Stanisław Skompski

Tide-dominated Middle Devonian sequence from the northern part of the Holy Cross Mountains (Central Poland)

SummaryThe dolomitic Wojciechowice Formation distinctly differs from the remaining, mainly shaly Middle Devonian succession in northern part of the Holy Cross Mountains (Central Poland). The upper Member of the Formation (Crystalline Dolostone Mb.), in greater part dolomitized but also containing limestone beds, is composed of shallowing-upward cyclothems well exposed in Skaly quarry in the Bodzentyn syncline.The lower parts of the cyclothems, interpreted as subtidal facies, contain fossils characteristic for restricted environments. They are grouped into two assemblages. The first, with brachiopods (largeBornhardtina andEmanuella), massive stromatoporoids, and subordinate gastropods and amphiporoids is related to a deeper subtidal environment, while the second (mainly amphiporoids, gastropods, ostracodes and calcareous algae) is shallower subtidal. Towards the top of succession the fossil content radically decreases. The upper parts of cyclothems are composed mainly of different types of laminites. In these parts of the section, interpreted as intertidal/supratidal units, stromatolites, desiccation polygons, intraformational breccias, and common bioturbations are present. The whole succession was deposited in a low-energy environment, only intermittently affected by high-energy events. For their most spectacular example of this, aBornhardtina-coquinite, a tempestitic origin is proposed.The interval with cyclic sedimentation studied correlates with the dolomitized lower “Unit I” of the Stromatoporoid-Coral Kowala Formation from the southern part of the Holy Cross Mountains, which exhibits sabkha-type cyclicity. The differences in development of cyclothems in both regions resemble outer and inner part of an extensive platform, and correspond well with basic trends of the Lower-Middle Devonian transgression in the Holy Cross Mountains. The general succession of formations deposited during this process coincides with transgressive events on Johnsons eustatic curve for the Devonian.

Reconstruction of a lost carbonate platform on the shelf of Fennosarmatia: evidence from Viséan polymictic debrites, Holy Cross Mountains, Poland

Abstract The sedimentary sequence of a totally eroded carbonate platform on the shelf of Fennosarmatia in Poland has been reconstructed based on the analysis of detrital material derived from the platform and deposited in an adjacent basin. The database was taken from a polymictic debrite unit intercalated in the Viséan basinal succession exposed in the southwestern Holy Cross Mountains. The unit represents a gravity-flow deposit and contains carbonate clasts ranging from Frasnian to Viséan in age. They provide evidence for a Frasnian carbonate platform located south of the Holy Cross area that drowned during Famennian and Tournaisian times but subsequently, during the early Viséan, started to recover. This reversed trend is interpreted to have resulted from the combined effect of eustatic sea level fall and tectonic uplift. The geographical extent of the inferred carbonate platform system, named here as the Nida Platform, cannot be precisely outlined, but most probably corresponded with the Jedrzejow High, an elevated fragment of Precambrian basement.

Paleobiogeographical Significance of the Late Silurian Microproblematicum Tuxekanella Riding and Soja

Abstract An enigmatic microproblematicum, Tuxekanella Riding and Soja (1993), has been identified in the shallow water carbonate succession of the Late Silurian Skala formation (Podolia, Ukraine). The newly found specimens suggest most probably the algal nature of this enigmatic microfossil. Tuxekanella is known only from two extremely distant regions at the moment: the Alexander terrane in Alaska and Podolia. The possibility of their paleobiogeographical link is discussed in the context of paleotectonic models, assuming the peri-Gondwanan origin of the Alexander Terrane.