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

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
1) Mapping the ocean floor
Methods (modern) Submersibles, Sonar (echoes of
sound waves), Drill Ships, Seafloor Observatory
Fig. 17.2
1) Mapping the ocean floor
Methods (modern, contd)
 satellite radar
(microwave beams)
1) Mapping the ocean floor
Methods (old)
 depth sounding lines (weighted line)
First exploration of deep-sea floor with HMS Challenger (1872-1876)
2) Marine provinces
1. 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
2) Marine provinces
Passive and active continental margins
Passive margin
= Atlantic type margin
Active margin
= Pacific type margin
*no plate boundary
*no seismic activity
*sediments accumulate
to 10-20km thick layer
*convergent plate boundary
*trenches mark the boundary
of continent and ocean, strong earthquakes
*sediment accumulation few km
*wide continental margin
*narrow continental margin
Note vertical exaggeration!
Fig. 17.8
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
2) Marine provinces
1. 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
Oceanic divergent plate boundaries: Oceanic ridges and rises
Axial valley
Atlantic: Mid-Atlantic Ridge
Pacific: East-Pacific Rise
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
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:
Features of Deep-Ocean basins
NOT ridges, NOT margins
30% of Earth’s
surface
 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:
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
3) Seafloor sediments
Types
Derived from:
 terrigenous
land
Mineral grains from cont. rocks
 biogenous
organisms
Marine animal shells, skeletons
 hydrogenous
water
Minerals crystallize out of water
Terrigenous sediments
Most lithogenous sediment
is made up of quartz (SiO2 )
and clay
Transport media include
Rivers, glaciers, and wind.
Biogenous sediments
Biogenic ooze contains at least 30% of skeletons from
single celled microscopic algae and protozoa.
Calcareous ooze
Siliceous ooze
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
Calcium carbonate in modern surface sediments in the
world oceans. The distribution follows the relatively shallow
mid-ocean ridge that is above the CCD.
Hydrogenous sediments
•Limestones
•Evaporite salts
•Manganese nodules
Ancient evaporites (halite, NaCl and gypsum, CaSO4)
Manganese
nodules
Manganese nodules
on the Pacific Ocean
Floor
Cross section
through a
manganese nodul
Mining of nodules
SEM of the surface
of a nodule, evidence
for microbial mediation
of nodule formation?
cContain Mn, Fe, Co, Cu, N
Manganese nodules distribution in the world ocean’s.
4) Sampling the ocean floor
JOIDES Resolution
(Joint Oceanographic Institutions for DeepEarth Sampling)
Can drill 1 km long
sediment cores from over
8,000 m water depth
Cores represent millions of
years of Earth’s history
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
Tertiary
Only after 5000 yrs, biogenous
sediment is being deposited
Fireball and fallout, iridium
anomaly
Impact ejecta, tektites, spherules,
shocked quartz
K-T Boundary
Cretaceous