Otwornice cechsztyńskie Monokliny Przedsudeckiej i paleoekologia

Tadeusz Marek Peryt, Danuta Peryt


Zechstein foraminifera from the Fore-Sudetic monocline area (West Poland) and their paleoecology

Foraminifers from the Zechstein Limestone (Upper Permian) of the Fore Sudetic Monocline (Western Poland; Fig. 1) were studied in order to establish their paleoenvironmental significance. A very rich and diversified foramniferal assemblage was found (Pl. I—VIII) which, apart from forms known from other parts of the Zechstein basin, includes many species (Frondicularia woodwardi, Geinitzina taurica, G. multicamerata, Glomospira regularis, Gl. tenuifistula, Pachyphloia exilis, and others), typical of the Tethys area. It is not unlikely that such a composition of the foraminiferal assemblage is related to similar environmental conditions in the Tethys and the Zechstein basins (cf. T. M. Peryt, D. Peryt 1975a). Foraminifers from the Zechstein Limestone are characterized by a strongly marked zonation of occurrence and display variable proportions of genera between particular foraminiferal assemblages (Figs 2—4 and 6; note that sessile tubular foraminifers are not included). It is possible to distinguish two foraminiferal biofacies. One is characterized by the prevalence of nodosarians and agathammins, while the other — by the occurrence of a large number of sessile tubular foraminifers and common glomospirs and geinitzins. Nodosaria — Agathammina assemblage was found within deposits originating in relatively deep-water environment (several dozen meters), mainly in the basinal zone. A variety of that assemblage, occurring in a more shallow-water environment contains a considerable amount of geinitzins. Sessile tubular foraminifers, the Glomospira — Geinitzina assemblage, is associated with the shallow-marine environment. Its substancial variability depends upon the sedimentary facies. This variability can be observed in a sample taken from the Borzęcin region, where the Upper Zechstein Limestone is developed in tour lithofacies (Fig. 5). In the biolithitic lithofacies, forming the central parts of reefs and banks (Fig. 5), sessile tubular foraminifers constitute more than 95% of the total amount of foraminifers. The prevailing ones are geinitzins, glomospirs and agathammins are common, while nodosarians are lacking altogether (Fig. 6A). In the oncolitic lithofacies, developed outside biolithitic lithofacies (Fig. 5), sessile tubular foraminifers prevail (as a rule they make up more than 75% of the total number of specimens), while among other genera agathammins and glomospirs are most commonly found (Fig. 6D). Nodosarians are occasionally abundant, but their content decreases in the vicinity of the biolithitic lithofacies (Fig. 6F); very close to the latter, geinitzins prevail in number over oodosarians (Fig. 6E). In the biomicritic lithofacies agathammins dominate, but glomospirs and geinitzins are common, as well (Fig. 6B). The number of sessile tubular foraminifers (as a rule, 20 to 60% of the total number of specimens) increases in close proximity to the biolithitic lithofacies. The small percentage of sessile tubular foraminifers (less than 20%) and a conspicous quantitative prevalence of nodosarians among the other foraminiferal genera are typical of a sparitic lithofacicies, which is the outermost lithofacies of the reefs and bank environment (Fig. 5). In oncolites of the lagoonal subzone (Fig. 1) foraminifers, are, as a rule, lacking, but if present sessile tubular foraminifers are prevalent, most probably due to .increased salinity of water. In the biomicriites of the fore-barrier subzone (Fig. 1) nodosarians, agathammins are the prevailing forms, but the content, of sessile tubular foraminifers is often significant. Although all foraminiferal genera found in the Zechstein Limestone are euryfacies forms, respective genera and groups of genera prevail only in some environments; the quantitative analysis of foraminiferal assemblages shows that they are good indicators for paleoenvironmental interpretation. Sessile tubular foraminifers occur both in the basinal and near-shore zones, and their content is closely associated with the presence of algae (T. M. Peryt, D. Peryt 1975b). Agathammins and earlandias are, evidently, euryfacies forms. Nodosarians, dentalins, frondicularians and lingulonodosarians prefer low-energy environments, so in high-energy environments are scarce and usually appear as thick-walled forms. Brackish environments or/and those with a high rate of supply of ter rigenous material are the most favourable environments for ammodiscs. Geinitzins and glomospirs are typically reefal organisms, and their abundant occurrence suggests a close neighbourhood of organogenic sediments. Other foraminifers are scarse, therefore their paleoenvironmental significance remains obscure.

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