Chapter 12: The Seafloor
Introduction

The seafloor makes up the largest part of the Earth’s
surface.
Introduction

The seafloor makes up the largest part of the Earth’s
surface.
Introduction

Why is it important to know about the
seafloor?
◦ The seafloor constitutes the largest part of
Earth’s surface.
◦ Studies of the seafloor provide some of the
evidence for plate tectonic theory, and
various resources are found in seawater and
on or in the seafloor.
Methods Used to Study the Seafloor

Direct Sampling
◦ clamshell samplers
◦ piston corers.
Methods Used to Study the
Seafloor
Oceanic Crust - Its Structure and Composition
The Continental Margins
The Continental Margins
The Continental Margins
The Continental Margins

Passive continental margins
◦ Passive continental
margins lack volcanism
and have little seismic
activity.
◦ These margins usually
have a wide continental
shelf, and a slope which
merges with a continental
rise. Abyssal plains
commonly extend
seaward of the
continental rise.
Features Found in the Deep-Ocean
Basins

Oceans evolve through a series of
stages
◦ beginning with crustal thinning and rifting of a continent to create
a rift valley
◦ followed by a long, narrow sea as a fully-developed spreading
center evolves
◦ then eventually an ocean. As the cooling oceanic crust is
subducted along ocean margins, the ocean begins to close on
itself.
Submarine Hydrothermal Vents
◦ These vents on the seafloor at
or very near spreading ridges
are where circulating water is
heated and discharged into
seawater.
◦ As the hot water circulates
through the oceanic crust it
becomes a metal-rich brine
from which deposits of
various minerals and metals
are deposited.

Submarine hydrothermal vents

Seamounts and guyots

Seamounts and guyots are common, widespread features of
the sea floor.
◦ Seamounts are remnants of extinct oceanic volcanoes. Many rise
more than a kilometer from the ocean floor. They form as the
oceanic crust moves over a hot mantle plume( hot spot).
◦ Guyots have the same origin but have flat tops created when the
ocean volcano sinks to sea level. Once the top is near sea level,
erosion by waves flattens the top.
SEAMOUNT
GUYOT

Seamounts and Guyots
Aseismic Ridges
◦ Aseismic ridges consisting of seamounts and
guyots extend in a perpendicular orientation from
many spreading ridges.
Sediments on the Deep Seafloor

What are the two main types of
sediment found on the seafloor?

Sediments of the deep sea consist largely of the
◦ carbonate and siliceous skeletons of microscopic organisms (ooze)
◦ pelagic clays which are derived from continents and oceanic
islands.
Sediments on the Deep Seafloor