LUBANAS Lake, Latvia Lubanas Lake (56 46˘26˛N, 26 55˘26˛E, 90.8 m a.s.l.) lies in the centre of the Eastern Latvian Lowland. This is a relatively flat plain surrounded by uplands: Seli Ridge, Central Vidzeme Heights, Gulbene Ridge and Aluksne Heights to the north, and the Augshzeme and Latgale Heights to the south and southeast (Loze, 1988). The underlying bedrock consists of Upper Devonian dolomites, siltstones and sandstones, but there is a mantle of Quaternary deposits some 5-20 m thick over most of the basin. The Quaternary deposits include tills, limnoglacial and lacustrine clays, silts and sands, lacustrine lime, gyttja and peats (Loze, 1988). Lubanas Lake is a shallow drainage lake, fed by the Rezekne, Malta, Malmuta and Lisinja rivers and several smaller brooks, with an outflow via the Aiviekste River into the Daugava River. Catastrophic spring floods in 1926 resulted in the deepening and modification of the Aivienste outflow. Several dams and ditches have been built to prevent such catastrophic floods, and the modern lake elevation is allowed to fluctuate between ca 90 and 93 m. At an elevation of 90.75 m the lake has an area of 2500 ha, increasing to ca 10,000 ha at 92.75 m. Other small relict lakes within the Lubanas basin, such as Zvidze Lake, were artificially drained in the early part of the century. Zvidze Lake is now very shallow and partially overgrown with an extensive mire belt (Loze, 1988). The Lubanas basin is highly paludified with peat bogs occupying an area of 49,500 ha of which ca 17,000 ha is covered by raised bogs. The thickness of the peat is of the order of 0.75-1.20 m in the fen areas and 2.0-4.0 m in the raised bogs. The history of Lubanas Lake has been extensively studied because there are many archaeological sites in the basin. Detailed archaeological studies have been carried out on 19 dwelling places at eleven separate sites within the basin. Pollen and plant macrofossil analyses have been made at most sites, including Zvidze, Osa, Sulka, Piestinya, Eini, Abora and Lagazha (Levkovskaya, 1987). There are also diatom analyses from Zvidze and Abora. Ilves and Medne (1979) have published a pollen diagram from a mire site within the basin. There are at least 96 radiocarbon dates from the Lubanas Basin (Davydova and Raukas, 1986; Loze, 1988; Levkovskaya, 1987). Loze and Eberhards (1983) have reconstructed changes in water level on the basis of archaeological and shoreline evidence. Levkovskaya (1987) has published a more detailed record of the water-level changes between 7700 and 4100 yr B.P., based on a synthesis of data from Zvidze, Osa, Sulka, Zveisalas, Nainiekste, Abora and Eini. Our synthesis, which is based on all the available data, is in broad agreement with both these reconstructions. Lake terraces provide evidence of higher lake levels in the past. The highest terrace (Lubanas I) lies at an elevation of 107-108 m; the second terrace (Lubanas II) at 104-105 m; the third (Lubanas III) at 99-102 m; and the lowest terrace (Lubanas IV) at 95 m a.s.l. (measured by Eberhards, cited by Loze, 1988). Only Lubanas IV encircles modern Lubanas Lake; the three higher terraces are only found to the north or northeast of the lake. All of the terraces are thought to be erosional in origin. The highest terrace is thought to have been formed when the basin was occupied by a proglacial lake during the late glacial (Loze and Eberhards, 1983). With the ice regression and the decrease in meltwater discharge, the area of the lake decreased and regressional terraces were formed at 104-105 m (Lubanas II), 99-102 m (Lubanas III) and 95 m (Lubanas IV). At the beginning of Alleröd (ca 11,800 yr B.P.) water level decreased when the Aiviekste River outflow was formed and Lubanas Lake became isolated. Lake level continued to fall as the drainage system became established during the Alleröd. During the Younger Dryas the level of the lake fell dramatically to 92 m (Loze and Eberhards, 1983). Shoreline terraces at lower elevations (95-91 m) are depositional in origin and are overlain by archaeological settlements. They can therefore be dated more closely. The most important archaeological sites from the point of view of reconstructing lake-level changes are Zvidze (elevation 93-95 m), Osa (93-94 m) and Sulka (92.5 m). Zvidze: Zvidze archaeological site lies 3 km northwest of Lubanas Lake, at an elevation of between 93 and 95 m (Loze, 1988), on a steep-sloping part of the ancient shoreline cut into a morainic hill (Loze, 1988). The archaeological settlements are of middle Mesolithic up to middle Neolithic Age (ca 7650-4300 yr B.P.). A lithological transect through the Zvidze site revealed five lacustrine terraces buried under peat, lacustrine and colluvial deposits: at 93.0 m, 92.3-92.0 m, 90.2-90.0 m, 89.2-89.0 m and 87.5-87.2 m (Levkovskaya, 1987). The archaeological material is associated with the uppermost terrace, and contemporaneous with gyttja formation in the lake. The four lowest terraces predate this gyttja unit. Lake clays were deposited in the lake during the time when the lower terraces were formed. Samples from the gyttja unit have been radiocarbon dated to 7180±100 (TA-1723), 7480±80 (TA-1745) and 7650±100 (TA-1722) yr B.P. The most complete stratigraphical record was obtained from a 1.82 m thick sequence from excavation Zvidze C (94-93 m) (Loze, 1988). This sequence is not radiocarbon dated. The basal deposits are silts, formed before 10,200 yr B.P. This unit is covered by thin gravel layer (1.80-1.82 m) which deposited ca 10,200-9000 yr B.P. Gyttja (1.68-1.80 m) was deposited in the second half of the Boreal (ca 8500-8000 yr B.P.). The gyttja is overlain by the cultural layer (1.46-1.68 m), sandy peat (1.33-1.46 m), fine sand (1.25-1.33 m), fine sand with organic matter (1.22-1.25 m), dark grey sand enriched with charcoal (1.21-1.22 m), sand with charcoal and plant detritus (1.11-1.21 m), peat with wood and sand (0.86-1.11 m) and peat with sand (0.78-0.86 m). All these units were formed during the Atlantic (7600-4600 yr B.P.). An additional gyttja unit (1.11-1.21 m) is shown on the actual pollen diagram (Loze, 1988), indicating a brief transgression at the end of Atlantic (Davydova and Raukas, 1986; Levkovskaya, 1987). The overlying units are sandy gravel (0.72-0.78 m), herbaceous peat with sand (0.57-0.72 m), gravel with organic matter and plant detritus (0.51-0.57 m), woody-herbaceous peat (0.38-0.51 m) and peat with gyttja (0.30-0.38 m). These beds were formed during Subboreal (2500-4600 yr B.P.). The uppermost bed is peat and peaty soil (0.00-0.30 m), formed during the Subatlantic (2500-0 yr B.P.). This part of the record is very compressed and there may be material missing. Sulka: The Sulka archaeological site is also located on an old shoreline of Lubanas Lake, at an elevation of ca 92.5 m (Loze, 1988). The site is buried under 0.2-1.0 m of peat. The stratigraphy is reconstructed on the basis of a transect of four cores (Loze, 1988). The pollen analyses and the radiocarbon dates were apparently obtained from different cores and the depths of the units are therefore quoted differently in the different sources. The basal deposits are fine lacustrine sands, typical of a relatively shallow lake. The overlying unit is a thin layer of lacustrine clay (below 2.45 m). An increase in water depth is indicated by gyttja (2.10-2.45 m) deposition. The gyttja contains woody remnants and mollusc shells. The aquatic assemblage was characterised by Trapa natans, Typha and Sparganium, consistent with moderately deep water. The presence of Trapa natans is thought to indicate warm summers. Samples of this unit from nearby sections have been radiocarbon dated to 6380±120 (LE-838, 1.8-1.9 m) and 5940±95 (LE-837, 1.5-1.6 m) yr B.P. The terrestrial pollen assemblages indicate that the gyttja started forming during the late Boreal (Loze, 1988). This early part of the record is apparently missing in the section analysed by Levkovskaya (1987). The overlying unit is peaty gyttja (1.70-2.10 m), indicating a decrease in water depth. This trend continued with the deposition of fen peat (1.08-1.70 m) indicating a further decrease in depth to ca 90.5 m sometime after 5580 yr B.P. The aquatic assemblage is still characterised by Trapa natans, Typha and Sparganium. Two samples from within the peat have been radiocarbon dated to 4850±60 (LE-834, 0.8-0.9 m) and 5260±70 (LE-836, 1.1-1.2 m) yr B.P., respectively. The overlying units consist of thin clay (1.02-1.08 m), or a sand layer, and sandy gyttja (0.80- 1.02 m). The sequence suggests a return to open water conditions after ca 4800-4500 yr B.P. The sand is devoid of pollen, which is consistent with deposition as a beach. Aquatics are rare in the gyttja, which is consistent with deeper water. The uppermost unit is fen peat (0.0-0.80 m) indicating shallowing. According to the terrestrial pollen assemblage, peat deposition began during the later part of mid-Subboreal (ca 3000 yr B.P.) and has continued to the present. The artefacts are concentrated into lower part of uppermost fen peat and sandy gyttja (Loze, 1988). Osa: Osa archaeological site lies northeast of Lubanas Lake in the Pieskinja River valley, at 93- 94 m. The stratigraphy of the cores provides little direct evidence for changes in the level of Lake Lubanas, but radiocarbon samples provide dating constraints on the age of archaeological settlement. The cultural layers at Osa are sometimes 1.5 m thick and contain Mesolithic-Neolithic artefacts, covering the time span between ca 7200 and 4900 yr B.P. The sedimentation here was not continuous. The most complete sequence is from excavation A (Zagorskis et al., 1984). In Osa G the lowermost silt (1.55-1.65 m) and sandy gravel (1.45-1.55 m) were formed in the late Boreal. There is an hiatus during the early Atlantic. The unit between 1.15 and 1.45 m is sand with organic matter, formed ca 5900-5700 yr B.P. The uppermost sandy peat (0.45- 1.15 m) accumulated in the late Atlantic and early Subboreal period. These beds between 0.70 and 1.30 m are consists artefacts. The uppermost sand was deposited at the end of early Subboreal. The uppermost beds have been destroyed by human activities. The lake-level history of Lubanas Lake can be summarised as follows. The lake was low during the Younger Dryas. At the beginning of the Preboreal (10,200-9600 yr B.P.) lake level rose to 94-95 m. The first early Mesolithic settlement Suljagals was erected on the Lubanas coast. Cultural material from this site is dated to 9575±80 yr B.P. (TA-1317). After 9500 yr B.P. lake level fell and terraces at 94 and 93 m a.s.l. were formed (Loze and Eberhards, 1983; Loze, 1988). The absence of early Boreal (9000-8000 yr B.P.) sediments from Zvidze V and the deposition of only a thin sand layer during the late Boreal suggests the water level was below 93 m. An increase in water level between 7650 and 7480 yr B.P. is marked by gyttja accumulation in Zvidze (Loze, 1988). Lake level fell sharply to 91-90.5 m some time after 7480 yr B.P. and the basin started to paludify, as shown in the Zvidze cores. The Osa settlement was built during this interval of low lake levels. Material from the base of the cultural layer was dated to 7180±60 yr B.P. (Bln-770). In the deeper part of basin, e.g. at Sulka, there was gyttja accumulation. The water level was probably around 91 m. The low water phase probably lasted to ca 6000 yr B.P. According to Davydova and Raukas (1986) and Levkovskaya (1987), there was a lake transgression at the end of Atlantic (6400-5900 yr B.P.). There are discrepancies in the limited amount of published information that make it difficult to evaluate what was happening at this time. A return to gyttja deposition at Zvidze (sequences V and B) and at Sulka indicates a brief increase in water level between 6000 and 5600 yr B.P. The accumulation of beach sand with organic detritus at Osa (sequence G) suggests that the elevation of the lake was ca 93 m. The aquatic pollen assemblage in the gyttja, which is characterised by abundant aquatics including Typha and Sparganium, is consistent with moderate water level. Peat deposition in Sulka (sequence A), in Zvidze B and at Osa indicates a fall in lake level after 5600 yr B.P. The water level decreased to 90.8 m, reaching a minimum between 4700 and 4500 yr B.P. A sand layer was formed at Zvidze V during this minimum. The increase in the abundance of Alisma and Sparganium is consistent with low lake levels. The date of 4430±50 yr B.P. (TA-1802) from the uppermost minerotrophic peat at Zvidze B fixes the end of the regression. The burial of the settlement at Sulka by gyttja indicates a short-lived rise in water level after ca 4500 yr B.P. In Zvidze V well decomposed peat with gyttja was formed, but Osa remained dry. This suggests that the water level was ca 92 m. Lake level fell again after ca 4300 yr B.P. The construction of the Nainiekste settlement (91.5 m) indicates that the water level was lower than this. The cultural layer of this settlement was dated to 4170±130 (LE-648, Loze, 1988). According to Loze and Eberhards (1983) water level was low and stable between 4100 and 3500 yr B.P. This regression could have lasted until 2700 yr B.P. based on the radiocarbon date of Lagazha peat (3640±70 yr B.P., TA-396, 0.80 m, Levkovskaya, 1987). Gyttja deposition at Piestinya, Abora and Eini indicates a moderate increase in lake level about 4200-4100 yr B.P. (Levkovskaya, 1987). There are few data on lake level changes during the last 2500 yr B.P. and the sedimentary records are very compressed. According to Loze and Eberhards the lake level rose to 93 m at the beginning of Subatlantic (about 2500-2700 yr B.P.) and was at ca 92.2 m during the entire Subatlantic (2500- 0 yr B.P.), until drainage at the beginning of the 1930 when the water level was regulated to the mean 90.8 m. The elevation of Lubanas has varied between 90 and 95 m, if we exclude the high shorelines created in pre-Alleröd and Alleröd times when Lubanas was a proglacial lake. We begin coding from the Younger Dryas, by which time the lake was isolated and the drainage system well-established. In the status coding, low (1) is indicated when the lake was at or below 91 m, intermediate (2) when the lake was between 91 and 93 m, and high (3) when the lake was above 93 m. References Davydova, N. and Raukas, A., 1986. Geological development of large lakes of the humid zone in the European part of the Soviet Union, and Holocene climatic changes on the basis of lake sediment data. J. Biogeography, no. 13, pp. 173-180. Eberhards, G.J., 1981. Ancient Lubanas Lake water level changes and inhabitation of its coasts. In: Izotopnye i geokhimicheskie metody v biologii, geologii i arkheologii (Isotopic and geochemical methods in biology, geology and archaeology). Abstracts, Tartu, pp. 182-186. Ilves, E. and Medne, L., 1979. The Holocene chronostratigraphy of the western Lubanas Lowland (Latvian SSR). Izv. Akad. Nauk ESSR, Ser. Geol., vol. 28, no. 1, pp. 26-32. Levkovskaya, G.M., 1987. Priroda i chelovek v srednem golotsene Lubanskoi niziny (Nature and man in mid- Holocene on the Lubanas Lowland). Riga, Zinatne, 93 p. Loze, I., 1988. Poselenie kamennogo veka Lubanskoi niziny. Mezolit, rannii i srednii neolit (The stone age habitation sites of the Lubanas Lowland. Mesolithic, early and middle Neolithic). Riga, Zinatne, 212 p. Loze, I. and Eberhards, G., 1983. Principal stages of development and sedimentation of Lubanas Lake in Holocene (Eastern Latvia). In: Istoriya ozer v SSSR (Lake history in the USSR), Abstract of papers, vol. 3, pp. 116-117. Zagorskis, F.A., Eberhards, G.Y., Stelle, V.Y., and Yakubovskaya, I.Y., 1984. Osa - Mesolithic and Neolithic settlement history at the Lubanas Lowland. In: Arkheologiya i paleogeografiya mezolita i neolita Russkoi ravniny (Archaeology and palaeogeography of Mesolithic and Neolithic age at the Russian Plain). Moscow, pp. 55-67. Radiocarbon Dates TA-881 1820±60 0.10-0.15 m complex peat, Zosu (r2) TA-880 2210±60 0.30-0.35 m limnotrophic peat, Zosu (r2) TA-992 2470±70 0.40-0.45 m Sphagnum peat, Zosu (r2) 2655±26 ca 0.5 m peaty gyttja, Sulka LE-868 3240±70 0.80 m basal peat, associated with cultural layer, Lagazha LE-903 3330±50 wood, associated with cultural layer, Zveisalas LE-2354 3500±50 sample, associated with cultural layer, Zvidze, ATY (r2) TA-396 3640±70 0.80 m basal peat, associated with cultural layer, Lagazha TA-749 3685±80 0.85 m peat, associated with cultural layer, Lagazha TA-394 3770±60 0.6 m peat, associated with cultural layer, Abora I LE-749 3860±100 0.6 m peat, associated with cultural layer, Abora I LE-670 3870±70 0.7 m peat, associated with cultural layer, Abora I LE-865 3880±80 ca 0.20 m peat, Piestinya LE-751 4000±60 wood, associated with cultural layer, Eini LE-758 4060±60 sample, associated with cultural layer, Osa LE-752 4060±60 0.90-1.25 m wood, Sulka TA-921 4160±70 0.55-0.60 m peat, Zosu (r2) TA-921B 4570±70 0.55-0.60 m wood, Zosu (r2) LE-648 4170±130 sample, associated with cultural layer, Nainiekste LE-867 4250±50 sample, associated with cultural layer, Piestinya I TA-675 4370±80 sample, associated with cultural layer, Zvidze TA-1802 4430±50 0.40-0.45 m minerotroph peat, associated with cultural layer, Zvidze (V) (r1) LE-748 4520±120 sample, associated with cultural layer, Piestinya TA-674 4540±60 sample, associated with cultural layer, Zvidze LE-750 4670±150 sample, associated with cultural layer, Piestinya TA-1801 4750±60 0.55-0.60 m minerotroph peat, associated with cultural layer, Zvidze (V) (r1) LE-834 4850±60 0.80-0.90 m Phragmites peat, Sulka A (r1) TA-395 4905±70 wood, associated with cultural layer, Zveisalas LE-798 4970±80 0.80-0.85 m sandy peat, Osa R(G) (r2) LE-798 4970±50 charcoal, associated with cultural layer, Osa LE-836 5260±70 1.10-1.20 m Phragmites peat, Sulka A (r2) TA-1800 5320±50 0.75-0.80 m sandy peat, associated with cultural layer, Zvidze (V) (r1) TA-1594 5440±80 sample, associated with cultural layer, Zvidze TA-1799 5510±70 0.80-0.85 m minerotroph peat, associated with cultural layer, Zvidze (V) (r1) TA-879 5620±70 0.80-0.85 m woody peat, Zosu (r2) 5646±40 ca 1.30 m detrital gyttja, Sulka LE-850 5730±80 1.15-1.20 m sand with organics, Osa R(G) (r2) TA-1818 5770±60 sample, associated with cultural layer, Zvidze LE-962 5780±70 1.30-1.35 m sand with organics, associated with cultural layer, Osa R(G) (r2) TA-1819 5870±60 sample, associated with cultural layer, Zvidze LE-961 5880±80 1.40-1.45 m, sand with organics, associated with cultural layer, Osa R(G) (r2) LE-837 5940±95 1.50-1.60 m detritic gyttja, Sulka A (r1) TA-1782 5990±60 1.18-1.23 m peat with wood, associated with cultural layer, Zvidze (V), ATY? (r1) TA-1798 6050±100 1.02-1.07 m peat, associated with cultural layer, Zvidze (V), ATO? (r1) Ri-359 6050±150 sample, associated with cultural layer, Zvidze TA-897 6060±70 1.00-1.05 m Carex peat, Zosu (r2) LE-1724 6080±70 sample, associated with cultural layer, Zvidze TA-1608 6110±80 sample, associated with cultural layer, Zvidze TA-1592 6170±70 sample, associated with cultural layer, Zvidze Vs-521 6180±150 sample, associated with cultural layer, Zvidze Tln-812 6195±40 sample, associated with cultural layer, Zvidze MGU-1010 6200±240 sample, associated with cultural layer, Zvidze TA-1609 6210±80 sample, associated with cultural layer, Zvidze TA-1593 6210±80 sample, associated with cultural layer, Zvidze TA-883 6260±60 sample, associated with cultural layer, Zvidze TA-852 6315±60 sample, associated with cultural layer, Zvidze TA-1746 6350±60 1.30-1.35 m peat with wood, associated with cultural layer, Zvidze (V) (r1) IGAN-614 6360±40 sample, associated with cultural layer, Zvidze LE-838 6380±120 1.80-1.95 m gyttja, Sulka A (r1) MGU-1008 6450±250 sample, associated with cultural layer, Zvidze Vs-518 6530±140 sample, associated with cultural layer, Zvidze Ri-272 6533±120 sample, associated with cultural layer, Osa TA-862 6535±60 sample, associated with cultural layer, Zvidze TA-898 6560±80 1.25-1.30 m Carex peat, Zosu (r2) MGU-1009 6560±440 sample, associated with cultural layer, Osa LE-810 6580±80 1.25-1.30 m sandy peat, Osa B(V) (r2) LE-641 6590±90 ca 0.7 m peat Abora I, ATO (r2) TA-1612 6610±80 sample, associated with cultural layer, Zvidze 6620±80 Zvidze TA-1607 6630±80 sample, associated with cultural layer, Zvidze TA-1820 6710±80 sample, associated with cultural layer, Osa LE-812 6760±80 1.70-1.75 m peaty gyttja, associated with cultural layer, Osa B(V), ATY ? (r2) TA-856 6770±60 sample, associated with cultural layer, Zvidze TA-861 6780±60 sample, associated with cultural layer, Zvidze LE-811 6960±80 Osa B(V), 1.45-1.50 m, peat, r2 TA-851 7020±60 sample, associated with cultural layer, Zvidze TA-864 7020±60 sample, associated with cultural layer, Zvidze TA-1634 7060±80 sample, associated with cultural layer, Zvidze TA-899 7100±80 1.45-1.50 m Carex peat, Zosu (r2) TA-863 7110±60 sample, associated with cultural layer, Zvidze TA-1723 7180±100 1.45-1.50 m gyttja, associated with cultural layer, Zvidze (V), ATY? (r1) Bln-770 7180±60 1.55-1.60 m peat, Osa B(V), ATO? (r2) TA-1611 7240±100 sample, associated with cultural layer, Zvidze LE-2795 7340±80 sample, associated with cultural layer, Zvidze TA-857 7370±90 sample, associated with cultural layer, Zvidze TA-900 7450±70 1.80-1.85 m, Carex peat, Zosu (r2) TA-1745 7480±80 1.40-1.45 m gyttja, associated with cultural layer, Zvidze (V), ATO? (r1) TA-1722 7650±100 1.58-1.62 m gyttja, associated with cultural layer, TA-923 7700±70 2.10-2.15 m Carex peat, Zosu (r2) TA-875 8020±80 2.95-3.00 m gytjja, Zosu, ATY? (r2) TA-878 8160±80 2.20-2.25 m Carex peat, Zosu, ATO? (r2) TA-876B 8360±70 ca 2.85-2.90 m Carex peat, Zosu, ATO? (r2) TA-876A 8400±70 ca 2.85-2.90 m Carex peat, Zosu, ATO? (r2) TA-877 8550±80 2.70-2.75 m Carex peat, Zosu, ATO? (r2) TA-877B 8700±80 2.70-2.75 m Carex peat, Zosu, ATO? (r2) Zvidze (V) (r1) TA-1317 9575±80 woody pieces, associated with cultural layer, Suljagals Note: The radiocarbon dates are devided from Loze, 1988 (r1), Levkovskaya, 1987 (r2) and Ilves and Medne, 1979 (r3). There are some discrepancies between radiocarbon dates as given in different publications, or between the text and the diagrams in a single publication. We have tried to eliminate obvious typographical errors. We assume that dates listed in Radiocarbon are correct. For dates not yet published in Radiocarbon, we assume that the information is most likely to be correct when radiocarbon lab numbers are also quoted, and that a date quoted in the text is more likely to be correct than that given on a figure. Coding ca 11,000-10,200 yr B.P. low (1) 10,200 - 9000 yr B.P. high (3) 9000 - 8000 yr B.P. intermediate (2) 7650 - 7480 yr B.P. high (3) 7480 - 6000 yr B.P. low (1) 6000 - 5600 yr B.P. high (3) 5600 - 4700 yr B.P. intermediate (2) 4700 - 4500 yr B.P. low (1) 4500 - 2700 yr B.P. intermediate (2) 2700 - 2500 yr B.P. high (3)