2020 | Newly identified Pleistocene maar volcanoes in Western Bohemia (Czech Republic) used as palaeo-environmental and palaeo-volcanological archives

A first field campaign was conducted in October 2019 at the Ztracený rybník (LIB) and Bažina maar (BAZ) structures. We drilled core LIB 5A with a 16 m and core BAZ 1A with a 10 m sedimentary se-quence, respectively. The lower section of core LIB 5A shows seismically and/or kryogenically al-tered deposits not suitable for further analyses. In contrast, BAZ 1A shows a very promising, undis-turbed sedimentary sequence (fig. 1). Following a 5.65 m thick section of peat we encountered dark-grey to light-brown sandy silt with intercalated grus fragments, the latter reflecting slope dynam-ics. Further down-core, we found dark-grey, laminated clayey silt with significantly increased magnet-ic susceptibility values by incorporated volcanic material in the sediments and rich in organics. Core BAZ 1A reflects lacustrine deposition from 6.65 m downward and is thus highly suitable for further multi-proxy investigations to decipher palaeoenvironmental and palaeovolcanological issues. The main objectives of the 2nd phase of this project thus are (i) to extend the palaeoenvironmental record of the Bažina maar structure down to maximum 30 m by Direct Push sensing and coring (Col-laboration with Dr. Horst Kämpf from GFZ Potsdam is envisaged), (ii) to set up a chronostratigraphy for the Ztracený rybník and Bažina maar structures using luminescence dating techniques in order to understand the formation of both structures and their sedimentary fill using post-IR IRSL (e.g. Thiel et al., 2011; Buylaert et al., 2012 Lauer and Weiss, 2018, Fedorov et al., 2019) and infrared-radiofluorecence (IR-RF) allowing dating back to the Middle Pleistocene (e.g. Kreutzer et al., 2018), (iii) to carry out high-resolution multi-proxy measurements of magnetic susceptibility, colour and ele-ment concentration as well as further rock magnetic properties (PI Hambach) and pollen determina-tion (PI Hŏsek) with no further costs for TeMaS. PI Bagdassarov will conduct measurements of the dielectric constant and the electrical conductivity of sediment samples in order to further character-ize depositional changes in the sedimentary sequence. New light will be shed on the tectonical and volcanological development within the Eger Rift system, which is an active element of the European Cenozoic Rift System (e.g. Dahm et al., 2013). If it can be proven that the Ztracený rybník maar formed prior to the Bažina Maar by our dating approach, significant disturbance in the Ztracený rybník sequence was possibly due to the younger eruption.

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