Cent Eur J Geosci • 3(1) • 2011 • 43-52 DOI: 10.2478/s13533-011-0007-5 Central European Journal of Geosciences Late Quaternary palaeoenvironment and palaeoclimate of the Lake Fehér (Fehér-tó) sequence at Kardoskút (South Hungary), based on preliminary mollusc records Research article Pál Sümegi, Tünde Lócskai, Júlia Hupuczi∗ Department of Geology and Paleontology, University of Szeged H-6722 Szeged, Egyetem utca 2-6, Hungary Received 15 December 2010; accepted 12 January 2011 Abstract: Forty (22 freshwater gastropod, 14 gastropod, bivalves) species and 3428 specimens of molluscs were collected and identified from a 6.3 m sequence, obtained from a core profile, of lake and fluvial sediments at Kardoskút, South Hungary According to changes in the molluscan fauna, six malacological–palaeoecological zones can be identified in this profile The Quaternary malacological data from the Lake Fehér core profile suggests that the Late Pleniglacial and Early Holocene development of the molluscan fauna, and local palaeoclimatic and palaeoenvironmental conditions in this area, differed from other regions in Europe Keywords: Late Quaternary ã malacofauna ã lake sequence ã palaeoenvironment â Versita Sp z o.o Introduction Lake Fehér can be found on the surface of an alluvial fan belonging to the Maros river at Kardoskút, in the southeastern part of the Great Hungarian Plain, in Hungary (Figure 1); this nature-reserve protected, natron lake system, formed in a palaeochannel of the ancient Maros river [1, 2] Only a few alkaline lakes with Late Quaternary deposits in the central and southeastern part of the Great Hungarian Plain offer exceptional opportunity for mollusc-based palaeoenvironmental studies, and Lake Fehér is one of them (Figure 1) ∗ E-mail: hupuczi@gmail.com This lake can be found in the dry steppe (specifically, oak forest steppe) zone today, and is surrounded by alkaline, hydromophic and chernozem soils, with steppe vegetation within alkaline spots The seasonal lake is 500 m wide in the north-south direction and its total length is 4000 m in an east-west direction (Figure 2) The present vegetation of Lake Fehér consists of alkaline marsh communities Likewards the marshland, the vegetation is dominated by alkaline plant communities, and include species such as Suaedetum maritimi, Bolboschoenetum maritimi, Crypsidetum aculeatae, Camphorosmetum annuae and Puccinellietum limosae This lake was selected for a Quaternary malacological study in order to examine the full glacial environment of the southeast Great Hungarian Plain 43 Late Quaternary palaeoenvironment and palaeoclimate of the Lake Fehér Figure The Carpathian Basin within the Great Hungarian Plain, showing Lake Fehér Black square = investigated area, black circle = town, 1-1 = Maros Alluvial Fan The Quaternary malacological investigation was carried out on a 6.3 m long core sequence of fluvial, lake and marshy sediment layers obtained from Lake Fehér at Kardoskút The aim of this paper is to develop a more reliable palaeoecological and palaeoclimatological framework of fluvial-lake-marsh sediment sequences in southeastern Hungary, using Quaternary mollusc remains Location of the coring site on the Lake Fehér Black circle = Position of borehole in the bed of Lake Fehér, C = Birdwatching site Methods Sediment cores from Lake Fehér were taken in 1995 using Russian and Livingston piston corers Overlapping core segments were obtained at each of the core locations (Figure 2) and stored at 4o C until further treatment For the purpose of this study, the entire core sequence (6.3 m deep) was sub-sampled for malacological analyses (41 samples) Radiocarbon dating was performed on drift wood fragments recovered from the bottom of the core sequence, as well as on macro-charcoal and mollusc shells recovered from the silty lake sediment 14 C analyses were done at the Light Isotope Laboratory of the Nuclear Research Center of the Hungarian Academy of Sciences The preparation of the samples and the actual steps of the measurement followed the methods of Hertelendi et al [3, 4] Subsequently, five bulk radiocarbon dates were calibrated using CALPAL 2007, and the most recent CALPAL-HULU 2007 calibration curve [5] The original dates are indicated as yr BP, whereas the calibrated dates are indicated as cal BP years (Table 1) To assess the concordance of the measurement results, the raw dates obtained were checked against their 44 Figure relative lithostratigraphic position in the sequence The raw 14 C ages received for the mollusc material were corrected for any reservoir effect based on the inferred age difference (only 190-130 cal BP years) of the control material derived from the Quaternary sediments of the Nagykör˝ u site [6] and from the Tokaj loess series [7] Samples for malacological analysis were dispersed in water and wet-sieved through 0.5 mm meshes After sieving, the mollusc shells were dried, sorted and identified under a dissecting stereomicroscope at magnifications of 6-50x The shells were identified using the keys of Kerney et al [8], Liharev & Rammel’meier [9], Ložek [10] and Soós [11, 12] Shells were classified into ecological and biogeographical groups (Table 3) based on the system published by Krolopp & Sümegi [13, 14] and Sümegi & Krolopp [15, 16] Relative frequencies of each taxon, and of the ecological groups, were plotted on diagrams Biozones were delineated using cluster analysis Bray– Curtis similarity calculations [17] were followed by Orlóci– Ward-type clustering [18, 19] Numerical analyses were done with NUCOSA [20] Clusters on the dendrograms were taken to represent a single biozone (MZ-1, MZ2 etc.) [21, 22] Pál Sümegi, Tünde Lócskai, Júlia Hupuczi Table Radiocarbon dates from Lake Fehér, Kardoskút, southeastern Hungary Depth (cm) Material dated 14 C age years uncal BP Calibrated range years BP Lab code 150–160 Charcoal 8239 ±70 9026–9410 Deb-4910 210–220 Chalk (Chara fragments) 10 498 ± 90 12 105–12 605 Deb-4883 400–420 Pisidium shells 17 715 ±250 20 331–21 737 Deb-7694 490–510 Pisidium shells 20 323 ± 300 23 525–24 992 Deb-7695 620–630 Charcoal (Salix sp.) 23 303 ±280 27 521–28 723 Deb-4572 Results 3.1 Numeric age datings and sequence changes As the depth/age models suggested a near-linear sediment accumulation, linear interpolation was chosen It involves connecting the date estimates to each other by lines of constant gradient and gives an overall model that can change at each date Constrained by five radiocarbon dates, this depth/age model (Figure 3, Table 3) suggests gradually declining sediment accumulation rates since the formation of the lake c 28 200 cal BP years ago Initially, each centimetre represented c 31-36 years between 28 200-24 300 cal BP years, followed by 45 years between 24 300-12 400 cal BP years, and finally, the lowest accumulation rate characterized the Holocene, where each centimetre represented 52-60 years The lake bed consists of fine- and medium-grained sand, with the basal sandy silt in the centre of the palaeochannel containing a significant amount of driftwood (Salix sp.) and cattail (Typha sp.) fragments between 610 and 620 cm depth (28 000-26 660 cal BP years) Fine- and mediumgrained sand content remains high up to 560 cm depth (26 100 cal BP years) in the core sequence, suggesting that the meander received floods regularly between 28 200 and 26 100 cal BP years Between 560-510 cm (26 100-24 570 cal BP years), alternating layers of greenish gray calcareous fine sands and clayey silts were found in the sediment sequence, with upward increasing silt content Grain size composition, together with the sediment features, suggest gradually decreasing flood intensity in this period, and the formation of an oligotrophic lake following the relocation of the active riverbed for either climatic or tectonic reasons (Table 2) Between 510 and 250 cm (24 570-15 250 cal BP years), greenish gray clayey silts alternate with occasional flood layers that are confined to the core profile, suggesting predominantly oxbow lake conditions and occasional lowamplitude floods, entailing re-connection of this channel belt to the active river These flood events show up in the grain-size record as occasional increases in the amount of fine- and medium-grained sand Between 250 and 190 cm (13 910-11 050 cal BP years) both the structure and colour of the sediment showed remarkable change: the clay content increased and amorphous limonite (hydrated iron-oxides) appeared, suggesting intensified weathering and oxic conditions at the sediment/lake water interface Furthermore, pH measurements suggest that the lake water became strongly alkaline (pH ≥ 10) after 13 000 cal BP years (230 cm), likely in connection with an increasing inwash of carbonate-rich minerals that in turn indicate soil alkalinization in the catchment area A further increase in carbonate input characterizes the next sediment unit between 130 and 190 cm (11 0507 700 cal BP years), when carbonate-rich lake mud accumulated, indicating benthonic eutrophication and biogenic carbonate formation under shallow open lake conditions On the other hand, the increasing relative frequency of coarse silt in this unit suggests intensifying inwashed loess material from the lakeshore Biogenic carbonate sediment was replaced by eutrophic lake and marsh sediments between 130 and 40 cm (7 7202 330 cal BP years) suggesting a decrease in water depth The uppermost light gray alkaline silty clay unit started to develop c 300 cal BP years 3.2 Malacological changes Six mollusc zones (MZ) were identified in the sediment profile The sediment contained mollusc shells between 630-150 cm (28 280-8920 cal BP years) and yielded altogether 3428 specimens in 40 species (22 aquatic gastropods, 14 terrestrial gastropods and bivalves) Results of the analyses are presented in Figures and The first malacological zone (MZ-1), between 630-600 cm (28 28027 350 cal BP years) is characterized by the dominance of branchiate species The presence of the rheophile Valvata naticina suggests fluvial conditions Valvata naticina occurs in South-southeastern Europe and Baltic areas today [23], but during the Late Pleistocene the species is characterized by a south- and southeastern European distribution [24] The most abundant terrestrial gastropod is 45 Late Quaternary palaeoenvironment and palaeoclimate of the Lake Fehér Figure 46 Changes in dominance of mollusc species within the Lake Fehér core profile Pál Sümegi, Tünde Lócskai, Júlia Hupuczi Figure Changes in dominance of mollusc-based palaeoecological groups at Lake Fehér Granaria frumentum, which was a typical member of the Balkan fauna during the Last cold stage (equivalent to the Weichselian glacials) [16] This malacological data suggests that South-southeastern European freshwater and terrestrial snails expanded in the southern part of the Great Hungarian Plain between 28 000-27 000 cal BP years, indicating a short, temperate climatic (interstadial) phase during this interval Very few shell fragments were recovered between 600530 cm (27 350-25 200 cal BP years), rendering quantitative analyses unfeasible The scarcity of mollusc shells can most likely be explained by decreasing oxygen content in the water typical for fluvial-lacustrine transitions, found in several oxbow lake sediments elsewhere in Hungary [25] The sudden decrease of available oxygen during palaeochannel formation leads into the extirpation of the fluvial elements, followed by gradual re-expansion of some surviving fluvial mollusc species, and finally, by the arrival of new lacustrine elements once lake conditions stabilize This process also involves the gradual increase of branchiate and pulmonate gastropods, as observed in the core profile above 530 cm In the second malacological zone (MZ-2), between 530-450 cm (27 350-22 470 cal BP years), mollusc species preferring still or slow-moving waters appeared (e.g Armiger crista) Rheophile elements disappeared, suggesting stabilization of stagnant lake conditions The mollusc assemblages suggest that the oligotrophic lake was probably around m deep Periodic and antagonistic relative frequency fluctuation of the Palaearctic Bithynia leachii and the Euro–Siberian Valvata pulchella [26] is also characteristic for this zone, as for the rest of the profile (Figure 5), and most likely reflects periodic fluctuation in water depth as the two species have different optima in this regard Relative frequency peaks of Valvata pulchella likely indicate water depths above m, while those of Bithynia leachii infer water depths between 1.5-2.0 m It is also notable that increases in the relative frequencies of Planorbis planorbis and Armiger crista strongly correlate with the relative frequency maxima of Bithynia leachii As these two species also show preference for lakes 1.5-2.0 m deep [27, 28], they further corroborate the periodic water-depth fluctua- 47 Late Quaternary palaeoenvironment and palaeoclimate of the Lake Fehér Table Depth Table Lithological Symbols, Sediment description Species (cm) after Troels-Smith [43] 0–40 As3Shl 40–80 80–110 110–130 130–190 190–250 250–280 280–320 320–390 390–430 Ah2As2Ag+ Sh3AslAg+ Sh2As2Ag+ As2Lc2Ag+ As2LclLflAg+ Ag2 Asi Lei Ag2AslGalLc+ Ag2AslLc+ Ag2AslGalLc+ C3 Valvata pulchella (Studer, 1820) A2 B2 C3 Dark brown silty clay with high organic content (alkaline eutrophic lake sediment) Valvata naticina (Menke, 1845) A1 B3 C4 Bithynia tentaculata (Linnaeus, 1758) A2 B3 C2 Bithynia leachii (Sheppard, 1823) A2 B2 C2 Aplexa hypnorum (Linnaeus, 1758) A2 B1 C1 Lymnaea stagnalis (Linnaeus, 1758) A1 B1 C1 Lymnaea palustris (Muller, 1774) A2 B1 C1 10 Lymnaea truncatula (Muller, 1774) A3 B1 C1 11 Planorbarius corneus (Linnaeus, 1758) A2 B1 C3 12 Planorbis planorbis (Linnaeus, 1758) A2 B1 C2 13 Anisus septemgyratus (Rossmassler, 1835) A2 B1 C4 blackish brown silty clay, with plant remains (humified marsh sediment) Dark brown and greenish grey silty clay, with high organic content (eutrophic lake sediment) Grayish white silty clay with high carbonate content; frequent mollusc and Chara remains (calcareous lake mud) Calcareous silty clay with limonite precipitates; frequent mollusc remains (mesotrophic lake sediment) Greenish gray calcareous silty clay and claysilt with frequent mollusc remains (mesotrophic lake sediment) greenish gray claysilt alternating with fine and medium sand lenses (mesotrophic lake sediment with occasional flood layers) Greenish gray claysilt (mesotrophic lake sediment) Greenish gray claysilt alternating with fine and medium sand lenses (mesotrophic lake sediment with occasional flood layers) Greenish gray calcareous claysilt alternating with fine sand lenses, upward increasing silt content (oxbow lake sediment) Ga4 C2 A2 B1 As2LclGal 630–650 C A1 B1 510–580 Dg2Ga2 B Valvata piścinalis (Muller, 1774) Greenish gray claysilt (calcareous oxbow lake sediment) 610–630 A Valvata cristata (Muller, 1774) Ag2As2Lc+ Ga2Ag2 Mollusc species, and bioindicator groups, from the core sequence of Lake Fehér Grayish white silty clay (alkaline lake sediment) 430–510 580–610 48 Lithostratigraphic description of core FT-1, Lake Fehér, Kardoskút, southeast Hungary Dark gray fine and medium sand; occasional claysilt lenses (Ag2as2) Greenish gray silty sand mixed with black organic-rich layers and dark grey fine and medium sand; occasional charcoal fragments (initial palaeochannel sediment with driftwood) Dark gray fluvial fine and medium sand with shell fragments 14 Anisus spirorbis (Linnaeus, 1758) A3 B1 C2 15 Anisus leucostoma (Millet, 1813) A3 B2 C2 16 Anisus vortex (Linnaeus, 1758) A2 B1 C2 17 Bathyomphalus contortus (Linnaeus, 1758) A2 B1 C2 18 Gyraulus riparius (Westerlund, 1865) A2 B2 C7 19 Gyraulus albus (Muller, 1774) A2 B1 C1 20 Gyraulus laevis (Alder, 1838) A2 B1 C1 21 Armiger crista (Linnaeus, 1758) A2 B1 C2 22 Segmentina nitida (Muller, 1774) A2 B1 C2 23 Sphaerium rivicola (Lamarck, 1799) A1 B1 C2 24 Pisidium cf obtusale (Lamarck, 1818) A3 BI C2 25 Pisidium cf casertanum (Poli, 1791) A3 BI C2 26 Pisidium sp A3 B1 C1 27 Succinea putris (Linnaeus, 1758) A4 B2 C3 28 Succinea oblonga (Draparnaud, 1801) A4 B2 C3 29 Oxyloma elegans (Risso, 1823) A4 B2 C3 30 Cochlicopa lubrica (Muller, 1774) A5 B1 C1 31 Granaria frumentum (Draparnaud, 1801) A5 B3 C5 32 Vertigo antivertigo (Draparnaud, 1801) A5 B3 C5 33 Pupilla muscorum (Linnaeus, 1758) A5 B1 C1 34 Vallonia pulchella (Muller, 1774) A5 BI C1 35 Chondrula tridens (Muller, 1774) A5 B3 C5 36 Limacidae A5 BI C1 37 Vitrea crystallina (Muller, 1774) A5 BI C2 38 Helicopsis striata (Muller, 1774) A5 B3 C5 39 Perforatella bidentata (Gmelin, 1788) A4 BI C2 40 Cepaea vindobonensis (Ferussac, 1821) A5 B3 C5 A = Palaeoecological groups A: Rheophilous species, A2: Ditch species, A3: Slum species, A4: Hygrophilous species, A5: Mesophilous and Xerophilous species B= Palaeoclimatological groups B1: Intermediate species, B2: Cold-resistant species, B3: Thermophilous species C= Biogeographical groups C1: Holarctic species, C2: Palearctic species, C3: Eurosiberian species, C4: Eastern European species, C5: Central and SSE European species Pál Sümegi, Tünde Lócskai, Júlia Hupuczi tion inferred above Specimens of the terrestrial Granaria frumentum were also found in this zone at 540 cm (25 500 cal BP years), suggesting mild summers with temperatures above a minimum of 17-18 o C July palaeotemperature The third malacological zone (MZ-3), between 450-340 cm (22 470-17 900 cal BP years) is characterized by the dominance of Pisidium species Many of the bivalve shells are broken, and the dominant species is P obtusale lapponicum Also characteristic is the presence Valvata piscinalis and Gyraulus laevis, both of which have wide ecological tolerances [29] This makes this faunal assemblage very similar to the Late Pleniglacial (equivalent to the Late Weichselian) loess fauna of Sparks & West [30], and can therefore be viewed as its aquatic equivalent [28] Similar faunal assemblages were recovered from several other Hungarian lowland lake sequences [31], and are considered the characteristic aquatic assemblages of the final stage of the Hungarian loess formation [16] In the fourth malaco-zone (MZ-4) (340-300 cm; 17 90016 140 cal BP years) the relative frequency of Pisidium species decreases significantly and several branchiate molluscs show increasing abundance (Bithynia leachii, Planorbis planorbis, Gyraulus laevis) These changes suggest recurrent fluvial activity in line with the increasing sand content of the sediment (Figure 3) The fifth zone (MZ-5), between 300-220 cm (16 14012 600 cal BP years), is characterized by a second marked increase in the relative frequency of Pisidium species, and in that relative frequencies of Armiger crista exceed 30% This strong faunal change suggests shallow lake conditions and the initiation of benthic eutrophication [29, 32] On the basis of the composition of the molluscan fauna, water depth ranged 1.0-1.5 m in the basin The sixth zone (MZ-6), between 220-150 cm (12 6008 920 cal BP years), is characterized by the dominance of Lymnaea palustris, Planorbis planorbis, Anisus spirorbis and A leucostoma They indicate a m water depth for the lake The appearance of elements preferring eutrophic conditions (Valvata cristata, Planorbarius corneus, Segmentina nitida) suggests a transition from oligotrophic to mesotrophic conditions [27, 33] The inwashed terrestrial, waterbank fauna is dominated by Succinea putris, Succinea oblonga and Oxyloma elegans The collective appearance of Bithynia tentaculata, Granaria frumentum and Cepaea vindobonensis, and the retreat of Valvata pulchella, imply that this zone dates to Pleistocene/Holocene boundary [16], with the radiocarbon chronology confirming this inference The admixture of cold-resistant, Holarctic, Euro-Siberian and Northeastern European elements, with thermophilous Southeastern European elements make this period similar to other sites in the Carpathian Basin [34] Gradual eutrophication of the lake was likely enhanced in this phase by both the increasing inwash of organic matter, and the gradual warming of the climate Increasing dominance of Anisus spirorbis above 230 cm (c 13 000 cal BP years) suggests an increase in dissolved Na+ and HCO− ions, and the development of alkaline conditions within the lake [35, 36] This is congruent with the pH values measured from this horizon, which had values around 10 Discussion The changes in the Quaternary malacofauna composition, obtained from the core sequence at Kardoskút, suggest the development of dynamic climatic and local environmental changes in the Maros Alluvial Fan area during the Late Quaternary Six sedimentological layers, four Quaternary malacological assemblages (Figure 5) and six malacological zones can be reconstructed for the lake using lithostratigraphic and Quaternary mollusc data In the lower fluvial sandy sediment horizon, which developed during an interstadial phase, the proportion of rheophilous elements in the molluscan fauna (Valvata naticina) increased, with thermophilous terrestrial elements coming from the Balkans also intruding into the central parts of Great Hungarian Plain (e.g Granaria frumentum), which corresponded their northeastern distribution boundary during this period (c 28 300-26 300 cal BP years) Just like today, the highest temperatures, plus duration and accumulated quality of solar radiation, must have been restricted to these areas during the studied period On the other hand, thanks to the relatively low topography, this region is geographically open towards the south, enabling a relatively rapid expansion of thermophilous elements into the area from refugia located along the northern margin of the Balkans, during the interstadials and the terminal phase of the Middle Pleniglacial [16, 37–39] During the terminal phase of the Middle Pleniglacial and at the beginning of the Late Pleniglacial, the molluscan fauna composition changed drastically Thermophilous, South-southeastern European species disappeared and cold-resistant elements (Valvata pulchella, Bithynia leachii, Anisus leucostoma) appeared in the core section These cold-resistant elements, along with very tolerant freshwater species, such as Planorbis planorbis, Armiger crista, Pisidium sp., dominated in this phase (26 300-15 400 cal BP years) In parallel with the development of this molluscan fauna, a silt-rich lake sediment layer with unweathered silicate minerals formed in the analysed catchment basin It is probable that during this cold phase of Late Pleniglacial, a mass of dust material accumulated in the oxbow lake 49 Late Quaternary palaeoenvironment and palaeoclimate of the Lake Fehér Figure Mollusc assemblages and lithological units in the analysed catchment basin of Lake Fehér and a special mineral-organic [40] sediment developed on the lakebed This Valvata pulchella – Bithynia leachii – Anisus leucostoma assemblage corresponded with the cold maximum of the Late Pleniglacial, but a brief occurrence of the thermophilous Granaria frumentum (23 300-23 000 cal BP years) and some interbedding of fluvial sand layers with the rheophilous Valvata piscinalis (c 22 300-22 000, 19 300-18 900 cal BP years) suggests that this cooling event with lake sediment forming phases was not homogenous After this cold event, the cold-resistant freshwater elements underwent a gradual retreat between 15 400 and 14 000 cal BP years, before finally disappearing completely from the deposits of the southern part of the Great Hungarian Plain This was accompanied by a new occurrence of the rheophilous (Valvata piscinalis), followed by thermophilous (Chondrula tridens) elements (14 00011 600 cal BP years) The molluscan record in the late glacial/postglacial transition (11 600-9 300 cal BP years) also indicates an intermixture of two ecologically different faunas: those which are characteristically Late Glacial cold-resistant species (Bithynia leachii, Gyraulus riparius), and those Early Postglacial thermophilous species (Bithynia tentaculata, Granaria frumentum, Chondrula tridens) This transition period lasted for approximately 2300 years In parallel with the changes in the malacological assemblages (Figure 5) came the development of some new sediment units in the analysed catchment basin, partic- 50 ularly carbonate-rich lake sediment (chalk), followed by marshy and alkaline marshy sediment Conclusion Lake Fehér is the remnant of a deep and long palaeochannel formed between 28 000-26 000 cal BP years, in an interstadial climatic cycle of the Middle Pleniglacial terminal phase The malacological data suggest that the climate around the analysed catchment basin, and the level of the formed lake, changed rhythmically between 26 0009 300 cal BP years According to the malacofauna composition changes, cooler periods 1400-1500 years long and warmer periods with a 300-400 year interval, developed during the Late Pleniglacial around the analysed catchment basin This cold Late Pleniglacial event ended, and between 15 400 and 11 600 cal BP years, the cold-resistant freshwater elements underwent a gradual retreat, and a new occurrence of rheophilous (Valvata piscinalis) and thermophilous (Chondrula tridens) elements formed The transition from Late Glacial to postglacial took between 11 600 and 300 cal BP years, as the ”coldstage” taxa declined and the ”warm-stage” taxa increased Therefore, in the first phase of the postglacial, there were highly mixed communities in the malacofauna, with coldresistant and warm-loving mollusc species living together As shown by our malacological data from the lake sedi- Pál Sümegi, Tünde Lócskai, Júlia Hupuczi ment section of Lake Fehér, the Late Pleniglacial and Late Glacial development of the fauna may be correlated with malacological changes detected in the loess profiles in the southern part of Great Hungarian Plain [39, 41, 42] Acknowledgement This project is currently funded by the research grant TÁMOP-4.2.1/B-09/1/KONV-2010-0005 References [1] Molnár B., Mucsi M., A Kardoskúti-Fehértó vízfưldtani viszonyai (Hydrogeological studies of the Fehértó at Kardoskút) Hidrológiai Kưzlưny, 1966, 46, 413-420 [2] Molnár B., Szónoky M, On the origin and geohistorical evolution of Natron-lakes of the Bugac Region Móra Ferenc Múzeum Évkưnyve, 1975, 75, 257-270 [3] Hertelendi E., Csongor É., Záborszky L., Molnár I., Gál I., Gy˝orffy M., Nagy S., Counting system for high precision C-14 dating Radiocarbon, 1989, 31, 399408 [4] Hertelendi E., Sümegi P., Szö˝or Gy., Geochronologic and paleoclimatic characterization of Quaternary sediments in the Great Hungarian Plain Radiocarbon, 1992, 32, 399-408 [5] Weninger B, Jöris O, Danzeglocke U., CalPal-2007 Cologne Radiocarbon Calibration & Palaeoclimate Research Package http://www.calpal.de/, Accessed 09-02-01, 2008, [6] Gulyás S., Sümegi P., Molnár M., New radiocarbon dates from the 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Valvata naticina occurs in South- southeastern Europe and Baltic areas today [23], but during the Late Pleistocene the species is characterized by a south- and southeastern European distribution