Bruce F. Bohor (1932–2019)

Bruce Forbes Bohor, the 2011 Barringer Medalist of the Meteoritical Society (Glass, 2011), passed away at his home in Green Valley, Arizona, on November 17, 2019. Bruce is best known in our community for his discovery of shocked quartz in layers marking the Cretaceous–Tertiary (K-T, now called the Cretaceous–Paleogene, K-Pg) boundary in the central United States in the early 1980s, following the famous paper by Alvarez and co-authors in Science in 1980, in which they report geochemical evidence for an asteroid impact from K-Pg layers in Italy. The so-called asteroid impact hypothesis to explain the mass extinction at the K-Pg boundary had created quite a controversy in the early 1980s, as some researchers (unencumbered by knowledge of planetary processes such as impact cratering or shock effects) had contemplated multiple other explanations for the geochemical signals. Bruce F. Bohor (1937–2019) (photo at the Meteoritical Society meeting in Chicago, 2000, by D. Jalufka). Bruce and Leah Bohor at the Cretaceous–Tertiary boundary in Frontale, Marche Region, Italy, near the Osservatorio Geologico di Coldigioco, and not far from the site in Gubbio where the first evidence for an impact was discovered through geochemical data in 1980, and confirmed by Bruce Bohor by shock metamorphic studies in 1984. Another important publication was a second Science paper, in 1987, demonstrating the global distribution of the shocked minerals, all in the same coeval layer. His work, with colleagues, on the geographic variations in size of shocked quartz grains in K-Pg layers of various locations led to the proposal that the geographic variation in the maximum size of shocked quartz grains and the ratio between shocked and unshocked quartz grains suggested that the source crater is on or close to the North American plate, helping to narrow down possible locations of the source crater (which ultimately resulted in the discovery of the Chicxulub impact structure). In addition, the 1987 paper contained data that indicated that the impact was into continental crust rather than oceanic crust as previously proposed, and they that the geochemical evidence for a basaltic target rock was rather the result of a vaporized mafic chondritic projectile forming a major component of the layer, especially at the more distal sites. In the early 1990s, Bruce and colleagues studied zircons recovered from rocks in the Sudbury impact structure and documented a series of textures that they proposed represent different degrees of shock metamorphism. This sets the stage for using zircon as an impact indicator, and, in addition, they found that the degree of resetting of the U-Pb isotopic system correlates with the degree of shock metamorphism exhibited by the zircons. This helped to tie shocked zircons from all over the world to the Chicxulub structure and provided further evidence that other features, such as the Manson impact structure in Iowa, can be excluded. For his zircon studies, Bruce developed methods for etching zircons to reveal shock textures⁄features that are still used in such investigations. Further work concerned the distinction between the fireball and the fallout layers, or detailed studies of K-Pg boundary impact spherules, and where he was able, with his background in clay mineralogy, to provide a better understanding of the postimpact environment and the alteration of impact glasses. Bruce was born on May 4, 1932 in Chicago, Illinois, to Alexandria and Rudolph Bohor, who both were teachers in the Chicago school system. He received his BS from Beloit College in Wisconsin, his Master's Degree from the University of Indiana, and his PhD from the University of Illinois. As a geologist, he began his career at Conoco in Ponca City, Oklahoma, in the Production Research Division; he then moved to the Illinois State Survey in the Clay Mineral Section and then to the United States Geological Survey in Colorado. For his exceptional achievements in the study of impact processes, he was awarded the Barringer Medal at the Meteoritical Society meeting in Greenwich, UK, in 2011, among other awards and recognitions. After his retirement from the U.S. Geological Survey in 1995, he continued as an emeritus and volunteer at the USGS; during this time, he returned to earlier studies of minerals in both ancient and present-day Mayan potters in the Yucatan Peninsula of Mexico. He authored or coauthored more than 100 technical publications over his research career. Because of health issues, Bruce discontinued his active research and moved to Green Valley, Arizona in 2010. He is survived by his wife of 36 years, Leah, as well as by four children. Bruce was a very meticulous scientist, who did not rush work or conclusions, and it is interesting to note that his main research on impacts was done in just a bit more than a decade, yet will have long-lasting consequences. On a personal note, Bruce (with Leah) came to Vienna as a visiting professor at the University of Vienna in 1995, and even though teaching had not been part of his career before, he engaged very successfully with all our students. Bruce had a very dry but acute sense of humor and being with him always was an experience. We will miss him. Bohor, B. F., Foord, E. E., Modreski, P. J., and Triplehorn, D. M. (1984) Mineralogic evidence for an impact event at the Cretaceous-Tertiary boundary. Science 224:867–869. Bohor, B. F., Foord, E. E., and Ganapathy, R. (1986) Magnesioferrite from the Cretaceous-Tertiary boundary, Caravaca, Spain. Earth and Planetary Science Letters 81:57-66. Bohor, B. F., Modreski, P. J., and Foord, E. E. (1987) Shocked quartz in the Cretaceous-Tertiary boundary clays: Evidence for a global distribution. Science 236:705–709. Bohor, B. F., Triplehorn, D. M., Nichols, D. J., and Millard Jr, H. T. (1987) Dinosaurs, spherules, and the “magic” layer: A new KT boundary clay site in Wyoming. Geology 15:896–899. Bohor, B. F. (1990) Shock-induced microdeformations in quartz and other mineralogical indications of an impact event at the Cretaceous-Tertiary boundary. Tectonophysics 171:359–372. Pollastro, R. M., and Bohor, B. F. (1993) Origin and clay-mineral genesis of the Cretaceous/Tertiary boundary unit, western interior of North America. Clays and Clay Minerals 41:7–25. Bohor, B. F., and Triplehorn, D. M. (1993) Tonsteins: altered volcanic ash layers in coal-bearing sequences. GSA Special Paper 285. Boulder, Colorado: Geological Society of America. p. 44. Bohor, B. F., Betterton, W. J., and Krogh, T. E. (1993) Impact-shocked zircons: discovery of shock-induced textures reflecting increasing degrees of shock metamorphism. Earth and Planetary Science Letters 119:419–424. Bohor, B. F., and Glass, B. P. (1995) Origin and diagenesis of K/T impact spherules—from Haiti to Wyoming and beyond. Meteoritics 30:182–198. Kyte, F. T., and Bohor, B. F. (1995) Nickel-rich magnesiowiistite in Cretaceous/Tertiary boundary spherules crystallized from ultramafic, refractory silicate liquids. Geochimica et Cosmochimica Acta 59:4967–4974. Glass, B. P., Muenow, D. W., Bohor, B. F., and Meeker, G. P. (1997) Fragmentation and hydration of tektites and microtektites. Meteoritics & Planetary Science 32:333–341. Maruoka, T., Koeberl, C., Newton, J., Gilmour, I., and Bohor, B.F. (2002) Sulfur isotopic compositions across terrestrial Cretaceous-Tertiary (K-T) boundary successions. In Catastrophic events and mass extinctions: Impacts and beyond, edited by Koeberl C. and MacLeod K. G. GSA Special Paper 356. Boulder, Colorado: Geological Society of America. pp. 337–344. Maruoka, T., Koeberl, C., and Bohor, B. F. (2007) Carbon isotopic compositions of organic matter across continental Cretaceous–Tertiary (K–T) boundary sections: Implications for paleoenvironment after the K–T impact event. Earth and Planetary Science Letters 253:226–238. Arnold, D. E., Bohor, B. F., Neff, H., Feinman, G. M., Williams, P. R., Dussubieux, L., and Bishop, R. (2012) The first direct evidence of pre-Columbian sources of palygorskite for Maya Blue. Journal of Archaeological Science 39:2252–2260.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.