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input or changes in carbonate production. For the Arguis Formation, though,
Kodama et al. (2010) argue that the locality was too far north to be affected
by equatorial upwelling and hence changes in carbonate production.
The platform carbonate sections studied, the Cretaceous Cupido For-
mation and the Latemar from the Italian Dolomites, are interpreted to have
acquired their magnetite by eolian deposition, and thus the magnetite
concentration variations are reacting to changes in global aridity, driven by
precession and modulated by eccentricity. This last option for encoding
probably works best in depositional environments where continental sedi-
mentation, delivered by rivers, is not important, so that the magnetic
particles associated with eolian dust are not overwhelmed by the magnetic
particles transported by runoff.
No encoding mechanism has been proposed for the fluvial deposi-
tional environment of the Mauch Chunk Formation. For the Mauch
Chunk, the susceptibility probably detects variations in antiferromag-
netic hematite for these red rocks. Since magnetostratigraphic studies
of  the Mauch Chunk Formation (DiVenere & Opdyke 1991) show that
the hematite is either depositional or a very early secondary magnetic
mineral, the hematite could indicate changes in runoff (transport) or,
more likely, if the hematite grew in the sediment above the water table
during the dry season (Whidden et  al. 1998; Kodama 2012), then the
growth of hematite could be a sensitive measure of the average length of
the dry season at precessional timescales. Gunderson et  al. (2012) also
suggest an interesting correlation between obliquity-driven sea level
change and anoxia in the Mediterranean basin, thus creating conditions
for relatively more production of Fe sulfides.
It is clear from the case studies presented that magnetic mineral concentra-
tion can encode climate variations. The exact encoding mechanism can only
be determined by detailed examination of the rock magnetic mineralogy on a
case-by-case basis, but in general, it appears that variations in the delivery of
terrigenous sediments, by air or by sea, to a background of relatively nonmag-
netic marine carbonate may be the most likely mechanism.
References
Berger, A. & Loutre, M.F. (1994) Astronomical forcing through geological time.
Special Publication—International Association of Sedimentologists , 19 , 15-24.
DOI:10.1002/9781444304039.CH2.
Channell, J.E.T., Poli, M.S., Rio, D., Sprovieri, R., & Villa, G. (1994) Magnetic stratig-
raphy and biostratigraphy of Pliocene 'argilleazzurre' (Northern Apennines, Italy).
Palaeogeography, Palaeoclimatology, Palaeoecology , 110 , 83-102. DOI:10.1016/
0031-0182(94)90111-2.
Corsetti, F.A. & Kaufman, A.J. (2003) Stratigraphic investigations of carbon isotope
anomalies and Neoproterozoic ice ages in Death Valley, California. Geological
Society of America Bulletin , 115 , 916-932. DOI:10.1130/B25066.1.
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