Anticipated ages of the samples, if known. This helps select procedures and appropriate artificial irradiation exposures. While knowing the expected age will not influence our results, it does prompt us to look for explanations when our date does not correspond with expectations. Since the dating event is last exposure to light, the most important consideration in selecting sediment samples for dating is the likelihood that the sample was exposed to sufficient light prior to deposition and burial. Sufficient light may be as little as a few minutes of direct sunlight, although complete bleaching usually takes several hours.
Aeolian deposits have a high likelihood of long exposures because of airborne time.
The bleaching of fluvial deposits depends on the sediment load and the turbity of the flow, deposits from meandering streams generally being well bleached while glacial outflow tending to be less so. Colluvial deposits can be problematic, depending on the nature of the deposition and the grain size of the sediments. Buried soils have been successfully dated because of cycling of A-horizon sediments to the surface by pedoturbation. Bleaching is also affected by shade conditions and cloud cover. Any kind of crystalline material is potentially datable, but most research has been conducted on quartz and feldspars.