Formation of ferrimagnets in well-drained, buffered, unpolluted soils appears to be related to climate, and especially rainfall. If robust, this magnetism/rainfall couple can be used to estimate past rainfall from buried soils, particularly the multiple soils of the Quaternary loess/soil sequences of Central Asia. However, dispute exists regarding the role of climate vs. dust flux for the magnetic properties of modern loessic soils. Here, we examine the mineralogical basis of the magnetism/rainfall link for a climate transect across the loess-mantled Russian steppe, where, critically, dust accumulation is minimal at the present day. Magnetic and independent mineralogical analyses identify in situ formation of ferrimagnets in these grassland soils; increased ferrimagnetic concentrations are associated with higher annual rainfall. XRD and electron microscopy show the soil-formed ferrimagnets are ultrafinegrained ( 6 V50 nm) and pure. Ferrimagnetic contributions to Mo « ssbauer spectra range from 17% in the parent loess to 42% for a subsoil sample from the highest rainfall area. Total iron content varies little but the systematic magnetic increases are accompanied by decreased Fe 2þ content, reflecting increased silicate weathering. For this region, parent materials are loessial deposits, topography is rolling to flat and duration of soil formation effectively constant. The variations in soil magnetic properties thus predominantly reflect climate (and its co-variant, organic activity)ŝ tatistical analysis identifies strongest relationships between rainfall and magnetic susceptibility and anhysteretic remanence. This magnetic response correlates with that of the modern soils across the Chinese Loess Plateau. Such correlation suggests that the rainfall component of the climate system, not dust flux, is a key influence on soil magnetic properties in both these regions. ß

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This case study provides insight into magnetic susceptibility (MS), iron and bulk-sample geochemistry patterns in an Upper Mississippian siliciclastic–carbonate cyclothemic section Polotnyanyi Zavod (Moscow Basin, Russia), with many subaerial disconformities and Stigmaria impressions. The goal of this paper is to test whether the MS and geochemical signals in this section are linked to any specific geological processes. The section is dominated by limestones but contains several siliciclastic units and numerous subaerial disconformities. This lithological heterogeneity is vividly expressed on MS and bulk geochemical logs. MS shows the strongest positive correlation to bulk iron and also strong correlations to Al2O3, MgO, K2O and TiO2, pointing to close association of iron with siliciclastic fines rich in detrital mica and clays. The correlation of iron and MS to siliciclastic fines or subaerial exposure horizons is not straightforward. The highest ferruginization with most intense MS excursions occurs in basal sooty silts and shales of three main siliciclastic units of the studied section. In addition, many other thin pedogenized shales are ferruginized and show a relative high magnetism, but some ferruginized shales are not palaeosols.

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