A new Cretaceous-Tertiary boundary locality in the western Powder River basin, Wyoming: Biological and geological implications

D. J. Nichols; J. L. Brown; M. Attrep; C. J. Orth

doi:10.1016/0195-6671(92)90026-m

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A new Cretaceous-Tertiary boundary locality in the western Powder River basin, Wyoming: Biological and geological implications

D. J. Nichols·J. L. Brown·M. Attrep·C. J. Orth

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Abstract

A newly discovered Cretaceous-Tertiary (K-T) boundary locality in the western Powder River basin, Wyoming, is characterized by a palynologically defined extinction horizon, a fern-spore abundance anomaly, a strong iridium anomaly, and shock-metamorphosed quartz grains. Detailed microstratigraphic analyses show that about one third of the palynoflora (mostly angiosperm pollen) disappeared abruptly, placing the K-T boundary within a distinctive, 1- to 2-cm-thick claystone layer. Shocked quartz grains are concentrated at the top of this layer, and although fern-spore and iridium concentrations are high in this layer, they reach their maximum concentrations in a 2-cm-thick carbonaceous claystone that overlies the boundary claystone layer. The evidence supports the theory that the K-T boundary event was associated with the impact of an extraterrestrial body or bodies. Palynological analyses of samples from the K-T boundary interval document extensive changes in the flora that resulted from the boundary event. The palynologically and geochemically defined K-T boundary provides a unique time-line of use in regional basin analysis.

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Cretaceous Research Article

Source-reported bounding extent: 42.77342548065519° to 44.968647289949615° latitude; -107.18966568341567° to -104.73512272902725° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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D. J. Nichols, J. L. Brown, M. Attrep, C. J. Orth. 1992. A new Cretaceous-Tertiary boundary locality in the western Powder River basin, Wyoming: Biological and geological implications. https://doi.org/10.1016/0195-6671(92)90026-m

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