Cykliczność w utworach dolnopermskich rejonu Zielonej Góry

Wojciech Nemec



The author presents results of detailed sedimentological textural-structural analysis of Lower Permian rocks from Zielona Góra area, western part of the Fore-Sudetic monocline (Wrocław monocline) (Fig. 1), based on core material (9). The analysis has shown that the rocks originated in continental semidesert fluvial environment and that they were temporarily subjected to subaerial conditions. • Such genesis of these deposits is connected with a specific type of cyclicity displayed by them. The profiles display several asymmetric cyclothems with distinct decrease of grain size upwards. Such cyclothems were previously termed as "normal" (3), "Fining-upwards" (1), or "simple" (4) cycles. Three lithological links of the cyclothems may be distinguished, namely: conglomerates, sandstones (conglomeratic sandstones), and siltstones-claystones deposits. The cyclothems and their lithological links markedly differ in development and thickness (Figs. 2-4). The complete cyclothems display distinct bipartition. Their lower, conglomerate-sandstone link represents channel deposits, whereas upper, silstone-claystone link - flood-plain deposits (1, 11). The origin of this type of cyclicity was the subject of controversy (see 3, 10, 5). According to some recent works (2, 8) it is related to the nature of fluvial environment and the cyclothems originate in result of migration of braided stream or river channels cross alluvial plain (Figs. 2, 5-7) under semi-arid climatic conditions. Subsidence of the bottom of sedimentary basin, and compaction and aggradation of previously deposited sediments lead to repeated occurrence of the cyclothems in vertical profile.

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