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■ SUMMARY
THE NuCELLA TRANSGRESSION 1N SOUTH
ICELAND.
Marine sediments deposited during the Mid-
Holocene Nucella transgression have been
known in Northwest Iceland, mainly in the
western part of the Húnaflói area and Isafjarðar-
djúp, since the beginning of this century. They
are littoral with a macrofauna consisting mainly
of gastropods, bivalves, and barnacles with a
few polychaets, bryozoans, and echinoids. The
faunal assemblage lived in high energy environ-
ment close to the coast and intertidal species are
dominating. The temperatures of the coastal wa-
ters were 1-2°C higher than now in Icelandic
waters, and the salinity was normal. The age of
the sediments is 5000-2000 BP, but the trans-
gression was probably at its highest level 4400-
4000 BP and by about 2000 BP it was obviously
settled. The rise in sea level up to 4.7 m above
the present surface of the sea was caused by the
melting of ice during the warmest subboreal time
of the Holocene. Then the sea level gradually
lowered to the present stage.
Sediments deposited during the Nucella trans-
gression have now also been found in the
Stokkseyri-Eyrarbakki area of central South lce-
land and most probably elsewhere along the
south coast. At Stokkseyri, marine, littoral
sediments containing thermophilic intertidal
faunal assemblage has been encountered behind
the coastal ridge lying along the coast. The shelly
layers are up to 5 m in thickness and are found
up to about 7 m above the present sea level and
300 m inland. During the Nucella transgression,
when the sea level was higher, the sea brought
sediments and shell material from the coast into
the bog behind the ridge where it accumulated.
Then, after the sea subsided, a thin soil layer
formed on top of the marine series. Marine
sediments of similar age containing thermophilic
littoral species, that have been found in peat lay-
ers in the tidal zone of Garðskagi, Reykjanes,
Southwest Iceland, were probably also depos-
ited during the Nucella transgression. Further-
more, sediments that have suffered glacio-
tectonic transport have been found interfolded
within till around Jökulsárlón in Southeast Ice-
land. They contain sublittoral faunal assem-
blages and were at least in part deposited during
the initial phases of the transgression. Thus, we
have sporadic occurrences of Mid-Holocene ma-
rine sediments with thermophilic fauna along the
Icelandic south coast, especially in sheltered
places.
The Nucella transgression is correlative with
the Littorina/Tapes transgression in Scandina-
via, the Mid-FIandrian transgression in the Brit-
ish Isles, and the Vega transgression in East
Greenland. In fact sediments deposited during
this transgression have been found as far as Bra-
zil, South America.
PÓSTFANG HÖFUNDA /AuTHORs'ADDRESS
Ólöf E. Leifsdóttir
e-mail: oel@rhi.hi.is
Leifur A. Símonarson
e-mail: leifuras@raunvis.hi.is
Raunvísindastofnun Háskólans/
Science Institute
Jarðfræðahús Háskólans
IS-101 Reykjavík
224