Stratigraphical studies on Lake Iidesjärvi sediments. Part II. Geological and mineralogical characteristics of the sedimentary sequence

This paper presents data on the geochemical and mineralogical characteristics of a core pertinent to the limnological history of Lake Iidesjärvi in the town of Tampere (S. Finland). The geochronology together with the pollen and diatom stratigraphy of its sediment sequence have been given earlier (Alhonen 1981). The new palaeolimnological results from Lake Iidesjärvi show the anthropogenic enrichment of heavy metals such as Cd, Cu, Hg, Pb and Zn in the topmost sulphide-banded clay-gyttja of its lithostratigraphy. This cultural eutrophication was interpreted by studying extraction kinetics of Fe, Si, Ca, Mg, K, Cu and Zn using ammonium oxalate and hydroxylammonium chloride plus acetic acid solutions. The productivity history of Lake Iidesjärvi was studied by the determinations of ignition loss, sedimentary chlorophyll and sedimentary humus. The mineralogical composition of the lithostratigraphy shows that the presence of clay minerals, particularly vermiculite, with extractable Mg, Fe and Na has probably led to minero-eutrophy of Lake Iidesjärvi since its isolation from the Ancylus Lake in agreement with the results of the diatom stratigraphy.