SOME VENTIFACTS FOUND NEAR RECENT AND FOSSIL
COASTAL DUNES IN FINLAND
J. J. DONNER and M A R J A SIMOLA
DONNER, J. J. a n d SIMOLA, M A R J A 1977: Some v e n t i f a c t s f o u n d
n e a r recent and fossil coastal dunes in Finland. Bull. Geol. Soc. Finland 49: 19—23.
During t h e Holocene relative u p l i f t of l a n d in F i n l a n d coastal
were f o r m e d at various altitudes in a r e a s earlier submerged.
v e n t i f a c t s f o u n d n e a r these dunes, t h e oldest being about 4000
old, a r e described f r o m the H a n k o (Hangö) peninsula and f r o m
joki in Ostrobothnia. T h e h a r d rock v e n t i f a c t s h a v e a shiny
s u r f a c e w i t h no facets developed.
J. J. Donner and Marja Simola,
tology, University
of Helsinki,
dunes
Some
years
Kalaupper
Department
of Geology and PalaeonSF-00170 Helsinki
17, Finland.
Stones affected b y sand blasting in areas
w i t h f o r m e r or recent eolian activity h a v e the
surface typical for ventifacts, some having
clear facets and t h e r e f o r e called dreikanter.
However, as Cailleux (1973 p. 53) points out
»la f o r m e en d r e i k a n t e r n'a rien de caractéristique, tous les a u t e u r s qui ont étudié la
question sur le terrain en sont d'accord. Ce
qui est caractéristique, c'est d'abord 1'état de
surface, paraissant brillant au soleil
».
De Geer (1886) described wind-polished stones
found in d u n e areas in S k å n e and Halland
in South Sweden and similar stones w e r e
described by Fegraeus (1886) as occuring n e a r
the dunes on the Island of Gotska Sandön
n o r t h of Gotland. De Geer observed t h a t
no facets w e r e developed on those stones
which rested on sand because the position of
the stones has changed during t h e time they
h a v e been subject to sand blasting. Only
stones more f i r m l y attached to t h e ground
h a v e clear facets. F u r t h e r , the stones are
usually polished only on one side in contrast
to ventifacts f o r m e d in areas with intense
cryoturbation, w h e r e several sides h a v e been
polished because the stones h a v e been t u r n e d
round on an unstable surface (Cailleux 1973).
Large areas of southern and central F i n land w e r e submerged d u r i n g early Holocene
times. When, as a result of isostatic u p l i f t t h e
areas emerged f r o m the Baltic, dunes w e r e
f o r m e d on the beaches w h e r e suitable m a t e rial, particularly f r o m glaciofluvial f o r m a tions or river sediments, w a s available for
wind transport. As the shoreline receded t h e
beach dunes soon became covered by vegetation and inactive, and n e w dunes w e r e built
u p on the f r e s h l y exposed beaches. Thus,
20
J- J- Donner and Marja
Simola
t h e r e is a series of fossil coastal d u n e s in
a r e a s b e l o w t h e h i g h e s t b e a c h level, i.e. t h e
limit of s u b m e r g e n c e , r e a c h i n g a n a l t i t u d e
of m o r e t h a n 200 m in those p a r t s of t h e
c o u n t r y w i t h t h e g r e a t e s t u p l i f t . In addition,
d u n e s w e r e f o r m e d in t h e periglacial zone
on d r y l a n d outside t h e r e t r e a t i n g ice m a r g i n
d u r i n g t h e L a t e Weichselian a n d E a r l y F l a n d r i a n substages, p a r t i c u l a r l y in N o r t h K a r e l i a
a n d L a p l a n d . B u t e v e n t h e i r d i s t r i b u t i o n is
p a r t l y g o v e r n e d by t h e closeness of t h e s h o r e line at t h a t time.
As v e n t i f a c t s h a v e n o t p r e v i o u s l y b e e n
described f r o m t h e F i n n i s h d u n e a r e a s a f e w
e x a m p l e s a r e h e r e g i v e n of some f i n d s f r o m
1975 at or n e a r t h e p r e s e n t coastline. T h e sites
at w h i c h t h e y w e r e f o u n d a r e s h o w n in Fig.
1. T h e f i r s t t h r e e a r e f r o m t h e H a n k o (Hangö)
p e n i n s u l a , w h i c h is l a r g e l y b u i l t u p by t h e
glaciofluvial m a t e r i a l of t h e e n d - m o r a i n e of
the first Salpausselkä, whereas the fourth
site is in O s t r o b o t h n i a . T h e sites a r e t h e
following:
1. Hanko (Hangö), 1 : 20,000 m a p sheet no. 201108,
grid reference 6635.3—24°—444.4, altitude < 5
m. In the bay of Kolaviken in the outskirts of
Hanko, west of Tulludden, there are several
beach dunes about 1 m high a few metres
above the present beach. The dunes are in a
pine forest with a patchy ground vegetation,
mainly with lichens and b e a r b e r r y
(Arctostaphylos uva ursi).
2. Sandö, Hanko (Hangö) peninsula, 1 :20,000
m a p sheet no. 201109, grid reference 6640.6—24°
—449.2, altitude 15 m. Fossil dune about 1.5 m
high, cut by the m a i n road. Pine forest with
b e a r b e r r y and cowberry (Vaccinum
vitis-idaea).
3. Koverhar, L a p p o h j a (Lappvik), Hanko (Hangö)
peninsula, 1 : 20,000 m a p sheet no. 201112, grid
reference 6643.6—24°—455.2, altitude 20 m.
Large fossil dune about 2—3 m high, seen in
gravel pit section east of the main road, resting
on an even surface of coarse glaciofluvial m a terial. Vegetation same as at site 2.
4. Kalajoki, 1:20,000 m a p sheet no. 241312, grid
reference 7126.8—24°—491.4, altitude < 5 m.
The present gently rising beach consists of
coarse sand with some stones up to an altitude
of about 5 m. Above this a sub-recent dune
about 10 m high along the beach, partly covered
by lyme-grass ( E l y m u s arenarius).
Fig. 1. Sites with ventifacts.
F o r stones to b e e f f e c t i v e l y polished b y
sand b l a s t i n g of t h e eolian m a t e r i a l a c c u m u l a t e d in t h e d u n e s m e n t i o n e d a b o v e t h e stones m u s t h a v e b e e n f o r some t i m e at t h e
s u r f a c e over w h i c h t h e s a n d m o v e d . It is
t h e r e f o r e n a t u r a l t h a t only a s m a l l p e r c e n t age of stones in a d u n e a r e a h a v e developed
into v e n t i f a c t s . T h e y w e r e , h o w e v e r , f o u n d
at all sites w h e r e t h e y w e r e looked f o r a n d n o
a t t e m p t w a s m a d e to collect a g r e a t n u m b e r
of t h e m . T h o s e f o u n d at sites 1, 2 a n d 4 w e r e
Some ventifacts f o u n d near recent and fossil coastal d u n e s in F i n l a n d
21
Fig. 2. P h o t o g r a p h s of t h r e e ventifacts, w i t h closeups on the right, f r o m sites 2, 3 and 4 f r o m top to
bottom as listed in text.
all close to the dunes on their w i n d w a r d side
w h e r e a s t h a t f r o m site 3 w a s in t h e lower
part of the d u n e sand, as exposed in the section. The size of the ventifacts and the rocks
they consist of are listed below:
Site 1. 4 x 3 x 2 cm, red granite
1. 5 x 4 x 2 cm, gneiss
2. 5 x 4 x 2.5 cm,
quartz-feldspar-peg-
m a t i t e (photo in Fig. 2)
3. 6 x 4.5 x 2.5 cm, red g r a n i t e
(photo
in Fig. 2)
4. 8.5 x 6.5 x 1.5 cm, red granite (photo
in Fig. 2)
22
J- J• Donner and Marja
Simola
4. 8 x 6 x 2 cm, r e d g r a n i t e
4. 4.5 x 4 x 1 cm, r e d g r a n i t e
All v e n t i f a c t s consist of cobbles or coarse
p e b b l e s of t h e local P r e c a m b r i a n rocks, t h e
size v a r i a t i o n being r a t h e r small. O n e cobble
f r o m site 4 (see Fig. 2) is a v e n t i f a c t f o r m e d
f r o m one half of an originally l a r g e r cobble.
T h e u n e v e n s u r f a c e of t h e cobble has b e e n
w i n d - p o l i s h e d a n d h a s i r r e g u l a r f a c e t s on t h e
s u r f a c e . T h e r o u n d e d u n d e r s i d e of t h e v e n t i f a c t s h o w s some e f f e c t of w i n d blasting. All
o t h e r v e n t i f a c t s a r e well r o u n d e d a n d a r e
c l e a r l y w i n d - p o l i s h e d only on one side, as
seen f r o m t h e t w o e x a m p l e s in Fig. 2. N o n e
of t h e cobbles or p e b b l e s h a v e c h a n g e d s h a p e
b e c a u s e of t h e polishing b u t t h e y all h a v e
t h e s h i n y s u r f a c e t y p i c a l for v e n t i f a c t s . T h e
u n a f f e c t e d sides of t h e m h a v e a m a t s u r f a c e .
T h e c o m p a r a t i v e l y w e a k i n f l u e n c e of s a n d
blasting on t h e v e n t i f a c t s r e s t i n g on a loose
u n s t a b l e s u r f a c e h a s n o t b e e n able to f o r m
detailed m o r p h o l o g i c a l f e a t u r e s on t h e basis
of w h i c h f o r m e r w i n d - d i r e c t i o n s could be
d e t e r m i n e d , as f o r i n s t a n c e on t h e w i n d - p o lished b o u l d e r s a n d stones in Weichselian
i n t e r s t a d i a l deposits n e a r G o t h e n b u r g in
S w e d e n (Hillefors 1961, 1964).
In a d d i t i o n to t h e m e c h a n i c a l e f f e c t of
s a n d b l a s t i n g on t h e v e n t i f a c t s some of t h e
s h i n e can also b e caused by w e a t h e r i n g p r o cesses c a u s i n g t h e deposition of m a n g a n e s e
a n d i r o n on t h e s u r f a c e , r e s u l t i n g in a d e s e r t
v a r n i s h (Engel a n d S h a r p 1958). On t h e second v e n t i f a c t in Fig. 2 f r o m site 3 t h e r e is a
b r o w n colouring of t h e u p p e r s h i n y side
w h i c h is missing on t h e lower side w i t h o u t
polish. T h e r e is t h u s on this v e n t i f a c t , a n d
also less clearly on s o m e of t h e others, t h e
f i r s t indication of a v a r n i s h caused by c h e mical processes r e l a t e d to those f o u n d in deserts.
Fig. 3 gives c u m u l a t i v e c u r v e s f o r t h e d u n e
m a t e r i a l in t h e a r e a s w i t h v e n t i f a c t s . T h e
c u r v e s of 15 s a m p l e s a n a l y z e d of eolian m a t e r i a l f r o m H a n k o a r o u n d site 1 (anal, by
100
%
75
50
25
0.06
0.2
0.6
2..0 mm
Fig. 3. Cumulative curves of dune material. Curves of samples f r o m Hanko (site 1) fall within
shaded area. The two d r a w n curves are f r o m
Kalajoki (site 4).
M a r j a Simola) f a l l w i t h i n t h e s h a d e d a r e a
a n d t h e t w o c u r v e s d r a w n in Fig. 3 a r e f r o m
earlier published results from the Kalajoki
d u n e s ( L e m b e r g 1933, O k k o 1949). One of
these r e p r e s e n t s m e d i u m s a n d (0 0.20—0.60
mm) and the other represents a material bet w e e n m e d i u m a n d f i n e sand. All s a m p l e s
f r o m H a n k o a r e m e d i u m sand. According to
t h e s o r t i n g i n d e x of T r a s k (1932) a n d t h e
classification of S i n d o w s k i (1961) t h e m a t e r i a l
in both s a m p l e s f r o m K a l a j o k i a n d in 13 f r o m
H a n k o a r e w e l l s o r t e d a n d in t h e t w o r e m a i n ing s a m p l e s f r o m H a n k o m o d e r a t e l y sorted.
T h e eolian m a t e r i a l in t h e d u n e s w a s t r a n s p o r t e d by t h e w i n d s f r o m t h e sea, a w a y f r o m
t h e b e a c h over t h e cobbles a n d pebbles. T h e
most f r e q u e n t s u m m e r w i n d s on t h e H a n k o
p e n i n s u l a a r e s o u t h - w e s t e r l y a n d in K a l a j o k i
westerly, t h e m e a n velocities being a b o u t 6
m/sec., s t o r m s w i t h velocities exceeding 14
m/sec. being r a r e in s u m m e r ( K e r ä n e n a n d
K o r h o n e n 1952, A t l a s of F i n l a n d 1960).
T h e ages of t h e coastal d u n e s at w h i c h t h e
v e n t i f a c t s w e r e f o u n d can r o u g h l y be calculated using t h e a m o u n t of t h e r e l a t i v e u p l i f t
of l a n d a n d t h e a l t i t u d e s of t h e sites. A l i n e a r
e x t r a p o l a t i o n b a s e d on t h e p r e s e n t u p l i f t of
land ( K ä ä r i ä i n e n 1966) cannot, h o w e v e r , be
used b e c a u s e it m u s t be a s s u m e d t h a t t h e r e -
Some v e n t i f a c t s found near recent and fossil coastal d u n e s in F i n l a n d
lative lowering of sea level has slowed down
during the last few thousand years. This can
be seen already f r o m the geologically dated
altitude of the upper limit of the Litorina
Sea f r o m about 7000 B.P. (Eronen 1974). A
linear regression f r o m this limit, which at
Hanko peninsula is about 39 m, would give
an age of about 3700 years for the d u n e at
20 m (site 3), of about 2800 years for the
d u n e at 15 m (site 2) and about 900 years for
the dunes at about 5 m (site 1). At K a l a j o k i
the limit of the Litorina Sea is at about 108
m, which gives an age of about 300 years for
the large d u n e above the 5 m contour (site
4) These are m i n i m u m ages, the t r u e ages
being somewhat higher. The oldest d u n e is
probably about 4000 years old on the H a n k o
peninsula, and the others also somewhat older
t h a n the dates given above. T h e ventifacts
h a v e t h u s been preserved since the time of
23
the formation of these dunes. It has been
estimated t h a t wind-abrasion on hard-rock
stones on modern beaches requires about 100
years, the formation of facets even more
(Flint 1971). Ventifacts like those described
h e r e may however r e q u i r e less t h a n 100 years
to be formed.
In contrast to the Holocene ventifacts described above several ventifacts h a v e been
found in Alpua in Vihanti, about 60 km
north-east of K a l a j o k i (found by A. L u m i aho, oral communication by P. Markkanen).
Some of t h e m consist of quartzite and most of
t h e m have clearly developed facets. T h e y are
all w o r n and come f r o m the local late P r e c a m b r i a n bedrock, which partly consists of
quartzites, sandstones and conglomerates.
Material f r o m these rocks has been incorporated in the till (Hyyppä 1948).
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Manuscript received, M a r c h 30, 1976.