Dieter Mader

Using Instrumental Neutron Activation Analysis for geochemical analyses of terrestrial impact structures: Current analytical procedures at the University of Vienna Geochemistry Activation Analysis Laboratory

The Instrumental Neutron Activation Analysis Gamma Spectroscopy Laboratory at the Department of Lithospheric Research, University of Vienna, has been upgraded in the year 2006. This paper describes the sample preparation, new instrumentation and data evaluation for hundreds of rock samples of two terrestrial impact structures. The measurement and data evaluation are done by using Genie 2000 and a custom-made batch software for the used analysis sequences.

40Ar/39Ar dating of a Langhian biotite-rich clay layer in the pelagic sequence of the Cònero Riviera, Ancona, Italy

A nearly complete and undisturbed Miocene carbonate sequence is present in the easternmost part of the Umbria-Marche basin, Italy, which is ideal for detailed and integrated stratigraphic investigations of the Miocene Epoch. In this study, we were trying to obtain evidence for the presence or absence of distal ejecta from the 15 Ma Ries impact structure in southern Germany, located about 600 km to the north–northwest of the Umbria-Marche basin. The first step is to find coeval strata in the Umbria-Marche sequence. At the La Vedova section, Conero Riviera, we dated a volcaniclastic biotite-rich clay layer, the Aldo Level, which is situated within planktonic foraminiferal Zone N8, at 14.9±0.2 Ma, using the 40Ar/39Ar method. Together with detailed geologic and stratigraphic information about the Aldo Level, the resulting age can be used confidentially to calibrate the Langhian stage. Besides providing new constraints on Miocene geochronology, this age can now be used for impact stratigraphic studies. To directly correlate the biotite ages of the La Vedova section with rocks from the Ries impact event, Ries impact glass was also analyzed and found to be coeval. Although unrelated to this impact event, the biotite-rich clay layer should help in the search for evidence of distal ejecta related to the Ries crater.

Paleomagnetism and 40Ar/39Ar Age Determinations of Impactites from the Ilyinets Structure, Ukraine

Oriented hand samples were collected at the Ilyinets impact structure, western Ukraine, for paleomagnetic and petrographic studies. The samples consist of suevites, melt-breccias, impact melt rocks, autochthonous granite breccias, fractured granites, and unfractured gneisses. Three melt-breccias and one impact glass sample were used for laser 40Ar/39Ar dating. The characteristic remanent magnetization (ChRM) of the impact rocks has been acquired during the post-shock cooling, presumably in the presence of hydrothermal fluids. The alternating field demagnetization data indicate that this “impact” ChRM is of dual polarity and distinct from the ca. 1830-Ma-old pre-impact “target” remanence in the unfractured basement rocks. Some fractured autochthonous granites give evidence for impact overprinting, suggesting a fully positive paleomagnetic impact test. Paleomagnetic results suggest that no large-scale post-impact structural tilting of the melt sheets have taken place. The data allow a minor ~5° tilting towards the north. The combined paleomagnetic and 40Ar/39Ar dating results suggest an age of ca. 445 ± 10 Ma for the impact. The petrographic observations show that some secondary hydrothermal alteration took place in the rocks after the impact, which may have been responsible for some of the slightly younger Ar-Ar ages. The results show that the Ukrainian Shield was in contact with Baltica 445 Ma ago.

The successful "recipe" for a long-lasting tradition: Nubian ceramic assemblages from Sai Island (northern Sudan) from prehistory to the New Kingdom

Abstract Sai Island, in the Nile in northern Sudan, has a series of settlement sites spanning the entire period from the eighth millennium BC through to the Eighteenth Dynasty of the Egyptian New Kingdom. This long sequence provides an excellent opportunity to study continuity and discontinuity in long-term pottery traditions. Ceramics from the varying cultural phases of the occupation reflect changing dynamics between broader regional social identities, notably Kerma to the south and Egypt to the north. Combining studies of petrography with trace element composition and chaîne opératoire analysis, the authors present the first diachronic study of ceramic manufacture throughout the extended cultural history of Nubia, highlighting the varying manifestations of change and continuity.

Geochemistry of a Langhian Pelagic Marly Limestone Sequence of the Cònero Riviera, Ancona (Italy) and the Search for a Ries Impact Signature: A Progress Report

Samples from the mid-Miocene marine La Vedova section at the Conero Riviera, Umbria-Marche sequence, Italy, were analyzed for their chemical composition to provide data for impact- and cyclostratigraphic studies. The rocks from the La Vedova section provide new data for the Mediterranean Langhian. Major and trace elemental compositions demonstrate a clayey and (phyllo)silicatic terrigenous input. The rare earth elements show typical upper continental crustal composition and do not indicate seawater-fractionated patterns. Thus, despite of carbonate dilution, the siliciclastic input in the pelagic carbonates may reflect the composition and provenance of the source areas by using trace element ratios and rare earth elements. The Middle and Upper Miocene in the Alpine-Apennine region is mainly represented by synorogenic reworked siliciclastic deposits. The pelagic carbonate sequence at the Conero Riviera is nearly continuous, and one of the aspects of this work was a search for ejecta (and regional effects) of the medium-sized Ries impact crater event, about 600 km from the Conero Riviera. No clear chemical signal of an extraterrestrial component, from the Ries or any other impactor, was obvious in the present data set. However, the Ries impactor has previously been proposed to have been of achondritic composition, in which case only a detailed search for shocked minerals and microspherules could help to recognize a possible Ries-derived distal ejecta layer.