots Fringing reefs Barrier reefs

Ridges, rises, and trenches Plate tectonics

Fig. Fig. 4.44.4

Fig. 4.5Fig. 4.5Continental Continental ShelvesShelves

Passive Continental Margins Continental shelf, slope,

rise

The Continental Rise Types of Deposition

From turbidity currents

From contour currents

Abyssal plains

Florida continental shelfFlorida continental shelf

Shelf

Shelf

Slope

Slope

Break

Break

Abyssal Plain

Abyssal Plain

Rise

Rise

Active Continental Margins

On land- earthquakes, young mountain belt, volcanoes

Continental shelf, continental slope, oceanic trench

Oceanic Trenches Earthquakes of the Benioff seismic Zones Volcanoes Low Heat Flow Negative Gravity Anomalies

Active continental margin along Oregon Coast. Folded sea floor sediments being scraped from the Juan de Fuca Plate as it subducts beneath the N. American Plate

Active continental margin along Oregon Coast. Folded sea floor sediments being scraped from the Juan de Fuca Plate as it subducts beneath the N. American Plate

Fig. Fig. 4.64.6

Fig. 4.7 “Typical” Passive Fig. 4.7 “Typical” Passive MarginMargin

Submarine Canyons Abyssal Fans (at base like alluvial

fans)

Down-canyon movement of sand

Bottom Currents (tides?)

River erosion (during ice age shelf

exposure)

Turbidity Currents Graded bedding

Shallow water fossils

Submarine Canyon

Submarine Canyon

Fig. 4.8

Fig. Fig. 4.104.10

Turbidity current off Jamaica

Turbidity current off Jamaica

Field Notes: Giant Hawaiian Landslides Giant landslides

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

Frequency of occurrence Several per million years

Posed important hazard

Scientific research Identifying the causes

Predicting the next giant landslide

Fig. 4.11

Fig. 4.12Fig. 4.12

Box Fig. Box Fig. 22

Fig. Fig. 4.144.14

Fig. Fig. 4.134.13

Fig. Fig. 4.154.15

Fig. Fig. 4.164.16

Sediments Particle size

Classification Horizontal transport and

sorting

Location Classification: neritic or

pelagic

Rates of deposit Processes and variability

Source and chemistry Lithogenous sediments Biogenous sediments Hydrogenous sediments Cosmogenous sediments

Fig. Fig. 4.174.17

Fig. Fig. 4.184.18

Classifying Sediment by Classifying Sediment by SourceSource TerrigenousTerrigenous – composed of fragments of – composed of fragments of

pre-existing rock materialpre-existing rock material NeriticNeritic - - at the coastat the coast

Biogenous Biogenous – composed of hard remains of – composed of hard remains of once-living organismsonce-living organisms PelagicPelagic – open water – open water

HydrogenousHydrogenous - formed when dissolved - formed when dissolved materials come out of solution (precipitate)materials come out of solution (precipitate) AuthigenicAuthigenic – formed in place– formed in place

Cosmogenous SedimentCosmogenous Sediment – – outerouter space space derivedderived

Sediment Mixtures – Sediment Mixtures – mostly the casemostly the case

Origin of Origin of terrigenous terrigenous sedimentsediment Forms by:

Weathering =

breakup of

exposed rock

Transportation =

movement of

sediment

Deposition =

settling and

accumulation

Sediment-transporting media

Terrigenous sediment Terrigenous sediment texturetexture

Texture Texture

includes:includes:

Grain sizeGrain size

SortingSorting

RoundingRounding

MaturityMaturity

Wind blown dust as a source of terrigenous sediment in the Deep Ocean

Distribution of Distribution of terrigenous sedimentterrigenous sediment Terrigenous sediment occurs as:Terrigenous sediment occurs as:

Neritic (nearshore) depositsNeritic (nearshore) deposits BeachesBeaches

Continental shelvesContinental shelves

TurbiditesTurbidites

Glacial-rafted debrisGlacial-rafted debris

Pelagic (deep ocean floor) depositsPelagic (deep ocean floor) deposits Abyssal clayAbyssal clay

Fig. Fig. 4.194.19

Fig. Fig. 4.204.20

Fig. 4.21a

Fig. 4.21b

Fig. 4.21c

Demise of the Demise of the Dinosaurs Dinosaurs ExampleExample

Sediments Patterns of deposit on the sea floor

Processes and patterns

Climatic variations are recorded in layered sediments

Formation of rock - lithification Sedimentary rock

Metamorphic rock

Sampling methods Dredges, grab samplers, a corer, and acoustic

profiling

Sediments as historical records Distribution and isotopic composition of skeletal

remains

Fig. 4.23

Fig. Fig. 4.244.24

Fig. 4.25a

Fig. Fig. 4.25b4.25b

Fig. Fig. 4.264.26

Fig. Fig. 4.27a,b4.27a,b

Fig. Fig. 4.27c4.27c

Fig. Fig. 4.27d4.27d

Fig. Fig. 4.27e4.27e

Seabed Resources Sand and gravel

Sand and gravel, calcium oxide, calcium

carbonate, tin, iron, platinum, gold, and

diamonds (currently mined)

Phosphorite

Phosphate fertilizer (not currently mined)

Sulfur (no longer mined)

Coal (currently mined)

Oil and gas (currently extracted)

Gas hydrates (not mined)

Methane and water

Fig. 4.28

Seabed Resources Manganese nodules

Manganese, 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 treaties 200-mile economic zones

International treaties

Summary Methods for measuring ocean depth Bathymetric features

Continental shelf, slope, and rise Ocean basin floor Seamounts and barrier reef formation

Sediment classification Size, location, origin, and chemistry

Biogenous sediments Siliceous and calcareous sediments Carbonate compensation depth (CCD)

Sediment sampling methods Calcareous biogenous sediment

cores Used to study climate change

The End