Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub

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doi: 10.1016/j.epsl.2006.09.009
Author(s): Morgan, Joanna; Lana, Cristiano; Kearsley, Anton; Coles, Barry; Belcher, Claire; Montanari, Sandro; Díaz-Martínez, Enrique; Barbosa, Antonio; Neumann, Virginio
Author Affiliation(s): Primary:
Imperial College London, Earth Science and Engineering, London, United Kingdom
Natural History Museum, United Kingdom
Royal Holloway University of London, United Kingdom
Osservatorio Geologico di Coldigioco, Italy
Geological Survey of Spain, Spain
Universidade Federal de Pernambuco, Brazil
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 251(3-4), p.264-279. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 48 refs.; illus., incl. 4 tables, sketch map
Summary: The precise cause and timing of the Cretaceous-Paleocene (K-P) mass extinction 65 Ma ago remains a matter of debate. Many advocate that the extinction was caused by a meteorite impact at Chicxulub, Mexico, and a number of potential kill-mechanisms have been proposed for this. Although we now have good constraints on the size of this impact and chemistry of the target rocks, estimates of its environmental consequences are hindered by a lack of knowledge about the obliquity of this impact. An oblique impact is likely to have been far more catastrophic than a sub-vertical one, because greater volumes of volatiles would have been released into the atmosphere. The principal purpose of this study was to characterize shocked quartz within distal K-P ejecta, to investigate whether the quartz distribution carried a signature of the direction and angle of impact. Our analyses show that the total number, maximum and average size of shocked quartz grains all decrease gradually with paleodistance from Chicxulub. We do not find particularly high abundances in Pacific sites relative to Atlantic and European sites, as has been previously reported, and the size-distribution around Chicxulub is relatively symmetric. Ejecta samples at any one site display features that are indicative of a wide range of shock pressures, but the mean degree of shock increases with paleodistance. These shock- and size-distributions are both consistent with the K-P layer having been formed by a single impact at Chicxulub. One site in the South Atlantic contains quartz indicating an anomalously high average shock degree, that may be indicative of an oblique impact with an uprange direction to the southeast ±45°. The apparent continuous coverage of proximal ejecta in this quadrant of the crater, however, suggests a relatively high impact angle of >45°. We conclude that some of the more extreme predictions of the environmental consequences of a low-angle impact at Chicxulub are probably not applicable. Abstract Copyright (2006) Elsevier, B.V.
Year of Publication: 2006
Research Program: ODP Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; Atlantic Ocean; Cenozoic; Chicxulub Crater; Climate; Cretaceous; Ejecta; Framework silicates; Global; Grain size; Impact craters; Impact features; Impacts; K-T boundary; Leg 130; Leg 198; Leg 207; Leg 208; Lower Paleocene; Mass extinctions; Mesozoic; Metamorphism; ODP Site 1209; ODP Site 1258; ODP Site 1262; ODP Site 803; Oblique orientation; Ocean Drilling Program; Pacific Ocean; Paleocene; Paleogene; Quartz; SEM data; Shock metamorphism; Shocked quartz; Silica minerals; Silicates; Size distribution; Stratigraphic boundary; Tertiary; Upper Cretaceous; Volatiles
Coordinates: N323900 N324000 E1583100 E1583000
N022559 N022601 E1603229 E1603227
S271100 S271100 E0013500 E0013400
N092600 N092600 W0544400 W0544400
Record ID: 2007052445
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands