Tectonothermal history of the basement rocks within the NW Dinarides: new 40Ar/39Ar ages and synthesis
Abstract: Very low-grade and low-grade metamorphosed basement rocks from distinct inliers of the Africa-derived northwestern Dinarides (Medvednica Mts and Paleozoic Sana-Una Unit, respectively) have been studied with the multi-grain step-heating 40Ar/39Ar technique in order to compare and reveal their tectonothermal history. 40Ar/39Ar ages from detrital white mica of the very low-grade basement rocks of the Paleozoic Sana-Una Unit gave a Variscan age of ~335 Ma. The new age is in agreement with 40Ar/39Ar ages from the very low-grade basement exposed at Petrova and Trgovska Gora of the NW Dinarides. Within low-grade metamorphic basement rocks from the Medvednica Mts, we found no Variscan ages. White mica from phyllitic basement rocks of the Medvednica Mts gives predominantly early Alpine ages ranging between 135 and 122 Ma and younger Alpine ages of ~80 Ma. The early Alpine ages of 135 and 122 Ma are interpreted as the date to the onset of ductile nappe stacking predating the formation of Gosau-type collapse basins. The late early Alpine event of ~80 Ma can be traced in the entire Cretaceous-aged orogen of the Circum-Pannonian Region and is synchronous with subsidence of the Gosau-type basins and opening and closure of the neighbouring Sava-Vardar Zone.
Remagnetization of Upper Jurassic limestones from the Danubian Unit (Southern Carpathians, Romania): tectonic implications
Abstract: We present a pioneering paleomagnetic study on Upper Jurassic limestones from the Danubian Unit (Southern Carpathians, Romania). Thermal and alternating field demagnetizations were applied to define the characteristic remanent magnetization component in all six localities (81 samples). All samples have a normal polarity characteristic remanent magnetization. Negative regional and local fold tests suggest that this remanent magnetization is in fact a remagnetization produced by late diagenetic processes. The studied limestones were probably remagnetized during the collision of the Getic Unit and Danubian Unit which took place during the long normal polarity Chron C34 (82–118 Ma). The area mean direction (D=75.5°, I=50.0°, α95=10.2°, k=44) implies about 75° clockwise rotation post remagnetization. Our paleomagnetic results further indicate the absence of significant relative rotation between the Getic Unit and the Danubian Unit during the Cenozoic.
Tectonic control on the sedimentary record of the central Moldavidian Basin (Eastern Carpathians, Romania)
Abstract: The sedimentary record of the Tarcau and Vrancea Nappes, belonging to the flysch accretionary zone of the Eastern Carpathians (Eastern Carpathian Outer Flysch), registered Cretaceous-Miocene events during the evolution of the Moldavidian Basin. Our biostratigraphic data indicate that the deposits studied are younger than previously reported. The comparison of sedimentary record studied with the Late Cretaceous–Early Miocene global eustatic curve indicates that eustatic factor played a secondary role, after the tectonic one. Four main stages of different processes influenced by tectonics are recognized in the sedimentary record: (1) Campanian–Maastrichtian–earliest Paleocene; (2) latest Ypresian–Lutetian; (3) late Chattian–earliest Aquitanian, and (4) late Aquitanian-early Burdigalian. The late Chattian–earliest Aquitanian and late Aquitanian-early Burdigalian records indicate a high tectonic influence. The first event was related to the foredeep stage of the sedimentary domain studied, and the second one to the deformation stage of the same domain. The sedimentary records of tectonic influence recognized during these stages are useful tools for geodynamic reconstructions. The stratigraphic correlation of Tarcau and Vrancea sedimentary records are used to propose some constraints in the timing of the deformation for the central Moldavidian Basin and close domains.
Unconventional hydrocarbon resources of the Bjelovar Subdepression (Pannonian Basin System) in Croatia: an overview
Abstract: The Croatian part of the Pannonian Basin System includes several Miocene chronostratigraphic (sub)stages mostly characterized by weak permeable clastic sediments. They are often also mature source rocks at depths of more than 2500 m, from Late Badenian to Early Pannonian ages, represented by marls and calcitic marls, and kerogene Types II and III. The other types of weakly permeable sediments are tight sandstone mostly of Badenian age. Those two lithotypes are potential unconventional reservoirs described in the Bjelovar Subdepression, regarding their age, geological evolution, lithology, porosity and permeability. Domination of kerogene Type III and low total organic carbon defined marls as gas-bearing source rocks. Both marls and tight sandstones mostly have porosity less than 10 % and permeability less than 10–3 mm2. It is about 10–100 times lesser permeability than in conventional reservoirs. Weakly permeable zones are highly stochastically distributed and fluid flows are relatively short (several meters), which could be enhanced only by the using hydraulic or other fracturing techniques.
Selective mineral composition, functional test morphology and paleoecology of the agglutinated foraminiferal genus Colominella Popescu, 1998 in the Mediterranean Pliocene (Liguria, Italy)
Abstract: Specimens of Colominella (agglutinated Foraminifera) from a Pliocene Mediterranean succession were analysed through a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX) to document their test microstructure. Colominella develops a complex large test with a mostly biserial chamber arrangement, but with the internal chamber lumens partitioned by vertical and horizontal plates that form a labyrinthine structure of alcoves. This internal partition occurs from the first chambers but is completely masked from the outside by the thick wall. The test-wall microstructure is characterized by canaliculi (parapores) that are externally covered by a pavement of agglutinated grains. The mineralogical characterization of the agglutinated grains and the secreted cement shows that the grains are strongly selected as regards to size, arrangement and composition, with the coarse grains placed close to the outer wall. Moreover, these coarse grains, forming a pavement, are made of monocrystalline quartz, whereas the inner part of the skeleton is mostly composed of dolomite. The carbonate cement is less abundant and appears as cloudy light grey areas among the detrital grains. These shell features can be interpreted as functional adaptations to perform kleptoplastidy and/or to house functional photosymbionts, probably induced by stable environmental conditions as in warm shallow waters characterized by low nutrient flux.
Stability of kaolin sand from the Vysny Petrovec deposit (south Slovakia) in an acid environment
Abstract: Comprehensive characterization of kaolin sand from the Vysny Petrovec (VP) deposit in Slovakia by a variety of experimental methods was performed. The quantitative XRD analysis (RockJock software) revealed that the acid-untreated sample contained mainly kaolinite (~60 wt. %), a considerable amount of dioctahedral micas (~32 wt. %) and quartz (~7 wt. %). The Hinckley index (HI) and Aparicio-Galan-Ferrel index (AGFI) calculated from the 02l and 11l reflections showed medium-defect kaolinite to be present in the VP kaolin. The influence of the mineral composition of VP kaolin on its stability in 6 mol•dm–3 HCl at 95 °C was investigated. The solid reaction products were examined by chemical analysis; XRD and infrared spectroscopy in both middle (MIR) and near (NIR) regions. Considerably higher dissolution rate of Fe compared to Al indicated that Fe was bounded in a readily soluble phase rather than in kaolinite. While the MIR spectra confirmed the gradual release of the central atoms from the clay minerals layers and creation of amorphous silica upon acid treatment, the NIR spectra revealed the formation of Si-OH groups in the solid reaction product. Relatively high dissolution rate of VP kaolin resulted from the presence of small-grains of medium-defect kaolinite and clay admixtures in VP kaolin sand.