Analiza petrograficzna narzutniaków w żwirowni Łubienica-Superunki oraz ich skandynawskie obszary alimentacyjne
Abstract
Petrographic analysis of erratics in the £ubienica-Superunki gravel pit and their Scandinavian source areas.
A b s t r a c t. Petrographic studies covered 20–60 mm coarse gravel and 4–10 mm medium-grained fractions of two till horizons (units ŁS II and ŁS IV) and two beds of sand-gravelly-outwash deposits(units ŁS I and ŁS III) associated with the Odra Glaciation (MIS6) in Łubienica-Superunki on the North Mazovian Lowland. Regardless of the facies type and grain sise, crystalline rocks dominate over all other petrographic groups in all samples. The percentage of crystalline rocks is greater among coarse gravel (average 74.7%) than among medium-grain gravel (average 67.8%). The share of carbonate rocks is limited only to the both lower units ŁS I and ŁS II. The upper units (ŁS III and ŁS IV) are deprived of these rocks, both in the medium and coarse gravel fraction. Sandstones, presented in all samples, were in the range of 5–20%. From the other petrographic groups, individual chalk limestones clasts, dolomites, flints and quartz grains were identified in the material. The indicator erratics were identified in all four units. Their percentage content stands for 10–18% of the total sample of coarse-grained fraction. Among them, the most common were the erratics derived from the Åland Islands, and then from the area of south-eastern Sweden (Småland) and from Dalarna in central Sweden. Amongst the erratics with limited indicator significance, Lower Paleozoic limestones and Jotnian sandstones were most frequent. Single fragments of Ordovician red and Paleoporella limestone were present. These rocks, including the Lower Paleozoic grey limestone, occurred only in the lower units (ŁS I and ŁS II). The results of the research suggest that the two lower sediment units should be correlated with a ice-sheet advance (Middle Polish Complex, Odranian Stadial?), and the two upper ones – with a separate, subsequent advancement (Wartanian?). The paper is another methodological contribution to the consideration of abandoning the tedious testing of glacial till and focusing on a much faster petrographic analysis of fluvioglacial sediments associated with the same ice sheet. This is demonstrated by the comparable results of the petrographic analysis of short transport outwash sediments and till from a single glacial period.
A b s t r a c t. Petrographic studies covered 20–60 mm coarse gravel and 4–10 mm medium-grained fractions of two till horizons (units ŁS II and ŁS IV) and two beds of sand-gravelly-outwash deposits(units ŁS I and ŁS III) associated with the Odra Glaciation (MIS6) in Łubienica-Superunki on the North Mazovian Lowland. Regardless of the facies type and grain sise, crystalline rocks dominate over all other petrographic groups in all samples. The percentage of crystalline rocks is greater among coarse gravel (average 74.7%) than among medium-grain gravel (average 67.8%). The share of carbonate rocks is limited only to the both lower units ŁS I and ŁS II. The upper units (ŁS III and ŁS IV) are deprived of these rocks, both in the medium and coarse gravel fraction. Sandstones, presented in all samples, were in the range of 5–20%. From the other petrographic groups, individual chalk limestones clasts, dolomites, flints and quartz grains were identified in the material. The indicator erratics were identified in all four units. Their percentage content stands for 10–18% of the total sample of coarse-grained fraction. Among them, the most common were the erratics derived from the Åland Islands, and then from the area of south-eastern Sweden (Småland) and from Dalarna in central Sweden. Amongst the erratics with limited indicator significance, Lower Paleozoic limestones and Jotnian sandstones were most frequent. Single fragments of Ordovician red and Paleoporella limestone were present. These rocks, including the Lower Paleozoic grey limestone, occurred only in the lower units (ŁS I and ŁS II). The results of the research suggest that the two lower sediment units should be correlated with a ice-sheet advance (Middle Polish Complex, Odranian Stadial?), and the two upper ones – with a separate, subsequent advancement (Wartanian?). The paper is another methodological contribution to the consideration of abandoning the tedious testing of glacial till and focusing on a much faster petrographic analysis of fluvioglacial sediments associated with the same ice sheet. This is demonstrated by the comparable results of the petrographic analysis of short transport outwash sediments and till from a single glacial period.