[meteorite-list] Paleocene-Eocene Thermal Maximum Impact Disputed

From: Paul <bristolia_at_meteoritecentral.com>
Date: Thu, 27 Mar 2008 13:27:05 -0700 (PDT)
Message-ID: <438478.78213.qm_at_web36208.mail.mud.yahoo.com>

Back in 2003, it was argued that ?an abrupt and distinct
change in magnetic grain size (from multidomain (MD) to
single domain (SD) magnetite) across? a negative carbon
isotope excursion and initial Paleocene-Eocene Thermal
Maximum sediments underlying the New Jersey
continental margin is indicative of an extraterrestrial
impact at the beginning of the Paleocene-Eocene Thermal
Maximum. Kent et al. (2003) argued that the SD magnetite
condensed from an impact ejecta plume. However, this
conclusion has been disputed by three publications, which
where published in 2007. They are:

1. Kopp, R. E., and others, 2007, Magnetofossil spike during the
Paleocene-Eocene thermal maximum: Ferromagnetic resonance,
rock magnetic, and electron microscopy evidence from Ancora,
New Jersey, United States. Paleoceanography vol. 22, PA4103,
doi:10.1029/2007PA001473, 2007

http://www.agu.org/pubs/crossref/2007/2007PA001473.shtml

http://www.gps.caltech.edu/~jkirschvink/pdfs/KoppEtAlEoceneMagnetofossilSpike2007.pdf

In part the abstract states:

?This result, the first identification of ancient biogenic magnetite
using FMR, argues that the anomalous magnetic properties of
the PETM sediments are not produced by an impact. They
instead reflect environmental changes along the eastern margin of
North America during the PETM that led to enhanced production
and/or preservation of magnetofossils.?

2. Lippert, P. C., and Zachos, J. C., 2007, A biogenic origin for
anomalous fine-grained magnetic material at the Paleocene-
Eocene boundary at Wilson Lake, New Jersey. Paleoceanography.
vol. 22, VOL. 22, PA4104, doi:10.1029/2007PA001471, 2007

http://www.agu.org/pubs/crossref/2007/2007PA001471.shtml

http://www.es.ucsc.edu/~jzachos/pubs/Lippert_Zachos_2007.pdf

In part the abstract states:

?One suggested source for the carbon, a cometary impactor, is
based on the sudden appearance and high concentration of single-
domain (SD) magnetite in Paleocene-Eocene (P-E) boundary
cores from the North Atlantic continental margin.? and

?Our results show a similar increase in SD material but
demonstrate that the magnetic material has a biogenic origin.?

3. Kopp, R. E., 2007, The identification and interpretation of
microbial biogeomagnetism. Unpublished PhD dissertation,
California Institute of Technology, Pasadena, California.

http://etd.caltech.edu/etd/available/etd-04122007-135320/

?Anomalous magnetic properties of clay deposited in the Atlantic
Coastal Plain, New Jersey, during the Paleocene/Eocene Thermal
Maximum (PETM) led previous authors to speculate that an
extraterrestrial impact triggered the PETM. Reexamination of
the clay using FMR and transmission electron microscopy
reveals instead that the clay hosts abundant magnetofossils. The
first identification of ancient biogenic magnetite using FMR
indicates that the anomalous magnetic properties of PETM
sediments were not produced by an impact, but instead reflect
paleoenvironmental changes along the western North Atlantic
margin.?

There is a related abstract at:

http://gsa..confex.com/gsa/2007AM/finalprogram/abstract_123753.htm

Reference Cited:

Kent, D. V., B. S. Cramer, L. Lanci, D. Wang, J. D. Wright,
and R. Van der Voo, 2003, A case for a comet impact trigger for
the Paleocene/Eocene thermal maximum and carbon isotope
excursion, Earth Planetary Science Letters. vol. 211, pp . 13?26.

Yours,

Paul H.





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Received on Thu 27 Mar 2008 04:27:05 PM PDT