Mineralogic Evidence for an Impact Event at the Cretaceous-Tertiary Boundary

  title={Mineralogic Evidence for an Impact Event at the Cretaceous-Tertiary Boundary},
  author={Bruce Forbes Bohor and Eugene E. Foord and Peter J. Modreski and Don M. Triplehorn},
  pages={867 - 869}
A thin claystone layer found in nonmarine rocks at the palynological Cretaceous-Tertiary boundary in eastern Montana contains an anomalously high value of iridium. The nonclay fraction is mostly quartz with minor feldspar, and some of these grains display planar features. These planar features are related to specific crystallographic directions in the quartz lattice. The shocked quartz grains also exhibit asterism and have lowered refractive indices. All these mineralogical features are… 
Shocked Quartz in the Cretaceous-Tertiary Boundary Clays: Evidence for a Global Distribution
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 to confirm that an impact event at the CRETaceous-Tertiaries boundary distributed ejecta products in an earth-girdling dust cloud, as postulated by the Alvarez impact hypothesis.
Glass from the Cretaceous/Tertiary boundary in Haiti
Tektite-like glasses preserved at the Cretaceous/Tertiary boundary at Beloc in Haiti provide clear evidence of an impact event. The glass composition suggests that the impact occurred on a
Late Cretaceous and paroxysmal Cretaceous/Tertiary extinctions
The various geological signatures at Cretaceous/ Tertiary time including iridium and other associated elements, microspherules, and shock deformation features are compatible with the suggestion that
Geochemical delineation of the Cretaceous/Tertiary boundary in some New Zealand rock sequences
Abstract Calcium carbonate and other constituents of Upper Cretaceous and lower Tertiary rocks were determined at three localities in New Zealand where the Cretaceous/Tertiary boundary was believed
Emplacement of Cretaceous-Tertiary Boundary Shocked Quartz from Chicxulub Crater
Shock devolatilization and the expansion of carbon dioxide and water from impacted wet carbonate, producing a warm, accelerating fireball after the initial hot fireball of silicate vapor, may explain all three problems.
Shocked Quartz at the Triassic-Jurassic Boundary in Italy
Textural and stratigraphic observations support an interpretation of at least three closely spaced impacts at the end of the Triassic.
Impact production of C02 by the Cretaceous/Tertiary extinction bolide and the resultant heating of the Earth
EVIDENCE at the Cretaceous/Tertiary boundary suggests that the proposed 'extinction' bolide1 struck a continental or shallow marine terrane. This evidence includes: shocked quartz and feld-spar


An Iridium Abundance Anomaly at the Palynological Cretaceous-Tertiary Boundary in Northern New Mexico
An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater
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.
] makes a case for concentration of iridium in marine clays at the K-T ues for iridium of 5
  • Geol. Soc. Am. Spec. Pap
  • 1982
Gratz for their helpful comments; and C. Sanderson for laboratory assistance
    Bohor, paper presented at the 20th Annual Meeting of the Clay
    • Minerals Society,
    • 1983