Pleistocene malacofauna of the Po`arevac Danube Area (NE Serbia)

The results of recent analyses of loess samples from the localities: ]irikovac, Klenovnik, Novi Kostolac, Zatonje and Kisiljevo, confirm the idea that malacological associations identify biotope characteristics. Using palaeontological analyses, 25 species of gastropods were identified. Statistical analyses, tables and histograms based on ecological indices separate malacolgical associations: forest and species living mainly in woods, but also in mesophilous places and both damp and dry biotopes, steppe, open biotopes, mesophilous and hygrophilous species. Based on the current literature on the Po`arevac Danube Area, the species Vertigo pygmaea in ]irikovac and Columella columella in Klenovnik were recorded for the first time. Based on the following species: Succinella oblonga, Cochlicopa lubrica, Granaria frumentum, Vallonia costata, Vitrea crystallina, Pupilla muscorum, etc. it could be concluded that loessoid eolian sediments have their origin in the arid climate during the Pleistocene.


Introduction
The Po`arevac Danube Area is located along the right bank of the Danube River, from the mouth of the Velika Morava River to the city of Golubac.In the geomorphologic sense, this area belongs to Morava lowland and the Mlava valley, with an average altitude of 85-110 m (Fig. 1).
The relief of the area is composed of low-level lake terraces, desiccated by fluvial erosion.Fluvial erosion has had a huge effect as is evident by the broad fluvial planes and wide river valleys.Erosion significantly reduced the Pliocene lake coverage, and moved it from the recent Danube valley further to the south, which was sometimes left in the form of fold belts (i.e., the Po`arevac fold belt).
Quaternary eolian sedimentary loess and quicksand cover 97 % of the Po`arevac Danube Area, being the most extensive in this geographic region.Quicksand is limited to the immediate beach areas and lies along a distance of 5-6 km from the Danube River, while loess is stretches further to the south, up to 34 km from the river.In the Po`arevac Danube Area, loess sediments were, at the time of their formation, represented by one continuous cover, which was later, as a result of erosion, lowered, and broken into several separated parts: a) The nearest region between Velika Morava and Mlava rivers and from Po`arevac to Kostolac constitutes the "Po`arevac fold belt"; b.) Loess sediments between Mlava and Pek rivers follow the banks of the Danube River; from Ram to Pek River, loess outcrop at the lowest terrain between the villages Zatonja and Kisiljeva up to 100 m altitude, and to the highest terrain, where loess covers Tertiary relief from the village Topolovnik to Pek River; c.) Loess from Pek to the town of Golubac has the smallest geographic distribution and is situated at the base of loessoid sand, which according to its morphology and higher absolute altitude could not belong to the Po`arevac Slope.
The Holocene is represented with the formations of lower river terraces, fluvial and slope sequences.In the Ram Danube Area (south of Ram, Topolovnik, Kumane, Biskuplje and Kli~evac), eolian loessoid sands are well distributed and positioned over the Older Pleistocene sediments of the "Kli~evac Formation".The loessoid sediments of the Smederevo-Ram Danube Area are often changed into deluvial formations, composed of gravel which indicates repeated sedimentation through rinsing processes.

Material and methods
Quaternary malacofauna was collected from sediments in two ways: as individual specimens (visible to the naked eye) and in bulk samples of 3 kg.The specimens visible to the naked eye were collected individually.
During the mechanical processing and extraction of individual fossils from the loess sediments, hand tools, such as trowels, knives and brushes, were used.The taxonomical determination of the "naturally prepared fossils" was done depending on the degree of preservation, on the genus or species level.The extracted fossil snails with preserved sculpture were studied and prepared again in the laboratory.The restoration of the broken shell fragments was made by glue and polish.Employing table lenses, the extremely fragile and tiny specimens were "quickly" transferred in order to preserve the shell specimens.In order to perform the identification of macrofauna with stronger shells, when it was necessary to determine the elements of oral aperture, regularity and structure, these specimens were washed with 3% H 2 O 2 .
During the preparation of the histogram, ecological valences for species were used according to LO@EK (1964).In the text, the percent representation is shown in parentheses after the name of the species.The statistic processing of the results is shown Table 1 and in the histogram in Fig. 7.The material was inventoried and labeled under the Inventory number K 6306-6402 and kept in the collection of the Natural History Museum, Belgrade.
One of the most common representatives of the genus Vertigo, Vertigo pygmaea, (Pl. 1, Fig. 5) was recorded only at the locality of ]irikovac.It occurs in association with species inhabiting open habitats, as well as those living in forests.In the Late Pleistocene, V. pygmaea became more common in the sediments originating in cooler and moister periods (KROLOPP & SÜMEGI 1993).From the genus Vertigo, V. pygmaea is one of a few typical of loess formations (KROLOPP & SÜMEGI 2000).

Klenovnik
A profile of the Pleistocene sediments was discovered close to Klenovnik on the road to Kostolac, after the right turn towards the school.These sediments lie over Pontian gray coarse-grained quartz sands, 2.5 m thick.The profile (Fig. 3) shows brown silty sands (1.0 m thick), overlaid by reddish sandy clays (1.5 m thick) Table 1.Survey of Quaternary malacofauna with a column of percentage distribution on different localities, of the Po`arevac Danube area.Explanation of symbols according to LO@EK (1964).1W, forest associated species; 2W(M), species living mainly in woods, but also in mesophilous places and both damp and dry biotopess; 4S, steppe dry sunny places; 5O, species living in open places without arboreous vegetation; 7M, mesophilous species which sometimes, can live in damp or dry places; 7Wf, mesic rupestral and scree-forest species; 8H, humidity requiring, cold resistant species; No, number of the specimens.and light brown silty sands a (2.5 m thick).The exposed profile is covered with silty sands with a low humus content, 0.5 m thick.
In the region of the Po`arevac Danube Area, the species Columella columella was recorded only at this locality.It is a species typical of loess formations, indicating the existence of specific cold tundra areas in Upper Würm, but was also present in the more hygro-philous parts of the steppe (SÜMEGI & RUDNER 2001).It commonly appears in association with other characteristic loess species, such as Sucinella oblonga, Vallonia tenuilabris, etc.
In these sediments, land fauna of a steppe association was best represented (39.58%), a certain indication that they were formed by wind-blown particles being laid upon the already formed accumulative plain.Such a cover of aeolian dust is connected with the last glaciation or Würm in a broader sense.
The humidity from tree leaves or from moist soil was suitable for life of hygrophilous species, such as Sucinella oblonga (2.76%).According to the malacological results from the analyzed locality, the appearance together of warmth-loving, cold-loving and mesophilous fauna is obvious evidence that the loess series was deposited during several phases of stadial and interstadial.
In the gray, fine-grained quartz sands with small lenses of sandy silts (Fig. 5), the fauna of a forest biocoenosis was also recorded: Cochlodina laminata (5.21%), Aegopinella nitens (1.04%), as well as that of mesic forest biotopes: species Vitrea crystallina (15.63%) (Pl. 1, Fig. 11) and Fruticicola fruticum (MÜLLER) (1.04%).The species Vertigo alpestris was recorded for the first time at the open profile of the locality Zatonje.It is characteristic only for the Upper Pleistocene (Würm), including loess (but it is not typical) (KROLOPP & SÜMEGI 2000).This petrophilous species may be locally an indicator of forest and shrub habitats, during cold and moist climatic periods.According to the collected fauna, the hypothesis of MARKOVI]-MARJANOVI] (1951) on a multi-phase nature of land loess is supported.Additional proof are the limestone rock plates 1 cm thick, which appear serially in the water wells of the village Zatonje at a depth of 21 m.The other layers are not fossil-bearing.

Conclusions
By analyzing the abundances of malacofauna from loess sediments of the Po`arevac Danube Area, several biotopes were recognized (Fig. 7): forest, open areas within forest biotopes, steppe, open biotopes, forest-mesophilous areas and moist biotopes.
Forest and forest-mesophilous species are abundant with 32%; the most common species is Trochulus striolatus (]irikovac, Klenovnik, Novi Kostolac and Kisiljevo).The "warmth-loving forms" also belong to this group, and they appear mostly in the relatively warmer phases of the late Würm.
Steppe fauna is abundant with 28.78%, with species Chondrula tridens and Granaria frumentum present at all localities.The steppe species lived in intrazonal biotopes (forest valleys, flooded forests along rivers, etc.), while some of them are representatives of mesophilous groups.The steppe climate was characterized by cold and arid winters and humid summers; the succession of "cold-loving forms" and "warm-loving forms" indicate that the loess was deposited in three Würm stadials, while the basal part was deposited during the Ris-Würm interglacial.The majority of these dry, grass, steppes represented the biogeography area of the Pannonian-Dakian steppe, suggesting diluvium origin (MATVEJEV 1961).
The open biotope consists of places of moist meadows and steppe.It is hypothesised that the S and SE winds in the southern parts, enabled the development of open biotopes for many species represented with 11.76%.
The mesophilous species were continually distributed along all of the studied profiles, they are represented with 24.92 %, and could live in fallen leaves and in relatively moist meadows.
According to some hypotheses (RAKI] 1977), the ecological conditions with more humid environment formed during the deposition of the oldest horizon, matching the penultimate phase of glaciations.Although the terrestrial fauna of gastropods had the widest distribution, it does not necessarily mean that the sediment was formed on land, because terrestrial forms could also indicate open grassland areas in the vicinity of water or moist ground.The presence of hygrophilous species (2.54%) may indicate that this loess was also occasionally flooded, but still not long enough to develop water fauna.
During the Riss-Würm interglacial, an analogous type of Balkan-Middle European ecological conditions was occasionally widely distributed in Europe.In the regional sense, the sediments of the "Kli~evac Formation" of the Po`arevac Danube Area can partially be correlated with similar sediments of the "Srem Formation" at the slopes of Fru{ka Gora Mountain and the "Zagaji~ka Formation" in Southern Banat (RAKI] et al. 1998).

Fig. 2 .
Fig. 2. Detailed view of the upper part of the section from ]irikovac.

Fig. 3 .
Fig. 3. Detailed view of the upper part of the section from Klenovnik.

Fig. 5 .
Fig. 5. Detailed view of the upper part of the section from Zatonje.

Fig. 6 .
Fig. 6.Detailed view of the upper part of the section from Kisiljevo.

Fig. 7 .
Fig. 7. Percentrage distribution of the terrestrial gastropod fauna on the basis of ecological groups.