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.

Two global isotopic events, the early Sheinwoodian (early Wenlock) and that at the Silurian-Devonian transition, have been comprehensively studied in representative carbonate successions at Kytayhorod and Dnistrove, respectively, in Podolia, Ukraine, to

The carbon and oxygen isotope composition of marine carbonates (δ 13 C and δ 18 O, respectively) are studied in the fossiliferous, stratigraphically well-constrained and remarkably expanded successions of Podolia, SW Ukraine, spanning the Silurian-Devonian transition. Significant isotopic shifts are directly comparable to previously published global secular trends in well-preserved brachiopod calcite isotopic ratios from this region, and therefore may be taken as a reliable primary record of seawater δ 13 C changes. The sections reveal a major positive δ 13 C excursion, with an amplitude above 6 ‰, beginning in the upper Pridoli and reaching peak values as heavy as +4.2 ‰ in the lowermost Lochkovian. This turnover in carbon cycling is followed by a general trend toward more negative δ 13 C values in the upper Lochkovian. The Podolian isotopic signals provide strong support for the previously inferred global biogeochemical perturbation across the Silurian-Devonian transition, reflecting a complex combination of palaeogeographical, biogeochemical and evolutionary processes in the late Caledonian geodynamic setting, with a likely undervalued role of the expanding vegetation in vast near-coastal shallows and deltas.

In the Podolian Dniester Basin (southwestern Ukraine)

The Upper SilurianÀLower Devonian section of the Dniester gorge in Podolia and samples from boreholes located S and N of this area were studied in order to reconstruct the thermal history of Lower Paleozoic sedimentary rocks in the Dniester segment of the Peri-Tornquist margin of the East European Craton which is the most eastern part of a major shale-gas target in Europe. X-ray diffraction data for illite-smectite from shales and carbonates indicate very advanced diagenesis and maximum paleotemperatures of~200ºC, higher than interpreted from the 'conodont alteration index' (CAI) data. Diagenesis of the Devonian section is slightly less advanced than that of the underlying Silurian section, indicating that it is a regional feature and the result of burial. The regional distribution of the diagenetic grade based on illite matches well with the pattern established from the CAI data. K-Ar dating of illitesmectite from Silurian bentonites and shales gave a consistent set of dates ranging from 390 to 312 Ma. To explain such advanced levels of diagenesis and such K-Ar dates, the extension of the Carboniferous foreland basin (which today is only preserved to the NW of L'viv) toward the SE on the craton margin has to be assumed. The diagenetic zonation pattern of the Carboniferous coals supports this hypothesis. The Carboniferous cover may have been either sedimentary or partially tectonic (Variscan intracratonic duplexes) in origin and the thickness, necessary for the observed level of diagenesis, may have been reduced by an elevated heat flow along the major tectonic zone at the edge of the craton (TESZ). The presence of such cover is confirmed by completely reset Cretaceous apatite fission track (AFT) ages of the Silurian bentonites. The AFT dates also imply a Tertiary heating event in the area.The 10 Å clay mineral present in the dolomitic part of the profile (Silurian), both in bentonites and in other rocks, is aluminoceladonite or intermediate between illite and aluminoceladonite, while in the Devonian shale section only illite was documented. Chlorite is also common in the studied rocks and is at least partially authigenic. It is non-expandable in the samples from boreholes, while often expandable to variable extents in the samples from outcrops, which also contain goethite. Such variation in chlorite is attributed to contemporary weathering.