"Dobowe" iły warwowe w Jeleniej Górze

Alfred Jahn



In his publication of 1940 M. Schwarzbach reported his finding of the so-called diurnal varved clays (German: Tageswarwen) in the Bystrzyca Valley (Zagórze, formerly Erlenbusch) in the Sudety Mts. Schwarzbach found 73 to 158 secondary laminae within the light, summer layers; he considered them to be a sedimentary equivalent of daily temperature fluctuations. Schwarzbach's work had a great paleoclimatic value as its author put forward a bold hypothesis of the existence at the margin of the icesheet of a relatively warm summer season, lasting about 5-6 months and with the average daily temperature about 4°C. There are no clay outcrops in the former Erlenbusch. Moreover, since the time of Schwarzbach's studies diurnal varved clays have not been found anywhere, although marginal stagnant-lake deposits are found almost in each Sudetic valley. It was not until 1975 that a new profile (Fig. 3) was exposed in a clay-pit at Jelenia Góra. The author found secondarily laminated summer layers, up to 15 cm thick (Fig. 4), there. The number of these secondary laminae reaches almost 100, the figure similar to that given by Schwarzbach. A synthetic profile of the clay-pit is presented in Fig. 1. It should be noted that varved clays form two horizons here. The lower horizon is situated directly above granite periglacial debris with preserved faceted boulders (Fig. 2). The clays of this horizon were recently the subject of discussion, as some of the Sudetian researchers, e.g. J. Oberc, S. Dyjor and A. Sadowska recognized them as a Tertiary formation. According to the present author it is justified to contradict this view. Tertiary flora present in these clays appears to be redeposited and the clays overlay the substrata of Pleistocene surface characteristics, without any manifestation of chemical weathering. The upper horizon of varved clays displays the above mentioned "diurnal" laminae. Following this report, the upper horizon will be the subject of detailed analysis.

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