Okrzemki środkowego plejstocenu w osadach jeziornych z Krępca (Wyżyna Lubelska)

Abstract

 Osady jeziorne z profilu Krępiec 13 koło Łęcznej zostały uznane na podstawie analizy pyłkowej (Z. Janczyk-Kopikowa, 1980) za równowiekowe z osadami z Ciechanek Krzesimowskich, które według A. Środonia (1969) reprezentują interglacjał lubelski. W nawiązaniu do podziału palinologicznego opisywanego profilu dokonano korelacji wydzielonych okresów rozwoju roślinności wyższej z fazami rozwoju okrzemek – diatomofazami (KI, K2, K3). W obrębie diatomofaz wyróżniono ponadto ich części oraz subdiatomofazy reprezentujące poszczególne etapy rozwoju jeziora interglacjalnego.

MIDDLE PLEISTOCENE DIATOMS FROM LACUSTRINE DEPOSITS FROM KRĘPIEC (LUBUN UPLAND)

A thick packet of lacustrine deposits, about 20 m thick, was found at depth from 21.15 m to 41.50 m in the Krępiec 13 borehole column. They are represented by silts varying in lithology and with intercalations of gyttja, peat and peaty silts. They are underlain by sands with boulders, resting on till, and overlain by sands, peats, clay silts, chalk gravels and sandy silts.

The pollen analysis, carried out by Z. Janczyk-Kopikowa (in print), has shown that the Krępiec borehole column comprises Interglacial deposits coeval with those from Ciechanki Krzesimowskie.

According to A. Środoń (1969), the latter do not correspond to the Masovien I Interglacial but to the Lublin Interglacial.

On the basis of palynological subdivision of the studied borehole column, the differentiated periods of development of higher plants were correlated with phases of development of diatoms – diatom phases (K1, K2, K3). The diatom phases were further subdivided into parts and diatom subphases representing individual stages in evolution of the interglacial lake (Fig. 2).

The bulk of the studied lacustrie deposits from Krępiec, comprising diatom phases Kl, K2A and K3A, are characterized by predominance of nannoplankton diatoms Stephanodiscus and Cyclotella in the dominant group (Tables I – IV). Fragilaria crotonensis, Asterionella formosa and Synedra ulna and S. acus are fairly common in the subdominant group. Middle part of the studied column (diatom phase K2B) displays a transitional stage in the development of the lake, characterized by decrease of plankton, accompanied by increase in number of littoral, mainly epiphytic, and rheophilous species typical of flowing water. Upper part of the section (diatom phase K3B) is characterized by predominance of Melosira italica and Epithemia zebra and, subsequently, Synedra ulna and Fragilaria construens. The development of these species indicates a marked shallowing, eutrophication of waters in the lake, and its overgrowing by macrophytes. The changes are related to further amelioration of climate, recorded as an Interglacial optimum in the pollen spectrum (III) by Z. Janczyk-Kopikowa (in print).

The Krępiec section seems most close to that of the Lichwm Interglacial from Gwoznica in south-western Byelorussia (G.G. Gruzman et al., 1975).