Magnetic mineral composition and the assemblage feature in layer S_(5-1) of Xifeng and Duanjiapo sections

The strongest magnetic and fine components ( 30 μm, XS 4J and DS 4J) which are most environmentally sensitive were separated from S5-1 in Xifeng and Duanjiapo sections for morphometry and reflectance measurement by MPV 3, element content examination by SEM ESD and mineral phase analysis by XRD, respectively. The results show that detrital iron titanium oxides of aeolian origin are in majority in the magnetic mineral components of XS 4J and DS 4J. In XS 4J, the reflectance and Fe content of magnetic minerals are often higher, besides magnetite (Fe3O4), maghemite (γFe2O3) and hematite (Fe2O3), some oxide containing high Fe (mass fraction 72%～86.67%), ilmenite (FeTiO3), magnetite ulvospinel (Fe(FeCr)O4 and Fe(FeNi)O4) are also found. In DS 4J, the negative relationship of Ti and Fe is observed, and Mn, Si, Al and Ca elements are often found in the magnetic minerals, and a lot of goethite (FeOOH) and limonite (containing Si and OH) minerals, as well as magnetic mineral corrosion and some neogenic magnetic minerals are also found. The differences in the magnetic mineral compositions and the assemblages between Xifeng and Duanjiapo sections reflect that there are obvious differences in the source rocks and in the maintenance conditions.