Shocked Quartz in the Cretaceous-Tertiary Boundary Clays: Evidence for a Global Distribution

  title={Shocked Quartz in the Cretaceous-Tertiary Boundary Clays: Evidence for a Global Distribution},
  author={Bruce Forbes Bohor and Peter J. Modreski and Eugene E. Foord},
  pages={705 - 709}
Shocked quartz grains displaying planar features were isolated from Cretaceous- Tertiary boundary clays at five sites in Europe, a core from the north-central Pacific Ocean, and a site in New Zealand. At all of these sites, the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice. The grains display streaking indicative of shock in x-ray diffraction photographs and also show reduced refractive indices. These characteristic features of… 
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Bohor et al.1 have described shocked quartz, displaying one or more sets of planar elements indexed to rational crystallographic planes, associated with anomalous siderophile abundances at the
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Planar deformation features (PDFs) in quartz are a commonly used and well‐documented indicator of shock metamorphism in terrestrial rocks. The measurement of PDF orientations provides constraints on
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Solid-state silicon-29 magic-angle spinning nuclear magnetic resonance (silicon-29 MAS NMR) and X-ray diffraction of samples from the Cretaceous-Tertiary boundary layer at Raton, New Mexico, indicate that stishovite occurs in crystalline mineral grains.
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Mineralogic Evidence for an Impact Event at the Cretaceous-Tertiary Boundary
A thin claystone layer found in nonmarine rocks at the palynological Cretaceous-Tertiary boundary in eastern Montana contains an anomalously high value of iridium, suggesting a high velocity impact between a large extraterrestrial body and the earth.
Spheroids at the Cretaceous-Tertiary boundary are altered impact droplets of basaltic composition
Sand-size spheroids of K-feldspar in the Cretaceous-Tertiary (C-T) boundary clay at Caravaca, southern Spain, were interpreted by Smit and Klaver as having solidified from a melt resulting from the
Dynamic deformation of volcanic ejecta from the Toba caldera: Possible relevance to Cretaceous/Tertiary boundary phenomena
Plagioclase and biotite phenocrysts in ignimbrites erupted from the Toba caldera, Sumatra, show microstructures and textures indicative of shock stress levels higher than 10 GPa. Strong dynamic
Elemental Anomalies at the Cretaceous-Tertiary Boundary, Woodside Creek, New Zealand
The high concentration of iridium in the basal layer of the boundary, together with the enrichment of other siderophile elements supports the idea of an extraterrestrial source for much of the material.
Terminal Cretaceous Environmental Events
The geologic record of terminal Cretaceous environmental events indicates that iridium and other associated elements were not deposited instantaneously but during a time interval spanning some 10,000 to 100,000 years, which favors a mantle rather than meteoritic origin for these elements.
Extraterrestrial Cause for the Cretaceous-Tertiary Extinction
A hypothesis is suggested which accounts for the extinctions and the iridium observations, and the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the Cretaceous and Tertiary limestones, which are chemically similar to each other.
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Evidence indicates that the Cretaceous-Tertiary boundary is very sharp, and, within the limits of resolution, it is apparently synchronous at the various boundary localities. Arguments to the
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