Calendar year ages of palaeomagnetic features and tephra layers obtained from Holocene varved lake sediment sequences in W Sweden
by
Lovisa Zillén
Quaternary Geology, Lund University, Sweden
Coauthors: Stefan Wastegård (Quaternary Geology, Stockholm University, Sweden), Ian Snowball (Quaternary Geology, Lund University, Sweden)

Annually laminated lake sediments (or varved lake sediments) are ideal geological archives since they provide calendar year chronologies and the advantage to present palaeoclimate-and palaeoenvironmental data at a high- temporal resolution (Renberg and Segerström, 1981; Saarnisto, 1986). Two new annually laminated Holocene lake sediment sequences, which extend from the present day to c. 9500 cal. BP, have been located in the province of Värmland, west central Sweden (i.e. Furskogstjärnet and Mötterudstjärnet). The Furskogstjärnet sequence is thus the longest continuous geological archive in Sweden with an annual resolution. Regional Holocene palaeomagnetic master curves on calendar year time-scales can be constructed by palaeomagnetic secular variation measurements (PSV) of varved lake sediments and used for dating (Saarinen, 1999). Natural Remanent Magnetisation (NRM) measurements were performed on the two varved sequences in Värmland, where nine reproducible inclination/declination features have been recorded. The PSV curves are almost identical to the Finnish data and curves obtained from varved lake sediments in northern Sweden. Regional marker horizons, such as volcanic ash layers (tephra), can be used for objective correlation between geological records. Boygle (1998 identified and radiocarbon dated 3 tephras in the province of Värmland, which originated from Icelandic eruptions (Hekla volcano). The same tephra layers (i.e. Hekla 4, Kebister and Hekla 3) have been identified (i.e. by geochemical analysis) and dated in the varved lake sediment sequence in Värmland. Hekla 4, Kebister and Hekla 3 were distinguished by calculating MgO/CaO and FeO/TiO ratios of the relative concentration of these elements (Boygle, 1998). To improve the knowledge about the temporal leads and lags in climate change (e.g. between the North Atlantic region and terrestrial Europe) high-resolution palaeoclimate- and palaeoecology studies with good chronological control are essential. Such chronological control can be archived by linking geological records with palaeomagnetic time-scales and tephrochronology obtained from annually laminated lake sediments.

Date received: March 27, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cagc-38.