Ammonites and magnetostratigraphy of the Berriasian–Valanginian boundary deposits from eastern Crimea
Abstract: Euthymi, Crassicostatum and Callisto ammonite subzones, correlable with Paramimounum, Picteti, and Alpillensis subzones and probably with the Late Berriasian Otopeta Subzone of the Boissieri Standard Zone have been recognized in calcareous clays of the Berriasian–Valanginian boundary sequence in the Feodosiya district (eastern Crimea). The ammonite Leptoceras studeri (Ooster) suggests Late Berriasian to Early Valanginian age. Geomagnetic polarity indicates M16–M14r magnetozones. Therefore, the base of the Valanginian sequence in eastern Crimea should be placed within the M14r magnetozone.
Microbiostratigraphy of the Berriasian–Valanginian boundary in eastern Crimea: foraminifers, ostracods, organic-walled dinoflagellate cysts
Abstract: Thorough study of foraminifers, ostracods and dinoflagellate remnants from the Zavodskaya Balka and Koklyuk sections helps to characterize the detailed biostratigraphic division of the Berriasian / Valanginian boundary sequence in the Feodosiya district of eastern Crimea. The foraminifer and dinocyst associations from the lower part of the sequence are clearly comparable with common Berriasian associations throughout all Mountain Crimea. On the other hand, foraminifer, ostracod and dinocyst associations from its upper part have been recorded only in eastern Crimea. The upper foraminifer level corresponds to the boreal ammonite zones from the Tauricum–Verrucosum (Upper Berriasian–Valanginian). Most of the ostracod species are endemic. The base of the uppermost dinocyst level correlates with the Lower Valanginian Paratollia zone from north-western Europe.
Late Permian volcanic dykes in the crystalline basement of the Považský Inovec Mts. (Western Carpathians): U–Th–Pb zircon SHRIMP and monazite chemical dating
Abstract: This paper presents geochronological data for the volcanic dykes located in the northern Považský Inovec Mts. The dykes are up to 5 m thick and tens to hundreds of metres long. They comprise variously inclined and oriented lenses, composed of strongly altered grey-green alkali basalts. Their age was variously interpreted and discussed in the past. Dykes were emplaced into the Tatricum metamorphic rocks, mostly consisting of mica schists and gneisses of the Variscan (early Carboniferous) age. Two different methods, zircon SHRIMP and monazite chemical dating, were applied to determine the age of these dykes. U–Pb SHRIMP dating of magmatic zircons yielded the concordia age of 260.2 ± 1.4 Ma. The Th–U–Pb monazite dating of the same dyke gave the CHIME age of 259 ± 3Ma. Both ages confirm the magmatic crystallization at the boundary of the latest Middle Permian to the Late Permian. Dyke emplacement was coeval with development of the Late Paleozoic sedimentary basin known in the northern Považský Inovec Mts. and could be correlated with other pre-Mesozoic Tethyan regions especially in the Southern Alps.
Sedimentary record of subsidence pulse at the Triassic/Jurassic boundary interval in the Slovenian Basin (eastern Southern Alps)
Abstract: In the Alpine Realm the Early Jurassic is characterized by the disintegration and partial drowning of vast platform areas. In the eastern part of the Southern Alps (present-day NW Slovenia), the Julian Carbonate Platform and the adjacent, E–W extending Slovenian Basin underwent partial disintegration, drowning and deepening from the Pliensbachian on, whereas only nominal environmental changes developed on the large Dinaric (Friuli, Adriatic) Carbonate Platform to the south (structurally part of the Dinarides). These events, however, were preceded by an earlier — and as yet undocumented extensional event — that took place near the Triassic/Jurassic boundary. This paper provides evidence of an accelerated subsidence from four selected areas within the Slovenian Basin, which show a trend of eastwardly-decreasing deformation. In the westernmost (Mrzli vrh) section — the Upper Triassic platform-margin — massive dolomite is overlain by the earliest Jurassic toe-of-slope carbonate resediments and further, by basin-plain micritic limestone. Further east (Perbla and Liščak sections) the Triassic–Jurassic transition interval is marked by an increase in resedimented carbonates. We relate this to the increasing inclination and segmentation of the slope and adjacent basin floor. The easternmost (Mt. Porezen) area shows a rather monotonous, latest Triassic–Early Jurassic basinal sedimentation. However, changes in the thickness of the Hettangian–Pliensbachian Krikov Formation point to a tilting of tectonic blocks within the basin area. Lateral facies changes at the base of the formation indicate that the tilting occurred at and/or shortly after the Triassic/Jurassic boundary.
Exotic clasts, debris flow deposits and their significance for reconstruction of the Istebna Formation (Late Cretaceous – Paleocene, Silesian Basin, Outer Carpathians)
Abstract: The different types of calcareous exotic clasts (fragments of pre-existing rocks), embedded in the Paleocene siliciclastic deposits of the Istebna Formation from the Beskid Mały Mountains (Silesian Unit, Western Outer Carpathians), were studied and differentiated through microfacies-biostratigraphical analysis. Calcareous exotics of the Oxfordian–Kimmeridgian age prevail, representing a type of sedimentation comparable to that one documented for the northern Tethyan margin. The Tithonian exotic clasts (Štramberk-type limestones), which are much less common, were formed on a carbonate platform and related slope. The sedimentary paleotransport directions indicate the Silesian Ridge as a main source area for all exotics, which were emplaced in the depositional setting of the flysch deposits. The exotics constitute a relatively rare local component of some debrites. Proceedings of the sedimentological facies analysis indicate that these mass transport deposits were accumulated en-masse by debris flows in a deep-water depositional system in the form of a slope apron. Exotics prove that clasts of the crystalline basement and, less common, fragments of the sedimentary cover, originated from long-lasting tectonic activity and intense uplift of the source area. Mass transport processes and mass accumulation of significant amounts of the coarse-grained detrital material in the south facial zone of the Silesian Basin during the Early Paleogene was due to reactivation of the Silesian Ridge and its increased denudation. Relative regression and erosion of the emerged older flysch deposits were also forced by this uplift. These processes were connected with the renewed diastrophic activity in the Alpine Tethys.
Some perisphinctoid ammonites of the Štramberk Limestone and their dating with associated microfossils (Tithonian to Lower Berriasian, Outer Western Carpathians, Czech Republic)
Abstract: The present contribution deals with the taxonomy of seven species of perisphinctoid ammonite from the Štramberk Limestone (Outer Western Carpathians, Czech Republic) deposited in Moravian-Silesian museums. The age of these studied ammonites is compared with that of index microfossils contained in the matrix adhering to or infilling the studied specimens. The ammonites document a stratigraphic range from earliest Tithonian to early Berriasian. In addition to taxonomy and new ontogenetic data on some species, we also present data on their palaeogeographic distribution. The occurrence of Subboreal himalayitids in the Štramberk Limestone of an early Berriasian age is determined by both the microfauna and accompanying ammonites, which indicate connection of the Silesian-part of the Tethyan Carpathian area with the Subboreal Russian Platform Basin. These records also suggest an early Berriasian age (Jacobi Chron) for the lowermost part of the Ryazanian stage in its type area.