Late Glacial and Holocene palaeoenvironmental changes recorded in landslide fens deposits in the Polish Outer Western Carpathians (Southern Poland)

In the northern part of the Polish Outer Western Carpathians, the Beskid Makowski Mts., four landslides formed during the Late Glacial have been identified, so far. Within the depositional sequences (organic-mineral) of fens occurring in landslide depressions, palaeoenvironmental changes of the Late Glacial and the Holocene are recorded. The oldest of fen, started to form in the Oldest Dryas Stadial, the younger ones – in the Bolling Interstadial (two fens) and in the Older Dryas Stadial. The thickness of fen deposits varies from 1.5 m to 4.5 m. The sediments deposited in the Late Glacial represent long sequences (reaching 50–80% of the profile), whereas the Holocene deposits are reduced here due to the occurrence of long-lasting sedimentation gaps (hiatuses). The reconstruction of palaeoenvironment was carried out on the basis of pollen and lithological (loss on ignition, areometric) analyses along with more than 45 14C datings. In the Late Glacial sequences of the examined logs, mineral horizons interlaying organic deposits were affected by periodic climate warmings resulting in the permafrost melting during the Bolling and the Allerod Interstadials. In the Late Glacial deposits there are sequences (ca 0.5 m thick) deposited during the Older Dryas Stadial. The Allerod in the analyzed logs is bipartite: the lower sections (AL-1) are usually represented by peat deposition, whereas in the upper parts of the logs (AL-2) numerous minerogenic (clay, silty clay) inserts confirm the climate humidity growth (or permafrost melting) during the Gerzensee Oscillation. In the Late Glacial deposits, pollen of thermophilous trees, such as Corylus, Tilia, Quercus, Carpinus, as well as (typical for the Subboreal Phase) Abies alba and Fagus sylvatica occur, which may indicate the presence of thermophilous refugia in this part of the Carpathians. During the middle part of the Younger Dryas Stadial climate cooling, the widespread gradual increase in the delivery of allochthonous material to fens is related to permafrost melting. This process is finished by the deposition of clay and silty clay horizon at the beginning of the Holocene (Preboreal). The lack of the depositional sequences of the Boreal, Atlantic and partly the Subboreal phases in the majority of the logs is caused by the erosional removal of sediments during the climate humidity growth at the beginning of the Subboreal and the Subatlantic phases.