Anomalous magnetic susceptibility values and traces of subsurface microbial activity in carbonate banks on San Salvador Island, Bahamas

Abstract

Pure limestones beneath the paleosols on San Salvador Island, Bahamas, contain strong positive magnetic susceptibility anomalies, although the iron content is generally very low. These magnetic phenomena differ from those associated with disconformities, which are marked by accumulation of paramagnetic airborne dust deposits with relatively high iron content. The strength and characters of the magnetic response in these subsurface zones correspond to the presence of magnetite, particularly small single-domain magnetite crystals of microbial origin. These crystals are not present elsewhere in the intergranular rock pores or microvugs. They are preferentially concentrated in capillary microborings, which developed concurrently with formation of calcite cements that have soil-related C and O isotope compositions. These magnetic zones occur several meters below the overlying soil horizons. Very thin and long linear microborings may be attributable to cyanobacterial microborers. The single-domain magnetites in these micrometer-size tunnels plugged by calcite appear to result from later occupation of these tiny holes by magnetotactic bacteria. Inorganic origin of the magnetite seems unlikely. Numerous traces that suggest subsurface microbial activity provide evidence that may be used to develop possible scenarios for subsequent biological studies of the precise bacteria involved.

Correlating carbon and oxygen isotope events in early to middle Miocene shallow marine carbonates in the Mediterranean region using orbitally tuned chemostratigraphy and lithostratigraphy

“…Magnetic susceptibility in carbonates deposited on isolated carbonate platforms can result from two different processes: (1) Deposition of detrital paramagnetic and ferromagnetic particles by means of aeolian transport processes [e.g., Ellwood et al ., ; da Silva et al ., ; Hladil et al ., ] and (2) formation of biogenic magnetite by bacterial activity in the sediment [ Karlin et al ., ; Sparks et al ., ; Hladil et al ., ; Simmons et al ., ; Kopp and Kirschvink , ].…”

Magnetic susceptibility evolution and sedimentary environments on carbonate platform sediments and atolls, comparison of the Frasnian from Belgium and Alberta, Canada

“…However, numerous authors propose different origins for magnetic minerals like volcanism (Crick et al, 1997;Borradaile and Lagroix, 2000), black smokers (Borradaile and Lagroix, 2000), extraterrestrial impact (Ellwood et al, 2003a,b), pedogenetic minerals (Tite and Linington, 1975) and biogenic magnetite (Kirschvink and Lowenstam, 1979;Hladil et al, 2004). In our case, on a shallow-water platform and in atolls, volcanic ash, black smokers and extraterrestrial impact are considered as to have insignificant effects on the MS signal in view of oceanographic setting.…”

“…Since the work of Crick et al (1997Crick et al ( , 2000Crick et al ( , 2001Crick et al ( , 2002 and Ellwood et al (1999Ellwood et al ( , 2000Ellwood et al ( , 2001Ellwood et al ( , 2006Ellwood et al ( , 2007 on the use of magnetic susceptibility (MS) in correlating Palaeozoic sediments, this technique has become widely used (Racki et al, 2002;Hladil et al, 2003aHladil et al, , 2004Hladil et al, , 2005Whalen and Day, 2005;da Silva and Boulvain, 2002Mabille and Boulvain, 2007). Crick et al (1997) defined the correlations obtained with MS as intercontinental, facies independent and of a better precision than biozones.…”

Magnetic susceptibility application: a window onto ancient environments and climatic variations: foreword

“…The origin of these main magnetic minerals is generally assumed to result from detrital inputs, from fluvial or aeolian sources (Ellwood et al 2000;Stage 2001;Rey et al 2008;Hladil et al 2010a;Maher 2011). In some case, magnetic minerals are also related to soil formation (Tite & Linington 1975;Dearing et al 1996) or are of bacterial origin (Kirschvink & Chang 1984;Hladil et al 2004;Kopp & Kirschvink 2008). In Quaternary marine sediments, magnetofossils are locally relatively common, compared with the pre-Quaternary magnetofossil records (Kopp & Kirschvink 2008).…”