International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

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EXOTIC ORTHOGNEISS PEBBLES FROM PALEOCENE FLYSCH OF THE DUKLA NAPPE (OUTER EASTERN CARPATHIANS, POLAND)

Published: Jun 2005

Pages: 205 - 221

Authors: KRZYSZTOF BAK, ANNA WOLSKA

Abstract: Crystalline exotic pebbles have been found in the deep-water flysch of the Cisna Beds, in the Dukla Nappe, Polish part of the Outer Western Carpathians. Most of them occur in a layer, which extends over a distance of at least 3 km within the SE limb of the Chryszczata–Wolosan–Mala Rawka anticline. The dimensions of the pebbles vary between 2 and 18 cm (middle axis). The exotic pebbles consist of three types of granite derived orthogneisses: 1 — medium-grained, medium-banded orthogneiss with alkali feldspar porphyroblasts showing structural features of foliated granitic-gneiss, 2 — medium-banded, medium-layered orthogneiss containing small microcline porphyroblasts and showing structural features of foliated granitic-gneiss, and 3 — strongly cataclastic granitic-gneiss with chess-board albite porphyroblasts showing properties of partly mylonitized granite. The chemical composition of the orthogneisses indicates that the protolith was represented by peraluminous, poorly-evolved, S-type granites exhibiting features of orogen-related crustal granites. The discrimination shows that the protolith of the studied rocks evolved in active continental margin or continental collision environments. The biostratigraphical data on deep-water agglutinated Foraminifera suggest the position of the exotic-bearing layer in the lowermost part of the Rzehakina fissistomata Zone corresponding to the lowermost Paleocene. Petrographic affinities between orthogneissic pebbles and mineral/rock fragments grains of the Cisna-type sandstones show that they have the same provenance. These deposits were transported from the NE extension of the Marmarosh massif, which had the character of a continental bearing source cordillera, formed mainly by orthogneissic and granitic rocks.

Keywords: Paleocene, Outer Carpathians, Dukla Nappe, provenance, stratigraphy, geochemistry, petrography, orthogneissic pebbles

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