Evolution of a turbidite system in a narrow basin setting: the Ropianka Fm (Campanian–Paleocene) in the Skole Nappe of the Polish Carpathians

Abstract

The deposits of the Turonian–Paleocene Ropianka Fm (Skole Nappe, Polish Outer Carpathians) were subdivided into 11 sedimentary facies and subsequently 7 facies associations, corresponding to different depositional environments of the turbidite system. The depositional setting includes a wide range of processes in sedimentary environments from proximal channel-fill deposits to channel-lobe transition zone and a full spectrum of lobe sub-environments, i.e., lobe-axis, off-axis and lobe-fringe, distal-fringe, and interlobe areas. The Campanian–Paleocene evolution of the western Skole Basin shows several progradational-retrogradational cycles and corresponding shifts from carbonate- to siliciclastic-dominated sedimentation, mostly as a result of relative sea-level changes and tectonic activity. The progradational-retrogradational cycles start with the appearance of sand-rich bodies, which tend not to occur up the succession. Four evolutionary stages are distinguished, including 1) the early Campanian marlstone-dominated sedimentation (Kropivnik Fucoid Marl Mbr) in the lower-slope or base-of-slope settings, which correlates with a relative sea-level highstand, 2) the late Campanian progradation of the turbidite system with siliciclastic sedimentation (Turnica Flysch Mbr) and a major sediment distribution path, extending along the northern margin of the basin, 3) the Maastrichtian progradational-retrogradational cycle with the influence of a carbonate source, and 4) mixed carbonate-siliciclastic sedimentation (Leszczyny Mbr) with exotic-bearing mass transport deposits (Makówka Slump Debrites and Babica Clay) and a general trend of cessation of carbonate sedimentation up the sections. The complex facies distribution through the time interval studied is the effect of basin asymmetry with a relatively steep southern slope and a gentler northern slope and the action of multiple sediment sources. The highly aggradational trend of particular depositional elements, variability in calcareous sediment content and palaeotransport directions indicate the presence of morphological obstacles and/or the semi-confined character of the western part of the basin.