Magnetic mineral diagenesis

Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

“…Below the sulfidic zone, methanogenesis is the most important process for the degradation of reactive organic matter (Capone and Kiene, 1988;Roberts, 2015). Here, Fe species may react to form iron phosphate (vivianite) or iron carbonate (siderite; Berner, 1981;Roberts, 2015).…”

“…Typically, iron sulfides such as greigite and pyrite form in the sulfidic pore water zone, associated with the upward-migrating sulfate-methane transition zone (SMTZ), where H 2 S accumulates (Kasten et al, 1998). In contrast, siderite mainly forms in the methanogenic zone, if pore waters have high CaCO 3 concentrations (e.g., Berner, 1981;Roberts, 2015). However, siderite and greigite (iron sulfides) can form at the same time if the rate of Laskar et al, 2004).…”

Magnetic Properties of Cherts from the Basque-Cantabrian Basin and Surrounding Regions: Archeological Implications

“…Future rock magnetic analyses are necessary to further constrain and examine any potential controlling factor (e.g., depositional setting, age) on the magnetic mineralogy of different BCB chert types. It has been recently suggested that rock magnetic methods might play a role in elucidating the role of iron oxides in the formation of sedimentary chert (Roberts, 2015), which has important implications for interpreting chert as the imprint of past biological conditions (Meister et al, 2014). Florindo et al (2003) have suggested that magnetic minerals will tend to be dissolved in sedimentary environments undergoing silica formation.…”

“…Keeping in mind that our measurements were conducted with fresh chert samples, and therefore avoiding present-day weathering, we interpret that magnetic minerals in the studied BCB chert types represent primary constituents that have been enclosed in chert during early diagenetic replacement of the parent sediment by silica within concretions. Although hematite and goethite are less common in marine environments (Liu et al, 2012), their occurrence as primary minerals in deep and shallow marine rocks from the BCB can be explained as a result of oxidizing microenvironments or as survivors of reductive dissolution undergone typically in marine sedimentary environments (Roberts, 2015). Future rock magnetic analyses are necessary to further constrain and examine any potential controlling factor (e.g., depositional setting, age) on the magnetic mineralogy of different BCB chert types.…”

Seismic heating signatures in the Japan Trench subduction plate-boundary fault zone: evidence from a preliminary rock magnetic ‘geothermometer’

“…Textbooks on palaeomagnetism include Tauxe (2010), on rock magnetism Dunlop &Özdemir (1997) and on environmental magnetism, the study of magnetic properties applied to geological materials, Evans & Heller (2003). Useful review papers on various aspects of magnetic minerals include Hunt et al (1995), Verosub & Roberts (1995), Dekkers (1997), Roberts et al (2011), Liu et al (2012, Roberts et al (2014), Roberts (2015) and Heslop (2015).…”