Jökull - 01.12.1979, Side 16

m
Fig. 7. Simplified geologic map of the Esja volcanic region, southwest Iceland. Rocks date from
about 2.8 to 1.8 m.y. B.P. Only faults with vertical displacement more than 30 m are shown.
Approximately every third dike and sheet is shown. 1, Basaltic lavas; 2, subglacial basaltic hyaloc-
lastites and sediments; 3, rhyolite sheets and domes; 4, gabbro and dolerite intrusions; 5. postero-
sional lavas, landslips, and alluvial deposits; 6, rhyolite dikes; 7, mafic dikes; 8, mafic sheets; 9, dip;
10, fault; 11, caldera fault; 12, fault breccia. Note flattening out of southeasterly dips upwards
through the section. From I. B. Fridleifsson, 1977.
far is found on the Tjörnes Peninsula in northern
Iceland (Fig. 8). The Plio-Pleistocene in this section
is about 650 m thick, 400 m of which are sediment
of mainly marine or estuarine facies but in the
upper half also of glacial origin where at least 6
separate tillite layers have been identified. Tillites
first appear in this section in Gilsá or Olduvai time,
much later than farther inland, probably because
the locality lay at sea level far from the centre of
glaciation.
The Plio-Pleistocene section in Jökuldalur in
eastem Iceland (Fig. 9) ranges in age from the base
of the Plio-Pleistocene to the top of the Gilsá event
(1.6 m.y.) and includes the type locality for this
particular event. The whole section has a thickness
of 450 m of which ~ 20% are glacial and fluvio-
glacial deposits and volcaniclastic breccias.
Altogether 9 glacial events are fairly evenly dis-
tributed in the section from the Mammoth event
upwards.
Good and easily mapped exposures of Plio-
Pleistocene rocks occur to the west of the axial rift
zone in southwestern Iceland. Northeast of
Reykjavík (Esja) a composite section of 1650 m
thickness has been mapped, ranging in age from
the Mammoth event (3.1 m.y.) up to the base of the
Gilsá event (about 1.8 m.y.). Sedimentary and vol-
caniclastic rocks of primarily glacial origin make
up about 1/3 of this section, giving evidence for at
least 13 glaciations; the first occuring at the base of
the Mammoth event. An almost identical Plio-
Pleistocene section has been mapped west of
Langjökull (Húsafell) on strike with the previous
one. It is about 1000 m thick and is unbroken up to
just above the base of the Matuyama. It includes 8
glacial horizons some of which include thick sub-
14 JÖKULL 29. ÁR