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  2003 Best Student Paper in Planetary Sciences Award for Shoichi Itoh

  Ott, Ulrich (The Meteoritical Society, 2005-01-01)
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  2005 Leonard Medal for Joseph I. Goldstein

  Rubin, Alan (The Meteoritical Society, 2005-01-01)
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  Northwest Africa 011: A "eucritic" basalt from a non-eucrite parent body

  Floss, C.; Taylor, L. A.; Promprated, P.; Rumble, D. (The Meteoritical Society, 2005-01-01)

  We have carried out a detailed petrographic, mineralogical, and trace element study of Northwest Africa (NWA) 011. This meteorite bears many similarities to the eucrites it was initially identified with, although oxygen isotopic compositions rule out a genetic relationship. Like many eucrites, NWA 011 crystallized from a source with approximately chondritic proportions of REE, although a slightly LREE-enriched bulk composition with a small positive Eu anomaly, as well as highly fractionated Fe/Mg ratios and depleted Sc abundances (Korotchantseva et al. 2003), suggest that the NWA 011 source experienced some pyroxene and/or olivine fractionation. Thermal metamorphism resulted in homogenization of REE abundances within grains, but NWA 011 did not experience the intergrain REE redistribution seen in some highly metamorphosed eucrites. Despite a similarity in oxygen isotopic compositions, NWA 011 does not represent a basaltic partial melt from the acapulcoite/lodranite parent body. The material from which NWA 011 originated may have been like some CH or CB chondrites, members of the CR chondrite clan, which are all related through oxygen isotopic compositions. The NWA 011 parent body is probably of asteroidal origin, possibly the basaltic asteroid 1459 Magnya.
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  Noble gases in ten Nullarbor chondrites: Exposure ages, terrestrial ages, and weathering effects

  Schultz, L.; Franke, L.; Bevan, A. W. R. (The Meteoritical Society, 2005-01-01)

  We present concentration and isotopic composition of He, Ne, and Ar in ten chondrites from the Nullarbor region in Western Australia as well as the concentrations of 84Ke, 129Xe, and 132Xe. From the measured cosmogenic 14C concentrations (Jull et al. 1995), shielding-corrected production rates of 14C are deduced using cosmogenic 22Ne/21Ne ratios. For shielding conditions characterized by 22Ne/21Ne >1.10, this correction becomes significant and results in shorter terrestrial ages. The exposure ages of the ten Nullarbor chondrites are in the range of values usually observed in ordinary chondrites. Some of the meteorites have lost radiogenic gases as well as cosmogenic 3He. Most of the analyzed specimens show additional trapped Ar, Kr, and Xe of terrestrial origin. The incorporation of these gases into weathering products is common in chondrites from hot deserts.
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  Call for nominations: J. Lawrence Smith Medal

  The Meteoritical Society, 2005-01-01
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  Erratum

  The Meteoritical Society, 2005-01-01
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  Rumuruti chondrites: Noble gases, exposure ages, pairing, and parent body history

  Schultz, L.; Weber, H. W.; Franke, L. (The Meteoritical Society, 2005-01-01)

  In this paper, we present concentration and isotopic composition of the light noble gases He, Ne, and Ar as well as of 84Kr, 132Xe, and 129Xe in bulk samples of 33 Rumuruti (R) chondrites. Together with previously published data of six R chondrites, exposure ages are calculated and compared with those of ordinary chondrites. A number of pairings, especially between those from Northwest Africa (NWA), are suggested, so that only 23 individual falls are represented by the 39 R chondrites discussed here. Eleven of these meteorites, or almost 50%, contain solar gases and are thus regolithic breccias. This percentage is higher than that of ordinary chondrites, howardites, or aubrites. This may imply that the parent body of R chondrites has a relatively thick regolith. Concentrations of heavy noble gases, especially of Kr, are affected by the terrestrial atmospheric component, which resides in weathering products. Compared to ordinary chondrites, 129Xe/132Xe ratios of R chondrites are high.
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  From the Editors

  Riller, U.; Reimold, W. U. (The Meteoritical Society, 2005-01-01)
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  Iron oxidation state in impact glass from the K/T boundary at Beloc, Haiti, by high-resolution XANES spectroscopy

  Giuli, Gabriele; Eeckhout, Sigrid Griet; Paris, Eleonora; Koeberl, Christian; Pratesi, Giovanni (The Meteoritical Society, 2005-01-01)

  We 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]Fe^(3+) and [5]Fe^(3+), respectively. Thus, the XANES spectra can be interpreted as a mixture of [4]Fe^(2+), [5]Fe^(2+), [4]Fe^(3+), and [5]Fe^(3+). 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.
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  Chemical variation within fragments of Australasian tektites

  Son, T. H.; Koeberl, C. (The Meteoritical Society, 2005-01-01)

  In previous studies, intersample variation between compositions of different tektites from one particular group were studied and, in a few cases, major element variations within single tektites. No data for intra-sample trace element variations existed. Thus, we sectioned a Muong Nong-type tektite fragment from Vietnam and a splash-form tektite fragment from the Philippines into eleven and six pieces, respectively, and analyzed the individual fragments for major and trace element contents.The compositions obtained agree well with those found in previous studies, supporting argument that tektites have been derived from terrestrial upper crustal sediments. Chemical variations within the tektite fragments are present, but do not show any systematic trends, probably reflecting incomplete mixing of parent rocks. The intra-sample heterogeneity of the Muong Nong-type tektite is more pronounced than that in the philippinite. For the Muong Nong-type tektite, the intra-sample variation in the trace element contents is higher than that for the major elements, again reflecting target rock properties. For the philippinite the intra-sample variations mostly do not exceed the limits imposed by the precision of the analytical data, confirming that the splash form tektites are indeed well homogenized.
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  Book Review: Meteorite Impact! The Danger from Space and South Africa's Mega-impact, the Vredefort Structure, W. U. Reimold, R. L. Gibson

  King, D. T. (The Meteoritical Society, 2005-01-01)
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  Effects of asteroid and comet impacts on habitats for lithophytic organisms—A synthesis

  Cockell, Charles S.; Lee, Pascal; Broady, Paul; Lim, Darlene S. S.; Osinski, Gordon R.; Parnell, John; Koeberl, Christian; Pesonen, Lauri; Salminen, Johanna (The Meteoritical Society, 2005-01-01)

  Asteroid and comet impacts can have a profound influence on the habitats available for lithophytic microorganisms. Using evidence from the Haughton impact structure, Nunavut, Canadian High Arctic, we describe the role of impacts in influencing the nature of the lithophytic ecological niche. Impact-induced increases in rock porosity and fracturing can result in the formation of cryptoendolithic habitats. In some cases and depending upon the target material, an increase in rock translucence can yield new habitats for photosynthetic cryptoendoliths. Chasmoendolithic habitats are associated with cracks and cavities connected to the surface of the rock and are commonly increased in abundance as a result of impact bulking. Chasmoendolithic habitats require less specific geological conditions than are required for cryptoendolithic habitats, and their formation is likely to be common to most impact events. Impact events are unlikely to have an influence on epilithic and hypolithic habitats except in rare cases, where, for example, the formation of impact glasses might yield new hypolithic habitats. We present a synthetic understanding of the influence of asteroid and comet impacts on the availability and characteristics of rocky habitats for microorganisms.
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  A case study of impact-induced hydrothermal activity: The Haughton impact structure, Devon Island, Canadian High Arctic

  Osinski, Gordon R.; Lee, Pascal; Parnell, John; Spray, John G.; Baron, Martin (The Meteoritical Society, 2005-01-01)

  The well-preserved state and excellent exposure at the 39 Ma Haughton impact structure, 23 km in diameter, allows a clearer picture to be made of the nature and distribution of hydrothermal deposits within mid-size complex impact craters. A moderate- to low-temperature hydrothermal system was generated at Haughton by the interaction of groundwaters with the hot impact melt breccias that filled the interior of the crater. Four distinct settings and styles of hydrothermal mineralization are recognized at Haughton: a) vugs and veins within the impact melt breccias, with an increase in intensity of alteration towards the base; b) cementation of brecciated lithologies in the interior of the central uplift; degrees C) intense veining around the heavily faulted and fractured outer margin of the central uplift; and d) hydrothermal pipe structures or gossans and mineralization along fault surfaces around the faulted crater rim. Each setting is associated with a different suite of hydrothermal minerals that were deposited at different stages in the development of the hydrothermal system. Minor, early quartz precipitation in the impact melt breccias was followed by the deposition of calcite and marcasite within cavities and fractures, plus minor celestite, barite, and fluorite. This occurred at temperatures of at least 200 degrees C and down to ~100-120 degrees C. Hydrothermal circulation through the faulted crater rim with the deposition of calcite, quartz, marcasite, and pyrite, occurred at similar temperatures. Quartz mineralization within breccias of the interior of the central uplift occurred in two distinct episodes (~250 down to ~90 degrees C, and <60 degrees C). With continued cooling (<90 degrees C), calcite and quartz were precipitated in vugs and veins within the impact melt breccias. Calcite veining around the outer margin of the central uplift occurred at temperatures of ~150 degrees C down to <60 degrees C. Mobilization of hydrocarbons from the country rocks occurred during formation of the higher temperature calcite veins (>80 degrees C). Appreciation of the structural features of impact craters has proven to be key to understanding the distribution of hydrothermal deposits at Haughton.
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  Intra-crater sedimentary deposits at the Haughton impact structure, Devon Island, Canadian High Arctic

  Osinski, Gordon R.; Lee, Pascal (The Meteoritical Society, 2005-01-01)

  Detailed field mapping has revealed the presence of a series of intra-crater sedimentary deposits within the interior of the Haughton impact structure, Devon Island, Canadian High Arctic. Coarse-grained, well-sorted, pale gray lithic sandstones (reworked impact melt breccias) unconformably overlie pristine impact melt breccias and attest to an episode of erosion, during which time significant quantities of impact melt breccias were removed. The reworked impact melt breccias are, in turn, unconformably overlain by paleolacustrine sediments of the Miocene Haughton Formation. Sediments of the Haughton Formation were clearly derived from pre-impact lower Paleozoic target rocks of the Allen Bay Formation, which form the crater rim in the northern, western, and southern regions of the Haughton structure. Collectively, these field relationships indicate that the Haughton Formation was deposited up to several million years after the formation of the Haughton crater and that they do not, therefore, represent an immediate, post-impact crater lake deposit. This is consistent with new isotopic dating of impactites from Haughton that indicate an Eocene age for the impact event (Sherlock et al. 2005). In addition, isolated deposits of post-Miocene intra-crater glacigenic and fluvioglacial sediments were found lying unconformably over remnants of the Haughton Formation, impact melt breccias, and other pre-impact target rock formations. These deposits provide clear evidence for glaciation at the Haughton crater. The wealth and complexity of geological and climatological information preserved as intra-crater deposits at Haughton suggests that craters on Mars with intra-crater sedimentary records might present us with similar opportunities, but also possibly significant challenges.
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  Application of organic geochemistry to detect signatures of organic matter in the Haughton impact structure

  Parnell, John; Lee, Pascal; Osinski, Gordon R.; Cockell, Charles S. (The Meteoritical Society, 2005-01-01)

  Organic geochemistry applied to samples of bedrock and surface sediment from the Haughton impact structure detects a range of signatures representing the impact event and the transfer of organic matter from the crater bedrock to its erosion products. The bedrock dolomite contains hydrocarbon-bearing fluid inclusions which were incorporated before the impact event. Comparison of biomarker data from the hydrocarbons in samples inside and outside of the crater show the thermal signature of an impact. The occurrence of hydrocarbon inclusions in hydrothermal mineral samples shows that organic matter was mobilized and migrated in the immediate aftermath of the impact. The hydrocarbon signature was then transferred from bedrock to the crater-fill lacustrine deposits and present-day sediments in the crater, including wind-blown detritus in snow/ice. Separate signatures are detected from modern microbial life in crater rock and sediment samples. Signatures in Haughton crater samples are readily detectable because they include hydrocarbons generated by the burial of organic matter. This type of organic matter is not expected in crater samples on other planets, but the Haughton data show that, using very high resolution detection of organic compounds, any signature of primitive life in the crater rocks could be transferred to surface detritus and so extend the sampling medium.
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  Tectonics of complex crater formation as revealed by the Haughton impact structure, Devon Island, Canadian High Arctic

  Osinski, Gordon R.; Spray, John G. (The Meteoritical Society, 2005-01-01)

  The results of a systematic field mapping campaign at the Haughton impact structure have revealed new information about the tectonic evolution of mid-size complex impact structures. These studies reveal that several structures are generated during the initial compressive outward-directed growth of the transient cavity during the excavation stage of crater formation: (1) sub-vertical radial faults and fractures; (2) sub-horizontal bedding parallel detachment faults; and (3) minor concentric faults and fractures. Uplift of the transient cavity floor toward the end of the excavation stage produces a central uplift. Compressional inward-directed deformation results in the duplication of strata along thrust faults and folds. It is notable that Haughton lacks a central topographic peak or peak ring. The gravitational collapse of transient cavity walls involves the complex interaction of a series of interconnected radial and concentric faults. While the outermost concentric faults dip in toward the crater center, the majority of the innermost faults at Haughton dip away from the center. Complex interactions between an outward-directed collapsing central uplift and inward collapsing crater walls during the final stages of crater modification resulted in a structural ring of uplifted, intensely faulted (sub-) vertical and/or overturned strata at a radial distance from the crater center of ~5.0-6.5 km. Converging flow during the collapse of transient cavity walls was accommodated by the formation of several structures: (1) sub-vertical radial faults and folds; (2) positive flower structures and chaotically brecciated ridges; (3) rollover anticlines in the hanging-walls of major listric faults; and (4) antithetic faults and crestal collapse grabens. Oblique strike-slip (i.e., centripetal) movement along concentric faults also accommodated strain during the final stages of readjustment during the crater modification stage. It is clear that deformation during collapse of the transient cavity walls at Haughton was brittle and localized along discrete fault planes separating kilometer-size blocks.
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  Impactites of the Haughton impact structure, Devon Island, Canadian High Arctic

  Osinski, Gordon R.; Spray, John G.; Lee, Pascal (The Meteoritical Society, 2005-01-01)

  Contrary to the previous interpretation of a single allochthonous impactite lithology, combined field, optical, and analytical scanning electron microscopy (SEM) studies have revealed the presence of a series of impactites at the Haughton impact structure. In the crater interior, there is a consistent upward sequence from parautochthonous target rocks overlain by parautochthonous lithic (monomict) breccias, through allochthonous lithic (polymict) breccia, into pale grey allochthonous impact melt breccias. The groundmass of the pale grey impact melt breccias consists of microcrystalline calcite, silicate impact melt glass, and anhydrite. Analytical data and microtextures indicate that these phases represent a series of impact-generated melts that were molten at the time of, and following, deposition. Impact melt glass clasts are present in approximately half of the samples studied. Consideration of the groundmass phases and impact glass clasts reveal that impactites of the crater interior contain shock-melted sedimentary material from depths of >920 to <1880 m in the pre-impact target sequence. Two principal impactites have been recognized in the near-surface crater rim region of Haughton. Pale yellow-brown allochthonous impact melt breccias and megablocks are overlain by pale grey allochthonous impact melt breccias. The former are derived from depths of >200 to <760 m and are interpreted as remnants of the continuous ejecta blanket. The pale grey impact melt breccias, although similar to the impact melt breccias of the crater interior, are more carbonate-rich and do not appear to have incorporated clasts from the crystalline basement. Thus, the spatial distribution of the crater-fill impactites at Haughton, the stratigraphic succession from target rocks to allochthonous impactites, the recognition of large volumes of impact melt breccias, and their probable original volume are all analogous to characteristics of coherent impact melt layers in comparatively sized structures formed in crystalline targets.
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  Re-evaluating the age of the Haughton impact event

  Sherlock, Sarah C.; Kelley, Simon P.; Parnell, John; Green, Paul; Lee, Pascal; Osinski, Gordon R.; Cockell, Charles S. (The Meteoritical Society, 2005-01-01)

  We have re-evaluated the published age information for the Haughton impact structure, which was believed to have formed ~23 Ma ago during the Miocene age, and report new Ar/Ar laser probe data from shocked basement clasts. This reveals an Eocene age, which is at odds with the published Miocene stratigraphic, apatite fission track and Ar/Ar data; we discuss our new data within this context. We have found that the age of the Haughton impact structure is ~39 Ma, which has implications for both crater recolonization models and post-impact hydrothermal activity. Future work on the relationship between flora and fauna within the crater, and others at high latitude, may resolve this paradox.
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  Spaceborne visible and thermal infrared lithologic mapping of impact-exposed subsurface lithologies at the Haughton impact structure, Devon Island, Canadian High Arctic: Applications to Mars

  Tornabene, Livio L.; Moersch, Jeffrey E.; Osinski, Gordon R.; Lee, Pascal; Wright, Shawn P. (The Meteoritical Society, 2005-01-01)

  This study serves as a proof-of-concept for the technique of using visible-near infrared (VNIR), short-wavelength infrared (SWIR), and thermal infrared (TIR) spectroscopic observations to map impact-exposed subsurface lithologies and stratigraphy on Earth or Mars. The topmost layer, three subsurface layers and undisturbed outcrops of the target sequence exposed just 10 km to the northeast of the 23 km diameter Haughton impact structure (Devon Island, Nunavut, Canada) were mapped as distinct spectral units using Landsat 7 ETM+ (VNIR/SWIR) and ASTER (VNIR/SWIR/TIR) multispectral images. Spectral mapping was accomplished by using standard image contrast-stretching algorithms. Both spectral matching and deconvolution algorithms were applied to image-derived ASTER TIR emissivity spectra using spectra from a library of laboratory-measured spectra of minerals (Arizona State University) and whole-rocks (Ward's). These identifications were made without the use of a priori knowledge from the field (i.e., a "blind" analysis). The results from this analysis suggest a sequence of dolomitic rock (in the crater rim), limestone (wall), gypsum-rich carbonate (floor), and limestone again (central uplift). These matched compositions agree with the lithologic units and the pre-impact stratigraphic sequence as mapped during recent field studies of the Haughton impact structure by Osinski et al. (2005a). Further conformation of the identity of image-derived spectra was confirmed by matching these spectra with laboratory-measured spectra of samples collected from Haughton. The results from the "blind" remote sensing methods used here suggest that these techniques can also be used to understand subsurface lithologies on Mars, where ground truth knowledge may not be generally available.
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  Geological overview and cratering model for the Haughton impact structure, Devon Island, Canadian High Arctic

  Osinski, Gordon R.; Lee, Pascal; Spray, John G.; Parnell, John; Lim, Darlene S. S.; Bunch, Theodore E.; Cockell, Charles S.; Glass, Brian (The Meteoritical Society, 2005-01-01)

  The Haughton impact structure has been the focus of systematic, multi-disciplinary field and laboratory research activities over the past several years. Regional geological mapping has refined the sedimentary target stratigraphy and constrained the thickness of the sedimentary sequence at the time of impact to ~1880 m. New 40Ar-39Ar dates place the impact event at ~39 Ma, in the late Eocene. Haughton has an apparent crater diameter of ~23 km, with an estimated rim (final crater) diameter of ~16 km. The structure lacks a central topographic peak or peak ring, which is unusual for craters of this size. Geological mapping and sampling reveals that a series of different impactites are present at Haughton. The volumetrically dominant crater-fill impact melt breccias contain a calcite-anhydrite-silicate glass groundmass, all of which have been shown to represent impact-generated melt phases. These impactites are, therefore, stratigraphically and genetically equivalent to coherent impact melt rocks present in craters developed in crystalline targets. The crater-fill impactites provided a heat source that drove a post-impact hydrothermal system. During this time, Haughton would have represented a transient, warm, wet microbial oasis. A subsequent episode of erosion, during which time substantial amounts of impactites were removed, was followed by the deposition of intracrater lacustrine sediments of the Haughton Formation during the Miocene. Present-day intracrater lakes and ponds preserve a detailed paleoenvironmental record dating back to the last glaciation in the High Arctic. Modern modification of the landscape is dominated by seasonal regional glacial and niveal melting, and local periglacial processes. The impact processing of target materials improved the opportunities for colonization and has provided several present-day habitats suitable for microbial life that otherwise do not exist in the surrounding terrain.

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