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7375 years (4). Cores of the sea floor
in the Gulf of Mexico off Texas include a transgressive salt-marsh and
freshwater peat whose seaward limit
at about 25 m has been dated by radio-
Reports
carbon at 10,200 years (5). Dates for
many freshwater peats encountered in
borings of the Mississippi Delta have
been reported (6). Bridge borings off
western Australia penetrated fresh-
water peat, at 21 m, having an age of
9850 years (7), Other bridge borings
Freshwater Peat on the Continental Shelf
Abstract. Freshwater peats from the continental shelf off northeastern United
States contain the same general pollen sequence as peats from ponds that are
above sea level and that are of comparable radiocarbon ages. These peats indicate
that during glacial times of low sea level terrestrial vegetation covered the region
that is now the continental shelf in an unbroken extension from the adjacent land
areas to the north and west.
Evidence of sea levels lower than
the present level has long been pro-
vided by submerged intertidal or shallow-water topography, sediments, fauna,
one that is related to the low sea levels
is deeply submerged peat, especially
that of freshwater bogs. These deep
deposits are much older than the well-
and flora. So many examples of these
features are known throughout the
known peat and tree stumps that are
the continental shelves that they must
denote eustatic changes of sea level
rope. One is Dogger Bank in the English Channel (/), where a sample from
39 m has been dated, by the radiocarbon method, as 9300 years old (2);
another ts in the Baltic Sea (3), where
a deposit at 35 to 37 m dates from
world in the narrow depth range of
recent enough to have been associated
with Pleistocene glaciation.
One
of the
most interesting sedi-
ments on the continental shelf and
common just beyond the shoreline. The
longest-known examples are off Eu-
off British Guiana reached freshwater
peat, which had an age of 8590 years.
at 20 m (8). Freshwater peat cored
in Malacca Strait, off Malaya, at a
depth of 27 m has been dated at 10,000 years (9); similar peats containing
the bivalve Cyclina have been dredged
from 50 to 80 m in Naruto Strait,
an entrance to the Inland Sea of Japan,
and others containing large palm trees
have been observed in Toyama Bay,
Japan (0). Submerged soils rich in
organic debris, and about 12,000 years
old, have also been cored off Nigeria
(71) and elsewhere. Hence, freshwater,
as well as salt-marsh, peats are widely
distributed on the continental shelves
of the world.
In 1964 a large mass of peat was
recovered by Captain Norman Lepire
. fiPorttand)
~——s
199 KM
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Fig. 1. Positions of peat samples (closed circles) and of near-intertidal oyster shells (open circles} on the continental shelf
and in coastal areas from New England south to Cape Hatteras. Sources of data are listed in Teble 1; contours te in Meiers. Cross-
hatching denotes the area of the more detailed Fig. ?.
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