Rozwój późno glacjalny zbiorników jeziornych z Niechorza (Pomorze Zachodnie) w świetle analizy diatomologicznej i geochemicznej

Abstract

 Badaniami objęto osady organogeniczne dwóch kopalnych zbiorników wytopiskowych odsłoniętych w klifie Morza Bałtyckiego koło Niechorza (Pomorze Zachodnie). W obu analizowanych profilach (Niechorze I i II) przedstawiono zakres występowania i sukcesję okrzemek oraz zmiany koncentracji pierwiastków śladowych. W profilu Niechorze II podano także skład chemiczny osadów. Etapy rozwoju zbiornika Niechorze I określono w nawiązaniu do wyników badań palinologicznych (E. Brykczyńska, 1978), natomiast w przypadku profilu zbiornika Niechorze II, wobec braku podziału palinologicznego późnoglacjalnej części osadów, podjęto próbę wydzielenia poziomów o zróżnicowanej zawartości pierwiastków śladowych – chemofaz, które zestawiono z uprzednio wyróżnionymi diatomofazami (B. Marciniak, 1979). DEVELOPMENT OF LATE GLACIAL LACUSTRINE DEPOSITS AT NIECHORZE (WESTERN POMERANIA) IN THE LIGHT OF DIATOMOLOGICAL AND GEOCHEMICAL DATA The studies covered organogenic deposits infilling two ancient thaw depressions (Niechorze I and II) at Niechorze (western Pomerania – see Fig. 1). Figures 2 and 3 show distribution and succession of diatoms and Figures 4A, Band 5A, B – changes in concentration of trace elements in sections of the deposits displayed in the Baltic cliff near Niechorze. Chemical composition of deposits displayed by the Niechorze II section is also given (Figs. 5C, 6, 7). The stages in development of the Niechorze I were reconstructed with reference to the results of palynological studies (E. Brykczyńska, 1978). In the case of the Niechorze II reservoir, palynological data needed for subdividing Late Glacial part of the sequence are lacking so attempt is made to establish horizons differing in content of trace elements, i.e. chemophases, and to correlate them with previously established diatomphases (B. Marciniak, 1979).The diatomological and geochemical studies showed that the deposits originated in two separate small lacustrine reservoirs, Niechorze I and n, differing in the rate and type of mineral and organic deposition in the Late Glacial and Holocene.The section of deposits of a smaller reservoir, Niechorze 1, displays somewhat larger breaks in sedimentation of diatoms and higher variability and differentiation of predominating diatoms than those of the Niechorze II (Figs. 2, 3, Tables 1, 2). In the former section, diatomphases IN1, IN2, and IN3 (comprising the Oldest Dryas, Bolling and Older Dryas deposits) display predominance of Fragilaria pinnata, characteristic of the first stage in the development of that reservoir. The second stage, comprising the next three diatomphases (lN4, IN5, and IN6, comprising the Allerod, Younger Dryas and pre-Boreal period), is characterized by predominance of Fragilaria construens var. venter (see B. Marciniak, 1981).The above discussed part of the Niechorze I section may be similarly subdivided on the basis of results of trace element analysis. The first three time intervals of the Late Glacial show some increase in content of trace elements (Ni, Cu, V, Cr and Ti), followed by a decrease in solifluction loam layer separating Balling deposits. The content of these elements in the Younger Dryas and a major part of pre-Boreal deposits was found to be very low, often below the identifiability limit (Figs. 5A, B).In the diatom section of the Niechorze U reservoir, all the evidenced Allerod, Late Glacial diatomphases display predominance of Fragilaria construens var. venter. A change in composition of dominants did not take place before the pre-Boreal time, when the genus Synedra began to predominate (Table 2). In that section, the group of subdominants and characteristic diatoms appears to be highly differentiated in composition and frequency of occurrence (Table 2). In turn, the results of geochemical analysis of that part of the Niechorze U section showed higher differentiation in content of trace elements than in the Niechorze I section, making it possible to establish chemophases and to correlate them with diatomophases (Fig. 5A, B). Other chemical components also appeared highly variable in that section (Figs. 5C, 6, 7).The studied reservoirs seem similar in age (see palynological and radiometric, 14C data – Figs. 2, 3). However, it appears that differences in size of the reservoirs as well as in their depth and geological structure of bedrock and surroundings were bearing decisive influence on chemical composition of deposits and succession of diatom flora. In the case of these reservoirs, the above mentioned geological features and related paleohydrogeological conditions presumably had stronger influence on character of deposits than climatic changes taking place in the Late Glacial and Holocene times.