Jökull - 01.12.1988, Blaðsíða 9

Fig. 5. Schematic profile of the Hrepphólar section. 1) Diamicton (Búðaberg diamicton). 2) Till. 3) Lam-
inated silt. 4) Sand. 5) Gravel. 6) Dated sample. 7) Shell.
Mynd5. Jarðlagasnið við Stóru-Laxá hjá Hrepphólum. 1) Leirsteinsvöluberg (Búðabergsset). 2)Jökulurð.
3) Lagskipt silt. 4) Sandur. 5) Möl. 6) Aldursgreint sýni. 7) Skel.
buried ridge. We interpret it as a till deposit related
to the glacial advance which caused the deformation
of the diamicton.
The ridge is buried by unit C, a 10-15 m thick unit
of laminated sandy silt. It contains scattered shells,
of several species (Table IV). A radiocarbon dating
of a sample gave the value of 9.595±160 BP (Table
II: Lu-2402). We interpret it as a marine deposit.
Unit C is overlain by a succession of cross
stratified sand and gravel (units D and E), probably
related to the isostatic rebound of the depositional
basin and the consequent marine regression.
DYNJANDI (Lu-2400)
Upstream of the farm Spóastaðir, at c. 60 m a.s.l.,
the Brúará river flows in a shallow rocky channel as
rapids and small cascades. Hollows and depressions
in the bedrock exposed on both sides of the river are
filled with laminated silt and stratified sand. The
sediments contain shells (Table IV). Einarsson
(1964) reported shell-bearing strata on the riverbank
close to the farm Spóastaðir. He reported an
uncorrected radiocarbon date of 9.930±140 BP
(Table I: T-362) for shells from this locality. We
sampled shells from a sandy silt strata 2 km further
north in the bank of a brook, just upstream of the
Vhm 43 water gauge at the Dynjandi cascades. This
locality is 4 km south of the Búði moraines in the
Torfastaðaheiði moor, 42 km from the present
coastline. The radiocarbon date of the sample is
9.825±90 BP (Table II: Lu-2400).
RIVER SOG AT BÍLDSFELL (Lu-2399)
The Sog river originates in Lake Þingvallavatn.
During the deglaciation of the Þingvallavatn depres-
sion, the first sign of the lake appeared in the south-
west comer of the depression as an ice-lake. It had
an outlet over the hills of the Grafningur district
(,Sæmundsson, 1965) and it reached the shore south
of Bíldsfell, relative sea level then being 60-70 m
higher than today. In the area west of Sog, between
Bíldsfell and Ingólfsfjall, thick glaciofluvial sedi-
ments were deposited. Later the river found its
present channel and now flows east of these sedi-
ments. In the riverbanks east of the Bíldsfell farm is
a locality very rich in shells (Áskelsson, 1934). The
riverbanks there are about 8 m high. The lower part
of the sediments is made of semi-lithified, stratified
silt but the uppermost 2.0-2.5 m are of sand and
gravel. Shells are found both in the banks near the
water level and in the bottom layers of the river. A
lot of shells are washed out from the silt and lie on
the riverbottom and on the riverbanks. Most of the
shells in the silt are in situ. Some of them contain
small needles of calcite; some are partly filled, oth-
ers contain only few.
The radiocarbon date of a shell from this locality
is 9.055±80 BP (Table 1: Lu 2399). This sample is
JÖKULL, No. 38, 1988 7