Fauna eoceńska z egzotykowego wapienia w rejonie Ustrzyk Dolnych

Abstract

EOCENE FAUNA FROM AN EXOTIC LIMESTONE FRAGMENT FOUND IN THE REGION OF USTTRZYKI DOLNE

Summary

A single fragment of limestone with fossils was found by W. Sikora (1959) in a mountain stream (the Czarny stream gorge in the Ostry belt), within the occurrence area of the Krosno Beds, in the eastern part of the Slesian unit of the Polish Flysch Carpathans, in the vicinity of Polana, near Ustrzyki Dolne. This large fragment, having no lithological equivalents among the Oligocene formation of the region, is thought by W. Sikora to be a block that has ''fallen out" of the shales referred to the Lower Krosno Beds. The purpose of these examinations is to describe fauna prepared out by the present author of the grey arenaceous limestones that passes into a siltstone of fragmentary structure, at place in the form of shell conglomerate (Table III, Fig. 2). In thin slides of the limestone (Tables IV-V) are found: abundant planktonic fauna (Table VI), quartz grains, altered biotite and muscovite (hyodrobiotites), microcline and pyrite (T. Wieser). Petrographical analysis shows the presence of feldspars, chlorites, garnets, magnetite, ilmenite, zircon (sporadically), apatite (sporadically). The macrofauna assemblage (Tables I-III) consist of abundant representatives of pelecypod Pitar laevigata L a m. var. (about 200 specimens) and Modiola semilaevigata D e s h. var. characterized by small dimension of shells (7 specimens), as well as of gastropods Fusus sp. ind. (8 specimens and fragments). This macrofauna points to the Middle-Upper Oligocene age, the marine environment characterized by complete salinity, the depth of the basin amounting to about 100 metres, and the subtropical temperature. The macrofauna is contemporaneous with the calcareous-arenaceous deposit, its position corresponding to the living zone of these forms. This assemblage, poor in species, but rich in individuals, reflects an ecologic niche of a shallow neritic zone isolated from the marine environment. This fauna has no equivalents among the hitherto disocovered Eocene fauna sites in the Carpathians (S. Krajewski, J. Urbaniak, 1964). The limestone fragment from Polana is thought to be an exotic block, mainly on the analogy with the adjacent areas, where a horizon with exotic blocks is found to occur in the Krosno Beds, and on the fact that in this part of the Carpathians, the Krosno Beds - commonly considered to be of Oligocene age - are here predominant deposits. Taking into account the whole of the sedimentary and tectonic processes one can assume that the probable mother areas of the encountered limestone with fauna stretches far in the south, within the Central Carpathians.