Book Review: The Universe Unveiled: Instruments and Images through History, B. Stephenson, M. Bolt, A. F. Friedman (Eds.)
AuthorKelley, M. S.
MetadataShow full item record
CitationKelley, M. S. (2002). Book Review: The Universe Unveiled: Instruments and Images through History, B. Stephenson, M. Bolt, A. F. Friedman (Eds.). Meteoritics & Planetary Science, 37(1), 143-144.
PublisherThe Meteoritical Society
JournalMeteoritics & Planetary Science
DescriptionBook Review: The Universe Unveiled: Instruments and Images through History, B. Stephenson, M. Bolt, A. F. Friedman (Eds.). The Adler Planetarium and Astronomy Museum, Chicago, Illinois, USA, and Cambridge University Press, New York, New York, USA (2000).
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Boltysh, another end-Cretaceous impactKelley, S. P.; Gurov, E. (The Meteoritical Society, 2002-01-01)The Chixculub impact occurred at the Cretaceous/Tertiary (K/T) boundary, and although several other Late Cretaceous and Paleogene impact craters have, at times, been linked with the K/T boundary, isotope geochronology has demonstrated that all have significantly different ages. The currently accepted age of the 24 km diameter Boltysh crater, a K-Ar whole-rock age, places it in the Coniacian at 88 +/- 3 Ma. However, comprehensive Ar-Ar dating of a range of melt samples yields a mean age of 65.17 +/- 0.64 Ma, within errors of the K/T boundary. Several of the fresh samples exhibit signs of excess argon, but this seems to be concentrated in rapidly crystallized glass-rich samples. The Ar-Ar age confirms an earlier fission track measurement and thus two dating techniques have yielded an age within errors of the K/T boundary for this crater. Crucially, although the ages of Boltysh and Chixculub are within errors, they may not have formed synchronously. Craters of 24 km diameter occur much more commonly than impacts of Chixculub dimensions, but their proximity does raise the important question of how many impacts there might have been close to the K/T boundary.
Observations and interpretations at Vredefort, Sudbury, and Chicxulub: Towards an empirical model of terrestrial impact basin formationGrieve, R. A. F.; Reimold, W. U.; Morgan, J.; Riller, U.; Pilkington, M. (The Meteoritical Society, 2008-01-01)The structural, topographic and other characteristics of the Vredefort, Sudbury, and Chicxulub impact structures are described. Assuming that the structures originally had the same morphology, the observations/interpretations for each structure are compared and extended to the other structures. This does not result in any major inconsistencies but requires that the observations be scaled spatially. In the case of Vredefort and Sudbury, this is accomplished by scaling the outer limit of particular shock metamorphic features. In the case of Chicxulub, scaling requires a reasoned assumption as to the formation mechanism of an interior peak ring. The observations/interpretations are then used to construct an integrated, empirical kinematic model for a terrestrial peak-ring basin. The major attributes of the model include: a set of outward-directed thrusts in the parautochthonous rocks of the outermost environs of the crater floor, some of which are pre-existing structures that have been reactivated during transient cavity formation; inward-directed motions along the same outermost structures and along a set of structures, at intermediate radial distances, during transient cavity collapse; structural uplift in the center followed by a final set of radially outward-directed thrusts at the outer edges of the structural uplift, during uplift collapse. The rock displacements on the intermediate, inward and innermost, outward sets of structures are consistent with the assumption that a peak ring will result from the convergence of the collapse of the transient cavity rim area and the collapse of the structural uplift.
Non-impact origin of the crater-like structures in the Gilf Kebir area (Egypt): Implications for the geology of eastern SaharaOrti, L.; Di Martino, M.; Morelli, M.; Cigolini, C.; Pandeli, E.; Buzzigoli, A. (The Meteoritical Society, 2008-01-01)Several small crater-like structures occur in Gilf Kebir region (SW Egypt). It has been previously suggested that they could be the result of meteoritic impacts. Here we outline the results of our geological and geophysical survey in the area. The proposed impact origin for these structures is not supported by our observations and analyses, and we suggest an alternative interpretation. The crater-like structures in Gilf Kebir area are likely related to endogenic processes typical of hydrothermal vent complexes in volcanic areas which may reflect the emplacement of subvolcanic intrusives.