Madaras László – Szabó László – Tálas László szerk.: Tisicum - A Jász-Nagykun-Szolnok Megyei Múzeumok Évkönyve 8. (1993)
Sümegi Pál: A jászfelsőszentgyörgyi szunyogos felső-paleolit telephely üledékföldtani és sztratigráfiai elemzése
(Table III.). At the same time on the surface of the grains marks of impact characteristic of grains transported by wind are recognizable and as a result of eolian transportation the edges and corners of the grains became already weathered. Roundness values are already higher than those of the fluvial material, since eolian transformation had already begun - though the differences are not yet so remarkable. The microscope investigation of the material of the sand dune unambiguously demonstrates that the sediment is originated from an alluvial fan and resedimented locally in an eolian way. This eolian resedimentation, however, may occur on the surface of the alluvial fan only if its surface is dry. On the basis of paleogeographical, geomorphological and paleontological finds we suppose that becuse of tectonic (perhaps of climatic) reasons the alluvial fan of the Anicent Zagyva became dry at the end of the Middle Wurm. On the surface of the dried up alluvial fan, especially in periods with more arid climate when no vegetation cover to protect the surface could develope, eolian surface formation was able to start and the formation of drift sand underlying the Upper Paleolithic settlement had begun at that time, too. Similar development can be observed on several alluvial fans in the Great Hungarian Plain (Borsy Z. 1977, 1987). Geomorphological observations and the sedimentological analysis of the material of boreholes suggest that the drift sand formation developed as a result of eolian effects is a sand hummock. This is one of the characteristic dune forms of half-strengthened sandy areas. They are found everywhere in the drift sand areas of Hungary (Borsy Z 1977). This sand hummock is situated at the W margin of a small sand hummock group consisting of three loosely joint members. On the basis of the investigations made on the profiles in boreholes and in the trial trench (Figs. 1-3.) it became clear that the sand hummock was covered by a sequence of sediments consisting of sandy loess, loessy sand and loess layers. In the near-surface part of the loess layer a soil formation process took place. From the soil level the shells of the Gastropoda species Granaria frumentum (Draparnaud 1801), Chondrula tridens (Müller 1774), Helicopsis striata (Müller 1774) and of Cepaea vindobonensis (Férussac 1821) came to light. The malacofauna suggests that soil formation took palce already during the Holocene. Sand hummocks covered by different loessy sediments of finer grain composition already are not deformed further by eolian influence (Borsy Z. 1973). Therefore they preserve well that direction of wind which produced these sandy formations. In the case of the investigated sand hummock this direction is NNW which is identical which that direction of wind which is predominant in the N part of the Jászság even now. We investigated the upper parts of the drift sand layers of the sand hummock and also the sedimentological conditions of the overlying loessy layers in details (Figs. 2. and 3.). On the basis of the sediment statusticai parameters of the granulometric composition curves (Fig. 4.) and of the carbonata content in the direct sedimentary environment of the Upper Paleolithic settlement we can distingiush four bigger sediment levels which could be divided into further smaller layers of only a few em's thickness. Level 1. is between 1 and 1,3 m below the surface (Fig. 3). Medium grain size (M z ) values (0,14-0,2 mm) suggest that at the time of the formation of this level the energy of the eolian medium was rather considerable. The energy of the eolian medium was rather considerable. The nearly symmetrical granulometric composition curves (Fig. 4. 10 and 13), the skewness (S k ) values below 0,3 prove that for a while the kinetic energy of the medium was greater than average kinetic energy. Medium sorting values (a) between 0,5-1,0 suggest that the energy of medium which accumulated the sediment remained constant for a longer time. This level which consists of sandy, (according to the Munsell Soil Chart 2.5 Y 6/2) brownish grey medium grained sandy fine-grained sand was accumulated therefore by a sedimentary medium with considerable and uniform energy. Level 2. is between 0,6 and 1,0 m. On the basis of changes observed in the sediment statistical parameters we called it a "fluctuation" level because the energy of the sedimentary medium had changed several times in a fluctuating manner. Therefore bands of brownish grey (5Y 6/4) fine-grained sand, of yellowish grey (2,5Y 6/2) medium-grained sand with fine-grained sand and of brownish yellow (5Y 7/3) fine silt with coase-grained silt had deposited (Fig.3). The fine silt (loess) with coarse-grained silt and with a higher (10-12 %) clay content (Fig. 4. 8 and Fig. 3. 0,70,8 m) had deposited not only because of the decrease of energy of the settlement medium. The larger clay content is most probably the result of weathering started under an increasingly humid climate. Furthermore it is highly probable that a more intensive vegetation cover had been developed therefore we may reckon also with dust sedimentation lasting for a short time in the 67
