Explosive bolide impact designates the Cambrian Explosion, terminating the Cambrian event in New York

• Autores: Gerald M. Friedman
• Localización: Carbonates and Evaporites, ISSN 0891-2556, Vol. 22, Nº. 2, 2007, págs. 178-185
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • In 1978 as chairman of the Geology and Geography Section of the American Association for the Advancement of Science (AAAS) I planned a program for the 1980 annual convention in San Franscisco, California. The 1980 program included Louis W. Alvarez (1911�1988) who reported that an asteroid 10 kilometers in diameter struck the earth at the end of the Cretaceous. This conclusion resulted from Alvarez and colleagues discovery in Gubbio, Europe, of a centimeter-thick clay layer among carbonate rock containing iridium, a siderophile element, at the Cretaceous-Tertiary boundary. Involvement in this discussion stimulated my interest in the study of Taconic carbonate deposits of my home and university setting in the Troy, New York and contiguous areas dating to the base of the Cambrian. Analyses of the New York carbonate samples gave comparable iridium results to those from the end of the Cretaceous in Europe. From these iridium anomalies I concluded that an extraterrestrial source, namely an asteroid, produced the iridium anomalies in the Cambrian of New York.

    The studied Cambrian (Taconic) deposits of New York contain the highest87Sr/86Sr values of the past 2 b.y. Strontium is inferred to have been introduced by meteorite impact, yet meteorites generally have low 87/86 ratios. Stable isotope composition of the carbonate rock was likewise affected by meteorite impact. In summary the origin of the studied Cambrian carbonate deposits involved the "Cambrian Explosion".