Jökull - 01.12.1993, Blaðsíða 35

LATEGLACIAL RAISED BEACHES AND GLACIER
RECESSION IN THE ÞISTILFJÖRÐUR-BAKKAFLÓI
AREA, NORTHEAST ICELAND
Hreggviður Norðdahl
Science Institute, University oflceland,
Dunhaga 3, IS-107 Reykjavík, Iceland
Christian Hjort
Department of Quaternary Geology, Lund University,
Sölvegatan 13, S-223 62 Lund, Sweden
ABSTRACT
A survey of Lateglacial raised beaches in the
t’istilfjörður-Bakkaflói area in northeast Iceland has
revealed three marine levels at different altitudes
above present sea-level. The earliest and highest one,
situated at about 65 m, was onlyfound at the Viðarvík
cove in the Þistilfjörður area. A lower and younger
level at 50-45 m wasfowid at the Viðarvík cove and at
the Bakkafjörður bay in the Bakkaflói area. These liigh
marine levels are both associated with ice-marginal
deposits at thepresent coast. A still lower andyounger,
but very clistinct marine level at about 30 m some 1-
2 km inside the present coastline in the Þistilfjörður-
Bakkaflói area, is ofmore regional marine-limit char-
octer. It was imprinted onto an already deglaciated
landscape, either as low abrasional cliffs or as very
distinct, up to 5 m high and 30 m wide beach ridges. At
the time of the formation ofthe 30 m level the glacier
margins stood some 5 km inlandfrom the present coast,
m some cases associated with well developed sandurs
reaching the contemporaneous coastline. No relevant
datable material hasyet beenfound in the Þistilfjörður
°nd Bakkaflói areas and an apparent agefor the stud-
mdmarine levels is, therefore, inferredfrom i4C-dated
sequences in adjacent areas. Comparison with data
fiom the Melrakkaslétta peninsula immediately north
of the Þistilfjörður area suggests that the higher ma-
rine levels (65 m, 50-45 m) are younger than 12,700
BP, with the 50-40 m level most likely ofYounger Dryas
age. A glacier readvance and theformation ofthe 30 m
level is compared with a late Younger Dryas oran early
Preboreal marine level on the western Melrakkaslétta
peninsula and in the Vopnafjörðurarea. The 30 m ma-
rine limit is postdated by the early Holocene rhyolitic
Miðfjörður Tephra, a tentative chronostratigraphical
marker in north and northeast Iceland.
INTRODU CTION
This paper describes raised shorelines and flu-
vioglacial deposits of late Weichselian and early
Holocene age in northeast Iceland. They are compared
with similar features on the western Melrakkaslétta
peninsula and in the Vopnafjörður area, west and south
of the investigated area.
The studied area is the terrain south-west of Þistil-
fjörður and Bakkaflói bounded by the Melrakkaslétta,
Langanes, and Digranes peninsulas (Figure 1). The
oldest part of the area are glacially eroded bedrock for-
mations made of more than 3 Ma old lava flows with
intercalated sediments, situated south-west of Þistil-
fjörður and Bakkaflói and on the Digranes peninsula.
The bedrock of the Langanes peninsula and of the
JÖKULL,No. 43, 1993 33