Molybdenite Re-Os dating of Mo-Th-Nb-REE rich marbles: pre-Variscan processes in Moldanubian Variegated Group (Czech Republic)
Abstract: In an effort to contribute to the discussion concerning the age of rocks of the Moldanubian Variegated Group, we have undertaken Re-Os dating of molybdenite of banded carbonatite-like marbles (CLM) from the graphite mine Václav at Bližná (Southern Bohemia), which belong to the metamorphic sequence of this group. The Re-Os model ages for the molybdenites range between 493 and 497 Ma and apparently correspond to the early stages of metamorphism connected with pre-Variscan rift-related tectono-metamorphic events, which affected and recrystallized sedimentary CLM material rich in Mo-Th-Nb-REE. The molybdenite bearing carbonatite like marbles situated in the footwall of Bližná graphite mine have been interpreted as carbonates with a large share of volcano-detritic material derived from contemporaneous primitive alkaline (carbonatite-like) volcanism deposited in a shallow marine lagoonal environment. There is no geological evidence for the participation of fluids mobilized from host rocks in the formation of the CLM. Because the Re-Os chronometer in molybdenite is demonstrably stable through later Variscan facies metamorphism, the molybdenite chronometer has not been affected by subsequent thermal overprints associated with the Variscan orogeny.
Last occurrence of Abathomphalus mayaroensis (Bolli) foraminiferid index of the Cretaceous—Paleogene boundary: the calcareous nannofossil proof
Abstract: In the Gaj section (Polish Carpathians, Skole Nappe, Ropianka Formation), the Late Maastrichtian calcareousnannofossil biostratigraphy is compared with foraminiferal zonation based on the occurrence of the planktonic foraminiferidindex species Abathomphalus mayaroensis. It appears that the LO of A. mayaroensis, which has been used previously inthe studied section as the possible K/Pg boundary indicator is located below the boundary. The disappearance ofA. mayaroensis along with other planktonic foraminiferids before the Cretaceous—Paleogene (K/Pg) boundary massextinction event may be a consequence of the Late Maastrichtian rapid warming pulses. Moreover, the Paleogene agecannot be supported by the FO of the benthic foraminiferid Rzehakina fissistomata, because it first appears together withthe nannofossil Ceratolithoides kamptneri (zonal marker for the latest Maastrichtian UC20cTP Zone). According to thepresent study, the whole studied section represents the lower Upper to the upper Upper Maastrichtian UC20bTP and UC20cTPnannofossil zones, so that it corresponds to the lower-middle part of the planktonic foraminiferal A. mayaroensis Zone,which, according to the scheme by Caron (1985), should extend up to the K/Pg boundary.
Upper Cretaceous to Pleistocene melilitic volcanic rocks of the Bohemian Massif: petrology and mineral chemistry
Abstract: Upper Cretaceous to Pleistocene volcanic rocks of the Bohemian Massif represent the easternmost part of the Central European Volcanic Province. These alkaline volcanic series include rare melilitic rocks occurring as dykes, sills, scoria cones and flows. They occur in three volcanic periods: (i) the Late Cretaceous to Paleocene period (80—59 Ma) in northern Bohemia including adjacent territories of Saxony and Lusatia, (ii) the Mid Eocene to Late Miocene (32.3—5.9 Ma) period disseminated in the Ohře Rift, the Cheb—Domažlice Graben, Vogtland, and Silesia and (iii) the Early to Late Pleistocene period (1.0—0.26 Ma) in western Bohemia. Melilitic magmas of the Eocene to Miocene and Pleistocene periods show a primitive mantle source [(143Nd/144Nd)t= 0.51280—0.51287; (87Sr/86Sr)t= 0.7034—0.7038)] while those of the Upper Cretaceous to Paleocene period display a broad scatter of Sr—Nd ratios. The (143Nd/144Nd)t ratios (0.51272—0.51282) of the Upper Cretaceous to Paleocene rocks suggest a partly heterogeneous mantle source, and their (87Sr/86Sr)t ratios (0.7033—0.7049) point to an additional late- to post-magmatic hydrothermal contribution. Major rock-forming minerals include forsterite, diopside, melilite, nepheline, sodalite group minerals, phlogopite, Cr- and Ti-bearing spinels. Crystallization pressures and temperatures of clinopyroxene vary widely between ~ 1 to 2 GPa and between 1000 to 1200°C, respectively. Nepheline crystallized at about 500 to 770°C. Geochemical and isotopic similarities of these rocks occurring from the Upper Cretaceous to Pleistocene suggest that they had similar mantle sources and similar processes of magma development by partial melting of a heterogeneous carbonatized mantle source.
Decapod Crustacea of the Central Paratethyan Ottnangian Stage (middle Burdigalian): implications for systematics and biogeography
Abstract: Decapod crustaceans from the Ottnangian (middle Burdigalian, Lower Miocene) of the Western and Central Paratethys remain poorly known. In this study, we review and re-describe mud shrimps (Jaxea kuemeli), ghost shrimps (Gourretia sp., Calliax michelottii) and brachyuran crabs of the families Leucosiidae, Polybiidae and Portunidae. A dorsal carapace of the genus Calliax is reported for the first time in the fossil record. Re-examination of the type material of Randallia strouhali (Leucosiidae) and Geryon ottnangensis (Geryonidae) resulted in a transfer of these species into Palaeomyra (Leucosiidae) and Liocarcinus (Polybiidae), respectively. Achelous vindobonensis, originally described as a chela of a portunid crab, probably belongs to a member of Polybiidae and is provisionally treated as Liocarcinus sp. Only two species, J. kuemeli and C. michelottii, are also known from the Karpatian, the succeeding Paratethyan stage. In most cases, the decapod assemblages of the Ottnangian consist of rather shallow-water taxa whereas the assemblages of the Karpatian consist of deep-water taxa from the middle and outer shelf. The Central Paratethyan assemblages show similarities in genus composition to the Proto-Mediterranean and recent Indo-Pacific regions. Gourretia sp. represents the earliest occurrence of the respective genus in the fossil record. The Oligocene—Early Miocene appearance of Palaeomyra and Liocarcinus in the circum-Mediterranean implies that sources of present-day diversity hotspots in the Indo-Pacific trace to the Western Tethys (as for other decapod genera), although coeval decapod assemblages in the Indo-Pacific remain poorly known.
The correlation of the Neogene of Central and Eastern Paratethys segments of Ukraine with the International Stratigraphic Chart based on planktonic microfossils
Abstract: Detailed analysis of microplankton occurrence (planktonic foraminifera, nannoplankton, dinocysts) in Neogene sediments situated at the north-western and south-eastern margins of Ukraine enabled us to distinguish 10 associations of oceanic plankton which specified the relative age of lithostratigraphic units of various regions and were used as correlation levels within the Central and Eastern Paratethys strata. Moreover, an attempt to correlate regional stages and the International Stratigraphic Chart (ISC) is performed. The Oligocene/Miocene boundary (of ISC) represented by the correlation level I was placed within the Central Paratethys regional stage Egerian and in the middle part of the Eastern Paratethys regional stage Caucasian s.l. The latter regional stage is subdivided by the correlation level into two substages: Lower Caucasian (Chattian of ISC) and Upper Caucasian (Aquitanian of ISC). The correlation level II was placed within the upper part of the Eggenburgian and lower part of the Batisifonian (Sakaraulian) regional stages and is correlated approximately with the middle part of the Burdigalian (of ISC). The base of the Middle Miocene is marked by level IV and was recognized only in deposits of the Eastern Paratethys belonging to the Tarkhanian regional stage. This level corresponds to the lowermost Badenian and Langhian (of ISC) stages. Correlation level V is traced in the Konkian sediments of the Eastern Paratethys and is compared with the Upper Badenian and Lower Serravalian (of ISC) stages. Level VI at the Middle/Upper Miocene boundary is situated in the middle part of the Bessarabian regional substage of the Eastern Paratethys and enables its correlation with the Serravallian/Tortonian boundary (of ISC). Level VII is recognized in the Baherovo Member (Meotian stage), while level VIII is fixed at the top of the Meotian regional stage in the Azov and Black Seas, Crimea and adjacent region named Northern Prichornomorye. Both these levels are also identified in the Berezhnytsya Formation of the Eastern Carpathian Foredeep. Correlation of these sediments is similar to the correlation of sediments of Lake Pannon (Pannonian regional stage), hence with the Tortonian stage (of ISC). Level IX was recognized in sediments of the Azov Member belonging to the Kimmerian regional stage of the Eastern Paratethys and represents the top of the Miocene strata. Level X occurs within the Taman Member of the Black Sea shelf and is correlated with the upper part of Kuyalnikian regional stage; corresponding to the Pliocene/Pleistocene boundary.
Quaternary faulting in the Tatra Mountains, evidence from cave morphology and fault-slip analysis
Abstract: Tectonically deformed cave passages in the Tatra Mts (Central Western Carpathians) indicate some fault activity during the Quaternary. Displacements occur in the youngest passages of the caves indicating (based on previous U-series dating of speleothems) an Eemian or younger age for those faults, and so one tectonic stage. On the basis of stress analysis and geomorphological observations, two different mechanisms are proposed as responsible for the de- velopment of these displacements. The first mechanism concerns faults that are located above the valley bottom and at a short distance from the surface, with fault planes oriented sub-parallel to the slopes. The radial, horizontal extension and vertical σ1 which is identical with gravity, indicate that these faults are the result of gravity sliding probably caused by relaxation after incision of valleys, and not directly from tectonic activity. The second mechanism is tilting of the Tatra Mts. The faults operated under WNW-ESE oriented extension with σ1 plunging steeply toward the west. Such a stress field led to normal dip-slip or oblique-slip displacements. The faults are located under the valley bottom and/or opposite or oblique to the slopes. The process involved the pre-existing weakest planes in the rock complex: (i) in massive limestone mostly faults and fractures, (ii) in thin-bedded limestone mostly inter-bedding planes. Thin-bedded limestones dipping steeply to the south are of particular interest. Tilting toward the N caused the hanging walls to move under the massif and not toward the valley, proving that the cause of these movements was tectonic activity and not gravity.