Iły krakowieckie jako wskaźnik litostratygrafii w dolinie rzeki Sopot na Roztoczu

Abstract

The Krakowiec Clays as an indicator of lithostratigraphy in the Sopot River valley in the Roztocze Region (estern Poland).S u m m a r y. The results of micropaleonthological studies of the Sarmatian (upper Miocene) Krakowiec Clays from primary deposit as well as re-deposited ones were applied to the analysis of the stratigraphic profile of the Sopot valley fills. The study site was at the break section of the Sopot River valley in a contact zone of southern escarpment between the central part of the Roztocze and Sandomierz Basin regions (SE Poland). Species of fossil microfauna (foraminiferans, radiolarians), sponges and mollusks, as well as residual deposits were used. The documented, even if apparently small change in the lithostatigraphic profile of the Sopot valley fills, i.e., the presence of pre-Pleistocene deposits in its floor, is very important for the valley history and for interpreting other problems of river breaks and the Roztocze escarpment zone itself, e.g., sclae of the Holocene movements elevating the Roztocze Region, and their effect on expected intensity of deep fluvial erosion. In the sub-scarp zone of the Tomaszów Roztocze subregion the Krakowiec Clays occur rather shallowly. In the Sopot valley (‘Czartowe Pole’landscape preserve) they are in contact with calcareous formations. In two levels of natural clays’exposures, a dozen or so foraminiferan taxa were found. They were also below the primary deposit on the floor levels of the Sopot valley fills. The residuum of the studied strata consists of glauconite and pre-Pleistocene quartz sands, without silicate and alumosilicate, typical for postglacial formations. The Sarmatian clays present in residue were redeposited at least in the pre-Pleistocene. From the clays top up to the surface of valley fills, are Holocene deposits. The study revealed that: (1) during the Holocene and earlier the Sopot valley fills were not removed completely; (2) the floor of the valley is made not of the youngest, Holocene strata, but much older; (3) the presence of the Sarmatian microfauna in the alluvia allows to date the studied deposits as pre-Pleistocene (Pliocene?); (4) fine quartz sands and glauconite (a specific form of hydromica) both forming the residuum of the studied valley fill levels, together with the absence of other silicates and alumosilicates that are common in the Pleistocene formations, exclude the studied Krakowiec Clays from the group of glacial or fluvioglacial (Pleistocene) formations; (5) the youngest (latest Pleistocene– Holocene) movements elevating the Roztocze Region and the resulting deep fluvial erosion do not correspond with shallow occurrence of the pre-Pleistocene valley fills; this requires further discussion.