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František Vacek, Jindřich Hladil and Petr Schnabl

Stratigraphic correlation potential of magnetic susceptibility and gamma-ray spectrometric variations in calciturbiditic facies (Silurian-Devonian boundary, Prague Synclinorium, Czech Republic)

Magnetic susceptibility (MS) and gamma-ray spectrometry (GRS) stratigraphy were used for correlation and characterization of eight Silurian-Devonian (S-D) sections in the Prague Synclinorium (Czech Republic). They represent two different facies developments: lower subtidal to upper slope deposits and slope-to-basin-floor distal calciturbidites. Sections from relatively shallow- and deep-water sections are easy to compare and correlate separately, although the detailed relationship between these two facies is still not entirely clear and correlations between the two settings are difficult. This may be due to sharp facies transitions and presence of stratigraphic gaps. The MS and GRS stratigraphic variations combined with sedimentologic data have been also used for reconstruction of the evolution of the sedimentary environment. The beds close above the S-D boundary show noticeably enhanced MS magnitudes but weak natural gamma-ray emissions. It may correspond to an increased amount of terrigenous magnetic material occurring with short-term shallowing (sedimentological evidence). In deep-water sections the uppermost Silurian is characterized by high MS and GRS values. It corresponds to a supply of recycled sediment to the lower wedge which occurred during the late Pridoli regression phase. The basal Devonian beds correspond to gradual deepening, but the overlying sequences reflect other shallowing episodes which are expressed in increasing MS and gamma ray activity of rocks. The MS and GRS fluctuations are interpreted as a result of local subsidence of the sea bottom along synsedimentary growth-faults and/or a biotic event rather than of eustatic sea-level changes.

Open access

Petr Schnabl, Petr Pruner and William A.P. Wimbledon

Abstract

In this contribution we examine and discuss recently published magnetostratigraphic data from the Nordvik section (north Siberia) around the Tithonian–Berriasian (J/K) boundary, with a special emphasis on calibration with biostratigraphy and the reliability of both the fossil and magnetic records, as well as sedimentation rates. Specifically, we discuss original new interpretations by Bragin et al. (2013) and the commentary on that work by Guzhikov (2013). We consider some limitations of the Nordvik section, and conclude that the base of M18r, because it is in a condensed part of the sequence, makes a poor contender for precise long-range correlation. We discuss the lack of ammonites at several magnetozone boundaries, and whether the bases of the local zones of Craspedites taimyrensis and Arctoteuthis tehamaensis can be used to bracket the correlative horizon of Calpionella alpina, a widespread marker in the middle of M19n.2n in Tethys.

Open access

Alexander Lukeneder, Eva Halásová, Andreas Kroh, Susanne Mayrhofer, Petr Pruner, Daniela Reháková, Petr Schnabl, Mario Sprovieri and Michael Wagreich

High resolution stratigraphy of the Jurassic-Cretaceous boundary interval in the Gresten Klippenbelt (Austria)

The key objective of investigation of hemipelagic sediments from the Gresten Klippenbelt (Blassenstein Formation, Ultrahelvetic paleogeographic realm) was to shed light on environmental changes around the Jurassic-Cretaceous (J/K) boundary on the northern margin of the Penninic Ocean. This boundary is well exposed in a newly discovered site at Nutzhof. Around the critical interval including the boundary, this new outcrop bears a rich microplanktonic assemblage characterized by typical J/K (Tithonian/Berriasian) boundary faunas. The Nutzhof section is located in the Gresten Klippenbelt (Lower Austria) tectonically wedged into the deep-water sediments of the Rhenodanubian Flysch Zone. In Late Jurassic-Early Cretaceous time the Penninic Ocean was a side tract of the proto-North Atlantic Oceanic System, intercalated between the European and the Austroalpine plates. Its opening started during the Early Jurassic, induced by sea floor spreading, followed by Jurassic-Early Cretaceous deepening of the depositional area of the Gresten Klippenbelt. These tectonically induced paleogeographic changes are mirrored in the lithology and microfauna that record a deepening of the depositional environment from Tithonian to Berriasian sediments of the Blassenstein Formation at Nutzhof. The main lithological change is observed in the Upper Tithonian Crassicollaria Zone, in Chron M20N, whereas the J/K boundary can be precisely fixed at the Crassicollaria-Calpionella boundary, within Chron M19n.2n. The lithological turnover of the deposition from more siliciclastic pelagic marl-limestone cycles into deep-water pelagic limestones is correlated with the deepening of the southern edge of the European continent at this time. Within the Gresten Klippenbelt Unit, this transition is reflected by the lithostratigraphic boundary between siliciclastic-bearing marl-limestone sedimentation in the uppermost Jurassic and lowermost Cretaceous limestone formation, both within the Blassenstein Formation. The cephalopod fauna (ammonites, belemnites, aptychi) and crinoids from the Blassenstein Formation, correlated with calcareous microfossil and nannofossil data combined with isotope and paleomagnetic data, indicate the Tithonian to middle Berriasian (Hybonoticeras hybonotum Zone up to the Subthurmannia occitanica Zone; M17r-M21r). The succession of the Nutzhof section thus represents deposition of a duration of approximately 7 Myr (ca. 150-143 Ma). The deposition of the limestone, marly limestone and marls in this interval occurred during tectonically unstable conditions reflected by common allodapic material. Along with the integrated biostratigraphic, geochemical and isotopic analysis, the susceptibility and gamma-ray measurements were powerful stratigraphic tools and important for the interpretation of the paleogeographic setting. Two reverse magneto-subzones, Kysuca and Brodno, were detected within magnetozones M20n and M19n, respectively.

Open access

Vladimír Cajz, Petr Schnabl, Zoltan Pécskay, Zuzana Skácelová, Daniela Venhodová, Stanislav Šlechta and Kristýna Čížková

Abstract

This paper presents the results of a paleomagnetic study carried out on Plio-Pleistocene Cenozoic basalts from the NE part of the Bohemian Massif. Paleomagnetic data were supplemented by 27 newly obtained K/Ar age determinations. Lavas and volcaniclastics from 6 volcanoes were sampled. The declination and inclination values of paleomagnetic vectors vary in the ranges of 130 to 174 and -85 to -68° for reversed polarity (Pleistocene); or 345 to 350° and around 62° for normal polarity (Pliocene). Volcanological evaluation and compilation of older geophysical data from field survey served as the basis for the interpretation of these results. The Pleistocene volcanic stage consists of two volcanic phases, fairly closely spaced in time. Four volcanoes constitute the Bruntál Volcanic Field; two others are located 20 km to the E and 65 km to the NW, respectively. The volcanoes are defined as monogenetic ones, producing scoria cones and lavas. Exceptionally, the largest volcano shows a possibility of remobilization during the youngest volcanic phase, suggested by paleomagnetic properties. The oldest one (4.3-3.3 Ma), Břidličná Volcano, was simultaneously active with the Lutynia Volcano (Poland) which produced the Zálesí lava relic (normal polarity). Three other volcanoes of the volcanic field are younger and reversely polarized. The Velký Roudný Volcano was active during the Gelasian (2.6-2.1 Ma) and possibly could have been reactivated during the youngest (Calabrian, 1.8-1.1 Ma) phase which gave birth to the Venušina sopka and Uhlířský vrch volcanoes. The reliability of all available K-Ar data was evaluated using a multidisciplinary approach.

Open access

Jozef Michalík, Daniela Reháková, Jacek Grabowski, Otília Lintnerová, Andrea Svobodová, Ján Schlögl, Katarzyna Sobień and Petr Schnabl

Abstract

A well preserved Upper Tithonian–Lower Berriasian Strapkova sequence of hemipelagic limestones improves our understanding of environmental changes occurring at the Jurassic/Cretaceous boundary in the Western Carpathians. Three dinoflagellate and four calpionellid zones have been recognized in the section. The onset of the Alpina Subzone of the standard Calpionella Zone, used as a marker of the Jurassic/Cretaceous boundary is defined by morphological change of Calpionella alpina tests. Calpionellids and calcified radiolarians numerically dominate in microplankton assemblages. The first occurrence of Nannoconus wintereri indicates the beginning of the nannofossil zone NJT 17b Subzone. The FO of Nannoconus steinmannii minor was documented in the lowermost part of the Alpina Subzone. This co-occurrence of calpionellid and nannoplankton events along the J/K boundary transition is typical of other Tethyan sections. Correlation of calcareous microplankton, of stable isotopes (C, O), and TOC/CaCO3 data distribution was used in the characterization of the J/K boundary interval. δ13C values (from +1.09 to 1.44 ‰ VPDB) do not show any temporal trends and thus show a relatively balanced carbon-cycle regime in sea water across the Jurassic/Cretaceous boundary. The presence of radiolarian laminites, interpreted as contourites, and relatively high levels of bioturbation in the Berriasian prove oxygenation events of bottom waters. The lower part of the Crassicolaria Zone (up to the middle part of the Intermedia Subzone) correlates with the M19r magnetozone. The M19n magnetozone includes not only the upper part of the Crassicollaria Zone and lower part of the Alpina Subzone but also the FO of Nannoconus wintereri and Nannoconus steinmannii minor. The reverse Brodno magnetosubzone (M19n1r) was identified in the uppermost part of M19n. The top of M18r and M18n magnetozones are located in the upper part of the Alpina Subzone and in the middle part of the Ferasini Subzone, respectively. The Ferasini/Elliptica subzonal boundary is located in the lowermost part of the M17r magnetozone. A little bit higher in the M17r magnetozone the FO of Nannoconus steinmannii steinmannii was identified.

Open access

William A.P. Wimbledon, Daniela Reháková, Andrzej Pszczółkowski, Cristina E. Casellato, Eva Halásová, Camille Frau, Luc G. Bulot, Jacek Grabowski, Katarzyna Sobień, Petr Pruner, Petr Schnabl and Kristýna Čížková

Abstract

This paper discusses the results of a study of the Le Chouet section, its lithologies, facies, magnetic properties and fossil record (ammonites, calcareous nannofossils, calpionellids and calcareous dinoflagellates). Data obtained have been applied to give a precise biostratigraphy for this carbonate sequence as well as a paleoenvironmental reconstruction. Its relationship to magnetostratigraphy, based on a modern study of a French site, is important. Investigation of the micro- and macrofossils shows that the site comprises a sedimentary sequence in the Microcanthum to Jacobi ammonite Zones, and the Chitinoidella, Crassicollaria and Calpionella Zones. Several calpionellid and nannofossil bioevents have been recorded on the basis of the distribution of stratigraphically important planktonic organisms. The site allows us to calibrate the levels of various biomarkers and biozonal boundaries, and correlate them with the magnetozones M20n, M19r and M19n.