A Móra Ferenc Múzeum Évkönyve, 1974/75-1. (Szeged, 1975)

Molnár Béla–Szónoky, Miklós: On the Origin and Geohistorical Evolution of the Natron Lakes of the Bugac Region

(M. Mucsi 1963, 1965, 1966; M. Faragó 1966, 1968; M. Faragó—

M. Mucsi 1971). Relying on their own investigations of gastropods and pollen grains, respectively, M. Mucsi and M. Faragó gave the generalized profile of the Pleistocene and Holocened epositsof the Danube

—Tisza Inerfiuve (Fig. 2). The stratigraphie subdivision of the Latest Pleistocene and of the Holocene can be readily seen on the profile as well as the sedimentary types of the various climati cphases have been illusztrated. Fig. 2 : Subdivision of the latest Quaternary and Holocene * sediments of the Danube

—Tisza Interfluve according to о M. Mucsi. Type sections A

—

В from the Danube

—Tisza Interfluve 1. Heavily and slightly humic strata 2. Plant remains 3. Peat 4. Calcareous silt 5. Calcareous carbonate-silty layers 6. Wind-blown sand accumulated in standing water 7. Lacustrine, finesandy, unsorted silt 8. Coarse

—silty fine silt 9. Small-grained wind-blown sand 10. Fine sand 11. Loessic fine sand and fine-sandy loess 12. Loess The results of the afore-mentioned authors have also shown that teh basement of one group of the lakes occurring on the Danube

—Tisza Interfluve Ridge, e. g: that of Lake Kunfehér by Kiskunhalas, is represented by Latest Pleistocene loess (Wurm

3

). In another group the Latest Pleistocene loess is first overlain by the wind blown sands of the Holocene pine-birch and of the dry hazelnut phases. Accordingly, it was not until the next, more humid period that lacustrine sediments could be deposited. A lake of this kind is e. g. Lake Petőfi near Soltvadkert which has been studied, too. GEOLOGICAL FORMATIONS OF THE BUGAC LAKES The Bugac lakes to be shown here lie north of the natron lakes studied earlier,, on the side of the Ridge sloping towards the Tisza (Fig. 1). Of the lakes selected for study, Lake Bogárzó and Lake Ródliszék dry out once in every 7—8 years. In Lake Kerek, open water, if any, is available in entirely humid years only. Its area is covered by reeds and sedges. Therefore the process of filling up is more advanced here as compared to the former two. Lake Kerek is of narrower shape with regard to its size, and its immediate vicinity is uplifting in every direction more rapidly than the surroundings of the other two lakes are. Because of the different environment the geological history of Lake Kerek developed in a different way, too. The aim of the study of the Bugac lakes was to explore the history of evolution of the lakes and to get acquainted with their sedimentary sequence. In the case of 17* 259