The late Badenian–Sarmatian (Serravallian) environmental transition calibrated by sequence stratigraphy (eastern Danube Basin, Central Paratethys)
Abstract: The late Badenian and Sarmatian (Serravallian) evolution of depositional environments in the Danube Basin (Želiezovce Depression) has never been fully explored. Here, we clarify the paleoenvironmental changes which took place in this area during the late Badenian and Sarmatian on the basis of sedimentological, petrographic, biostratigraphic and paleobotanical analyses performed at multiple sections. The combination of these methods with sequence stratigraphy allowed us to divide the sedimentary record into three main intervals: 1) the transgressive late Badenian rocky shore deposits (transgressive and/or highstand system tract), followed by a gap in the stratigraphic record (that can approximately coincide with the latest Badenian falling stage system tract). 2) Earliest Sarmatian terrestrial deposits connected with the beginning of the Sarmatian transgression (synchronous with the lowstand system tract). 3) The early Sarmatian deltaic environment influenced by tidal processes associated with the highstand system tract. The fossil leaf association indicates a climatic turnover from subtropical to temperate conditions between the earliest (lowstand system tract) and the early Sarmatian (highstand system tract). Sediments of the late Sarmatian (falling stage system tract) were not deposited or were later eroded. However, they may be present in the neighbouring depressions, which tectonically opened during the late Sarmatian. The Badenian–Sarmatian boundary in the Želiezovce Depression is developed in transgressive shallow marine to terrestrial volcano-sediments as is typical for this boundary in most other Paratethys depocentres.
Hydrocarbon potential of the Lower Cretaceous (Barremian–Albian) Shypot Formation in the Chornohora nappe, Ukraine
Abstract: Organic matter-rich rocks occur in the Carpathians, both in the Lower Cretaceous and Oligocene. Whereas, the Oligocene Menilite Formation has been intensely studied, the hydrocarbon potential of Lower Cretaceous rocks is less well understood. In the present paper a 405 m thick succession of the lower part of the Shypot Formation in the Chornohora nappe (Ukraine) is studied using 94 outcrop samples. Maturity parameters for the Lower Cretaceous rocks indicate peak oil maturity (~0.85 % Rr) and organic carbon content averages 2.8 wt. % for all samples. As a result of the enhanced maturity, the hydrogen index (88 mg HC/g TOC) and the remaining petroleum potential (2 tHC/m²) are low. Comparisons with coeval rocks from the same tectonic unit, but with lower maturity suggest that the original petroleum potential was significantly higher (4 tHC/m²). Probably about 2 tHC/m² were generated during deep burial (6 km?), but were lost during uplift and erosion. Macerals analysis reveals a mixed type III-II kerogen, with domination of terrigenous components, which is also supported by HI values of nearby marginal mature samples (~200 mg HC/g TOC). Lower Cretaceous organic matter-rich rocks are found along the entire Carpathian arc. A compilation of published data for age-equivalent rocks across the Carpathian Fold-Thrust Belt shows that HI values are mainly controlled by maturity as well as the moderately high original HI values. Most of these rocks contain predominantly type III-II kerogen, whereas Lower Cretaceous rocks in the Skole-Skyba nappe near the Polish–Ukrainian border contain type (III-) IV kerogen.
Syn-sedimentary and early deformation structures as indications for Jurassic pre-orogenic deformation in the SW Bükk Mts.
Abstract: Detailed fieldwork was carried out in the SW Bükk Mts. at six locations in order to understand the Jurassic pre-orogenic deformation. All localities expose Middle Jurassic oolitic limestones with grains probably derived from the Adriatic Carbonate Platform and therefore from the Dinaridic passive margin of the Neotethys Ocean. Results of the structural analysis revealed early, soft-sedimentary deformation structures. The observed small-scale normal faults are characterized by rounded, curved shapes without any discrete fault planes (sealed faults) and the displaced beds often thicken towards the faults. These faults were interpreted as syn-sedimentary/syn-diagenetic faults, meaning that the deformation took place in unconsolidated or semi-consolidated sediments. During the early diagenetic silica mobilization, the already-present early faults may have served as conduits of silica-rich fluids, which led to the formation of planar silica injection dykes. Sedimentary slump folds were also identified based on the presence of underlying detachment slip surfaces and the observed thickness changes and onlap surfaces within the folded layers. The significance of these early normal faults and slump folds is that they are the first direct evidence for pre-orogenic deformation in the Bükk Mts. The overall structural data suggest NE–SW or NNE–SSW striking early faults and SE to S verging slump folds in the present-day coordinates. By reconstructing the Cenozoic rotations of the Bükk Mts. this means a roughly NW–SE striking original margin and a south-westward facing paleoslope for the Middle Jurassic. Considering the paleogeographic setting of the Adriatic Platform, this paleoslope direction is possible if the deposition area was located above a deeply submerged tilted normal fault block or alternatively, along the landward side of a larger intra-oceanic high. The extensional structures may indicate that the Bükk Mts. were closer to the passive margin than the already ongoing intra-oceanic subduction and related trench, all governed by compression.
Zirconian–niobian titanite and associated Zr-, Nb-, REE-rich accessory minerals: Products of hydrothermal overprint of leucocratic teschenites (Silesian Unit, Outer Western Carpathians, Czech Republic)
Abstract: Sills of hydrothermally altered alkaline magmatic rock (teschenite) of Lower Cretaceous age at the Čerťák and Řepiště sites in the Silesian Unit (Flysch Belt of the Outer Western Carpathians, Czech Republic) host leucocratic dykes and nests which contain accessory minerals enriched in Zr, Nb and REE: Zr-, Nb-rich titanite, zircon, gittinsite, pyrochlore, monazite, REE-rich apatite, epidote, and vesuvianite. Titanite forms wedge-shaped crystals or irregular aggregates enclosed in the analcime groundmass or overgrowths on Zr-rich ferropargasite and taramite or Zr-rich aegirine–augite to aegirine. Titanite crystals show oscillatory or irregular patchy to sector zoning and contain up to 17.7 wt. % ZrO2 and 19.6 wt. % Nb2O5, and ≤1.1 wt. % REE2O3. High-field-strength elements (HFSE) are incorporated into the structure of the studied titanite predominantly by substitutions: (i) Ti4+ ↔ Zr4+; (ii) Ti4+ + Al3+ ↔ Zr4+ + Fe3+; and (iii) 2Ti4+ ↔ Nb5+ + (Al, Fe)3+. Magmatic fractional crystallization, high-temperature hydrothermal autometasomatic overprint and low-temperature hydrothermal alterations resulted in the formation of the HFSE-rich mineral assemblages within the leucocratic teschenites. Autometamorphic processes caused by high-temperature hypersaline aqueous solutions (salinity ~50 wt. %, ~390–510 °C), which were released from the HFSE-enriched residual melt, played a major role in the crystallization of Zr-, Nb-, and REE-rich minerals. The mobilization of HFSE could have occurred either by their sequestration into a fluid phase exsolved from the crystallizing melt or by superimposed alteration processes. The distinctive positive Eu anomaly (EuCN/Eu* = 1.85) of leucocratic dykes infers possible mixing of Eu2+-bearing magmatic fluids with more oxidized fluids.
The Late Cretaceous A-type alkali-feldspar granite from Mt. Požeška Gora (N Croatia): Potential marker of fast magma ascent in the Europe–Adria suture zone
Abstract: An alkali-feldspar granite (Požega granite) of reddish colour occurs in northern Croatia in the Cretaceous suture zone (Sava Zone) between the collided plates of Europe and Adria (Africa). This granite is mainly composed of alkali feldspar (perthite) and quartz, with small amounts of albite. Accessories are hematite with ilmenite exsolution, zircon, apatite and monazite. Anatase, rutile (?), kokchetavite, and kumdykolite are found only as inclusions in zircon. The granite shows a geochemical signature typical for an A2-subtype granite, characterized by a peraluminous, highly siliceous and alkaline composition, and belongs to the group of oxidized and ferroan granites with low CaO, MgO, and MnO contents and high FeOT / FeOT + MgO ratios. Trace element contents plotted in chondrite and primitive mantle normalized element diagrams show positive anomalies of K, Pb, and Zr and negative anomalies of Ba, Nb, P, Eu, and Ti. Based on whole-rock geochemical data, the magma originated mainly from melting of lower continental crust. According to the zircon typology (D and J5 types prevail), zircon and whole-rock chemistry, and high Zr-saturation temperatures (T=860–950 °C), the melting process at high temperature and dry conditions could have been triggered by upwelling hot mantle. The ascent of the thus produced A-type granitic magma into the Europe–Adria suture was fast. The Požega granite indicates the transition from compression to extension accompanied by opening of a sedimentary basin. According to the 206Pb/238U versus 207Pb/235U concordia age determined on zircon, this event occurred 83.6±1.5 Ma ago.
40Ar/39Ar step-heating dating of phlogopite and kaersutite megacrysts from the Železná hůrka (Eisenbühl) Pleistocene scoria cone, Czech Republic
Abstract: 40Ar/39Ar step-heating of mica and amphibole megacrysts from hauyne-bearing olivine melilitite scoria/tephra from the Železná hůrka yielded a 435±108 ka isotope correlation age for phlogopite and a more imprecise 1.55 Ma total gas age of the kaersutite megacryst. The amphibole megacrysts may constitute the first, and the younger phlogopite megacrysts the later phase of mafic, hydrous melilitic magma crystallization. It cannot be ruled out that the amphibole megacrysts are petrogenetically unrelated to tephra and phlogopite megacrysts and were derived from mantle xenoliths or disaggregated older, deep crustal pegmatites. This is in line both with the rarity of amphibole at Železná hůrka and with the observed signs of magmatic resorption at the edges of amphibole crystals.