A detailed magnetic record of Pleistocene climate and distal ash dispersal during the last 800 kyrs - The Suhia Kladenetz quarry loess-paleosol sequence near Pleven (Bulgaria)

Loess-paleosol sequences (LPS) from the Lower Danube area are valuable terrestrial archives of environmental change in SE Europe during the Pleistocene. A twenty-seven meters thick sequence has been sampled in Central North Bulgaria near the city of Pleven within the Suhia Kladenetz (SK) quarry. The sedimentary sequence consists of seven loess units and six interbedded paleosol complexes covering the last 800 kyrs. The continuous 2 cm resolution sampling depth interval enabled the recovery of several cryptotephras in addition to a ~ 20 cm thick tephra deposit observed in the field within the L₂ loess unit. All cryptotephras are clearly identified in laboratory analyses by their strong magnetic signal, particularly well expressed by concentration – dependent anhysteretic susceptibility (χARM), isothermal remanence (IRM), low field magnetic susceptibility (χₗf) and in some cases by frequency dependent magnetic susceptibility (Δχ), coercivity of remanence (BCR), and hard isothermal remanence (HIRM₂.₀–₀.₃T). Complementary optical and scanning electron microscope analyses of single grains from the tephra deposit and cryptotephra intervals reveal the presence of volcanogenic grains with smooth glassy surfaces and vesicular internal structure; fluidal grains with bulbous surfaces and dense irregular grains. Grain size sensitive magnetic ratios χARM/χₗf, ARM/IRM₁₀₀ₘT, IRM₂T/χₗf are not always discriminative, suggesting that (crypto)tephras do not have a single uniform source. Preliminary correlative age models are used to estimate ages for the (crypto)tephras and propose likely associated volcanic eruptions. Finally, strong pedogenic magnetic enhancement of the younger paleosols (S₄, S₃, S₂ and partly S₁) contrasts with the smeared and low magnetic signal of the older paleosols (S₆ and S₅). Moreover, an enhanced content of low-coercivity hematite observed from the upper part of the S₅ paleosol upwards to the present and a sharp increase in the concentration of maghemite at the expense of magnetite observed for the S₃, S₂ and S₁ paleosols provides strong evidence for a significant paleoenvironmental change. The timing of this change, based on the SK LPS age models, is compatible with the mid-Brunhes climate transition.