End of the Kiaman Superchron in the Permian of SW England: Magnetostratigraphy of the Aylesbeare Mudstone and Exeter groups

The chronology of Permian strata in SW England is fragmentary and largely based on radiometric dating of associated volcanic units. Magnetostratigraphy from the c. 2 km of sediments in the Exeter and Aylesbeare Mudstone groups was undertaken to define a detailed chronology, using the end of the Kiaman Superchron and the overlying reverse and normal polarity in the Middle and Upper Permian as age constraints. The palaeomagnetic directions are consistent with other European Permian palaeopoles, with data passing fold and reversal tests. The end of the Kiaman Superchron (in the Wordian) occurs in the uppermost part of the Exeter Group. The overlying Aylesbeare Mudstone Group is early Capitanian to latest Wuchiapingian in age. The Changhsingian and most of the Lower Triassic sequence is absent. Magnetostratigraphic comparison with the Southern Permian Basin shows that the Exeter and Aylesbeare Mudstone groups are closely comparable in age with the Havel and Elbe Subgroups of the Rotliegend II succession. The Altmark unconformities in these successions appear similar in age to the sequence boundaries in SW England, indicating that both may be climate controlled. Clasts in the Exeter Group, from unroofing of the Dartmoor Granite, first occurred at a minimum of c. 8 myr after formation of the granite

New data on the origin of the Fe-Cu-As skarn deposit at Obří důl, West Sudetes, Bohemian Massif

The Obří důl Fe-Cu-As sulfide deposit is hosted in metamorphosed lenses of marble, calc-silicate rocks and skarns. The deposit is located up to a few hundred meters away from the contact of the large, late-orogenic Variscan Krkonoše-Jizera Plutonic Complex (KJPC). Mineralogical and fluid inclusion studies of the Gustavská ore lens show that the main sulfide stage, dominated by pyrrhotite, chalcopyrite and arsenopyrite, originated from water-rich hydrothermal fluids with salinities up to 8 wt.% NaCl eq. at temperatures ranging from 324 to 358°C.These fluids replaced mainly the carbonate-rich lithologies. The 34S values indicate a magmatic source of sulfur and Re/Os dating of molybdenite are consistent with simultaneous formation of the main sulfide stage ore and the KJPC

Trace element variations as a proxy for reconstruction of palaeoenvironmental changes during the Late Aeronian faunal and carbon isotope perturbations: new data from the peri-Gondwanan region

Trace element variations in the Upper Aeronian (Llandovery, Lower Silurian), deep-water, black shale succession of the Barrandian area (Perunica) were studied across an interval associated with a graptolite mass extinction and global, positive carbon isotope anomaly. The main aim of the paper is to test whether distinct changes in graptolite diversity during Late Aeronian were linked with changes in deep sea water oxygenation. Using multiple geochemical proxies we documented high-frequency changes in oxygenation of sea water from sediments of the convolutus to linnaei (guerichi) biozones. Detailed comparison of graptolite diversity with those high-frequency oxygenation changes suggests that the long-term and step-wise Late Aeronian graptolite crisis was not significantly influenced by changes in oxygen level and thus it probably resulted by another causes. The collapse of global carbon cycle during the Late Aeronian probably only temporarily increased extinction rate of the long-term graptolite crisis and considerably decreased evenness of the uppermost Aeronian graptolite communities. The Aeronian graptolite mass extinction was thus primarily driven by other biotic and/or abiotic cause

Chromium isotope variations (delta(53)/(52)Cr) in mantle-derived sources and their weathering products: Implications for environmental studies and the evolution of delta(53)/(52)Cr in the Earth's mantle over geologic time

Abstract not availableJuraj Farkaš, Vladislav Chrastný, Martin Novák, Eva Čadkova, Jan Pašava, Ramananda Chakrabarti, Stein B. Jacobsen, Lukáš Ackerman, Thomas D. Bulle