Geologiczna i geomorfologiczna charakterystyka torfowiska Rąbień oraz wstępne wyniki badań osadów biogenicznych
Geological and geomorphological features of the Rąbień peatland and preliminary results of investigations of biogenic sediments

Summary/Abstract: The Rąbień peatland is located within the Łask Plateau, approximately 11 km west of the centre of the city of Łódź, in the direct vicinity of the watershed between the catchments of the Vistula and Odra Rivers. Geological and palaeobotanical studies have been conducted on the peatland for a dozen or so years. In the late 1990’s, in the scope of archaeological works carried out in the area of dunes adjacent to the peatland, a dozen or so corings were performed on the peatland. A profile with biogenic sediments with a thickness of 3.25 m was determined, with gyttjas at the bottom, and peats in the uppermost part (Marosik 2011). In the scope of a programme of studies on raised bogs in Poland, further corings were performed, confirming the previous results (Kloss 2005, 2007; Kloss, Żurek 2005; Kucharski , Kloss 2005). In 2010, detailed geological mapping of the peatland was undertaken, permitting for the determination of the deepening of the peatland’s basin, where the thickness of biogenic sediments reaches as much as 6.2 m. Sediments were sampled and subject to palaeoecological analyses. The peatland studied occupies a closeddrainage depression, closed to the west and north by dunes, and to the east and south adjacent to slopes of glaciogenic landforms transformed by denudational processes. The migration of dunes in the Late Vistulian resulted in the development of the final shape of the depression. The peatland’s basin is reached to the east by a small denudational valley, earlier connected with the upper section of the Bełdówka River valley, draining the area west of the peatland. Core R-II was sampled at the place of maximum thickness of biogenic sediments. The core was subject to palaeoecological analyses (plant macrofossils, palynological, geochemical, and palaeozoological analyses) and radiocarbon dating. The results obtained so far permit the determination of four stages of the peatland’s development: − lake (620–180 cm) – at the time of deposition of detritus gyttja, − transitional mire (180–170 cm) – as a result of functioning of a hollow mire, − raised bog (170–10 cm) with phases of a hummock mire and raised shrub bog, − transitional mire (10–0 cm) as a result of the development of a transitional shrub bog. Results of geochemical analyses permitted distinguishing nine horizons differing significantly in terms of the chemical composition of sediments. At first (horizons II, III, and IV), sedimentation of gyttjas occurred in the conditions of variable, although gradually decreasing supply of mineral matter to the lake’s basin. Horizon R-IV developed in the period of a substantial increase in the supply of mineral matter, with a simultaneous increase in the contribution of the main lithophilic elements. Horizon R-V represents the period of a gradual increase in the content of organic matter.

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