Optically Stimulated Luminescence (OSL)
Dating - Taylor Valley
Figure 1 Location of OSL samples in Taylor Valley.
There are about 100 fluvial terraces in Taylor Valley, ranging in elevation from sea level to 314 m. These terraces have been dated by 14C dating of buried algal layers, yielding ages ranging from 8,340 – 23,800 14C years BP (Stuiver et al. 1981, Hall et al. 2000).
What's wrong with the 14C dates?Cold-dry environments tend to act like freezers, preserving organic carbon and recycling old material. It is well documented that algae in the Dry Valleys is readily transported by streams and wind, making issues of carbon recycling a major problem. Potential recycling sources are described below:
- RadioCarbon Reservoir Effect - Old carbon from glacial meltwater can be incorporated into growing algal mats.
- Wind-Blow Algae - Algal mats desicate during the wintermonths and are blown away by strong katabatic winds from the Antarctic Plateau.
- Water-Transported Algae - Upstream errosion can recycle old burried algae that is then incorporated into fluvial deposits.
ages of fluvial terraces in Taylor Valley organized by the drainage or
stream in which they were found (compiled from Hall et al.
2000). Terraces at similar
elevations, but different drainages, do not have similar ages, as would
be expected from a valley-wide paleolake.
Figure 3 A large fluvial
terrace located at 80 m on
Crescent Stream (a), a soil profile with foreset beds
evident and no aeolian horizon (b), cross-bedded topsets
(c), and gravelly sand with an aeolian horizon evident (d).
These fluvial features are thought to have formed when small ehpemeral streams from alpine glaciers flowed into paleo Lake Washburn. 14C dates of these deposits have been used to constrain lake levels, and by inference the retreat history of WAIS. In contrast, we believe that the origin of these deposits is uncertain. They may have formed in small ponds marginal to the WAIS ice lobe, as kame mounds, as deltas in a lake, or by downcutting older fluvial deposts.