Toward establishing precise ⁴⁰Ar/³⁹Ar chronologies for Late Pleistocene palaeoclimate archives: an example from Suigetsu SG06, Japan

The varved Suigetsu (SG06) sediment core is potentially one of the most important and well-constrained mid-latitude palaeoclimate archives, recording continuous deposition during the last ∼150 kyrs. Numerous visible and non-visible volcanic ash layers form unique age markers within SG06. These ash layers are too fine and crystal-poor to be directly dated using the <sup>40</sup>Ar/<sup>39</sup>Ar technique so the tephra were correlated to proximal volcanic deposits using their glass shard compositions. A high-precision <sup>40</sup>Ar/<sup>39</sup>Ar sanidine age of 10.0 ± 0.3 ka (1σ, n = 34, MSWD = 0.71, p = 0.89) was obtained for the SG06-1288 (U-Oki) proximal tephra (Ulleungdo U4). <sup>40</sup>Ar/<sup>39</sup>Ar yields a precision of ±3% near the younger limit of the method, with improved precision possible for older SG06 samples. Such <sup>40</sup>Ar/<sup>39</sup>Ar ages for tephra layers can provide invaluable tie-points within the Lake Suigetsu SG06 sequence, giving independent verification of the core’s varve chronology, allowing for the calibration of cosmogenic nuclide production, and providing a precise chronology beyond the varve limit