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Chicxulub impact ejecta deposits in southern Quintana Roo, México, and central Belize

By
Kevin O. Pope
Kevin O. Pope
Geo Eco Arc Research, 16305 St. Mary's Church Road, Aquasco, Maryland 20608, USAPope: kpope@starband.net. Note: Pope and Ocampo contributed jointly to this paper.
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Adriana C. Ocampo
Adriana C. Ocampo
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA
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Alfred G. Fischer
Alfred G. Fischer
Department of Earth Sciences, University of Southern California, University Park, Los Angeles, California 90089, USA
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Francisco J. Vega
Francisco J. Vega
Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitária, México D.F. 04510, México
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Doreen E. Ames
Doreen E. Ames
Geological Survey of Canada, Natural Resources Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada
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David T. King, Jr.
David T. King, Jr.
Department of Geology, Auburn University, Auburn, Alabama 36849, USA
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Bruce W. Fouke
Bruce W. Fouke
Department of Geology, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, USA
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Richard J. Wachtman
Richard J. Wachtman
Department of Geology, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, USA
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Gunther Kletetschka
Gunther Kletetschka
Department of Physics, Catholic University of America, Washington D.C., USA; Institute of Geology, Academy of Sciences, Prague, Czech Republic, and NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
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Published:
January 01, 2005

Discoveries of Chicxulub impact ejecta of the Albion Formation in road cuts and quarries in southern Quintana Roo, México and Belize, broaden our understanding of ejecta depositional processes in large impacts. There are numerous new exposures of ejecta near the Río Hondo in Quintana Roo México, located at distances of 330–350 km from the center of the Chicxulub crater. A single ejecta exposure was discovered near Armenia in central Belize, 470 km from Chicxulub. The Albion Formation is composed of two lithostratigraphic units: the spheroid bed and diamictite bed, originally identified at Albion Island, Belize. The new spheroid bed exposures range from 2 to 5 m thick and are composed of altered glass fragments, accretionary lapilli, and pebble-sized carbonate clasts in a fine-grained calcite matrix. The base of the spheroid bed is exposed at Ramonal South in México and at Albion Island and Armenia in Belize, and at all three locations, the spheroid bed was deposited on a weathered karst land surface that had emerged in the Late Cretaceous. The new diamictite bed exposures are composed of altered glass fragments and carbonate clasts up to 9.0 × 3.2 m in size. In all but one of the new exposures, the diamictite bed extends to the surface with observed thicknesses up to 8 m. At Agua Dulce in México, the weathered top of the diamictite bed is overlain by thin-bedded Tertiary carbonates. No diamictite bed is found in Armenia, where the spheroid bed is overlain with a limestone conglomerate containing altered glass shards and shocked quartz. These discoveries indicate that ejecta are emplaced in large terrestrial impacts by at least two distinct flows: (1) an initial flow involving a volatile-rich cloud of fine debris similar to a volcanic pyroclastic flow, which extends >4.7 crater radii (the spheroid bed), and (2) a later flow of coarse debris that may not extend much beyond 3.6 crater radii (the diamictite bed). The former deposit we attribute to material entrained in the impact vapor plume, and the latter to the turbulent collapse of the ejecta curtain.

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GSA Special Papers

Large Meteorite Impacts III

Thomas Kenkmann
Thomas Kenkmann
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Friedrich Hörz
Friedrich Hörz
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Alex Deutsch
Alex Deutsch
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Geological Society of America
Volume
384
ISBN print:
9780813723846
Publication date:
January 01, 2005

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