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Title: Abrupt appearance of shocked quartz at the Cretaceous-Tertiary boundary, Raton Basin, Colorado and New Mexico

Abstract

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 themore » 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.« less

Authors:
;
Publication Date:
Research Org.:
Geological Survey, Denver, CO (USA)
OSTI Identifier:
6461096
Report Number(s):
CONF-8510489-
Journal ID: CODEN: GAAPB
Resource Type:
Conference
Journal Name:
Geol. Soc. Am., Abstr. Programs; (United States)
Additional Journal Information:
Journal Volume: 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 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)

Citation Formats

Izett, G A, and Pillmore, C L. Abrupt appearance of shocked quartz at the Cretaceous-Tertiary boundary, Raton Basin, Colorado and New Mexico. United States: N. p., 1985. Web.
Izett, G A, & Pillmore, C L. Abrupt appearance of shocked quartz at the Cretaceous-Tertiary boundary, Raton Basin, Colorado and New Mexico. United States.
Izett, G A, and Pillmore, C L. Tue . "Abrupt appearance of shocked quartz at the Cretaceous-Tertiary boundary, Raton Basin, Colorado and New Mexico". United States.
@article{osti_6461096,
title = {Abrupt appearance of shocked quartz at the Cretaceous-Tertiary boundary, Raton Basin, Colorado and New Mexico},
author = {Izett, G A and Pillmore, C L},
abstractNote = {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.},
doi = {},
journal = {Geol. Soc. Am., Abstr. Programs; (United States)},
number = ,
volume = 17,
place = {United States},
year = {1985},
month = {1}
}

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