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Magnetic properties of sediments deposited in suboxic-anoxic environments: relationships with biological and geochemical proxies

Abstract Several studies of the rock magnetic properties of sediments deposited in suboxicanoxic environments show that bacterial degradation of organic matter leads to selective dissolution of magnetite with a decrease in magnetic mineral concentration and an increase in magnetic grain size. This study of upper Quaternary sediments from both marine and lacustrine environments shows many similarities, although diagnetic processes appear to be enhanced in the marine sediments. When the remanence is controlled by fine-grained materials, the magnetic susceptibility can be considered a leading indicator of such changes, and the coercivity parameters, such as S ratio and B0 cr, are also useful discriminants suggesting when antiferromagnetic minerals become more important in intervals characterized by reductive diagenesis. Generally, magnetic properties show close correlations with other environmental indicators: diatoms and foraminiferal concentrations and compositions and geochemical properties. This suggests that the magnetic analyses are very sensitive to environmental variations and provide powerful tools for monitoring past depositional and diagenetic environments.