Review and assessment of the potential of post-IR IRSL dating methods to circumvent the problem of anomalous fading in feldspar luminescence

Quartz has been the main mineral used for optically stimulated luminescence (OSL) dating of sediments over the last decade. The quartz OSL signal, however, has been shown to saturate at relatively low doses of ～200–400 Gy, making it difficult to be used for dating beyond about 200 thou-sand years (ka), unless the environmental dose rate is low. The infrared stimulated luminescence (IRSL) from feldspars has been shown to continue to grow to higher dose levels than quartz OSL. The application of IRSL dating of feldspars, however, has long been hampered by the anomalous fading effect. Recent progress in understanding anomalous fading of the infrared stimulated luminescence (IRSL) signals in potassium-feldspar has led to the development of post-IR IRSL (pIRIR) protocols and also a multiple elevated temperature (MET) stimulation (MET-pIRIR) protocol. These procedures have raised the prospect of isolating a non-fading IRSL component for dating Quaternary deposits containing feldspars. In this study, we review the recent progress made on (1) overcoming anomalous fading of feldspar, and (2) the development of pIRIR dating techniques for feldspar. The potential and problems associated with these methods are discussed.     

Taiwan: Changes and Challenges

In January and March 2008, Taiwan's citizens voted primarily for domestic political reasons to oust the Democratic Progressive Party administration and promulgate the second peaceful transfer of power in Taiwan's relatively young democracy. Surveys suggest that the new administration of President Ma Ying-jeou in its first few months in office has failed to meet voter expectations. Taiwan's new international relations with the United States, Japan and China have also raised concerns both within Taiwan and overseas.

     

New ages for the post-Howiesons Poort,late and final Middle Stone Age at Sibudu,South Africa

Optically stimulated luminescence (OSL) measurements are reported for single grains of quartz from deposits within Sibudu rock shelter. Such measurements enable rejection of unrepresentative grains and application of the finite mixture and central age models to obtain the most reliable age estimates. Three types of single-grain equivalent dose (D_e) distributions were observed: one sample represented a single dose population, three samples indicated mixing between Iron Age (IA) and Middle Stone Age (MSA) deposits, and 10 samples (in addition to the three mixed samples) showed scattered distributions. The latter type resulted from differences in the beta dose received by individual grains. For these samples, the beta doses were modelled and adjusted accordingly. Ages for the 14 samples collected from MSA deposits post-dating the Howiesons Poort (HP) resulted in three age clusters, which are stratigraphically consistent with the three informally named cultural phases at Sibudu: namely, the post-HP, late MSA and final MSA. Weighted mean ages of 58.5 ± 1.4 ka, 47.7 ± 1.4 ka and 38.6 ± 1.9 ka were calculated for these phases, respectively. The three phases were separated by two occupational hiatuses with durations of 10.8 ± 1.3 ka and 9.1 ± 3.6 ka. We hypothesise that the punctuated presence of humans at Sibudu was determined by large-scale fluctuations in climate during oxygen isotope stage (OIS) 3, which resulted in alternating wet and dry periods. Phases of occupation correspond to wet periods when fresh water was available in the Tongati River, whereas intervals of site abandonment correspond to dry periods when people were forced to migrate in search of a reliable source of fresh water. Where people migrated to, remains unresolved.     

Book reviews

STRENGTHENING THE FRAMEWORK OF PEACE. A Study of Current Proposals for amending, developing, or replacing present International Institutions for the Maintenance of Peace. By Alan de Rusett. (London and New York, Royal Institute of International Affairs, 1950. xiii +225 pp.)

VOTING AND THE HANDLING OF DISPUTES IN THE SECURITY COUNCIL. By Eduardo Jiménez de Aréchaga. Carnegie Endowment, N.Y., 1950. This is a lawyer's study of the operations of the Security Council. The author, a Uruguayan, was an officer in the U.N. Secretariat for some time and is now Under Secretary of Foreign Relations in Uruguay.

IMMIGRATION. By W. D. Borrie, 1949. Sydney and London, Angus and Robertson, pp. 105 + viii.

THE BRITISH COMMONWEALTH SINCE 1815. By C. H. Currey. 2 vols. Sydney, Angus & Robertson, 1950–51. Vol. I, pp. viii +471; Vol. II, pp. viii +287.

DEFENCE IN THE COLD WAR. By a Chatham House Study Group. London: R.I.I.A. 1950, pp. viii +123.

ASPECTS OF AMERICAN GOVERNMENT. A Symposium edited by Sidney Bailey. London: The Hansard Society. 1950.