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Alleged Caboniferous (Viséan) volcanism at the eastern margin of the Moravo-Silesian Basin, Kraków region, Southern Poland

Lewandowska A., Rospondek M. J., Kobuszewski Ł.

Annales Societatis Geologorum Poloniae

2018

Vol. 88, No. 1

59--69

The volcanic rocks, represented by clasts in the breccias occurring within the Viséan Culm sequence at Głuchówki, previously were considered to provide evidence of the earliest record of Variscan volcanism on the eastern margin of Moravo-Silesian Basin in the Kraków area. The breccias have been described as the deposits of submarine slides, accompanying the Viséan volcanic activity. This paper provides evidence of a different mode of origin. The present study, based on new field observations, combined with petrological and geochemical data, showed that volcanic rocks are major framework constituents of a breccia and are accompanied by clasts of spotty hornfels and Culm mudstone. Some clasts originated in erosion of the nearby Permian Zalas rhyodacite laccolith and the spotty hornfelses of the contact aureole, while other clasts came from the Culm mudstones. The breccia framework components are not rounded and poorly rounded, which reflects their short distance of transport. Therefore, an alternative scenario for the genesis of the breccia is proposed. The breccias represent material deposited in erosional pockets formed along the bedding of the Culm mudstones. The red iron oxide shells around clasts may indicate weathering in a warm continental climate, thus constraining the breccia formation to either the Permian or the Early or Late Triassic. Thus, the only well documented Viséan igneous rock in the study area remains the diabase, known from the Klucze borehole. Conversely, no volcanic rocks of this age have been documented in the area under consideration.

Foraminiferal colonization related to the Zechstein (Lopingian) transgression in the western part of the Wolsztyn Palaeo-Ridge area, Western Poland

Peryt D., Peryt T. M., Raczyński P., Chłódek K.

Geological Quarterly

2012

Vol. 56, No 3

529--546

The basal Zechstein succession in SW Poland is dominated by breccias and/or conglomerates or extraclast-bearing bioclastic limestones, which were deposited during rapid flooding of the pre-existing intracontinental basin in the early Lopingian (Late Permian). Of these, the boulder-cobble breccias and conglomerates are interpreted as deposited in a rocky shore-zone where density flows and upwelling prevailed. The breccias gradually pass up into bryozoan (or other bioclastics) grainstones. The matrix-supported breccias were deposited as large extraclasts and blocks of Carboniferous rock were rolled down or detached from a cliff and were then either embedded into a carbonate sand or formed a framework supplying voids that could be colonized by tubular encrusting foraminifers. These foraminifers abound in all basal Zechstein facies (except in the debris-flow deposits) and are attributed to Palaeonubecularia. The associated faunas include other foraminifers (uniserial and hemigordiopsids), bryozoans, brachiopods, bivalves, gastropods, and microbial deposits. The prolific growth of tubular encrusting foraminifers has resulted from nutrient supply from the basin by upwelling. Botryoidal aragonite cements (also interpreted as due to upwelling) also characterize the basal Zechstein strata, although they were previously reported only from the upper Zechstein Limestone. The ẟI3C values of the basal Zechstein deposits show small variation and oscillated around 4.0%o, suggesting that these deposits are younger than the Kupferschiefer.