170,072 research outputs found
Book Review: Tektites in the Geological Record: Showers of Glass from the Sky by Joe McCall
No full textC. Koeberl: Tektites in the Geological Record: Showers of Glass from the Sky by Joe McCal
Catastrophic events & mass extinctions, impacts and beyond
No full textsponsors University of Vienna, Austria, Lunar and Planetary Institute ... [and others]international organizing and program committee, Walter Alvarez [and others] ; local organizing committee, Christian Koeberl [and others]PARTIAL CONTENTS: Global Distribution of Chicxulub Ejecta / P. Claeys, W. Kiessling, and W. Alvarez--Long-Term Environmental Perturbations Following a Late Eocene Impact? Evidence from the Massignano GSSP, Italy / R. Coccioni, D. Basso, H. Brinkhuis, S. Galeotti, S. Gardin, S. Monechi, and S. SpezzaJerri--Radio Search for Extrasolar Cometary Impacts at 22 GHz (Water MASER Emission) / C.B. Cosmovici, S. Pogrebenko, S. Montebugnoli, and G. Maccaferri--Comparison of the Chemical Composition Between Bosumtwi Rocks and Ivory Coast Tektites: Search for a Meteoritic Component in Impact Breccias / X. Dai, C. Koeberl, W.U. Reimold, and I. McDonal
Silicified cone-in-cone structures from Erfoud (Morocco): A comparison with impact-generated shatter cones
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Iron oxidation state in the Fe-rich layer and silica matrix of Libyan Desert Glass: a high-resolution XANES study
No full textLibyan Desert Glass (LDG) is an enigmatic type of glass that occurs in western Egypt in the Libyan Desert. Fairly convincing evidence exists to show that it formed by impact, although the source crater is currently unknown. Some rare samples present dark-colored streaks with variable amounts of Fe, and they are supposed to contain a meteoritic component. We have studied the iron local environment in an LDG sample by means of Fe K-edge high-resolution X-ray absorption near edge structure (XANES) spectroscopy to obtain quantitative data on the Fe oxidation state and coordination number in both the Fe-poor matrix and Fe-rich layers. The pre-edge peak of the high-resolution XANES spectra of the sample studied displays small but reproducible variations between Fe-poor matrix and Fe-rich layers, which is indicative of significant changes in the Fe oxidation state and coordination number. Comparison with previously obtained data for a very low-Fe sample shows that, while iron is virtually all trivalent and in tetrahedral coordination ([4]Fe3+) in the low-Fe sample, the sample containing the Fe-rich layers display a mixture of tetra-coordinated trivalent iron ([4]Fe3+) and penta-coordinated divalent iron ([5]Fe2+), with the Fe in the Fe-rich layer being more reduced than the matrix. From these data, we conclude the following: a) the significant differences in the Fe oxidation state between LDG and tektites, together with the wide intra-sample variations in the Fe-oxidation state, confirm that LDG is an impact glass and not a tektite-like glass; b) the higher Fe content, coupled with the more reduced state of the Fe, in the Fe-rich layers suggests that some or most of the Fe in these layers may be directly derived from the meteoritic projectile and that it is not of terrestrial origin
40Ar/39Ar dating of a Langhian biotite-rich clay layer in the pelagic sequence of the Cònero Riviera, Ancona, Italy.
No full textIron oxidation state in impact glass from the K/T boundary at Beloc, Haiti, by high-resolution XANES spectroscopy
No full textWe examined the local iron environment in nine impact glasses from the Cretaceous-
Tertiary (K/T) boundary section at Beloc, Haiti, which formed as the result of impact melting during
the Chicxulub impact event. The samples have been analyzed by Fe K-edge high-resolution X-ray
absorption near edge structure (XANES) spectroscopy to obtain data on both the Fe oxidation state
and the coordination number. The pre-edge peak of our high-resolution XANES spectra display
noticeable variations indicative of significant changes in the Fe oxidation state spanning a wide range
from about 20 to 75 mol% trivalent Fe. All data plot along the same trend, falling between two mixing
lines joining a point calculated as the mean of a group of tektites studied so far (consisting of four- and
five-coordinated Fe2+) to [4]Fe3+ and [5]Fe3+, respectively. Thus, the XANES spectra can be interpreted
as a mixture of [4]Fe2+, [5]Fe2+, [4]Fe3+, and [5]Fe3+. There is no evidence for six-fold coordinated Fe;
however, its presence in small amounts cannot be excluded from XANES data alone. Our
observations can be explained by two possible scenarios: either these impact glasses formed under
very reducing conditions and, because of their small size, were easily oxidized in air while still
molten, or they formed under a variety of different oxygen fugacities resulting in different Fe
oxidation states. In the first case, the oxidation state and coordination number would imply similar
formation conditions as splash-form tektites, followed by progressive oxidation
Melting and cataclastic features in shatter cones in basalt from the Vista Alegre impact structure, Brazil
No full textAbstract–Shatter cones are one of the most widely recognized pieces of evidence for
meteorite impact events on Earth, but the process responsible for their formation is still
debated. Evidence of melting on shatter cone surfaces has been rarely reported in the
literature from terrestrial impact craters but has been recently observed in impact
experiments. Although several models for shatter cones formation have been proposed, so
far, no one can explain all the observed features. Shatter cones’ from the Vista Alegre
impact structure, Brazil, formed in fine-grained basalt of the Jurassic-Cretaceous Serra
Geral Formation (Parana large igneous province). A continuous quenched melt film,
consisting of a crystalline phase, mica, and amorphous material, decorates the striated
surface. Ultracataclasites, containing subrounded pyroxene clasts in an ultrafine-grained
matrix, occur subparallel to the striated surface. Several techniques were applied to
characterize the crystalline phase in the melt, including Raman spectroscopy and
transmission electron microscopy. Results are not consistent with any known mineral, but
they do suggest a possible rare or new type of clinopyroxene. This peculiar evidence of
melting and cataclasis in relation with shatter cone surfaces is interpreted as the result of
tensile fracturing at the tip of a fast propagating shock-induced rupture, which led to the
formation of shatter cones at the tail of the shock front, likely during the early stage of the
impact events
The Late Eocene Earth: Hot House, Ice House, and Impacts – Abstracts with Program and Field Trip Guide.
No full textA Geological Society of America Penrose Conference, Ancona, Italy
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