Calcite veins in the Terebowiec syncline, the Silesian Nappe, Southeastern Poland abstract /

Tyt. z nagłówka.The Terebowiec syncline is a part of the Zatwarnica fold which is located in the SE part of Silesian Nappe in the Polish Outer Carpathians. The Krosno beds (Late Oligocene) - thick-bedded sandstones and thin-bedded flysch consist of claystone alternating by mudstones and thin-bedded sandstones that occur in the axial part of the syncline. In the Wolosaty stream valley which crosses the syncline, two outcrops (Bereżki 1 and Bereżki 2) of thin-bedded Krosno sandstones and shales with calcite mineralization have been studied near village of Bereżki. The aim of the study was to recognize and compare calcite mineralization occurring in the Terebowiec syncline. Structural, petrographic, and isotopic (delta18O and delta13C) investigation have been carried out. In the Bereżki 1 outcrop, calcite mineralization occurs in a fault zone. Blocky, fibrous, and stretched crystals form veins which contain numerous claystone inclusions. Fibrous calcite with these inclusions shows curved shape. Blocky calcite shows twin lamellae. For fibrous calcite the delta18O value is -9.23%o, and the delta13C value is -1.56%o. In the Bereżki 2 outcrop, calcite mineralization occurs in several faults and joint fractures. Joint fracture (20 cm thick) filled by blocky calcite vein has been the main object of analysis. Three generations of calcite were recognized. The oldest, first generation is formed by small crystals (to 0.3 cm) with twins, growing directly on the fracture wall. The second generation is formed by big transparent crystals (up to 1 cm) with twins. These crystals show the zonality based on the cathodoluminescence study. The youngest, third generation is composed of small (to 0.1 cm) crystals without twins, growing directly on crystals which form second generation with observed hydrocarbon inclusions. In veins from the Bereżki 2 the delta18O values are between -9.88%o and -6.81%o and delta13C values vary from -0.24%o to 0.11%o. Values of oxygen isotopes in the second generation are little higher than in other generations. One value of oxygen isotope (-6.81%o) in the third generation is also distinct from other values. Two samples of host sandstone and shale have been investigated and the results of isotopic studies are different than in veins. Both C and O values are higher (for sandstone delta18O -4.59%o and delta13C 0.97%o, for shale delta18O -4.12%o and delta13C 0.96%o). Values of O and C isotopes suggest that in both studied sites filling of veins started in similar temperature and salinity conditions. However, the higher oxygen isotope values in sandstone and shale are probably connected with high contents of primary CaCO3. In the Bereżki 1 site, the fibrous calcites are synkinematic, related to faulting. Numerous claystone inclusions indicate that calcite veins were formed in soft sediment. In the Bereżki 2 site, the veins are related to brittle deformation. Based on the relationship between types of deformation and isotopic composition of calcites it seems that mineralization started in sediments showing differentiated lithification.Dostępny również w formie drukowanej.KEYWORDS: Zatwarnica fold, Polish Outer Carpathians, Krosno Beds