Low-temperature oxidation of magnetite in rock weathering - a humidity proxy?

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Previous work gave hints that low-temperature oxidation (LTO) of magnetite is a potential proxy of paleo-humidity. In this project, we intend studying LTO in magnetite during rock weathering. The Deccan basalts (W-India) providing strong magnetic und comparable bedrock lithology across a large gradient of mean annual precipitation (MAP of ~200 to >3000 mm/yr) shall serve as study area. We will also check for a possible influence of temperature by comparison with basalts and limestones in SW-China, located in a similar MAP regime but with much cooler conditions. To analyze the LTO effect we suggest performing a systematic study of magnetite alteration along a weathering gradient from non-weathered bedrock, weathered rock surfaces and nearby detached materials, avoiding influence of soil formation. At some of our locations, partners from India and China will add catchment studies. We assume that LTO first increases magnetic hardness of magnetite due to maghemitization, followed by transformation into lower magnetic hematite or goethite. One can identify these processes by bulk measurements, which will be important to use suitable fast-to-measure parameters sensitive for LTO for obtaining high-resolution data sets in reasonable time. The project results could provide important knowledge for paleoclimate studies using lacustrine archives, and may also explain magnetic signals in paleosols.