Ryszard K. Borówka

Holocene marine ingressions in the coastal zone of the pomeranian bay based on radiocarbon assays

In recent years, a team at the Geology and Paleogeography Unit, Marine Sciences Institute, University of Szczecin, has been performing geological, geochronological and paleogeographic surveys in (i) the Szczecin Lagoon and Świna Gate Sandbar and (ii) the estuary section of the Rega river valley near Mrzeżyno. These studies have helped to examine and identify not only the distribution of fossil marine sediments but also their lithological and sedimentological characteristics. The age of marine ingressions and regressions in the coastal zone of the Pomeranian Bay were determined using approximately 170 radiocarbon assays.It was found that the marine ingression associated with the ‘Littorina transgression’ was not synchronous at these two areas. It started earlier in the Mrzeżyno area, ca. 8300-8200 cal BP. In that first phase, marine sediments developed as tightly packed sands containing a few fragments of shells. In several profiles, these deposits were separated from the bottom and top with layers of peat, thus allowing an indirect determination of their age. The next phase of ingression began about 7300 cal BP. These younger marine sediments already contained quite numerous shells of marine malacofauna, especially Cardium glaucum, often found in a life position.In the area of the Szczecin Lagoon and Swina Gate Sandbar, the oldest marine ingression started as early as about 7350 cal BP. The quite clear trace is a considerably thicker series of marine sands with numerous sea shells representing marine and brackish-marine environments, including Cardium glaucum shells in a life position, which made it possible to identify the age and the rate of accumulation of marine sands.

Postglacial Evolution of the Odra River Mouth, Poland-Germany

As revealed by multidisciplinary research, the Odra River mouth area was evolving during the Late Glacial and Holocene by changing from glacio-fluvial to fluvio-limnic to marine through to the present lagoonal area. In the Late Pleistocene, the pre-Odra River was rolling westward along the Torun-Eberswalde ice-marginal valley to discharge, farther away and like the rivers Elbe and Rhine, to the Atlantic. After the Scandinavian icesheet retreat (ca. 14.5 ky BP), the ancient river was flowing north-west to discharge to the Baltic Sea, most likely close to the eastern part of today’s Island of Rugen. Initially, the Odra was a braided river of a type, with many wandering channels and sandbanks. In the early Holocene, the river became anastomosing, with stabilised channels. In the mid-Holocene, the Odra was most likely meandering through swamps and bogs. In the late Atlantic period, during the Littorina transgression (ca. 7 ky BP), the river valley was invaded by the sea water and was transformed into a marine embayment extending southward down to today’s city of Szczecin. The river mouth area became an estuary. During the marine transgression, erosion processes affected two islands composed of glacial sediments: the Wolin and the Usedom. Erosion of the islands and the intensifying longshore transport produced two sandy spits which grew in size and gradually blocked the embayment, turning it into a lagoon. At present, the Odra River mouth area shows characteristics of a lagoon.

Factors influencing temporal changes in chemical composition of biogenic deposits in the middle Tążyna River Valley (Kuyavian Lakeland, central Poland)

Abstract The present paper discusses the influence of geochemical properties on biogenic deposits in the Wilkostowo mire near Toruń, central Poland. The analysed core has allowed the documentation of environmental changes between the older part of the Atlantic Period and the present day (probably interrupted at the turn of the Meso- and Neoholocene). In order to reconstruct the main stages in the sedimentation of biogenic deposits, we have used stratigraphic variability of selected litho-geochemical elements (organic matter, calcium carbonate, biogenic and terrigenous silica, macro- and micro-elements: Na, K, Mg, Ca, Fe, Mn, Cu, Zn, Pb, Cr and Ni). The main litho-geochemical component is CaCO3; its content ranges from 4.1 per cent to 92 per cent. The variability of CaCO3 content reflects mainly changes in hydrological and geomorphological conditions within the catchment area. The effects of prehistoric anthropogenic activities in the catchment of the River Tążyna, e.g., the use of saline water for economic purposes, are recorded in a change from calcareous gyttja into detritus-calcareous gyttja sedimentation and an increased content of lithophilous elements (Na, K, Mg and Ni) in the sediments. Principal component analysis (PCA) has enabled the distinction the most important factors that affected the chemical composition of sediments at the Wilkostowo site, i.e., mechanical and chemical denudation processes in the catchment, changes in redox conditions, bioaccumulation of selected elements and human activity. Sediments of the Wilkostowo mire are located in the direct vicinity of an archaeological site, where traces of intensive settlement dating back to the Neolithic have been documented. The settlement phase is recorded both in lithology and geochemical properties of biogenic deposits which fill the reservoir formed at the bottom of the Parchania Canal Valley.