Variscan high-pressure metamorphism of kyanite-bearing paragneisses hosting eclogites in the Veporic unit, Western Carpathians: Evidence from Th–U–Pb dating of monazite
Abstract: In view of a polyphase development of the northern Veporic pre-Alpine basement of the Western Carpathians it is important to determine the age of high pressure (HP) metamorphism known from eclogites occurring in this area. To do this, several monazite-bearing paragneisses were studied petrologically and monazite was dated by chemical (U–Th–Pb) method. Identified were remnants from high-pressure stage, i.e. phengite (Si apfu = 3.2–3.3), kyanite, rutile and Ca-rich garnet rims. Part of the present mineral assemblage may have been preserved from prograde stage (plagioclase) and part reflects re-equilibration during retrogression (biotite, major elements in garnet cores). However, Y and HREE in garnet cores were not homogenised and their profiles indicate origin during temperature rise. Peak metamorphic conditions (P = 21 kbar; T = 650 °C), and retrogression stage (P = 9 kbar; T = 520 °C) were calculated using Zr-in-rutile, and Y-in-garnet and monazite thermometry, phengite composition and pseudosection modelling. Monazite yielded dominant Early Carboniferous age (354 Ma) with subordinate amounts of Ordovician (485 Ma) and Cambrian (505 Ma) ones, and no Alpine record. The monazite position in garnet cores predating the growth of Ca rims suggest that the Carboniferous age of 354 Ma probably predates the peak conditions and refers to the prograde stage of the Variscan metamorphic evolution.
Cyclicity of Middle Jurassic calciturbidites of the Travnik Formation, Bovec Basin, NW Slovenia
Abstract: We investigate calciturbidite cyclicity using statistical method based on time-series analysis (Fourier analysis) of bed thickness patterns. This method was applied to four members of the Jurassic calciturbidite-dominated Travnik Formation of the Bovec Trough outcropping in three adjacent and correlated sections. Our study has shown that the Fourier analysis of calciturbidite bed thicknesses is not successful for reconstruction of cyclicity in erosional upper slope depositional environments (Member 3). On the contrary, the method shows meaningful results for lower slope and distal basin floor depositional setting (Members 1, 2, 4). Here we detected variability of cyclicity in the same time frame of deposition and also subtle lateral variation of the stacking pattern between different sections. Each section contains regional low-frequency cycles common to all sections, and superimposed specific “local” high-frequency cycles. Tectonic factors have an influence on the low frequency, and other factors, such as the local topography, climate, different position on a depositional lobe or magnitude of the turbidite event, can force the high-frequency cycles. We calculated nine cycles for Bajocian and Bathonian (Members 1 and 2), and also nine cycles from Early Callovian to Middle/Late Oxfordian (Member 4). Due to the erosional nature of the Member 3 (Bathonian to Early Callovian) sedimentary environment, reliable comparison to Jurassic sea-level variations was not possible.
Comments on the geology of the Crimean Peninsula and a reply to a recent publication on the Theodosia area by Arkadiev et al. (2019): “The calcareous nannofossils and magnetostratigraphic results from the Upper Tithonian–Berriasian of Feodosiya region (Eastern Crimea)”
Abstract: Here we assess the evidence for the placing of magnetic and fossil biozonal boundaries in Upper Tithonian to Lower Berriasian (Jurassic–Cretaceous boundary) sedimentary rocks on the Black Sea coast south of Theodosia (Ukraine): that is, in magnetozones M19n to M17r. We consider our earlier-published results from these sections in relation to the correlative pattern that has become well established further west in Tethys. Additionally, this is compared and contrasted with other, alternative, results from Crimea that have been published in recent times.
Geodynamic interpretation of the Late Cretaceous syn-depositional magmatism in central Serbia: Inferences from biostratigraphic and petrographical investigations
Abstract: High-resolution biostratigraphic dating of (hemi)pelagic limestones stratigraphically adjacent to syn-depositional bimodal magmatites in central Serbia, based on planktonic foraminiferal assemblages, determines that the magmatism occurred during Coniacian to Santonian. This bimodal magmatism, which includes both basaltic magmas with associated peperites and trachydacitic magmas, was associated with syn-subductional extension, which was triggered by roll-back and steepening of subducting Neotethys oceanic lithosphere, located between the converging continental margins of Adria and Europe. The Late Cretaceous extension led to subsidence and formation of a fore-arc basin above the subduction zone. Co-genetic magmatic occurrences, including basalts, trachydacites, and lamprophyres, are distributed in the same fore-arc domain along the entire European continental margin. The fore-arc magmatism migrates in space and time from the south towards the north and north-west.
Numerical age dating of cave sediments to quantify vertical movement at the Alpine-Carpathian transition in the Plio- and Pleistocene
Abstract: The paleoenvironmental and tectonic history at the southwestern end of the Malé Karpaty Mountains was reconstructed using sediment analysis, mineralogy, and dating. Numerical ages using 26Al/10Be burial age dating, 230Th/U ages and luminescence age dating are combined to infer the Pliocene and Pleistocene development of the Hainburg Hills region. This study investigates sediments from two caves separated by a height difference of 92 m as well as aeolian cover sands from a fissure. The cave deposits are very unlike as one is a carbonate precipitate and the other sediment infill, but both preserve information on the uplift/incision at the Alpine-Carpathian border. Emplacement of coarse-grained fluvial deposits from the upper cave was dated to 4.1–4.6 Ma using terrestrial cosmogenic 26Al and 10Be in selected quartz cobbles. Calcite precipitates from the lower cave were 230Th/U dated on three morphologically slightly different cave rafts. Ages calculated from pristine calcite are least prone to alteration and give a time of formation at ~0.31–0.34 Ma. Vertical offset rates calculated from ages and positions above the recent streambed of the Danube vary between 36–42 m/Ma for the higher position and 162 m/Ma at maximum for the lower cave and point to increased uplift/incision that has been described from other areas in the Eastern Alps and the Pannonian Basin System. Deposition of aeolian sand cover was constrained to 13.1–17.2 ka (pIRIR225 signal) and the presence of sand as opposed to its transport/erosion suggests a change in wind velocities at the Hainburg Gate. This can possibly be correlated to the termination of a cold phase with decreasing continentality accompanied by decreasing atmospheric pressure gradients. Minerals such as hematite and smectite as well as traces of poorly crystallized iron oxides found in the matrix of the upper (older) cave, were formed during warm and humid climate conditions facilitating lateritic soil formation. This is a remnant from the late Miocene or Early Pliocene soil that formed in a subtropical climate.