Climatic control of magnetic granulometry in the Mircea Voda loess/paleosol sequence (Dobrogea, Romania)

摘要

A detailed rock-magnetic investigation of loess/palaeosol samples from the section at Mircea Voda (Dobrogea Plateau, Romania) is presented. Investigation of climatic control on magnetic granulometry used several grain-size and concentration-dependent proxies (magnetic susceptibility and its frequency dependence, anhysteretic remanent magnetization, isothermal remanent magnetization, hysteresis properties and FORC distributions) and an unmixing model for isothermal remanent magnetization curves. The paleosol layers in the Mircea Voda sequence experienced significant pedogenic alteration, resulting in high amounts of ultrafine grained SP, grains at SP/SD threshold, stable SD grains and PSD magnetite/maghemite grains. The loess layers in the Mircea Voda sequence are dominated by MD and/or PSD oxidized magnetite probably of aeolian origin. The unmixing model for IRM curves shows the presence of three components with different coercivities. The soft (～21 mT) and medium (～42 mT) coercivity components are produced by pedogenesis during interglacial and interstadial periods. The hard coercivity component (～60 mT) is of aeolian origin, being dominant in loess layers.