A Móra Ferenc Múzeum Évkönyve, 1971. 1. (Szeged, 1971)
Molnár, Béla–Mucsi, Mihály–Magyar, László: Latest quaternary history of the southern stretch of the Tisza valley
Because of frequent dessication the loess-covering wind-blown sands and alluvial and lacustrine sediments have yielded just a few pollen grains. These include hardly any Conifersae, and it is the non-tree pollen that predominates (Chenopodiaceae, Artemisia and Compositae). According to Mrs. Miháltz, the representatives of Chenopodiaceae confined to the uppermost 20 cm may be connected with the alcalization of the soil. The drying trend of the climate is also evidenced by the lack of peaty lenses in this sequence and by the higher pH observed in all of the samples analyzed. On the basis of their superposition to the loess and of their pollen spectrum these strata can be referred to the Holocene. GEOLOGICAL HISTORY The history of the territory has been sketched in Fig. 5 and Fig. 6. During the last stadial (W 3 ) the amount of precipitations decreased under the cooler climate. Thus fluviatile sedimentation was replaced by loess deposition. Both the alluvium and the loess formation extend beyond the contemporary eastern boundary of the Danube-Tisza Interfluve. To the west they continue under the windblown sands. At the beginning of the Holocene the climate became again more humid and jthe flood-plain of the Tisza grew again wider. The loess of the W 3 stadial was dissected, and its upper part eroded in many places, by the river. The loess-covering sediment also continues a little farther westwards in to the Danube-Tisza Interfluve, below and within the wind-blown sand sequence (Fig. 3, Profile I, borehole 1, 2; Fig. 5, 2/b). In the profile of Fig. 6 the Holocene fluviatile sediment, overlying the loess elsewhere, is absent, However, a few kilometres to the N of the profile, in the vicinity of Lake Fehér, it does occur already. In the dry hazel-nut stage of the Holocene during which the wind-blown sand movement was common in the Danube-Tisza Interfluve, the sands were migrated southeastwards here too, in correspondance with the predominant wind direction. As a result of this process a part of the early Holocene alluvium was buried (Fig. 3, Profile I: boreholes 1 and 2, Fig. 5: 2/a). Where only the loess is present, the wind-blown sands rest directly on the loess layer (e. g. in the section of Fig. 6). Under the slightly more humid climate that followed the hazel-nut stage, the stagnant waters left over by the frequent floods evaporated in the summer seasons and led to alcalization. In the waters of already low energy farther off the Tisza, just finegrained sediments could settle and thus accumulation slowed down. In the areas close to the river bed, however, the accumulative power of the river was greater. Therefore the absolute height of the more distant areas decreased with the passing of time (i. e. these areas became relatively deeper) and the stagnant waters accumulated in intermittent natron lakes. Lake Dongér, Lake Csaj and Lake Fehér belong among these. Under natural conditions their waters are not recharged by anything else than the precipitations and the ground-waters migrasting from the Danube-Tisza Interfluve towards the local depressions. The eastern side of the southern Tisza valle/ shows a similar structure. However, the eastern boundary is not marked by the wind-blown sands, unlike in the west, so that the Tisza valley passes more gradually into the Trans-Tisza Plain (to the east of the river). Within the above-outlined area the Tisza valley s. str., the contemporary erosional depression of the river and its accumulation zone lie a few metres deeper (Fig. 6). The last-mentioned zone extends in general to the east of the river. 10
