Luminescence dating of anthropogenic rock structures in the northern Rockies and adjacent High Plains, North America: A progress report

Anthropogenic rock alignments, both circular and linear, are common in the northern Rockies and adjacent High Plains of North America. Their ages are largely unknown. Luminescence dating of single-grain feldspars is applied to sediment under the rocks on the assumption that prior to rock placement turbation processes zeroed sufficient number of grains and that these processes ended with the rock placement. Ages of single grains are corrected for anomalous fading and the age of placement is estimated using the minimum age model. Vertical distributions of ages show that youngest ages are clustered just under the rock, conforming to the turbation model. Low precision in fading corrections led to attempts to reduce fading with higher temperature stimulations. These did reduce fading but also recovered known doses poorly, suggesting possible age over-estimation. This uncertainty coupled with a problem of small sample sizes from material with generally low sensitivity resulted in overall low precision in ages, but still an improvement over the current lack of chronological information.

► IRSL dating is applied to sediments under anthropogenic rock features.
► Minimum age model provides date of placement because of turbation.
► Problems with sample size and optimal stimulation temperature are encountered.
► Ages are provided for five localities, although precision is low.