Geochemistry and stratigraphy of the Cretaceous/Tertiary boundary impact ejecta.

Persistent Link:
http://hdl.handle.net/10150/186109
Title:
Geochemistry and stratigraphy of the Cretaceous/Tertiary boundary impact ejecta.
Author:
Hildebrand, Alan Russell.
Issue Date:
1992
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
An array of stratigraphic, chemical, isotopic, and mineralogical evidence indicates that an impact terminated the Cretaceous Period. The 180-km-diameter Chicxulub crater, which now lies buried on the Yucatan peninsula of Mexico, was probably formed by the impact. The impactor was probably a long-period comet. Shock devolatization of the thick carbonate/evaporite sequence impacted at Chicxulub probably led to a severe and long-lasting greenhouse warming and a prompt pulse of sulfuric acid rain. The fallout of crater ejecta formed two layers: a lower layer which varies in thickness following a power-law relation based on distance from the Chicxulub crater and an upper, globally-distributed, uniformly ∼3-mm-thick layer. The upper layer probably represents the fallout of condensates and entrained solid and liquid particles which were distributed globally by the impact fireball. The lower layer consists of brecciated rock and impact melt near the crater and largely altered tektites far from the crater. The clasts of this layer were probably ballistically transported. The Raton, New Mexico K/T boundary section preserves the fireball and ejecta layers in a coal-free nonmarine environment. Siderophile, chalcophile, and lithophile trace element anomalies occur similar to those found at marine K/T boundary localities. Soot occurs peaking in the 3-mm-thick fireball layer and the immediately overlying 3 mm of sediment, implying prompt burning of the Cretaceous forests. The Brazos River, Texas continental-shelf K/T sections preserve coarse boundary sediments which were probably produced by impact waves. Siderophile and chalcophile trace-element anomalies occur suggesting that the fireball layer and possibly part of the ejecta layer are interbedded with the coarse boundary sediments. The Beloc, Haiti deep-sea K/T sections preserve a thick ejecta sequence including altered and unaltered tektites and shocked minerals capped by the fireball layer. The thick K/T ejecta preserved at this and other nearby K/T localities require a source crater of Chicxulub's size and location. The composition of the tektites and shocked grains require an impact into recently extracted continental crust with a carbonate/evaporite component as found at the Chicxulub crater.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Geology, Stratigraphic -- Cretaceous.; Geochemistry.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Planetary Sciences; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Boynton, Bill

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleGeochemistry and stratigraphy of the Cretaceous/Tertiary boundary impact ejecta.en_US
dc.creatorHildebrand, Alan Russell.en_US
dc.contributor.authorHildebrand, Alan Russell.en_US
dc.date.issued1992en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractAn array of stratigraphic, chemical, isotopic, and mineralogical evidence indicates that an impact terminated the Cretaceous Period. The 180-km-diameter Chicxulub crater, which now lies buried on the Yucatan peninsula of Mexico, was probably formed by the impact. The impactor was probably a long-period comet. Shock devolatization of the thick carbonate/evaporite sequence impacted at Chicxulub probably led to a severe and long-lasting greenhouse warming and a prompt pulse of sulfuric acid rain. The fallout of crater ejecta formed two layers: a lower layer which varies in thickness following a power-law relation based on distance from the Chicxulub crater and an upper, globally-distributed, uniformly ∼3-mm-thick layer. The upper layer probably represents the fallout of condensates and entrained solid and liquid particles which were distributed globally by the impact fireball. The lower layer consists of brecciated rock and impact melt near the crater and largely altered tektites far from the crater. The clasts of this layer were probably ballistically transported. The Raton, New Mexico K/T boundary section preserves the fireball and ejecta layers in a coal-free nonmarine environment. Siderophile, chalcophile, and lithophile trace element anomalies occur similar to those found at marine K/T boundary localities. Soot occurs peaking in the 3-mm-thick fireball layer and the immediately overlying 3 mm of sediment, implying prompt burning of the Cretaceous forests. The Brazos River, Texas continental-shelf K/T sections preserve coarse boundary sediments which were probably produced by impact waves. Siderophile and chalcophile trace-element anomalies occur suggesting that the fireball layer and possibly part of the ejecta layer are interbedded with the coarse boundary sediments. The Beloc, Haiti deep-sea K/T sections preserve a thick ejecta sequence including altered and unaltered tektites and shocked minerals capped by the fireball layer. The thick K/T ejecta preserved at this and other nearby K/T localities require a source crater of Chicxulub's size and location. The composition of the tektites and shocked grains require an impact into recently extracted continental crust with a carbonate/evaporite component as found at the Chicxulub crater.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectGeology, Stratigraphic -- Cretaceous.en_US
dc.subjectGeochemistry.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplinePlanetary Sciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairBoynton, Billen_US
dc.identifier.proquest9313009en_US
dc.identifier.oclc703272803en_US
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