Some Preliminary Results on the Early Holocene Shore Displacement in the Oskarshamn Area, South Eastern Sweden

[Einige vorläufige Ergebnisse über die frühholozänen Strandverschiebungen im Oskarshamn Gebiet, südöstliches Schweden] K u r z f a s s u n g : In zwei 16 bzw. 2 6 m über Meeresspiegel gelegenen Seen sind Pollenund Sedimentanalysen durchgeführt worden. Der Beginn der präborealen Chronozone ist hier durch eine Regression gekennzeichnet, die wahrscheinlich durch eine kurz dauernde Transgression untetbtochen gewesen ist. Eine lasche und recht bedeutsame Ttansgtession, die mit der Ancylus-Transgression korre­ liert wird, setzte in beiden Lokalitäten um ca. 9 0 0 0 v. h. ein. Zwischen ca. 9500 und 8 5 0 0 v. h. wutden beide Seen vom Meet abgeschnürt, abet es ist bislang unbekannt, in weichet Höhenlage diese Regtession ausgeklungen ist.


Introduction
The early Holocene shore displacement in the vicinity of the investigation area has been studied by MUNTHE (1902MUNTHE ( , 1904) ) who during the geological mapping of the Kalmat Oskarshamn area and the island of Oland levelled the beach ridge corresponding to the Ancylus transgression.THOMASSON (1927) divided the early Baltic development in the Kalmat area into phases based on pollen and diatom stratigraphy.In THOMASSON (1935) the phases ate further subdivided.On Oland LUNDQVIST (1928) made pollenanalytical dating on organic layers below beach deposits corresponding to the Ancylus Lake, as well as on lake sediments with transgression sequences.KÖNIGSSON (1968) dates the Ancylus transgression on Öland with radiocarbon datings on pollen analysed profiles.This paper deals with the preliminary results from two out of several localities that will be used to determine the Late Weichselian and early Holocene shore displacement in the Oskarshamn area.Further work will be done on these two lakes with closer and deeper pollen analyses as well as diatom and grain size analyses.For comparison a study with the same aim is done on the island of Gotland (SVENSSON, in prep.).
The investigated lakes are situated west and southwest of Oskarshamn (Fig. 1) in a hummocky terrain with a granitic bedrock, mostly coveted by thin till.

Field and laboratory methods
The coring was done by the Russian type of corer.The sediment is described according to TROELS-SMITH (1955).Pollen samples of 1 cc.were taken with a cut syringe, tablets with Lycopodium spores were added to determine pollen concentration accord ing to STOCKMARR (1971).Pollen preparation was made in the usual way with NaOH, hydrofluoric acid and acetolysis and mounting in glycerol.During preparation some extra steps vere introduced.After boiling in 10 % NaOH and centrifuging, the remaining liquid was measured in a colourimetei to determine the relative amount of dissolved humic acids.After the NaOH treatment a careful decanting of the sample was done to separate the coatse minerogenic matter.The amount of this was measured and used to calculate the content of sand and coarse silt in the sediment.After acetolysis the clayey samples were sieved over a 7 /tm net to get rid of finer material.The method is slightly modified after CWYNAR et al. (1979).
The pollen diagrams were computer drawn ('polldata ' BIRKS 1979).Pollen sum and the composite diagram is based on all terrestrial pollen.

Indicators of isolation and inundation during early Holocene time
Loss on ignition is a good indicator and it always seems to rise during and aftei the isolation.The amount of humic acids shown by colour of NaOH extract reacts as 'loss on ignition' on isolation, but seems to be more sensitive.
BJORCK (1979) and BJÖRCK et al. (1982) shows that susceptibility reaches higher values just before the isolation, and decreases thereafter.The amount of sand and coarse silt seems to be directly related to susceptibility.
Pediastrum is often a good indicator, increasing close to and after isolation because of a more favourable environment (BERGLUND 1966).
Pollen concentration does also seem too be a good indicator, probably because of the regression bringing the vegetation closer to the coring point, and that the sedimen tation rate is normally higher during the Baltic stages thus diluting the pollen.

Djupeträskesjön
(UTM coord, zone 33 x = 634340 y = 57950.) The lake is situated in a small valley with a narrow outlet, 5 km north of Oskars hamn.The lake area is 110 000 m 2 .Maximum depth in the eastern pan is 15 m and in the western bay where the corings were carried out the depth is around 6 m.
The altitude noted on the map 'flygfotokartan' is 16 m a. s. 1. and the threshold has not yet been investigated.

Description of the local pollen assemblage zones
Zone D 1 (Fig. 2

Interpretation
The clay in layer 1 (Tab.1) indicates sedimentation in deep water.Layer 2, muddy clay with a slightly rising organic content (not discernible in the loss on ignition curve) and slightly higher pollen concenttation (Fig. 3  In layer 5, muddy clay, the loss on ignition is slightly rising and magnetic suscepti bility reaches a peak.It is possible that the basin is isolated from the Baltic in the upper part of this layer, that is in the upper part of pollen zone D 3. The low loss on ignition together with a relatively high amount of coarse minerogenic matter in layer 6 could indicate that the basin was a sheltered lagoon, never completely isolated.The high minerogenic content could else perhaps be explained by erosion of clayey sediments in the surroundings of the isolated lake.
The lamina in layer 6 is interpreted as annual varves, their mean thickness is 0.65 mm indicating that the layer is deposited in 150-200 years.
A transgression of the Baltic into the basin is indicated by layer 7 and layer 8 shows on a more shallow water with an isolation in the upper part, indicated mainly by the rising loss on ignition and the preceding high values of susceptibility.The isolation takes place in pollen zone D 7.

Bastgölen (UTM coordinates zone 33 x = 634340 y = 57950)
The lake is situated 10 km west of Oskarshamn.The area of the lake is 60 000 m 2 and the water depth at the coring point in the eastern bay is 1.2 m.The altitude of the lake is 24 m a. s. 1. on the topographic map and the threshold seems to have been deepened with ca.1.5 m.

Interpretation
The rising loss on ignition values and the maximum in susceptibility (Fig. 5) together with the Pediastrum rise show that the isolation takes place in layer 4 of pollen zone B 3.
The sediment change between layers 5 and 6 (Tab.2) with decreasing loss on ignition shows a transgression of the Baltic duting the first part of pollen zone B 4.
The second isolation takes place between layers 7 and 8 indicated by high values of susceptibility and coarse minerogenic matter.
Correlation and dating of the local pollen zones Datings of the rational limit of Corylus and Alnus in south Sweden is shown in DIGERFELDT (1982).Ten datings of Corylus rational limit between 9720 and 9360 yr B. P. gives a mean of 9500 yr B.P. Alnus rational limit is dated by 16 C-14 datings between 9320 and 8420 yr B.P., with a mean of 8700 yr B.P. Ten of those are within the 8500-8900 yr B.P. interval.These mean values of the rational limits of Alnus and Corylus are used in Fig. 6.
The C-14 date in layer 4 in Bastgölen (9840 ± 90 yr B.P.) dates the upper part of the Hippophae maximum.Hippophae seems to appeal approximately at the same time in the whole of S Sweden (cf BJÖRCK 1979(cf BJÖRCK , 1981;;BJÖRCK & DIGERFELDT 1982).
The dating of the uppermost part of layer 6 in Bastgölen (9610 ± 90 yr B. P.) seems to be too old or indicate that layer 7 is deposited during a long time or partly eroded.A reason for the dating to be too old is that the sediment is deposited in the Ancylus Lake during or immediately after the transgression maximum.This transgression inundates areas with vegetation, mostly Pinus and Betula forest, and great amounts of older organic material must have been eroded and partly incorporated in the sediment.

Shore displacement
The resulting shoreline displacement curve is shown in Fig. 6.The oldest pan of the curve shows a regression from Bastgölen.This regression seems to be interrupted by a transgression indicated by the stratigiaphy in Djupeträskesjön.This transgression could probably be correlated with the transgressive 'Gyrosigmasjön'.THOMASSON (1927), as well as with the Yoldia transgression in Estonia (KESSEL & RAUKAS 1979).
It seems probable that Djupeträskesjön 16 m a. s. 1., was never isolated during the following regression.Instead it formed a lagoon during 150-200 years.During this time a varved clay gyttja was deposited.
After this low water period a rapid transgression, correlated with the Ancylus trans gression reached both Djupeträskesjön and Bastgölen without any discernible difference in time.The tiansgression took place at the same time as Corylus appears.Thus the transgression is dated to ca. 9500 yr B.P. This age corresponds well with Finnish investigations (GLUCKERT & RISTANIEMI 1982;ERONEN & HAILA 1982) on the Ancylus transgression in South Finland.The altitude of the transgression maximum is not known in detail but according to a isobase map in MUNTHE (1904) it should teach ca.35 m a. s. 1.
The Ancylus regression seems to begin early, probably around 9000 yr B.P. Djupetraskejön is isolated around 8500 and the regression seems to have been slow at this altitude.
) named Betula-Pinus.Relatively high Betula, dominated by Pinus, Empetrum reaches its highest value in this zone.Poaceae and Cyperaceae are the dominating herbs.Zone D 2 named Betula-Pinus-Hippophae-Juniperus-Polypodiaceae.Betula is relatively high.The Hippophae maximum and the high Juniperus values are character istic.Spores of Polypodiaceae expands here.Zone D 3 named Betula-Juniperus.Characterized by a marked Betula peak and high Juniperus values.At the end of the zone Betula and Juniperus decrease markedly and the Pinus values increase.Artemisia almost disappears at the end of the zone and Ulmus attains low values.
Two radiocarbon datings have been done, one in the uppermost part of layer 4, 5.10-5.145m below surface (9840 + 90 yr B.P.), the second in the uppet part of layer 6, 4.81-4.84m below surface (9610 + 90 yr B.P.).Description of the local pollen assemblage zones Zone Bl (Fig. 4) named Artemisia-Chenopodiaceae-Pinus.High values of Arte misia Chenopodiaceae, Poaceae and low tree pollen values.Zone B2 named Pinus-Juniperus.Rising and high values of Pinus, high Juniperus and decreasing Artemisia values.Zone B3 named Betula-Hippophae-Juniperus-Empetrum.Betula is abundant (70 %).In this zone Hippophae has a marked maximum as well as other shrubs (Juniperus, Salix and Empetrum) and Filipendula.All these are decreasing markedly towards the upper part of the zone.Spores of Polypodiaceae begin to occur frequently at the beginning of the zone.Ulmus is found regularly in the upper part.Worth to notify is the occurrence of pollen and spores of waterplants as Isoetes and Myriophyllum alterniflorum togethet with high Pediastrum values.Zone B 4 named Pinus-Betula.Betula is decreasing and Pinus increasing markedly.Zone B 5 named Pinus-Betula-Corylus.Pinus reaches high values and Betula is still decreasing.Corylus has relatively low values until the end of the zone where it increases.Polypodiaceae almost disappears at the end of the zone.Zone B6 named Corylus-Pinus-Calluna.Increasing values of Corylus and decreasing values of Pinus.Scattered pollen of Alnus occurs and Calluna reaches a maximum.Zone B 7 named Alnus-Pinus-Corylus.Alnus occurs frequently and increases in the upper part of the diagram where some finds of Tilia and Fraxinus occur together with increasing but low Quercus values.
Tab. 1: Stratigraphy of the Djupeträskesjön cores Dominated by rising Pinus values and relatively high Poaceae and Filipendula frequencies which both decrease at the end of the zone.Characterized by rapidly rising Alnus values and a further increase of Corylus frequencies.
Zone D 5 named Pinus-Corylus.Dominated by Pinus and characterized by low but continuous Corylus values.Zone D6 named Corylus-Pinus.Corylus values are rising.Polypodiaceae is decreasing.Zone D 7 named Alnus-Corylus.
) together with high values of humic acids and susceptibility, seems to indicate a lower water level in first part of pollenzone D 2. The clay in layer 3 and 4 with low pollen concentration and low susceptibility indicates sedimentation in deeper water thus probably showing a minor transgression.