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Bernhard Peucker-Ehrenbrink uses a petrol-powered rock saw to cut into the Ghaub-Keilberg transition exposed in the Hoanib valley in northern Namibia (Agust 11, 2005). (Photo by Ricardo Trinidade)
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Paul Hoffman mapping in the Fransfontein Mts, northern Namibia. (Photo by BPE)
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Platinum group element anomalies in Snowball Earth deposits
Collaborators:
Paul Hoffman (Harvard University)
Mark Kurz (WHOI)
Birger Schmitz (Lund University, Sweden)
Christian Koeberl (Vienna University, Austria).
Bodiselitsch et al. (2005, Science) reported concentration anomalies of
iridium, a tracer of extraterrestrial material, in basal layers of cap
dolomite formations that overlie glacial sediments deposited during the
Sturtian (~710 Ma) and Marinoan (~635 Ma) Neoproterozoic "Snowball
Earth" glaciations. The authors hypothesize that these Ir anomalies
reflect instantaneous deposition, during deglaciation, of cosmic dust
that has been stored for millions of years on the global ice cover. If
correct, this hypothesis lends support to the "hard" Snowball Earth
hypothesis (i.e., Earth frozen to the equator) rather than the
"Slushball Earth" hypothesis, which allows for the existence of open
water in the tropics.
With funding from WHOI's Ocean and Climate Change Institute we are
using a range of geochemical tracers (osmium isotopes, platinum group
element concentrations, helium isotopes and concentrations) to detect
the presence of extraterrestrial matter in Snowball Earth deposits. Our
field work in Namibia in August 2005 was aimed at recovering continuous
sections across the glacial-postglacial transition (see Fig. 1). Work
on correlative sections from Canada (Mackenzie Mountains) China and,
possibly, Brazil is planned for the coming years.
If you want to learn more about the "Snowball Earth" hypothesis, Paul
Hoffman's website (http://www.snowballearth.org) provides a
comprehensive introduction with many stunning photographs and diagrams
developed for classroom use.
With support from NSF-grant EAR-0821878 "SGER: Platinum Group Element
Anomalies at Cryogenian Glacial Terminations", REU student Christine
Waters (University of Texas at El Paso) investigated two continuous
sections across the termination of the Marinoan glaciation in Namibia
for PGE and Re-Os isotope systematics. We will report on our
findings at the 2009 Fall AGU meeting.
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