the sea floor and its sediments an introduction to the world’s oceans sverdrup et al. - chapter...
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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