Assessing the timing of greigite formation and the reliability of the Upper Olduvai polarity transition record from the Crostolo River, Italy

The Crostolo River section in Italy yielded a detailed record of the Upper Olduvai geomagnetic polarity transition that has been used to support the hypothesis of deep mantle
control on the transitional geomagnetic field. The paleomagnetic record is carried by the authigenic iron sulphide, greigite, which was interpreted to have formed shortly after deposition. Our detailed scanning electron
microscope investigations indicate the presence of at least 3 generations of pyrite, which usually forms with greigite as a precursor. This suggests that the total magnetization is a complex composite that produced a smoothed record of transitional field behaviour.

Benning, L. G., R. T. Wilkin, and H. L. Barnes (2000), Reaction pathways
in the Fe-S system below 100 C, Chem. Geol., 167, 25–51.
Canfield, D. E., R. Raiswell, and S. Bottrell (1992), The reactivity of
sedimentary iron minerals toward sulfide, Am. J. Sci., 292, 659–683.
Cutter, G. A., and R. S. Kluckhohn (1999), The cycling of particulate
carbon, nitrogen, sulfur, and sulfur species (iron monosulfide, greigite,
pyrite, and organic sulfur) in the water columns of Framvaren Fjord and
the Black Sea, Mar. Chem., 67, 149–160.
Florindo, F., and L. Sagnotti (1995), Palaeomagnetism and rock magnetism
at the upper Pliocene Valle Ricca (Rome, Italy) section, Geophys. J. Int.,
123, 340– 354.
Horng, C. S., M. Torii, K. S. Shea, and S. J. Kao (1998), Inconsistent
magnetic polarities between greigite- and pyrrhotite/magnetite-bearing
marine sediments from the Tsailiao-chi section, southwestern Taiwan,
Earth Planet. Sci. Lett., 164, 467–481.
Jiang, W. T., C. S. Horng, A. P. Roberts, and D. R. Peacor (2001), Contradictory
magnetic polarities in sediments and variable timing of neoformation
of authigenic greigite, Earth Planet. Sci. Lett., 193, 1 –12.
Laj, C., A. Mazaud, R. Weeks, M. Fuller, and E. Herrero-Bervera (1991),
Geomagnetic reversal paths, Nature, 351, 447.
Liu, J., R. X. Zhu, A. P. Roberts, S. Q. Li, and J. H. Chang (2004), Highresolution
analysis of early diagenetic effects on magnetic minerals in
post-middle-Holocene continental shelf sediments from the Korea Strait,
J. Geophys. Res., 109, B03103, doi:10.1029/2003JB002813.
Pye, K. (1981), Marshrock formed by iron sulphide and siderite cementation
in saltmarsh sediments, Nature, 294, 650– 652.
Raiswell, R. (1982), Pyrite texture, isotopic composition and the availability
of iron, Am. J. Sci., 282, 1244–1263.
Reynolds, R. L.,M. L. Tuttle, C. A. Rice, N. S. Fishman, J. A. Karachewski,
and D. M. Sherman (1994), Magnetization and geochemistry of greigite-bearing
Cretaceous strata, North Slope basin, Alaska, Am. J. Sci., 294,
485– 528.
Reynolds, R. L., J. G. Rosenbaum, P. van Metre, M. Tuttle, E. Callender,
and A. Goldin (1999), Greigite as an indicator of drought — The 1912–1994 sediment magnetic record from White Rock Lake, Dallas, Texas,
USA, J. Paleolimnol., 21, 193– 206.
Roberts, A. P. (1995), Magnetic properties of sedimentary greigite (Fe3S4),
Earth Planet. Sci. Lett., 134, 227–236.
Roberts, A. P., and G. M. Turner (1993), Diagenetic formation of ferrimagnetic
iron sulphide minerals in rapidly deposited marine sediments, South
Island, New Zealand, Earth Planet. Sci. Lett., 115, 257–273.
Roberts, A. P., and R. Weaver (2005), Multiple mechanisms of remagnetization
involving sedimentary greigite (Fe3S4), Earth Planet. Sci. Lett.,
231, 263– 277.
Sweeney, R. E., and I. R. Kaplan (1973), Pyrite framboid formation:
Laboratory synthesis and marine sediments, Econ. Geol., 68, 618–634.
Tric, E., C. Laj, C. Jehanno, J.-P. Valet, C. Kissel, A. Mazaud, and
S. Iaccarino (1991), High-resolution record of the Upper Olduvai transition
from Po Valley (Italy) sediments: Support for dipolar transition
geometry?, Phys. Earth Planet. Inter., 65, 319– 336.