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Vrabec M.,University of Ljubljana | Janak M.,Slovak Academy of Sciences | Froitzheim N.,Steinmann Institute | De Hoog J.C.M.,University of Edinburgh
Lithos | Year: 2012

Phase relations among the mineral assemblages of UHP kyanite eclogite were investigated in the Pohorje Mountains of the Eastern Alps. Ultrahigh-pressure metamorphism resulted from intracontinental subduction during the Cretaceous (ca. 92Ma). Kyanite-bearing eclogites are associated with meta-ultramafic rocks including UHP garnet peridotites and are embedded in metapelitic gneisses and micaschists. The kyanite eclogites contain a peak metamorphic assemblage of garnet, omphacite, kyanite and phengite. Pyrope-rich garnet is unzoned and almost free of inclusions. The non-stoichiometric supersilicic omphacite contains up to 5mol% of Ca-Eskola molecule. Breakdown of omphacite during decompression resulted in exsolution of oriented rods of silica. Phengite contains up to 3.5 Si a.p.f.u. Polycrystalline quartz inclusions in peak-pressure minerals - garnet, omphacite and kyanite - are surrounded by radial fractures diagnostic of the former presence of coesite. Peak-pressure minerals are replaced by symplectites of diopside+plagioclase+amphibole after omphacite, plagioclase+biotite after phengite and sapphirine+corundum+spinel+anorthite after kyanite. Sapphirine has composition close to (Mg, Fe) 12.4 Al 38.9 Si 4.5 O 80 in average, which is amongst the most aluminous yet reported. Peak metamorphic conditions were constrained from calculated phase equilibria in the NKCFMASH system with the fixed bulk-rock composition, and conventional geothermobarometry. This approach led to consistent results, the calculated peak P-T conditions of 3.0-3.7GPa and 710-940°C, in the stability field of coesite and the same range as metamorphic conditions recorded by the associated garnet peridotites. This implies that eclogites and their host rocks were subducted to depths of about 100km. The relatively high temperature at peak pressure, compared to UHP rocks of Tertiary age in the Western Alps where mostly oceanic crust was subducted, probably resulted from radiogenic heat production by subducting continental crust, in the intra-continental setting of the Cretaceous subduction zone in the Eastern Alps. © 2012 Elsevier B.V.

News Article | November 7, 2016

Insect feeding damage on a fossil leaf, including holes and a leaf mine (bottom r.), made by a larval insect that fed on tissue within the leaf. The fossil is 67-66 million years old and from the Lefipán Formation in Patagonia, Argentina. Fossil leaf with insect feeding damage, including holes and feeding along the leaf margins. The fossil is from the latest Cretaceous Lefipán Formation (67-66 million years old) in Patagonia, Argentina. —Much of what scientists know about the mass extinction that killed perhaps as much as three-quarters of life on Earth, including the non-avian dinosaurs, comes from fossils unearthed in the western interior of North America. Fossils from other parts of the world at that time have been more scarce. Scientists had speculated that perhaps regions of the Southern Hemisphere, like South America, had been a sort of refuge for species during the Cretaceous-Palaeogene (K-Pg) extinction event, and then those organisms went on to repopulate the globe. But that actually might not be the case, a team of paleontologists suggest in a paper published Monday in the journal Nature Ecology & Evolution. In South America, "there was an extinction at the same time as there was an extinction in North America," study lead author Michael Donovan, a PhD student at Pennsylvania State University, tells The Christian Science Monitor in a phone interview. But that doesn't mean the mass extinction had the same effect in both regions. Mr. Donovan's research suggests that life in South America may have recovered in less than half the time it took in North America. The fossils Donovan and his colleagues studied were not the bones of ancient animals, they were leaves. "Plants deserve just as much attention as the major dinosaur finds," Regan Dunn, a paleobotanist at the Field Museum of Natural History in Chicago who was not part of the research, says in a phone interview with the Monitor. "They can tell us so much more than a single dinosaur fossil can tell us about ancient environments." These leaves weren't just dead plant matter, though. Donovan and his colleagues studied fossilized leaves that had been nibbled on or burrowed into by insects. And, because plant-eating insects are specialized in which plants they eat and the damage they cause, studying these fossilized plant-insect associations can tell the scientists about the diversity of both plants and insects alive at the time. "There aren't many insect body fossils," Donovan explains. "So we can use insect damage on fossil leaves as a sort of proxy for the diversity of plant-eating insects that were around." The team studied fossils from about 67 million years ago, just before the extinction event, and the insects apparently were voracious then. These leaves show a wide variety of insect-caused damage. But 65-million-year-old fossils showed the diversity of these bite marks had plummeted by about 21 percent right after the mass extinction swept the planet some 66 million years ago. Donovan also examined fossils from 64 million years ago and 62 million years ago, and found that the diversity of insect damage was back up to its pre-extinction levels in the most recent fossils – just 4 million years after the mass extinction event. Four million years may seem like a long time, but in the western interior of North America recovery took about 9 million years. Perhaps the ecosystem in what is now Argentina was such that organisms were less affected by the mass extinction. Or, Donovan suggests, perhaps this different recovery rate has something to do with the distance from the Chicxulub crater in Mexico. That's because most scientists agree that the mass extinction was likely triggered by an asteroid slamming into what is today the Yucatán Peninsula. The impact of that event may have been less severe in the southern tip of South America simply because it was farther away. "A lot of times when we think about mass extinctions or we think about these very abrupt events, we think about a global response," Daniel Peppe, a paleontologist at Baylor University in Waco, Texas, who was not part of the research, says in a phone interview with the Monitor. "I think it gets oversimplified in that you think the response is the same everywhere. And this is really showing that it's not." It's important to understand the nuances of how ecosystems have recovered from mass extinctions in the past, Dr. Peppe says, especially because scientists think we're in the midst of the Earth's sixth mass extinction right now. Given that there has been little material to study from the southern hemisphere across the K-Pg boundary, Stephen McLoughlin, a paleobiologist at the Swedish Museum of Natural History who was not part of the study, writes in an email to the Monitor, this study "makes a useful advance in our understanding of the evolution of biotic interactions through major Earth crises." Studying the fossilized interactions between plants and insects can yield crucial insights into major ecosystem changes in a few ways. "[Plant-insect associations] represent the most abundant and diverse groups of terrestrial organisms," Torsten Wappler, a paleontologist at the Steinmann Institute at the University of Bonn who was not involved in the research, writes in an email to the Monitor. "As such they have by far the most complete and diverse fossil record of terrestrial organisms for this period of time." And, Dr. Wappler says, not only do these fossils provide insight into the organisms themselves, "To look at the herbivory pattern could provide deep insights in fossil ecosystem and food web structures that were not possible when only look at them individually." Plants and insects are integral parts of food webs, Dr. Dunn says. Many animals eat them, they help degrade organic material, and insects are key pollinators. As such, studying them is a good way to study the overall ecosystem, she says. "You could say that insects are kind of a harbinger of what was going on ... If you have some major change going on in the insects, it's a pretty good sign that there's something going on in the whole ecosystem."

Peters S.T.M.,University of Cologne | Peters S.T.M.,Steinmann Institute | Munker C.,University of Cologne | Munker C.,Steinmann Institute | And 2 more authors.
Earth and Planetary Science Letters | Year: 2014

The decay of the rare nuclide 184Os by alpha emission to 180W has been theoretically predicted, but was previously never observed in experiments. Variable excesses of 180W were recently observed for iron meteorites, but the contribution to these excesses by 184Os-decay was regarded as insignificant. Here, we present combined 180W and Os-W concentration data for meteorites and terrestrial rocks, now indicating that the 180W heterogeneities can be explained by α-decay of 184Os. A combined 184Os-180W isochron for iron meteorites and chondrites yields a decay constant value of λ184Os(α) of 6.49 ± 1.34 × 10 -14a -1 (half life 1.12 ± 0.23 × 1013 yr), in good agreement with theoretical estimates. The 184Os-180W decay system may constitute a viable tracer and chronometer for important geological processes like core formation, silicate differentiation or late accretion processes. This is illustrated by a measured 180W-deficit in terrestrial basalts relative to chondrites by 1.16 ± 0.69 parts in 10 000, consistent with core formation ~4.5 Ga ago. © 2014 Elsevier B.V.

Pigozzi G.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Mukherji D.,TU Braunschweig | Elerman Y.,Ankara University | Strunz P.,Nuclear Physics Institute of Czech Republic | And 4 more authors.
Journal of Alloys and Compounds | Year: 2014

Nanostructured nickel silicides find application in electronics, high-temperature alloys, electrode materials and catalysis. In this work, the effect of size reduction on the structure and magnetic properties of β1-Ni3Si intermetallic phase nanoparticles is studied. Electrochemical selective phase dissolution (ESPD) was used to produce the β1-Ni3Si nanoparticles of different sizes (from 20 to 215 nm) by extracting β1 nano-size precipitates from two-phase Ni-Si and Ni-Si-Al precursor alloys. The extracted nanoparticles have a core-shell structure with β1-Ni3Si core and an amorphous silica shell. Particles size and shape are controlled by the composition and thermal treatment of the precursor alloys. Precipitates size is scaled without modifying the ordered L12 lattice structure. The bulk β1-Ni3Si is ferromagnetic below 260 K with low saturation magnetization (2 emu/g), while the core-shell Ni3Si/silica nanoparticles are superparamagnetic at low temperatures (<9-11 K) with low coercivity (<90 Oe) and magnetization >20 emu/g at 5 T. It is suggested that weak particle magnetic moments and low magnetic anisotropy of the L1 2 structure are responsible for these properties. The shell on one hand protects the core from degradation; however the oxidation of the core/shell interface region can influence the magnetic behavior of the nano-powders. © 2013 Elsevier B.V. All rights reserved.

Schulz T.,University of Cologne | Schulz T.,Steinmann Institute | Schulz T.,University of Vienna | Munker C.,University of Cologne | And 3 more authors.
Earth and Planetary Science Letters | Year: 2013

Heavy, proton-rich stable isotopes belong to the least abundant isotopes in the solar system. Their formation mechanisms and their stellar sources are most likely different from those of neutron-capture generated r- and s-process nuclei that comprise the majority of nuclides heavier than iron. Heavy p-nuclide abundances in meteorites are therefore potentially useful in deciphering distinct stellar contributions to the nascent solar system. We therefore conducted the first high-precision measurements of the heavy p-process isotope 180W, achieving a typical precision of ±0.7 ε-units for ca. 300ngW. Measured samples comprise metals from magmatic- and non-magmatic iron meteorites, as well as metal from one H4 chondrite (NWA 926) and two reduced terrestrial basalts (from Disko Island, Greenland and the Dzheltul'ski massif from Eastern-Siberia, Russia).The analyzed iron meteorites show clearly resolvable 180W anomalies of up to +6 ε-units. Conversely, the chondritic metal and both terrestrial samples exhibit 180W abundances indistinguishable from the standard value. As cosmogenic effects during space exposure of the meteoroids may have affected the 180W budget, cosmic-ray exposure of the meteorites has to be critically evaluated. We therefore propose a method to approximate cosmogenic contributions to the 180W signatures in order to unravel nucleosynthetic 180W abundance anomalies. Our study reveals significant cosmogenic effects only for the longest exposed meteorites, shifting 180W anomalies always to lower values (average cosmic-ray correction-factors can be estimated to lie between 0.01 and 0.30 ε180W-units per 100Myr of exposure). Cosmogenic effects for most of the analyzed meteorites therefore appear to be negligible with respect to the analytical precision achieved for iron meteorites. In addition to cosmic-ray exposure, radiogenic effects can be caused by putative decay of 184Os or by decay of 180Ta in its ground state. Whereas potential alpha decay of 184Os could shift 180W anomalies to higher values (but only up to levels that are within the analytical error of ~0.5 ε-units for most samples), no significant production of 180W could have occurred from 180Ta decay.Notably, we identified significant and systematic abundance variations in 180W between different iron meteorite groups, indicating that these isotope anomalies are characteristic for their entire parent asteroids. Our finding of decreasing excesses in 180W from early formed magmatic iron meteorites (+3.8±1.2 e{open}-units) towards later formed non-magmatic iron meteorites (+0.6±0.5 e{open}-units), the analyzed chondrite and both terrestrial rocks (-0.3±0.7 ε-units) may thus mirror progressive homogenization of 180W in the early solar nebula. This overall trend is also supported by a co-variation between 180W and metal segregation ages for the different iron meteorite groups as well as by a co-variation between 180W deviations and the respective asteroidal accretion ages. Such an interpretation would suggest progressive homogenization of the solar nebula within about ~2.5 to ~6Myr. © 2012 Elsevier B.V.

Hubner N.,RWE AG | Korner F.,Steinmann Institute | Schneider J.,Geologisches Institute
Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften | Year: 2011

The intr amontane basins of Saint Affrique and Lodève contain each about 2000 m of Permian sediments. These continental deposits, formed within alluvial, fl uvial, lacustrine and playa systems, comprise mudstones, sandstones and fanglomerates. Facies development during the Permian is similar in both basins, but the sediments of the Saint Affrique Basin are coarser than those of the Lodève Basin, which contains mainly clay- and siltstones. The tectonic development of the Saint Affrique and the Lodève basins is closely coupled with the tectonic evolution of the Variscan Massif Central, in particular, the Montagne Noire. Two major tectonic events have been recognised, which commences with the development of a macro scale sedimentary cycle. By using climate relevant indicators from geochemical, petrological and sedimentological analyses, six wet and dry climate cycles could be identifi ed. These have been used for the fi rst time to correlate the two basins resulting in a detailed correlation chart, especially in the upper part of the Permian where lithostratigraphic marker beds and biostratigraphic indicators are almost absent. The results also show that the assumption of a direct connection is not necessary for explaining the similarities in facies development, if both basins were controlled by the same climatic and tectonic infl uences. © 2011 E. Schweizerbart'sche Verlagsbuchhandlung.

PubMed | Birbal Sahni Institute of Palaeosciences, Steinmann Institute and University of Gdansk
Type: Journal Article | Journal: PloS one | Year: 2017

Indias unique and highly diverse biota combined with its unique geodynamical history has generated significant interest in the patterns and processes that have shaped the current distribution of Indias flora and fauna and their biogeographical relationships. Fifty four million year old Cambay amber from northwestern India provides the opportunity to address questions relating to endemism and biogeographic history by studying fossil insects. Within the present study seven extant and three fossil genera of biting midges are recorded from Cambay amber and five new species are described: Eohelea indica Stebner & Szadziewski n. sp., Gedanohelea gerdesorum Stebner & Szadziewski n. sp., Meunierohelea cambayana Stebner & Szadziewski n. sp., Meunierohelea borkenti Stebner & Szadziewski n. sp., and Meunierohelea orientalis Stebner & Szadziewski n. sp. Fossils of species in the genera Leptoconops Skuse, 1889, Forcipomyia Meigen, 1818, Brachypogon Kieffer, 1899, Stilobezzia Kieffer, 1911, Serromyia Meigen, 1818, and Mantohelea Szadziewski, 1988 are recorded without formal description. Furthermore, one fossil belonging to the genus Camptopterohelea Wirth & Hubert, 1960 is included in the present study. Our study reveals faunal links among Ceratopogonidae from Cambay amber and contemporaneous amber from Fushun, China, Eocene Baltic amber from Europe, as well as the modern Australasian and the Oriental regions. These findings imply that faunal exchange between Europe, Asia and India took place before the formation of Cambay amber in the early Eocene.

Kuhl G.,Steinmann Institute | Rust J.,Steinmann Institute
Palaontologische Zeitschrift | Year: 2010

The arthropod Mimetaster hexagonalis Gürich, 1931 from the Lower Devonian Hunsrück Slate (Germany) is re-described. With 123 available individuals, M. hexagonalis is the most abundant non-trilobite arthropod from this Lagerstätte. New (as well as old) specimen material shows new morphological features of M. hexagonalis. The ontogeny is described based on three juvenile specimens. The growth mode is similar to that in the marrellomorph Vachonisia rogeri Lehmann, 1955. The number of trunk segments increases from juvenile to adult. The mode of life of the arthropod is re-considered. The arthropod is considered to live in groups of several individuals. A mutualistic relationship with sponges of unknown systematic affinities is most likely. An ecological interaction with tentaculitoids is recognized but needs further investigation. The phylogenetic position of M. hexagonalis as a member of the Marrellomorpha is confirmed, but remains to be explored within the broader frame of euarthropod phylogeny. © 2010 Springer-Verlag.

Kroll H.,University of Munster | Kirfel A.,Steinmann Institute | Heinemann R.,University of Munster | Barbier B.,Steinmann Institute
European Journal of Mineralogy | Year: 2012

The thermal expansion of the Mg, Fe olivine solid-solution series was investigated from a total of 316 V(T) data, 141 of which were collected in this work by single-crystal X-ray diffraction over a wide range of temperatures. Functional forms currently in use for modelling thermal expansion are compared. The Kumar equation was found most useful for high-temperature extrapolation. With four parameters (θFo D, θ Fa D, kFo, kFa) fixed at values reported in the literature, it suffices to refine only two parameters (Q Fo 0, QFa 0) along with the composition-specific V(0 K) in order to describe the thermal expansion in the whole olivine series. The chosen data set is internally consistent as the thermal expansions of forsterite (Fo) and fayalite (Fa) are correctly predicted, even if only V(T) data of compositionally intermediate olivines are used. These results resolve the discrepancies between the thermal expansivities of Fo and Fa reported in the literature and are applied to a variety of thermophysical parameters with a significant dependence on the thermal expansion, as follows. (1) Experimental adiabatic bulk moduli KS of Fo are transformed into isothermal moduli KT so that both can be jointly fitted. (2) K S and KT values of Fa are deduced up to high temperatures assuming Fa to behave similarly to Fo with respect to the parameter αKT. (3) αKT of both Fo and Fa increases up to a temperature of 1.5 yD and then remains constant up to 4θD. (4) The respective Anderson-Grüneisen parameters of both compounds follow parallel paths, with δS steadily decreasing and δT becoming constant above 1.5 θD. (5) The isobaric and isochoric thermodynamic Grüneisen parameters γh are deduced for Fo and Fa. (6) The Mie-Grüneisen-Debye parameter γref MGD varies much less with temperature than the isochoric γth and may thus be approximated by a constant. (7) The thermal pressure ΔPth predicted by the Birch-Murnaghan equation-of-state (BM EoS) agrees with earlier experimental P-V-T results on Mg-rich olivines, according to which ΔP th depends on volume. (8) The thermodynamic (αKT) approach to ΔPth leads to small, however significant volume correction parameters. (9) The volume dependence of the isochoric heat capacity CV is deduced from a calculation of the entropy dependence on volume. Gillet-type polynomials yield CV as a function of temperature and compression. (10) The pressure dependence of α(T) between 0 and 15 GPa is determined from combining the BM EoS with the Kumar equation. The results were found to conform with a description using constant dT parameters. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung.

Kroll H.,University of Munster | Kirfel A.,Steinmann Institute | Heinemann R.,University of Munster
European Journal of Mineralogy | Year: 2014

The successful parameterization of the volume thermal expansion in the Mg,Fe olivine solid-solution series stimulated us to carry the analysis further in view of the orthorhombic symmetry of the olivines and thus augment the available thermophysical data. To this purpose we studied the three axial expansivities, αa,b,c, on the basis of the same body of data and the same model as used for our parameterization of the volume expansion. The results are applied to various thermophysical parameters that possess a significant dependence on αa,b,c. In particular, the temperature variations of the axial adiabatic and isothermal moduli (a), the axial thermodynamic Grüneisen parameters (b), and the axial isothermal Anderson-Grüneisen parameters (c) are obtained for both forsterite (Fo) and fayalite (Fa). This allowed us to also study the response of αa,b,c axial expansivities to pressure. Since Fo and Fa are isomorphous, it is striking that the axial thermophysical properties of Fo are distinctly less anisotropic than those of Fa. Whereas in Fo, both the axial compressibilities and the axial expansivities follow the same sequence, i.e. βT; b . βT, b βT, b and αb <αc <αa, respectively, this expectation is violated in Fa where αc <αa <αb above 400 K. It is shown that the different anisotropies of the expansivities and hence of the α-dependent thermophysical properties can be related to differing structural responses to heating. © 2014 E. Schweizerbart'sche Verlagsbuchhandlung.

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