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Finnish reference curves for palaeomagnetic dating of soft Holocene sediments

In favourable geological and geomorphological settings, some lakes accumulate and preserve varved sediments that reflect the annual cycle of sedimentation. Such records can be precisely dated and provide a high-resolution basis for investigations of environmental change (Ojala et al. 2000, Tiljander et al. 2003). Varve records, especially those composed of clastic-organic varves in Finland and Sweden, have been demonstrated to be highly suitable for studying the secular variation of the Earth’s magnetic field (Snowball & Sandgren 2002, Ojala & Tiljander 2003). They provide a high-resolution record for investigation of variations in the palaeomagnetic direction (inclination and relative declination) and relative palaeointensity. Here is demonstrated a careful construction of independent varve and paleomagnetic chronologies from lakes Alimmainen Savijärvi (10,295 ±340 varve years), Nautajärvi (9898 ±97 varve years) and Korttajärvi (9590 ±103 varve years) all located in central southern Finland (Ojala & Tiljander 2003). These independently varve-dated PSV records show very similar declination and inclination features commonly described in the UK and Sweden and evidently provide potential reference curves for regional paleomagnetic comparisons.



Caption. Relative declination variations derived from varved sediments from lakes Alimmainen Savijärvi, Nautajärvi and Korttajärvi, with varve calculation error estimates shaded in gray, and a combined average inclination changes (on the right).

Ojala, A.E.K., Saarinen, T. & Salonen, V.-P., 2000. Preconditions for the formation of annually laminated lake sediments in southern and central Finland. Boreal Environment Research, 5: 243–255.

Ojala, A.E.K. & Tiljander, M. 2003. Testing the fidelity of sediment chronology: comparison of varve and paleomagnetic results from Holocene lake sediments from central Finland. Quaternary Science Reviews, 22: 1787-1803.

Snowball, I.F. & Sandgren, P., 2002. Geomagnetic field variations in northern Sweden during the Holocene quantified from varved lake sediments and their implications for cosmogenic nuclide production rates. The Holocene, 12: 517–530.

Tiljander, M., Saarnisto, M., Ojala, A.E.K. & Saarinen, T. A 3000-year palaeoenvironmental record from annually laminated sediment of Lake Korttajärvi, central Finland. Boreas, 26: 566-577.