Inconsistent magnetic polarities between greigite- and pyrrhotite/magnetite-bearing marine sediments from
the Tsailiao-chi section,southwestern Taiwan
Li, Jhao-You
Abstract
We identified three major magnetic minerals, magnetites (Fe3O4), greigites (Fe3S4) and pyrrhotites (FeS1+x, 0<x<1) by XRD analysis from three marine-deposited sections (Tsengwen-chi, Erhjen-chi and Tsailiao-chi), together with sediment granulometry and calcareous nannofossil identification in TLC section. Paleomagnetic samples from 65 sites revealed two types: (1) single-component stable characteristic remanence in magnetite/pyrrhotite-dominated samples (Type S), and (2) abrupt changes in polarity when samples with significant greigite concentrations were heated above 320-340¢XC (Type C).
The polarities derived from Type S and from Type C samples are consistent with those determined from nannofossil biostratigraphy. This implies that the NRM carried by magnetite and pyrrhotite is reliable. The opposite polarities could have resulted from delayed formation of greigite or self-reversal. Pyrrhotite and greigite may have both formed authigenically, but there is no clear explain for the differences in direction.
References
Horng C.-S, Masayyuki Torii, Shea K.-S, Kao S,-J, Inconsistent magnetic polarities between greigite- and pyrrhotite/magnetite-bearing marine sediments from the Tsailiao-chi section, southwestern Taiwan, Earth Planet. Sci. Lett. 164 (1998) 467-481.
(Abstract) (Full text)
Horng C-S, Chen J.-C, Lee T.-Q, Variations in magnetic minerals from two Plio-Pleistocene marine-deposited sections, southwestern Taiwan, J. Geol. Soc. China 35 (4) (1992) 323-335.
(Abstract) (Full text)