Geology Reference
In-Depth Information
100
Sicilian I
or Emilian
80
Sicilian II
or Milazzian
60
Palaeotyrrhenian
or Tyrrhenian I
40
Eutyrrhenian
or Tyrrhenian II
Neotyrrhenian
or Tyrrhenian III
20
0
1,000,000
800,000
600,000
Time (years ago)
400,000
200,000
0
Figure 14.10
Quaternary sea-levels in the Mediterranean: the classic interpretation.
yardstick against which to discuss Quaternary sea-level
changes and predicted rises of sea level over the next
century.
Whatever the cause of sea-level change, higher and
lower sea levels, especially those that occurred during the
Quaternary, leave traces in landscapes (e.g. Butzer 1975;
Bloom and Yonekura 1990; Gallup
et al
. 1994; Ludwig
et al
. 1996).
Marine terraces
and
drowned landscapes
record highstands and lowstands of sea level during
Quaternary glacial and interglacial climates. High levels
during interglacial stages alternate with low levels during
glacial stages, glacio-eustatic mechanisms largely driving
the system. Classical work around the Mediterranean Sea
recognized a suite of higher levels corresponding to glacial
stages (Figure 14.10).
the
Patella
raised beach on the Gower Peninsula, South
Wales (Bowen 1973). A shingle deposit lies underneath
tills and periglacial deposits associated with the last glacial
advance. The shingle is well cemented and sits upon a
rock platform standing 3-5 m above the present beach.
It probably formed around 125,000 years ago during
the last interglacial stage, when the sea was 5 m higher
than now.
Ancient coral reefs sitting above modern sea level are
indicative of higher sea levels in the past. In Eniwetok
atoll, the Florida Keys, and the Bahamas, a suite of
ancient coral reefs correspond to three interglacial high-
stands of sea level 120,000 years ago, 80,000 years
ago, and today (Broecker 1965). Similarly, three coral-
reef terraces on Barbados match interglacial episodes
that occurred 125,000, 105,000, and 82,000 years ago
(Broecker
et al
. 1968).
Highstands of sea level
Many shorelines bear evidence of higher sea levels.
Various types of raised shoreline - stranded beach
deposits, beds of marine shells, ancient coral reefs, and
platforms backed by steep cliff-like slopes - all attest to
higher stands of sea level. Classic examples come from
fringing coasts of formerly glaciated areas, such as Scot-
land, Scandinavia, and North America. An example is
Lowstands of sea level
Submerged coastal features record lower sea levels dur-
ing the Quaternary. Examples are the drowned mouths
of rivers (rias), submerged coastal dunes, notches and
benches cut into submarine slopes, and the remains
of forests or peat layers lying below modern sea level.
