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Today: Chapter 17, part I Earth beneath the Ocean. Study guide. · Techniques of mapping the ocean floor Which parts make up a continental margin, and what is the difference between passive and active margin? · How are submarine canyons formed?

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slide1

Today: Chapter 17, part I

Earth beneath the Ocean

Study guide

  • ·Techniques of mapping the ocean floor
  • Which parts make up a continental margin, and what is the difference between passive and active margin?
  • ·How are submarine canyons formed?
  • ·How does the continental rise get most of its sediment (turbidity currents)
  • ·The three major provinces of the ocean floor (ocean basins, continental margins and mid-ocean ridges).
  • ·Features of deep-ocean basins: Trenches, seamounts, abyssal plains
  • ·Types of seafloor sediments.
  • ·When is a biogenic sediment called an ooze (at least 30%contribution to sediment)? What are the two main biogenous sediments (calcareous and siliceous oozes)
  • ·What are features of erosional and depositional shore
  • Sand budget of a beach
  • Example of shoreline subsidence and emergence
  • Cause of sealevel rise
slide2

Today: Chapter 17, part I

Earth beneath the Ocean

  • Mapping the ocean floor
  • Oceanic provinces
  • Seafloor sediments
  • Sampling the ocean floor
slide3

1) Mapping the ocean floor

Methods (modern) Submersibles, Sonar (echoes of sound waves), Drill Ships, Seafloor Observatory

Fig. 17.2

slide4

1) Mapping the ocean floor

  • Methods (modern, contd)
  • satellite radar

(microwave beams)

slide5

1) Mapping the ocean floor

  • Methods (old)
  • depth sounding lines (weighted line)

First exploration of deep-sea floor with HMS Challenger (1872-1876)

slide6

2) Marine provinces

  • Continental margin
  • boundary between continent and ocean
  • rift blocks of continental crust that are covered by sediment
  • passive or active margin
  • 2. Mid-ocean ridges
  • sea-floor spreading center
  • 3.Deep-ocean basins
  • Abyssal plain (Pacific: abyssal hill province)
  • deep ocean floor away from continental margins
slide7

2) Marine provinces

Passive and active continental margins

Passive margin

= Atlantic type margin

*no plate boundary

*no seismic activity

*sediments accumulate

to 10-20km thick layer

*wide continental margin

Active margin

= Pacific type margin

*convergent plate boundary

*trenches mark the boundary

of continent and ocean, strong earthquakes

*sediment accumulation few km

*narrow continental margin

Note vertical exaggeration!

Fig. 17.8

slide8

How are submarine

Canyons created?

  • Turbidity currents move downslope and erode submarine canyons in
  • the continental slope.
  • Deep sea fans are created by turbidite deposits at the mouths of the canyons,
  • merge at the base of the continental slope and make up most of the
  • sediments of the continental rise.
  • These turbidity deposits exhibit graded bedding.

See Fig. 17.9

slide9

2) Marine provinces

  • Continental margin
  • boundary between continent and ocean
  • rift blocks of continental crust that are covered by sediment
  • passive or active margin
  • 2. Mid-ocean ridges
  • sea-floor spreading center
  • 3.Deep-ocean basins
  • Abyssal plain (Pacific: abyssal hill province)
  • deep ocean floor away from continental margins
slide10

Oceanic divergent plate boundaries: Oceanic ridges and rises

Axial valley

Atlantic: Mid-Atlantic Ridge

Pacific: East-Pacific Rise

slide11

2) Marine provinces

3) Mid-ocean ridges

  • longest topographic feature on Earth (70,000 km!)
  • 2-3 km above ocean basins
  • Rift valley along ridge axis
  • basaltic rocks
slide12

2) Marine provinces

Features of Deep-Ocean basins

  • deep ocean trenches: - narrow… deep….where oceanic plates are subducted…dominant bathymetric feature of the Pacific Ocean.
  • abyssal plains:
  • seamounts:
slide13

Features of Deep-Ocean basins

30% of Earth’s

surface

NOT ridges, NOT margins

  • deep ocean trenches: - narrow, deep, where oceanic plates are

subducted, dominant bathymetric feature of the Pacific Ocean.

  • abyssal plains: - incredibly FLAT areas, thick sediments
  • seamounts:
slide14

Features of Deep-Ocean basins

  • deep ocean trenches: narrow, deep, where oceanic plates are subducted, dominant bathymetric feature of the Pacific Ocean.
  • abyssal plains: - incredibly FLAT areas, featureless, thick sediments
  • seamounts: - volcanoes, formed at ridge, or by hot spots, below sea-level, most are in the Pacific
slide15

land

Mineral grains from cont. rocks

organisms

Marine animal shells, skeletons

Minerals crystallize out of water

water

3) Seafloor sediments

Types

Derived from:

  • terrigenous
  • biogenous
  • hydrogenous
slide16

Terrigenous sediments

Transport media include

Rivers, glaciers, and wind.

Most lithogenous sediment

is made up of quartz (SiO2 )

and clay

slide17

Biogenous sediments

Biogenic ooze contains at least 30% of skeletons from

single celled microscopic algae and protozoa.

Calcareous ooze

Siliceous ooze

slide18

3) Seafloor sediments

Carbonate oozes are only found above the calcium carbonate dissolution depth (CCD). Deeper water is more acidic (has more dissolved CO2) and will dissolve the calcite shells.

Fig. 17.11

slide19

Calcium carbonate in modern surface sediments in the

world oceans. The distribution follows the relatively shallow

mid-ocean ridge that is above the CCD.

slide20

Hydrogenous sediments

  • Limestones
  • Evaporite salts
  • Manganese nodules

Ancient evaporites (halite, NaCl and gypsum, CaSO4)

slide21

Manganese

nodules

Manganese nodules

on the Pacific Ocean

Floor

Cross section

through a

manganese nodule

SEM of the surface

of a nodule, evidence

for microbial mediation

of nodule formation?

Mining of nodules

Contain Mn, Fe, Co, Cu, Ni

contain

slide23

4) Sampling the ocean floor

JOIDES Resolution

(Joint Oceanographic Institutions for Deep-Earth Sampling)

  • Can drill 1 km long sediment cores from over 8,000 m water depth
  • Cores represent millions of years of Earth’s history
slide24

Only after 5000 yrs, biogenous

sediment is being deposited

Tertiary

Fireball and fallout, iridium

anomaly

Impact ejecta, tektites, spherules,

shocked quartz

K-T Boundary

4) Sampling the ocean floor

Sediment core taken with drill-ship Joides Resolution in 1997 off Florida

reveals first complete K-T deposits with meteor-debris

Cretaceous