PRELIMINARY OPTICAL DATING STUDIES OF EOLIAN DEPOSITS FROM THE SOUTHERN ALBERTA FOOTHILLS, CANADA

Eolian landforms of Holocene age in the prairie dryland regions of southern Saskatchewan and Manitoba and in the Foothills of southwestern Alberta have been extensively dated using optical dating in order to establish periods of landscape stability and instability which, in turn, have been associated with short and long term fluctuations in climate. For this work, potassium feldspar and a multiple-aliquot technique have been exclusively employed providing reliable information [1]. A standard protocol of the SAR method has recently been tested on quartz at University of the Fraser Valley (UFV) on a series of sand dunes and loess deposits in the Alberta Foothills that are important in that they contain charcoal and tephra beds that provide well-constrained independent ages. However the SAR optical ages from quartz in these deposits significantly underestimate the independent ages [2]. This could be due to the large number of aliquots containing a significant, and likely unstable, medium component in their shine-down curves. To test this, we chose a site with an abundance of independent age control. In this poster we will present the results of De(t) plots that confirmed the presence of an unstable medium component as well as linear modulation measurements that were used to determine the significance and location of the medium and other components. Using the linear modulation data the optimal time intervals were chosen for the separation of the fast and medium components and the early light subtraction (ELS) method was employed [3]. While the ELS method showed significant improvement over the previous SAR ages, further testing is still required before the method can be utilized in the immediate region.

Sources cited: [1] Wolfe, S.A., & Hugenholtz, C.H. 2009. Barchan dunes stabilized under recent climate warming on the northern Great Plains. Geology, 37: 1039–1042; [2] Wolfe et al. 2009. Timing and rates of Holocene eolian deposition in the eastern Canadian Rockies: preliminary results. CANQUA Program & Abstracts, p. 175. [3] Pawley, S. et al. 2009. Quartz luminescence dating of Anglian Stage (MIS 12) fluvial sediments: Comparison of SAR age estimates to the terrace chronology of the Middle Thames valley, UK. Quaternary Geochronology, in press.