No abstract

Study of geochemistry, examination of isotope ages of detrital minerals, palaeomagnetic analysis, and a study of the trilobites were performed to provide constraints on the palaeogeographical position of the Holy Cross Mountains in Late Ediacaran–Early Palaeozoic time. The geochemical results indicate an active continental margin or continental island arc provenance of the Ediacaran sediments. Sediments from a passive continental margin were deposited here during the Cambrian and Ordovician. The palaeomagnetic pole isolated from Cambrian rocks of the Małopolska region of the Holy Cross Mountains corresponds to the Cambrian segment of the Baltic apparent polar wander path. Isotope age estimations indicate that Cambrian sediments of the Małopolska region contain detritus not only from a latest Neoproterozoic source but also from sources with ages of c . 0.8–0.9 Ga, 1.5 Ga and 1.8 Ga. The Małopolska, Brunosilesia, Dobrugea and Moesia terranes, which originally developed near the present southern edge of Baltica and were partly involved in the Cadomian orogen, were dextrally relocated along its Trans-European Suture Zone margin. The first stage of this movement took place as early as latest Ediacaran time, while Baltica rotated anticlockwise. Anticlockwise rotation of Baltica at the Cambrian–Ordovician boundary implies further dextral movement of the Małopolska block.

The Ludlow deposits of the Winnica Formation in the Rzepin section (Holy Cross Mountains, Poland) have been studied with respect to their facies evolution and stable carbon isotope ratios from whole-rock samples. The C-isotope curve of the Rzepin section records a distinct positive excursion with maximal values of ?8.9%. A Late Ludlow positive isotope excursion is known from different paleocontinents and thus is regarded as a global isotope event. The presence of the event allows for a chemostratigraphic correlation of the Rzepin profile with the classical, biostratigraphically well-dated Gotland section. The Ludlow deposits of the Holy Cross Mountains are interpreted in terms of sea-level changes during the isotope excursion. Because the Rzepin and Gotland sections are positioned on the opposite sides of the same foreland basin, a comparison of their sequence stratigraphy allows to test the regularities of the sea-level changes on the shelf of Baltica. In the present paper, a modified view of the recently published sequence stratigraphy of the Gotland succession is presented. Our results indicate that the positive Ludlow d 13 C excursion is connected with prolonged low-stand conditions with small, internal transgressive pulses.

Three Late Silurian carbonate proWles of the Malynivtsy and Skala Formations from Podolia (western Ukraine) are discussed in terms of sedimentation dynamics. Their common feature is the appearance of thick, stromatoporoid-rich beds within Wne-grained peritidal deposits. These intercalations are composed of fossils typical of oVshore sedimentary environments. In the most spectacular case, a channel, several tens of metres wide and inWlled with stromatoporoids, is incised in a peritidal cyclic complex. The successions investigated exhibit sedimentary features that are diagnostic of onshore redeposition. Independently of the scale of the recorded sedimentary events, the onshore redeposition was caused by factors with energy levels exceeding those of average storms, probably by hurricanes or even tsunami waves. The dynamic nature of some of the stromatoporoid beds has to be taken into account when constructing the curves illustrating bathymetrical and facies development of the Silurian succession of Podolia. The genesis of lens-shaped stromatoporoid beds, elongated depending on their origin, either parallel or perpendicular to the facies belts, should be considered an important factor in reconstructions of the depositional architecture of sedimentary hydrocarbon collectors.

The mid-Ludfordian Carbon Isotope Excursion (CIE) is one of the biggest perturbation in the isotope and facies record in the Palaeozoic. However, its causes still remain unknown. In the periplatform setting of the Baltica palaeocontinent the event interval contains rock-forming minute calcite crystals, interpreted here as suspension-originated analogues of recent whitings and calcite rafts. The grains were preferentially formed around picocyanobacterial filaments, which are preserved as tubes inside. An event-related, 9 m-thick, massive calcisiltite bed points to the persistent hypersaturated state conditions (HSS) during the increasing limb of the CIE. The studied interval contains also a significant admixture of minute-sized detrital dolomite grains, appear for the first time several meters below and reach peak abundance immediately below the calcisiltite interval. The dolomite grains show consistent δ 13 C values (~0‰) across the CIE. Their record is decoupled from the bulk-rock C-isotope record and thus indicates overwhelmingly pre-sedimentary formation and extrabasinal provenance of the dolomite. The size and provenance of the grains, along with their incorporation into surface water precipitates and formation of specific very thin laminas with internal density gradation of grains (dolomite-quartz couplets), suggest the eolian delivery of the grains to the basin. The dust influx pulses seem to have triggered the calcite precipitation events. Furthermore, the size-frequency distribution of the pyrite framboids across the studied interval shows that the progressing dust influx was followed by persistent euxinia occurring right before and during the increasing limb of the CIE. In the proposed model, globally enhanced eolian delivery of iron during the assumed glaciation promoted high net pyrite formation. The resulting "sulphate to bicarbonate exchange", a hypothetical dissolution of eolian carbonate dust particles in deep basins, a concurrent bicarbonate supply from the carbonates emerged due to the sea-level fall, and a parallel cessation of the carbonate factory (exposed carbonate platform tops), raised the alkalinity and formed the global carbonate hypersaturated state (HSS) of the ocean. The processes needed largescale invasion of the CO 2 , consumed in the ocean by bicarbonate formation processes. It is hypothesized that during the subsequent initial transgression, the HSS was discharged by massive carbonate precipitation. The rapid "carbonate reflux" returned the earlier uptaken CO 2 to the atmosphere by fast degassing. Its fast transfer resulted in the globally synchronized, kinetic, residual, 13 C DIC -enrichment of water pools localized over individual carbonate platforms. During "carbonate reflux", the local CIE amplitude depended on the carbonate production rate, water column thickness and pool residence time.•