Prof Christopher Ramsey

Abstract:

Peat is notoriously difficult to radiocarbon date as it is composed of a heterogeneous mix of organic materials of different radiocarbon ages and at different stages of humification. Different chemical fractions (most frequently humin and humic acid) have been observed to yield significantly different radiocarbon ages from some peat deposits. Here we present humin and humic acid dates on a range of grain-size fractions of peat from the open-air archaeological site of Ahrenshöft LA 58 D, northern Germany, which were measured to confirm the identity of the source of cryptotephra found at the site. Both the humin and humic acid ages increased with increasing grain size, and for all but one sample the humic acid fraction was younger than the corresponding humin date. When calibrated the 6 dates from the horizon containing the cryptotephra spanned a time period of up to 1500 years, and are insufficiently conclusive to definitively resolve which eruption is responsible for the observed ash horizon. © 2011 Elsevier B.V.

Abstract:

This is the thirty-fourth list of AMS radiocarbon determinations measured at the Oxford Radiocarbon Accelerator Unit (ORAU). Amongst the dates obtained for archaeological sites included here are the latest series of determinations from the key sites of Proskynas (Greece), Kovačevo (Bulgaria) and Khirbet Qeiyafa (Israel), as well as others dating to the Palaeolithic, Mesolithic and later periods. Submitters of the material provide comments on the significance of the results. © University of Oxford, 2011.

Abstract:

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 40Ar/39Ar technique so the tephra were correlated to proximal volcanic deposits using their glass shard compositions. A high-precision 40Ar/39Ar 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). 40Ar/39Ar yields a precision of ±3% near the younger limit of the method, with improved precision possible for older SG06 samples. Such 40Ar/39Ar 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. © 2011 Elsevier Ltd.