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| Titel |
A Detailed Study of the Drastic Worldwide Climatic Change by the Cretaceous/Paleogene (K/T)-Impact of Chicxulub |
| VerfasserIn |
Anton Preisinger, Selma Aslanian, Fritz Grass, Roman Beigelbeck, Johann Wernisch |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042226
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| Zusammenfassung |
| The impact of Chicxulub (Yucatan, Mexico) was a global event exhibiting a short-time
(fallout) and a long-time (boundary clay) sedimentation of the K/T-boundary [1].
The fallout is mainly characterized by iridium, Ni-Cr-rich magnesia-ferrite spinels
(K/T-spinels), spherules, as well as shocked quartzes. The amount of the sediments and their
distribution depend on the distance from the impact crater. The Cretaceous/Paleogene
(K/T) boundaries at three different locations namely Caravaca (Spain), Cerbara
(Italy), and Bjala (Bulgaria) have been well analyzed. About 65 million years ago,
they were located at the distances from the impact crater ~6000Â km, ~7500Â km,
and ~8800Â km, respectively. The boundary clay is characterized by transported
minerals like quartzes and feldspars, authigenically formed minerals, as well as
biominerals like Mg-calcites and greigites (Fe3S4). The samples were analyzed by
scanning X-ray diffractometry (Bruker Analytical X-ray System), scanning electronic
microscopy (XL30, ESEM-Philips), neutron activation analyses, Delta13C and Delta18O
analyses, and the determination of nannofossils and foraminifera. Owing to the
Earth’s rotation, the analyzed samples lie along a great circle (crossing the equator
under an angle of ~23Ë ) which covers Chicxulub, Caravaca, Cerbara, and Bjala
indicating the existence of only a single impact. The study of this K/T-boundary by
means of high resolution scanning X-ray diffractometry in combination with the
scanning electron microscopy and neutron activation analyzes revealed the time
dependency of the K/T-event in the fallout as well as in the boundary clay. The
biomineralization of sulfate-reducing bacteria by greigites provided the duration of the
sulfuric acid rain. The reoccurrence of algae is indicated by the appearance of Mg-calcite
at the end of the boundary clay. The K/T-spinels were formed on the nucleus of
metallic iridium [2]. They were built in the mesosphere (in a height of about 100Â km)
and grew during the fall to the Earth’s surface by forming ferrimagnetic twins,
which were etched by the H2SO4 content of the atmosphere. We developed an
extensive mathematical model incorporating all relevant physical effects (particle
growth, pressure dependence of the atmosphere, fluid resistance, centrifugal and
coriolis forces, etc.) in order to study the development of the particles during the
fall. For Caravaca, the shortest flight time for the Iridium fallout is approximately
6.5Â days, while the shortest flight time for the ejecta near Chicxulub last only a few
hours.
The K/T-impact took place about 65 million years ago in a sea depth of more than
2000Â m. Consequently, the impact heated up the sea water and the water molecules reacted
with the CaCO3, CaSO4, and the silicates down to a depth of 28Â km. This hydrothermal
reaction reduced the melt temperature significantly, especially those of silicates. Therefore,
the pyroxenes and plagioclases changed to clay minerals.
The sedimentation rate of Chron 29RK is about twice than that of Chron 29RT, which
equals to Chron 29N in Caravaca, Cerbara, and Bjala. The precession cycles of Chron 29R
and Chron 29N are 22.5Â kyears. The time span of the K/T-boundaries between Chron 29RK
and Chron 29RT is worldwide about 1Â kyear.
Concluding all our results, only one big impact took place at Chicxulub (Yucatan,
Mexico) about 65 million years ago and caused, during the formation of the K/T-boundary, a
worldwide climatic change.
References:
[1] Eder, G. and Preisinger, A.: Zeitstruktur globaler Ereignisse veranschaulicht an der
Kreide/Terziär-Grenze. Naturwissenschaften, Band 74, 35-37, 1987.
[2] Preisinger, A., Aslanian, S., Brandstätter, F., Grass, F., Stradner, H., and
Summesberger, H.: Cretaceous-Tertiary profile, rhythmic deposition, and geomagnetic
polarity reversals of marine sediments near Bjala, Bulgaria. Geo. Soc. Amer. special paper
356, 229-312, 2002. |
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