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

A: Curves of the calcareous silt layers extending beyond the present-day boundary of the lake: (the percentage values indicate the carbonate content of the sample) 1 2sz.f. 0.4—0.6 m: 31.2% 2 2sz.f. 0.6—0.8 m: 31.0% 3 lOsz.f. 0.5—1.0 m: 31.1% 4 lOsz. f. 1.0—1.2 m: 36.8% 5 10 sz. f. 1.2—1.5 m: 34.6% 6 10 sz. f. 1.5—2.0 m: 54.0% В : Curves of the calcareous silt layers deposited within the present-day area of the lake : 1 15sz.f. 0.3—0.7 m: 72.8% 2 16 sz. f. 0.0—0.3 m: 40.0% 3 16 sz. f. 0.3—0.7 m: 39.6% 4 17sz.f. 0.3—0.6 m: 42.3% 5 18 sz. f. 0.0—0.3 m: 46.8% 6 18 sz. f. 0.3—0.6 m: 46.8% С

—D: Sequence underlying the peat deposit as exposed by the borehole No 4 at Lake Kerek. С: 1 0.6—

0.7 m: 55.0% 2 0.7—

0.8 m: 59.1% 3 0.8—

1.0m: 63.7% 4 1.0—

1.5 m: 49.6% 5 1.5—

2.0 m: 45.0% 6 2.0—

2.8 m: 33.0% D: 7 2.8—3.2 m: 28.0% 8 3.2—

3.8 m: 33.0% 9 3.8—

4.2 m: 36.4% 10 4.8—

5.8 m: 33.7% oak phases. After the frequent dessiccations of the lakes their bottom silt layer is heavily cracked and fractured. The fissures reach down to very significant depths, 10 to 25 cm, so that the contemporary finer-grained, more clayey sediment is washed into the deeper strata by meteoric waters, to enrich the finer fractions there. The differences in carbonate content are, in their turn, due to the fact that the carbonate matter of the strata derives from the ground-waters flowing towards the lakes : the local depressions. Nota bene, the ground-water dissolves high amounts of carbonate from the sands and loesses of Danubian origin. Crossing the carbonate layers available beyond the present-day boundaries of the lakes, it can exsolve from the soil a carbonate quantity that is higher even than that mentioned previously. The carbonate in solution will then be precipitated in the lakes, to enrich on their bottom the carbonate content of the lacustrine sediment which is considerable even without that. It is true, by the way, that this process will diminish the carbonate content of the carbonate silts occurring beyond the present-day lake area. (b) At Lake Kerek the calcareous silts on the southwest and nordeast sides of the Lake are overlain by peat of loose structure, 0.6 to 1.0 m thick, grading progressively from the calcareous silt into the peat composition, though with a rather sharp boundary in the middle. The material of the peat consists of fibres of waterdwelling plants, predominantly reeds and sedge, still covering the water body of the lake. Its carbonate content too is very significant, attaining 50 and sometimes even 60%. Beside the vegetal and carbonate matter some wind-blown sand is also frequently present in the peat. Consequently, the peat is only partly organic in origin, the inorganic part being in many cases equal to the organic one. 267