The brackish Baltic Sea Yoldia Stage - palaeoenvironmental implications from marine benthic fauna and stable oxygen isotopes

Eighteen sites in middle Sweden with sediments deposited during the brackis h phase of the Yoldia Sea have been investigated with respect to the marine calcareous benthic fauna (i.e. foraminifera, ostracods and molluscs) and s table oxygen isotopes. At most sites the sediments consist of varved clay s equences which are correlated to the Swedish Time Scale and dated to the Ea rly Preboreal, A marine benthic fauna has been recorded at 11 sites. The fa una occurs during c. 100 clay-varve years and the total length of the brack ish phase is estimated to be 110-190 years. Near the inlet of saline water the fauna was dominated by the foraminifera Elphidium excavation (Terquem) and further to the east the ostracod Cytheropteron montrosiense (Brady, Cro sskey and Robertson) dominated. At shallower depths the fauna occurred duri ng a shorter period owing to the formation of a stratified water column wit h a low-saline surface water. Very low delta O-18(c), values were recorded, i.e. between -9.9 parts per thousand and -4.7 parts per thousand because o f the influence of meltwater from the ice sheet. A different isotope fracti onation between the foraminifera E. excavatum and the ostracod C. montrosie nse was recorded.