A 36CL COSMOGENIC ISOTOPE CALIBRATION STUDY IN ICELAND

The focus of this study is a calibration of cosmogenic ³⁶Cl production rates measured from >30 whole-rock and plagioclase feldspar samples of Icelandic basalts. Iceland is an ideal location for calibration because: Ca-rich volcanic rocks are ubiquitous; known numerical ages of uncovered and instantaneously exposed surfaces exist; many high resolution records exist in the North Atlantic region by which to compare the Icelandic chronology. The sites in Iceland differ from other calibration sites and are ideal for the following reasons:

1) They are all north of 63°, where production rates become independent of latitude and past geomagnetic variation.

2) The age of the lava flows is also the “exposure age”. There is no uncertainty regarding depositional history or inheritance.

3) Samples are near sea-level and close geographically, thereby eliminating the need for scaling.

4) All have been radiocarbon dated or exact age is known.

5) The relationship between the ¹⁴C dated material and the ³⁶Cl calibration surface is clear (i.e. deposition or emplacement was contemporaneous).

6) At 6 out of 7 sites there is a uniform rock type.

There is a need for a local calibration study/production rate in Iceland as more high resolution, numerical studies are being done to elucidate Late Quaternary environmental change in this climatically-sensitive region. Improving chronologies will lead to more robust comparison between terrestrial and marine records, a neccesary component to determining links between the earth-ocean-atmosphere system. It has been shown that the production rate of cosmogenic ³He in Iceland is up to 10% higher than normalized values elsewhere (Licciardi and Kurz 2002). This hypothesis will be tested for ³⁶Cl and “ground truthed”. This research establishes whether cosmogenic ³⁶Cl exposure dating is a viable technique to be used in Iceland on postglacial lava flows, erratics on moraines and marine shorelines.