Diagenetic imprints on magnetic mineral assemblages in marine ...

Summary
Verwey transition, which is indicative of magnetite. The titanohematite lamellae observed
by SEM analyses, most likely originate from high temperature oxidation (deuteric
oxidation), and have an approximate composition of TH85 to ilmenite. Below
approximately 210 K the mineral would become ferrimagnetic, but the moment is ordered
antiparallel to the magnetic moment of the (titano-)magnetite, which most likely carries the
remanence at room temperature. Consequently, the mechanism responsible for this self-
reversal is sought in magnetostatic interaction. This would also explain the absence of an
anomaly in the heating of a LT-SIRM (5 T) to ambient temperatures.
VI
A further investigation of sedimentary magnetic with the aid of electron backscatter
diffraction (EBSD) is documented in chapter 2.5. This method allows discrimination
between chemically identical but mineralogically different phases. In the sediments of the
Rio de la Plata estuary it confirmed the presence of high Ti bearing titanohematites as
well as ilmenite and titanomagnetite. The application of this technique on sediments and
on magnetic extracts is new, but has already proven itself to be valuable in the
identification of magnetic intergrowths.