Abstract
Tectono-sedimentary systems are readily recognized in Northeastern Tibet and elsewhere but they have proved difficult to date via conventional absolute dating techniques. In the Qilian Shan the application of cosmogenic methods is complicated by the presence of terrace blanketing loess deposits. We have chosen to explore the potential of applying optical dating techniques to directly date the loess cover deposits to provide minimum ages for terrace abandonment events. We focussed on a suite of six loess-mantled terraces cut into an abandoned alluvial fan sequence which was uplifted by thrust faulting on the Zhangye Thrust Fault, East of the Hei He river at its exit from the Qilian Shan. Application of single aliquot regeneration (SAR) optical dating techniques provides a chronology of terrace age. We employ a ‘Double-SAR’ procedure in which aliquots are subjected to both infrared ( λ in=830 nm) and blue ( λ in=470 nm) stimulation and two sets of D e determinations are produced and assumed to relate predominantly to feldspathic and quartz fine grain populations respectively. Our D e and age determinations are stratigraphically sensible and we do not observe a significant difference between IRSL and OSL D e estimates which has been the case in previous studies.
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