Charakterystyka paleobotaniczna młodotrzeciorzędowych osadów w Gozdnicy na Dolnym Śląsku

Anna Stachurska, Stanisław Dyjor, Maria Kordysz, Anna Sadowska

Abstract


Paleobotanic characteristic of the late Tertiary sediments at Gozdnica (Lower Silesia)

The regioln of Gozdnica is situated near the SW boundary of the continuous cover of the Poznań Clays. That is why the thickness of this series amounts only a few metres (Fig. 2). The palaeobotanical investigations also showed that the sedimentation of the Poznań Clays ended at Gozdnica in the Upper Miocene, while in the centre of the basin (Polish Lowland) in the Pliocene it still continued. The oldest beds of the young Tertiary sediments are the coal clays, overlying the brown coal seam „Henryk”, and gradually passing in to the Poznań Clays. After the regression of the margin of the basin to the North, a short period of erosion existed. The washouts in the Poznań Clays are mainly filled by gravels and sands, and, subordinately, by mudstones and carbonaceous clays of the Gozdnica series (Fig. 3). It is concluded that this series most probably represents the uppermost part of the Upper Miocene, or the junction between Miocene and Pliocene. The list of sporomorphs presented in Figs. 4 and 5 shows the prevalence of species known in Europe from Miocene strata. The majority of species present at Gozdnica lies in the zones X—XIII of the stratigraphic table of D. H. Mai (1967). These zones correspond to the Upper Seam (Oberfloz) in Lausitz and to overlying beds, ranging in age, according to the quoted author from Tortonian to Mio-Pliocene. Results of palynological analysis and description of the pollen diagram The percentages of sporomorphs were calculated for 200 or 400 pollen grains. In order to obtain a more clear picture the related groups present in small percentages are presented by a single curve (Abies and Keteleeria, both forms of Tsuga, the group Taxodiaceae — Taxaceae — Cupressaceae, excluding the Sequoia pollens, Nyssa — small and large form, Castanea and Castanopsis, Ulmus and Zelkova). The following groups of plants are indicated separately in the diagrams: conifers (trees and shrubs exclusive of the TTC group), plants of moist habitat, plants of dry habitat, shrubs, and herbs. The conifer group is dominated by Pinus in both types (silvestris and haploxylon) occurring in nearly equal quantities. The second group is represented by predominating Taxodiaceae — Taxaceae — Cupressaceae, also accompanied by numerous Liquidambar, Nyssa and Cyrillaceae- -Clethraceae. The plants of dry habitat are represented predominantly by Fagus, accompanied by Castanea, Castanopsis and Symplocos. Schrubs are occurring mainly as Ilex. Herbs are poorly represented in all diagrams, only Gramineae and Filicinae occurring in appreciable quantities. The pollen diagrams and the list of macroscopic fossil plants permit to reconstruct the flora existing during the formation of the described sediments. The presence of a water body with water and shore vegetations is supposed, with a surrounding marsh forest of Taxodium and Cyrillaceae; this was accompanied by mixed Fagus — Sequoia forest with brushwood and herb undergrowth in more dry habitats. Pine forests growing farther away provided the Pinus pollens carried by wind and occurring abundantly in all diagrams. All these assemblages existed simultaneously, since there are no traces of succession, which is so evident during the formation of brown coal in the Rhine graben (G. Neuy-Stolz, 1958, M. Teiclimuller, 1958). Only in the upper part of the Gozdnica profile, a decrease of pollen, frequently observed in several consecutive samples, is followed by a succession of encroaching pioneer vegetation requiring more humidity and not tolerating shadow (J. Bobrowska, 1966). The age of the described sediments based on palaeobotanic data and comparison with some other Late Tertiary floras The floristic assemblage of the brown coal seam Henryk corresponds to that of the I brown coal series of the Ścinawa deposit (M. Ziembińs k a and J. Nikle wski, 1966), and both are related to the I seam of Lower Lausitz (F. Thiergart, 1938, 1940). An analogous pollen diagram is characteristic for the brown coal seam at Wołów. This seam underlies the Poznań Clays, which were assigned on the evidence of microfauna to the Tortonian (E. Łuczkowska, S. Dyjor, 1970). The Poznań Clays are linked by a sedimentary passage with the brown coal seam Henryk. It may be concluded therefore, that the brown coal seam Henryk is coeval with the I seam of Lower Lausitz, and was formed in the uppermost part of the Middle Miocene, passing into the Upper Miocene. This conclusion is supported by a comparison of our diagrams with the stratigraphic table published by W. Krutzsch (1957). The brown coal of the Henryk seam is characterized by a higher proportion of typically Middle Miocene forms as compared with other Upper Miocene floras of Central and Southern Poland. However, some forms typical for Middle Miocene brown coals, corresponding to the II Lausitz seam (F. Thiergart, 1938), are entirely lacking in the Henryk seam. The coal clays, overlying the Henryk seam, contain less frequently Middle Miocene forms, and their Upper Miocene age is not doubted. A reduction of the number of older forms and a complete disappearance of them is seen also at Gozdnica — „Stanisław”, and in the profile of Gozdnica which is certainly somewhat younger than the former. The flora of Gozdnica is certainly older than the flora of Ruszów, where the fossil plant assemblage is characteristic for the Pliocene, and Miocene relics occur only in traces, while many Miocene forms are absent. Both the pollen and the macrofloristic data suggest a non-typical character of the Gozdnica flora. In the investigated profiles elements characteristic for both Pliocene and Miocene occur and it is difficult to compare this flora with the other young Tertiary floras from Poland. In Tortonian the climate of the investigated region was of the mediterranean type. In Miocene some warm climatic plants could find here suitable conditions of survival. It is possible that the Middle Miocene relics preserved in Sudety Mts expanded to the other regions in Upper Miocene and even in Pliocene.

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