Holocene environmental change and the accumulation-erosion balance of sheltered river-mouth sediments, Goteborg, SW Sweden

Holocene sedimentological change was investigated in 15 sediment piston cor es (250 cm long) from the mouth of the Gota alv River, outside of Goteborg, which is sheltered by an archipelago. The main objective was to interpret recent, natural and human-induced influences upon the accumulation-erosion balance and the sedimentary environment from Holocene sediment units. The f ive main units are: consolidated glaciomarine clay (Facies gC) lowermost, c onsolidated estuarine clay (Facies dC), soft sub-recent sediment (Facies om C and Facies C) uppermost and dumped sediment (Facies D) in some parts of t he study area. The sediment facies are divided by two major hiatuses: (a) t he early Holocene hiatus between Facies gC and dC involves a time gap of at least 7000 years, ending at ca. 4000 BP and (b) the late Holocene hiatus b etween the consolidated clays (Facies gC and dC) and Facies omC spans 1000 years and ends ca. 50 BP (i.e. 100 years ago). Both hiatuses probably relat e to the effects of isostatic land uplift. Surface sediments consist mainly of an organic-matter-rich clay facies, suggesting changes in the trophic s tate of the estuary during the last 100 years. Together with human-induced increased river erosion and loss of accommodation space in the estuary, thi s caused the onset of sedimentation in the estuary. The recent sediments ar e contaminated with heavy metals (Cu, Zn, Pb, Hg), with highest concentrati ons in the lower part of Facies omC. (C) 2000 Elsevier Science B.V. All rig hts reserved.