Annually laminated sediments date the drainage of the Ancylus Lake and early Holocene shoreline displacement in central Finland

摘要

Three independent varve (annually laminated) chronologies, verified by paleomagnetic dating, were used in the present biostratigraphical study to investigate the history of the Baltic basin in central Finland. Diatom analyses of the studied sediment sequences show the transition from the Ancylus Lake taxa to small-lake diatoms at the isolation boundary. These three varvcd profiles provide the following data and information on early Holocene events in central Finland: (ⅰ) a shoreline displacement curve between the deglaciation at ca, 9000 BC and ca. 7000 BC, (ⅱ) relative emergence of the land area between 116 and 96 m above the present day sea level, which proceeded at a rate of ca. 2.6 cm year~(-1), (ⅲ) the calendar year age for the Lake Ancylus at ca. 8250 8200 BC, and (ⅳ) the calendar year age for the Betula/Pinus pollen zone boundary (ca. 8100 BC) and Alnus arrival (ca. 7100 BC).