Cathodoluminescence petrography and isotope geochemistry of KT impact ejecta deposited 360 km from the Chicxulub crater, at Albion Island, Belize |
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| Authors: | Bruce W Fouke Aubrey L Zerkle Walter Alvarez† Kevin O Pope‡ Adriana C OcampO§ Richard J Wachtman Jose Manuel Grajales Nishimura¶ Phillipe Claeys & Alfred G Fischer†† |
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| Institution: | Department of Geology, University of Illinois, 245 Natural History Building, 1301 W. Green Street, Urbana, IL 61801, USA (E-mail:;), Earth and Planetary Science, University of California Berkeley, 307 McCore Hall, Berkeley, CA 94720, USA,;Department of Geology and Geophysics, University of California, Berkeley, CA 94720, USA,;Jet Propulsion Laboratory, California Institute of Technology, MS183-601, 4800 Oak Grove, Pasadena, CA 91109, USA, and National Aeronautics and Space Administration, Headquarters, Code SD, Washington, DC 20546, USA,;Instituto Mexicano del Petróleo, Eje Lazaro Cardenas #152, DFCP 07730, Mexico,;Department of Geology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium,;Department of Earth Sciences, University of Southern California, 3651 University Avenue, Los Angeles, CA 90089, USA |
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| Abstract: | The depositional and diagenetic history of Cretaceous–Tertiary (KT) impact ejecta deposited 360 km from the Chicxulub crater, at Albion Island, Belize, has been investigated using integrated cathodoluminescence and isotopic analyses. A quarry exposes 26 m of Upper Cretaceous Barton Creek Formation dolomitized marine limestone overlain by 16 m of dolomitized Albion Formation impact ejecta. The Albion Formation consists of a lower fine‐grained ≈1‐m‐thick spheroid bed and an upper 15‐m‐thick coarse conglomeratic diamictite bed. A 14‐event paragenetic sequence has been documented and used as a temporal framework to interpret chemostratigraphic trends in bulk rock δ18O, δ13C and 87Sr/86Sr. The uppermost surface of the Barton Creek Formation was subaerially exposed before the KT impact, as indicated by a brecciated palaeosol that caps upsection decreases in δ13C and δ18O. Small 1‐cm‐diameter spheroids in the spheroid bed exhibit vermicular crystalline textures but lack the concentric zonations common to accretionary lapilli. These spheroids are hypothesized originally to have been impact glass or reactive Ca and Mg oxide dusts that adhered to water vapour particles condensing from the cooling impact vapour cloud. The spheroids were dolomitized soon after deposition. The earliest dolomitization in the matrix sediments of the Albion Formation was also post‐depositional, replacing clays formed by devitrification of impact glass. Dolomite and clay 87Sr/86Sr exhibit a distinct symmetrical distribution in the spheroid bed ranging from 0·707745 to 0·707872. Although unproven, this may represent primary changes in the chemical composition of the impact glass. The limestone clasts in the diamictite bed were dolomitized before the KT impact and exhibit upsection decreases in bulk rock 87Sr/86Sr. This suggests that the clasts were excavated from strata equivalent in age or older than the Barton Creek Formation at locations closer to, or in, the Chicxulub crater. |
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| Keywords: | Carbonates cathodoluminescence Chicxulub Cretaceous–Tertiary (KT) boundary event ejecta isotopes |
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