A Móra Ferenc Múzeum Évkönyve, 1970. 1. (Szeged, 1970)

as late as the subsequent more humid period. An example of this group is Lake Petőfi (M. M.-Faragó 1966) (Fig. 3, Section A). The Latest Pleistocene loess (W

3

) was formed of air-borne dust deposited on a dry surface. Hence, it is looser than the infusion loess (sediment deposited on a wet surface), more sandy, poorer in fauna and characterized by a higher carbonate content as usual (Fig. 8a). The wind-blown sand consists of minute, well-rounded sand grains with a mat surface. A peculiar feature of the lacustrine sediment is that calcareous silt layers with a carbonate content of 30 to 90% are common in it. These are white, greyish-white, slightly humic, if at all; though commonly loose, crumbling in dry state, they are sometimes represented by a hard variety. In some places, the carbonate silt may extend well over the range of the present-day water-table, while in others it is the water-table that is of greater extension. This evidences that the lake must have meanwhile changed its shape, as carbonate silt could be deposited only in case of totally waterlogged environment (Fig. 2, 3, Section 3). The material of the carbonate layers derives from a local depression, i. e. from the high carbonate content of the ground-waters which have flowed toward the lake. Nota bene, the groundwaters exsolved great amounts of carbonate from the sands of Danube origin and from the loesses and precipitated them at the end of the Holocene hazel-nut phase and in the subsequent oak phase (M. Mucsi and M. M.-Faragó 1966). The calcareous silts are always overlain by humic, often dark-grey, lacustrine sediments. Having a substantially lower carbonate content, these were deposited in the oak phase of the Holocene. At last follows the recent, uppermost layer constituted either by totally loose, liquid, lacustrine mud, or by small-grained sands of wind-blown sand origin. As proved by palynological analyses (M. M.-Faragó 1966) and by the investigation of the fauna (M. Mucsi 1963, 1966), the lithology of sediments in the natron lakes of the Danube-Tisza Interfiuve is particularly suitable for investigations into the history of the Holocene climate of the region. NATRON LAKES OF THE SOUTHERN TRANS-TISZA REGION Out of the natron lakes of this region, Lake Fehér at Kardoskút and Lake Kakasszék by Orosháza have been investigated and treated in detail (Fig. 1, 4, 5) (B. Molnár and M. Mucsi 1966, B. Molnár and M. Szónoky 1969). These lakes have developed from the ox-bows of abandoned river channels, a fact evidenced by their narrow, long-outstretched shape. An important evidence in the dating of the lakes is the loess layer occurring in many places, which represents the last glaciation, W

3

, of the Pleistocene (Fig. 4, 5, 6). Accordingly, the fiuviatile sands and silts below the loess must have been deposited before the last glaciation, probably in the W

2

—W

3 interstadial. The vicinity of the lakes is of morphologically deeper position and loess is absent in these places, being replaced by channel-filling fiuviatile, flood-laid and lacustrine sediments (Fig. 4, 5, 6). At Lake Kakasszék the incision fo the river valley and its subsequent fillirig-up may have begun at the end of the Pleistocene, in one of the interstadials. This is suggested by the fact that on the eastern side of the lake the longshore dune range, extending parallel with the paleochannel, crops out still from below the loesses (Fig. 5, 6). The fine-grained sandy loesses of the eastern side (Fig. 8, C/2) and also the fine sand intercalations, observable within the loesses in many places, are proofs 68