Abrupt appearance of shocked quartz at the Cretaceous-Tertiary boundary, Raton Basin, Colorado and New Mexico
Unique quartz grains as large as 0.5 mm and having up to 6 sets of closely spaced microfractures (CSM) occur at the palynological K-T boundary at 9 scattered sites from Trinidad, Colorado, south 50 km to Raton, New Mexico. Similar quartz grains at the K-T boundary in Montana and Europe were ascribed a shock-metamorphic origin by B. Bohor and colleagues in 1984-85. In the Raton Basin, quartz grains with CSM are concentrated at the top and base of a 2.5-cm-tick kaolinite bed in a nonmarine sequence of somber-colored sandstone, siltstone, shale, and coal. No quartz grains with CSM have yet been found below the K-T bed in the Raton Basin, but a few have been found about 25 cm below the K-T bed at Brownie Butte, Montana. Most quartz grains having CSM are single optical units, but some are compound grains showing sutured boundaries (metaquartzite). Nearly all quartz grains with CSM have refractive indices and birefringence normal for quartz which suggests they formed at not more than 100 kb (low shock); however, a few have n/sub 0/ lowered to 1.538, but have normal birefringence. About half of 100 measured CSM in quartz make an angle of 15-25 degrees with the base (0001). The K-T kaolinite bed in the Raton Basin contains anomalously large amounts of Ir and is possibly coeval with marine, Ir-bearing K-T claystone beds in Europe described in 1980 by W. Alvarez and his associated who suggested they formed when a large bolide struck the Earth causing mass extinction of certain animals and plants. The shocked quartz and metaquartzite at the K-T boundary is compelling evidence that a bolide struck an onland-area of quartz-rich crustal rocks--not in an ocean.
- Research Organization:
- Geological Survey, Denver, CO (USA)
- OSTI ID:
- 6461096
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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GEOLOGIC FRACTURES
ORIGIN
QUARTZ
SURFACE PROPERTIES
COLORADO
CRETACEOUS PERIOD
IMPACT SHOCK
MICROSTRUCTURE
MINERALOGY
NEW MEXICO
ROCK MECHANICS
SANDSTONES
SEDIMENTARY BASINS
SEDIMENTS
TERTIARY PERIOD
CENOZOIC ERA
CHALCOGENIDES
CRYSTAL STRUCTURE
FEDERAL REGION VI
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC STRUCTURES
MECHANICS
MESOZOIC ERA
MINERALS
NORTH AMERICA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
ROCKS
SEDIMENTARY ROCKS
SILICON COMPOUNDS
SILICON OXIDES
USA
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)