Chicxulub Crater source for shocked zircon crystals from the Cretaceous-Tertiary boundary layer, Saskatchewan; evidence from new U-Pb data

• Published in: Geology (Boulder) 1995-03, Vol.23 (3), p.281-284
• Main Authors: Kamo, Sandra L, Krogh, Thomas E
• Format: Article
• Language: English
• Subjects: absolute age; Canada; Cenozoic; Chicxulub Crater; clastic sediments; clay; Cretaceous; Crystals; dates; ejecta; Geochronology; Geology; impacts; K-T boundary; lower Paleocene; Mesozoic; metamorphism; Meteors & meteorites; Minerals; Morgan Creek Saskatchewan; nesosilicates; new data; orthosilicates; Paleocene; Paleogene; Rock Creek Saskatchewan; Saskatchewan; sediments; SEM data; shock metamorphism; silicates; south-central Saskatchewan; stratigraphic boundary; Stratigraphy; Tertiary; U/Pb; Upper Cretaceous; Western Canada; zircon; zircon group
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/0091-7613(1995)023<0281:CCSFSZ>2.3.CO;2

New U-Pb data for five of six individual shocked zircon grains from the Cretaceous-Tertiary (K-T) boundary fireball layer, Rock Creek site, south-central Saskatchewan, yield a source age of 548±6 Ma. The collinear data points are variably discordant in proportion to the intensity of shock metamorphism exhibited by each zircon. The age and zircon shock features establish a strong temporal and genetic link with K-T distal ejecta from the fireball layer at the Berwind canyon site in the Raton basin, Colorado, where texturally similar zircons from a previous study gave an indistinguishable source age of 544 ± 5 Ma. These ages are in agreement with independent ages obtained from a previous study for single shocked zircons from the Chicxulub crater, Mexico, and from Beloc, Haiti. The U-Pb zircon data unequivocally support a meteorite impact origin for the global K-T boundary layer and imply that the Chicxulub crater is the sole North American target source.