BITTER SPRINGS STAGE IN THE AMADEUS BASIN, CENTRAL
AUSTRALIA
Intervals
of relatively light carbon isotopes in the Neoproterozoic
are commonly associated with regional or global glaciation.
The first low d13C excursion in the Neoproterozoic, the
Bitter Springs Stage (~800 Ma), is an exception as it
precedes all the known Neoproterozoic glacial events. In
Svalbard, Maloof et al. (2006) observed that this interval
of relatively low d13C is bracketed by paleomagnetic
reorientations and transient changes in sea level. They
explain these coincidental changes by inferring rapid
shifts in paleogeography associated with a pair of true
polar wander (TPW) events. The possibility of TPW, in which
there is relative motion between the silicate Earth and the
spin vector of up to 90 degrees at rates that far exceed
those of normal plate tectonics, has been discussed and
shown to be a theoretic possibility for years in the
geophysical literature. Such an event would occur to keep
the earth in rotational balance during changes in the
distribution of Earth's mass shifts. We are testing this
TPW hypothesis by performing integrated physical, chemical
and magnetic stratigraphy on the carbonates of the Bitter
Springs Formation in the Amadeus Basin of Australia (where
the d13C interval was first observed).
Our group's research on the project is in collaboration
with Galen Halverson (University
of Adelaide) and
Matt Hurtgen (Northwestern
University). During the summer of 2008 I worked in
Halverson's lab and developed organic carbon isotope
data to complement our detailed records of the isotopic
composition of inorganic carbonates across the basin.
These paired data sets are allowing us to further
constrain the behavior of the carbon cycle in the early
to middle Neoproterozoic and we presented
this work at
the 2008 Fall meeting of the American Geophysical Union.
Paired sulfate and pyrite sulfur isotope records from
the formation give evidence for a rise in sulfate
concentrations, and inferentially levels of atmospheric
O2, prior to the middle Cryogeneian glacial event
and these records were
also present at this year's AGU meeting.