Today: Chapter 17, part I

1
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 30contribution 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

2
Today Chapter 17, part I Earth beneath the Ocean

1. Mapping the ocean floor
2. Oceanic provinces
3. Seafloor sediments
4. Sampling the ocean floor

3
1) Mapping the ocean floor
Methods (modern) Submersibles, Sonar (echoes of
sound waves), Drill Ships, Seafloor Observatory
Fig. 17.2
4
1) Mapping the ocean floor

• Methods (modern, contd)
• satellite radar
• (microwave beams)

5
1) Mapping the ocean floor

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

First exploration of deep-sea floor with HMS
Challenger (1872-1876)
6
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

7
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
8
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
9
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

10
Oceanic divergent plate boundaries Oceanic
ridges and rises
Axial valley
Atlantic Mid-Atlantic Ridge
Pacific East-Pacific Rise
11
3) Mid-ocean ridges
2) Marine provinces

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

12
2) Marine provinces
Features of Deep-Ocean basins

• deep ocean trenches - narrow deep.where
  oceanic plates are subducteddominant bathymetric
  feature of the Pacific Ocean.
• abyssal plains
• seamounts

13
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, thick
  sediments
• seamounts

14
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

15
3) Seafloor sediments
Types
Derived from

• terrigenous
• biogenous
• hydrogenous

16
Terrigenous sediments
Transport media include Rivers, glaciers, and
wind.
Most lithogenous sediment is made up of quartz
(SiO2 ) and clay
17
Biogenous sediments
Biogenic ooze contains at least 30 of skeletons
from single celled microscopic algae and
protozoa.
Calcareous ooze
Siliceous ooze
18
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
19
Calcium carbonate in modern surface sediments in
the world oceans. The distribution follows the
relatively shallow mid-ocean ridge that is above
the CCD.
20
Hydrogenous sediments

• Limestones
• Evaporite salts
• Manganese nodules

Ancient evaporites (halite, NaCl and gypsum,
CaSO4)
21
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
22
Manganese nodules distribution in the world
oceans.
23
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 Earths
  history

24

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