Till stratigraphy and petrography of the northern part of Silesia (southwestern Poland)

Abstract

Almost 40 borings have been investigated in northern Silesia (Głogów-Miedzybórz region). Eight till horizons, which differ in petrographic composition, have been recognized here. Five of them have been easily correlated by means of petrographic features with tills described previously from the Silesian Lowland and central Great Poland Lowland. These are: Grońsko, Krzesinki, Wierzbno, Smolna/Dopiewiec and Górzno Tills. Other three occur locally. Four tills have been deposited during the Elsterian Stage, where the Grońsko Till represents the early and the Krzesinki Till the Middle Elsterian ice-advance. The latter formed its marginal zone in the region investigated, most probably along the present-day Silesian Rampart. The Wierzbno and Borowiec Tills represent the Late Elsterian ice-advance. They differ in petrographic composition and indicate different geographical distribution. The newly defined Borowiec Till is characterized by large content of Baltic limestones and in its upper part also dolomite. Another four tills have been deposited during the Saalian Stage. The Smolna/Dopiewiec Till represent the Early Saalian ice-advance (Odranian). The local Naratów and Taczów·Tills were formed during the Middle Saalian (Early Wartanian) ice-advance and they are equivalent to each other. occurring in different regions: the first one at Leszno Upland and the second along the Silesian Rampart and the Barycz River valley. They differ little in petrographic composition. mainly by dolomite content. The Górzno Till represents the Late Saalian (Late Wartanian) ice-sheet advance. Both Wartanian ice-sheets formed ice-marginal zones in the region investigated: the early one at the axis of Silesian Rampart and the late one probably at Krotoszyn-Wąsosz Hills being nonhwards. Besides tills. several fluvial series have been documented. The “pyroxene” series indicates ambiguous stratigraphic position. though it is known from surrounding regions as the Elsterian interstadial series. Also, the fluvial series from the Pilica Interstadial (Odranian/Wartanian) has been documented as well as fluvial series from the Early Eemian and Middle Weichselian. The latter is the most widespread and most thick fluvial deposit in the region, reaching thickness up to 50 rn. Additionally, several Eemian lacustrine sites are present, in part palynologically investigated. The northern Silesia has a complex Quaternary geology. where different regions, although indicating similar stratigraphic assemblages. represent various structural characteristics. Three sub-regions are discussed in the paper: the southern part of the Leszno Upland, the depressions along the Barycz River and a part of the Silesian Rampart (Dalków and Trzebnica Hills).