Discriminating tephra layers in loess–paleosol sequences by combining rock magnetic and mid-infrared spectroscopic approaches

Multi-proxy reconstructions of past environmental and climatic changes critically depend on robust age models. In loess–paleosol sequences (LPSs), the limited temporal range of commonly applied radiometric dating methods (< ~250 ka) hampers high-resolution chronologies. The identification of widespread marker horizons, such as visible or hidden (cryptic) tephra layers, offers an effective means to improve geochronological control.

Eastern European LPSs are located downwind of several highly explosive volcanic provinces, including the western Italian volcanic ridge and the Aeolian Islands, and may also have received volcanic ash from the Eastern Carpathians and Anatolia under different atmospheric circulation patterns. Consequently, volcanic glass shards are expected to be preserved in these archives over at least the last 1 Ma.

We present a high-resolution, multi-disciplinary investigation of the Pleven LPS in northern Bulgaria, integrating magnetic, colorimetric, mid-infrared (ATR-FTIR), and granulometric data. The 27 m thick sequence was sampled at 2 cm resolution (1,336 samples). Magnetic and colorimetric measurements were obtained for all samples, while ATR-FTIR and grain-size analyses were performed at lower resolution.

Mineralogical and grain-size–sensitive magnetic parameters, together with ATR-FTIR–derived smectite contents, reveal several preserved (crypto)tephra layers, of which only one is macroscopically visible. Preliminary correlations suggest equivalents in well-dated regional archives. These results demonstrate the potential of integrated multi-proxy approaches for identifying cryptotephra horizons in Eastern European LPSs and improving regional stratigraphic correlations and paleoclimate reconstructions.