Sarmatian paleoecological environment of the Machów Formation based on the quantitative nannofossil analysis — a case study from the Soko ów area (Polish Carpathian Foredeep)

The Machów Formation belongs to a supra-evaporitic succession of the Polish Carpathian Foredeep Basin (PCFB). Our studies were concentrated in the eastern part of the PCFB, north of Rzeszów. 33 samples were collected from five boreholes, at depth intervals as follows: Stobierna 2 — 1016-1338 m; Stobierna 3 — 715-1669 m; Stobierna 4 — 1016-1238 m; Stadnicka Brzóza 1 — 350-356 m and 1043-1667 m; Pogwizdów 2 — 1161-1390 m. The obtained biostratigraphical data gave evidence for the upper part of the NN6 (the Early Sarmatian) and for the NN7 (the lowermost part of the Late Sarmatian) Zones. All the nannofossil assemblages from Stobierna 2, Stobierna 4 and Pogwizdów 2 were assigned to the NN6 Zone. In the Stobierna 3 borehole the interval 1669-1113 m was assigned to NN6, whereas assemblages from depth interval 843-715 m belong to NN7 Zone. In Stadnicka Brzóza 1 interval 1667-1043 m belongs to NN6 Zone and interval 350-356 m to NN7 Zone. The Discoaster exilis Zone (NN6) was defined by the presence of Reticulofenestra pseudoumbilica, Sphenolithus abies, Helicosphaera walbersdorfensis and absence of Discoaster kugleri. The Discoaster kugleri Zone (NN7) assignment was based on the abundance of Coccolithus miopelagicus (> 10 μm), used as an alternative species essentially confined to that interval, and absence of Catinaster coalithus. The observed nannoplankton assemblages are predominantly composed of a high number of redeposited material, abundant long-ranging taxa and taxa resistant to carbonate dissolution. General assemblage compositions, obtained from quantitative data, indicate shallow near-shore environment and could confirm basin isolation.