Geoscience Reference
In-Depth Information
Shelby & Western
Lakes
Succotash Marsh
& Whale Beach
Cairns
Funafuti
Atoll
Gulf of
Carpentaria
Gre a t Barrier
Reef
Tubridgi Pt
Figure 4.4. Location of palaeotempestology studies globally.
that the storm tide (surge plus tide) and wave set-up combined, amounted to an
inundation level of 4.7--4.9 m (AHD). This suggests that wave run-up could have
only contributed 0.2--0.4 m of the ridge height at it highest elevation. Elsewhere,
where the ridge is only 4.5 m high (AHD), wave run-up does not appear to have
contributed to formation of the pumice ridge.
It would appear, therefore, that in at least some instances the height of the
crest of coral rubble and pumice ridges is close to or less than the height of
thestorm tide and wave set-up combined. This does not mean, however, that
progressive accumulation or accretion of a ridge cannot occur during the storm.
But it does mean that wave run-up may not always be an important process in
ridge accretion. Determining to what extent wave run-up does play a role in ridge
accretion is important when attempting to determine the intensity, or central
pressure, of tropical cyclones responsible for the deposition of prehistoric ridges.
Coral rubble ridges contain a number of distinct sedimentary facies or units
of sediment. These include storm beach face, berm, crest and washover facies
(Hayne and Chappell, 2001). Beach face and berm facies include porous, clast
supported, coarse biogenic shingle (rubble) deposits that occasionally dip sea-
wardsbut are usually structureless. Crest facies are horizontally bedded and
are finer grained than beach face deposits. Washover facies are bedded, dip
landward up to 15 and sometimes contain imbricated clasts (imbrication is a
sedimentary feature where particles are arranged in an overlapping shingle-like
pattern dipping in one direction). Each of these facies or units combine to make
astormdeposit. Storm deposits can be separated by 'ground surfaces' being
lenses of pumice pebbles and a weak sooty or earthy palaeosol (ancient soil).
These ground surfaces are really former ground surfaces or the surface of the
feature that was exposed for sufficient time between individual cyclone events
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