SEVAN Lake, Armenia Sevan (40 30˘N, 45 25˘E, 1898 m a.s.l.) is a large lake with an area of 1416 km2 in 1936 and catchment area of 4890 km2. Maximum depth is 83 m and mean depth is about 19 m. The water level has been artificially lowered since 1936 by 18.5 m and the surface area was reduced to ca 1254 km2 by 1988 (Sayadyan, 1991b). The water level was at 1898.06 m a.s.l. on 31 June 1989 (Sayadyan, 1991b from data of Department on Gydrometeorology of Armenia). Lake Sevan has an outflow via Razdan River into the Araks and Kura rivers and thence into the Caspian Sea. The lake is fed by 38 small rivers and brooks. About 0.25 km3/yr of water from the Arpa River is routed into Sevan for lake-level stabilisation (Sayadyan, 1991b). The artificial lowering of the lake has resulted in the exposure of several lacustrine sections, which provide information on the lake history. The most-well studied sections Norashen and Dzknaget are located on the southhwestern coast, where there are also ancient settlement sites (Lchashen and Norashen villages). A 4.5 m sequence (called the Norashen sequence) from the southwestern coast near Norashen village provides a sedimentary record back to ca 12,800 yr B.P. Changes in water depth are reconstructed from changes in sediment lithology, sedimentation rate, aquatic pollen, diatoms and molluscs and also archaeological records from this sequence. The Dzknaget sequence provides a pollen and diatom record for the last 2000 years. Five radiocarbon dates from the Norashen sequence, two from Lchashen and two from the Dzknaget sequence provide the chronology (Sayadyan et al., 1977; Aleshinskaya, 1980; Sayadyan, 1991a). The bottommost unit of the Norashen sequence is uniform clay (3.70-4.50 m) with rare ochre Fe spots. This unit is underlain by volcanic andesite-basalt rocks. The layer is characterised by low Cyperaceae and absence of other aquatics. The lithology and aquatic pollen assemblage are consistent with deep water. Extrapolation of the radiocarbon date of 8640±150 yr B.P. (MGU-467) from 3.5-3.6 m suggests this unit was formed between ca 12,800 and 9300 yr B.P. The next unit is peaty soil with plant remains (3.60-3.70 m). It indicates that lake level dropped. An increase in Cyperaceae pollen is consistent with this interpretation. This phase of low lake level has been dated to ca 9300-8900 yr B.P. The overlying unit is a medium-grained sand (3.50-3.60 m) containing mollusc shells and fish bones, thought to represent a nearshore deposit. The mollusc assemblage includes Limneae stagnalis (85%), L. (Radix) ovata, Radix auricularia, Planorbis planorbis, P. cartinatus, Gyraulus laevis, Pisidium casertanum, Succinea oblonga, characteristic of the littoral zone. Mollusc shells from 3.6-3.5 m were radiocarbon dated to 8640±150 yr B.P. (MGU-467). This suggests this interval of increased water depth occurred between 8900 and 8500 yr B.P. The overlying unit (3.30-3.50 m) is sandy loam containing occasional mollusc shells characteristic of littoral environments. The interpretation of this unit is uncertain. From a consideration of the geomorphology of the site, Aleshinskaya (1993) suggested that the lithology and presence of molluscs was indicative of deposition in a shallow, sheltered bay environment whereas the underlying sand was consistent with deposition in more open-water (though still shallow) conditions. This would imply that the transition from sand to sandy loam indicated a decrease in water depth. However, observations of modern day sedimentation processes in Sevan Lake (Sayadyan, 1991c) do not support this interpretation. These observations suggest that sand with abundant mollusc shells is confined to the shallowest littoral zone, and finer sandy loam sediments with only rare mollusc shells indicate deeper littoral zone. We follow this and interpret the transition to sandy loam as indicating increasing water depth after ca 8500 yr B.P. The overlying unit (3.15-3.30 m) is dark-coloured sandy loam containing small charcoal particles. The change in colour, and the presence of charcoal, probably indicate a fire event within the basin (Sayadyan, 1978). Since there is no change in lithology, this unit probably has no significance in terms of changes in water depth. The overlying unit (2.95-3.15 m) is medium-grained sand (3.50-3.60 m) containing mollusc shells consistent with nearshore sedimentation and decreased water depth. Molluscs shells from 3.05- 2.95 m were radiocarbon dated to 6270±110 yr B.P. (MGU-215), suggesting the unit was formed between 7000 and 6200 yr B.P. The overlying unit (1.50-2.95 m) is a cultural horizon of the ancient Norashen settlement, which consists of three building layers of early Bronze Age. It includes remnants of the ancient building (Sayadyan, 1978), and is rich in artefacts, especially ceramics, and stone and animal bone tools. When the settlement was built the lake must have been low. Based on the interpolation of the radiocarbon dates from Norashen sequence the cultural horizon covers the time span ca 4000-6200 B.P. This is consistent with archaeological data, suggesting the settlement existed in the third millennium B.C. (Sayadyan et al., 1977). The cultural horizon is covered by a thin soil layer (1.35-1.50 m), rich in ceramics and smashed tools, dated to the middle of the second millennium B.C. (late Bronze). In the ancient Lchashen settlement (3.5 km away from Norashen) the late Bronze cultural layer was radiocarbon dated to 3630±100 (MGU-IOAN-30) and 3500±100 (MGU-IOAN-29) yr B.P. (Aleshinskaya, 1980). Archaeological correlation with Lchashen sequence and estimation from the sedimentation rate suggest the soil layer was formed between ca 3400 and 3700 yr B.P. when the lake level was low. The absence of the middle Bronze Age cultural layers in Norashen and Lchashen settlement sequences may be interpreted as reflecting an increase in lake level ca 4000 yr B.P. (Aleshinskaya, 1993). The next unit (1.18-1.35 m) is sand with abundant mollusc shells (Limnaea stagnalis, L. (Radix) auricularia (27.5%), Valvata piscinalis, Planorbis planorbis (51.5%), Pisidium casertanum, Succinea putris), suggesting an increase in water depth. The aquatic assemblage includes pollen of Cyperaceae and Sparganium. Planktonic species (Cyclotella ocellata, C. kuetzingiana var. radiosa) are abundant in the diatom assemblage, consistent with increased water depth. A radiocarbon date 3180±130 (MGU-466) obtained from 1.20-1.25 m (Aleshinskaya, 1980) suggests this phase of increased depth occurred between 3400 and 2950 yr B.P. The abundant aquatic remains in the sand between 1.08 and 1.18 m is consistent with a decrease in lake level ca 2950 yr B.P. The overlying unit (0.98-1.08 m) is peaty soil suggesting low lake level. Interpolation between the radiocarbon dates suggests this phase occurred ca 2650-2350 yr B.P. The overlying unit (0.75-0.98 m) is sand, indicating an increase in water depth. The mollusc assemblage, analogous to previous transgressive sand layers, and the abundant planktonic diatoms are consistent with increased depth. Mollusc shells from 0.85-0.90 m have been dated to 2090±70 yr B.P.(MGU-244) and 2020±120 yr B.P. (MGU-215) (Aleshinskaya, 1980), suggesting deeper water occurred between 2350 and 1700 yr B.P. Sand deposits between 0.75 and 0.50 m contain abundant aquatic plant remains, suggesting shallowing after 1700 yr B.P. The extrapolation of sedimentation rate suggests this layer formed ca 1700-900 yr B.P. The uppermost unit (0.0-0.50 m) is deluvial cover, containing lava blocks and rock fragments and indicates decreased lake level since ca 900 yr B.P. A 12 m section (and a 30.5 m core extending this sequence) from the Dzknaget River delta, ca 600 m northwest of the lake, potentially cover the late Pleistocene and Holocene. Only the upper 4.5 m part of the section has been studied (Sayadyan et al., 1977). This provides information on lake-level changes during the last 2000 yr B.P. The unit between 3.6 and 4.5 m is clayey silt and sandy loam. The aquatic pollen assemblage consists of sporadic Typha, moderate Cyperaceae and low values of Sparganium, indicating relatively deep water. Among the diatoms planktonic species (Stephanodiscus astraea, Cyclotella kuetzingiana var. radiosa, C. ocellata, Stephanodiscus astraea var. minulutus) are abundant, especially near the base of the unit, suggesting deep water conditions. Extrapolation of radiocarbon dates 1010±250 (MGU-178) and 940±220 (MGU-55) yr B.P. from the depth of 2.00-2.10 m suggests the unit was formed between ca 2150 and 1700 yr B.P. This transgressive interval correlates with high lake-level phase indicated by the Norashen record. The overlying unit (2.0-3.6 m) is sand and sandy loam with pebble and gravel interbeds, characterised by increases in Cyperaceae, Typha and Sparganium pollen, suggesting shallowing. Diatoms are poorly represented and absent from the sandy deposits. The abundance of planktonics, mostly represented by Stephanodiscus astraea, Cyclotella ocellata and C. kuetzingiana, decreases to 4%, also indicating shallow water conditions. Among the benthic diatoms Meridion circulare, M. circulare var. constrictum, Cocconeis placentula et var., Amphora ovalis et var., Epithemia turgida, Rhopalodia gibba are most common. Hantzschia amphioxys, a soil diatom, is also found in the unit, suggesting that erosion may have been significant. The alternation of silts with sand, increase in aquatic pollen, the poor preservation of planktonic and domination of epiphytic diatoms are consistent with low lake level. Wood remains from the uppermost part of this unit (2.00-2.10 m) were radiocarbon dated to 1010±250 yr B.P. and mollusc shells to 940±220 yr B.P. Extrapolation of sedimentation rate suggests the unit was formed between 1700 and 950 yr B.P. The next unit (0.5-2.0 m) is silt with organic matter and alternation of sand and clayey silt with buried woody pieces, suggesting nearshore sedimentation. The percentages of aquatic pollen are variable, suggesting the lake level was unstable. Diatoms are abundant, consistent with the relatively increased water depth. Planktonics (9-48%) are represented by Cyclotella kuetzingiana, C. ocellata, Stephanodiscus atraea, Aulacoseira italica and benthics by Epithemia turgida, Meridion circulare, Fragilaria intermedia, Synedra ulna, Cocconeis placentula. This unit has been dated to 50-950 yr B.P. The topmost unit (0.50-0.00 m) is alluvial-delta pebbles and gravel-sand deposits, suggesting lake level lowering. The diatom composition is marked by decreasing abundance of planktonic species and abundant soil and aerophilic diatoms such as Navicula mutica and Hantzschia amphioxys. The uppermost 0.5 m was formed during the last ca 50 yr B.P., when the lake basin was influenced by human activities. In the status coding, (0) indicates an hiatus in lake sedimentation in Norashen sequence; low (1) by peaty soil sedimentation in Norashen sequence or dominance of benthic and epiphytic diatoms in Dzknaget sequence; intermediate (2) by sand with higher plants remains and decreasing planktonic diatoms; relatively high (3) by sandy deposition, abundance of planktonic diatoms and littoral molluscs assemblage; high (4) by sandy loam with absence of aquatic pollen and rare mollusc shells; and very high (5) by uniform clay deposits with low Cyperaceae in pollen assemblage. The record of the last 50 years has been extensively influenced by human activities, including engineering works, and is omitted from the coding. References Aleshinskaya, Z.V., 1980. Results of the radiocarbon datings of the Sevan Lake Holocene deposits. In: ???? (Isotopic and geochemical methods in biology, geology and archaeology). Abstracts. Tartu, pp. 5-7. Aleshinskaya, Z.V., 1993. Personal communication. Sayadyan, Yu.V., 1978. Postglacial times in Armenia and adjacent regions. In: Studia Geomorphologica Carpatho-Balcanica (Krakow), vol. XII, pp. 77-93. Sayadyan, Yu.V., 1991a. Archaeological relic and Sevan Lake history. In: Istoriya ozer Sevan, Issyl-Kul’, Balkhash, Zaisan i Aral (The history of lakes Sevan, Issyk-Kul, Balkhash, Zaisan, and Aral). Leningrad, Nauka, pp. 31-37. Sayadyan, Yu.V., 1991b. Natural features of Sevan Lake and its basin. In: Istoriya ozer Sevan, Issyl-Kul’, Balkhash, Zaisan i Aral (The history of lakes Sevan, Issyk-Kul, Balkhash, Zaisan, and Aral). Leningrad, Nauka, pp. 10-12. Sayadyan, Yu.V., 1991c. Peculiarities of present sedimentation in the lake. In: Istoriya ozer Sevan, Issyl-Kul’, Balkhash, Zaisan i Aral (The history of lakes Sevan, Issyk-Kul, Balkhash, Zaisan, and Aral). Leningrad, Nauka, pp. 23-27. Sayadyan, Yu.V., Aleshinskaya, Z.V., and Khanzadyan, E.V., 1977. Late glacial deposits and archaeology of the Sevan Lake. In: Geologiya chetvertichnogo perioda (Pleistotsen) (Geology of the Quaternary period (Pleistocene)), Sayadyan, Yu.V. (Ed.). Yerevan, Akad. Nauk Arm. SSR, pp. 91-109. Radiocarbon Dates MGU-55 940±220 2.00-2.10 m mollusc shells, Dzknaget MGU-178 1010±250 2.00-2.10 m wood, Dzknaget MGU-215 2020±120 0.85-0.90 m mollusc shells, Norashen MGU-244 2090±70 0.85-0.90 m mollusc shells, Norashen MGU-466 3180±130 1.20-1.25 m mollusc shells, Norashen MGU-IOAN-29 3500±100 cultural layer, woody artefacts, Lchashen MGU-IOAN-30 3630±100 cultural layer, woody artefacts, Lchashen MGU-215 6270±110 2.95-3.05 m mollusc shells, Norashen MGU-467 8640±150 3.50-3.60 m mollusc shells, Norashen Coding ca 12,800-9300 yr B.P. very high (5) 9300-8900 yr B.P. low (1) 8900-8500 yr B.P. relatively high (3) 8500-7000 yr B.P. high (4) 7000-6200 yr B.P. relatively high (3) 6200-4200 yr B.P. hiatus (0) 4200-3700 yr B.P. intermediate/very high (2/3/4/5) 3700-3400 yr B.P. hiatus (0) 3400-2950 yr B.P. relatively high (3) 2950-2650 yr B.P. intermediate (2) 2650-2350 yr B.P. low (1) 2350-1700 yr B.P. relatively high (3) 1700- 950 yr B.P. intermediate (2) 950- 50 yr B.P. low (1) Coded by: Aleshinskaya, Tarasov and Harrison (January 1994) SEVAN LAKE ARMENIA