Marjamurto, an interstadial site in a till covered esker area of central Ostrobothnia, western Finland

• Main Authors: H. Peltoniemi, B. Eriksson, T. Grönlund, M. Saarnisto
• Format: Article
• Language: English
• Published: Geological Society of Finland 1989-12-01
• Series: Bulletin of the Geological Society of Finland
• Subjects: stratigraphy; till; eskers; organic residues; pollen diagrams; diatom flora; interstadial environment; Weichselian; Marjamurto; Haapavesi; Finland
• Online Access: http://www.geologinenseura.fi/bulletin/Volume61/sgs_bt_061_2_pages_209_237.pdf
• ISSN: 0367-5211; 1799-4632

Till-covered glaciofluvial deposits, presumably eskers, are common in Central Ostrobothnia (Pohjanmaa) within a zone more than 50 km broad, in which no exposed eskers are present. The areal distribution, morphology and stratigraphy of these eskers are described with particular reference to the organic deposits found in many gravel pits within this zone. Some of the organic sediments, such as the Ollala site in Haapavesi, have been correlated with the Eemian Stage, whereas some sites such as Oulainen have been correlated with the Early Weichselian Brarup Interstadial. The Marjamurto site in Haapavesi, described here, probably belongs to the same esker chain as that at Oulainen. It is a freshwater sequence deposited in a kettle hole, and was later buried by littoral sands and till. The palaeovegetation represents an interstadial type of pine-dominated forest. On the basis of its lithostratigraphy and biostratigraphy, the Marjamurto sequence is correlated with that at Oulainen. A preliminary TL date for Marjamurto of 107 ka supports this correlation. The possibility of correlating the 'forested' interstadials of Ostrobothnia with the Early Weichselian Odderade Interstadial is also considered. The Early Weichselian deposits in Ostrobothnia are overlain by only one till unit, as indeed also are the deposits correlated with the Eemian Stage. This suggests that the Weichselian ice spread to southern Finland only once. Thus the till-covered eskers of Ostrobothnia must themselves date from the late Saalian Stage.