Biogreigites (Fe3S4) in sea water sediments and their paleohydrological applications

Biogreigites are formed inside sulfate reducing bacteria through crystallization of a 3D nanocrystal of Fe3S4 surrounded by a liposome. Two different types of clusters of twinned ferrimagnetic structures can be found, magnetotactic and framboidal biogreigites. Biogreigites are only stable under anoxic conditions. Under oxic conditions, ferrimagnetic biogreigites (Fe3S4) react to non-magnetic pyrite (FeS2) and FeOOH. We investigated gravity cores of the Black and the Marmara Sea as well as sediments of the Cretaceous/Paleogene (K/T) fallout from the meteorite impact (∼66 million years ago) at Chicxulub (Yucatan, Mexico) regarding their greigite content. The samples were analyzed by X-ray diffractometry, ore microscopy, transmission, and scanning electron microscopy. Four applications of cluster analyses of twinned nanocrystalline greigites in sediments are presented: Proof of the evidence of sulfuric acid rain, investigation of climatic cycles in the Black Sea, analysis of the evolution of water and sediment flow in a sublacustrine river valley, and determination of the velocity and the amount of the water transport through the Bosporus.