The Sea Floor and Its Sediments 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 – Bathymetry a study in 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 – km HMS Challenger – 1870’s – “steam powered” rock on a rope bottom soundings – confirmed Maury’s discovery of the Mid-Atlantic Ridge

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.

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. 4.4

Fig. 4.5 Continental Shelves

Passive Continental Margins Continental shelf, slope, rise The Continental Rise Types of Deposition From turbidity currents From contour currents Abyssal plains

Florida continental shelf Shelf Slope Break Abyssal Plain 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

Fig. 4.6

Fig. 4.7 “Typical” Passive Margin

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

Fig. 4.8

Fig. 4.10

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. 4.12

Box Fig. 2

Fig. 4.14

Fig. 4.13

Fig. 4.15

Fig. 4.16

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. 4.17

Fig. 4.18

Classifying Sediment by Source Terrigenous – composed of fragments of pre-existing rock material Terrigenous – composed of fragments of pre-existing rock material Neritic - at the coast Neritic - at the coast Biogenous – composed of hard remains of once-living organisms Biogenous – composed of hard remains of once-living organisms Pelagic – open water Pelagic – open water Hydrogenous - formed when dissolved materials come out of solution (precipitate) Hydrogenous - formed when dissolved materials come out of solution (precipitate) Authigenic – formed in place Authigenic – formed in place Cosmogenous Sediment – outer space derived Cosmogenous Sediment – outer space derived Sediment Mixtures – mostly the case Sediment Mixtures – mostly the case

Origin of terrigenous sediment Forms by: Weathering = breakup of exposed rock Transportation = movement of sediment Deposition = settling and accumulation Sediment-transporting media

Terrigenous sediment texture Texture includes: Texture includes: Grain size Grain size Sorting Sorting Rounding Rounding Maturity Maturity

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

Distribution of terrigenous sediment Terrigenous sediment occurs as: Terrigenous sediment occurs as: Neritic (nearshore) deposits Neritic (nearshore) deposits Beaches Beaches Continental shelves Continental shelves Turbidites Turbidites Glacial-rafted debris Glacial-rafted debris Pelagic (deep ocean floor) deposits Pelagic (deep ocean floor) deposits Abyssal clay Abyssal clay

Fig. 4.19

Fig. 4.20

Fig. 4.21a

Fig. 4.21b

Fig. 4.21c

Demise of the Dinosaurs Example

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. 4.24

Fig. 4.25a

Fig. 4.25b

Fig. 4.26

Fig. 4.27a,b

Fig. 4.27c

Fig. 4.27d

Fig. 4.27e

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