THE 'ECOSYSTEM' OF LUMINESCENCE DATING

TL (thermoluminescence) dating has been suitable for both heated and unheated minerals (generally quartz and feldspar in artifacts or sediments) in several settings. With the advent of OSL (optically stimulated luminescence) dating in 1985, most development of technique and application has focused on unheated sediments. Since ~2000 there has been the introduction of several additional variants of TL and OSL dating procedures, with a plethora of acronyms. Thus, an analogy to an ecosystem may be a helpful metaphor for understanding. In this context, each variant (e.g., SG-OSL, TT-OSL) can be viewed as a 'species' or 'hybrid' that exploits intrinsic properties (analogous to 'gene-pool' capabilities) of luminescence traits within each of the most useful mineral groups (feldspars and quartz). These properties encompass a variety of luminescence emission spectra and signal stabilities.

Attempts to utilize these intrinsic properties have led, and are leading, to procedural variants (e.g., SG-OSL) that are suited for application to different (sometimes overlapping) 'environmental niches'. Such niches are shaped by different types of geological deposits/processes and age ranges . Eolian sediments younger than 100-200 ka (even if only a few decades old) are suited to dating by quartz OSL. Eolian sediments > ~200 ka usually require dating by feldspar TL or OSL, but with some limitations that are still the subject of study. Fluvial and colluvial deposits generally require single-grain-quartz dating for consistent accuracy. One limitation ('genetic weakness') of the use of feldspars is the type of instability termed 'anomalous fading'. Recently some variants (e.g., IRSL-isochron and IR-RF procedures) of the luminescence family appear to overcome the limitation of this instability. Examples will be presented of basic concepts, and of applications of selected procedural variants to sediments spanning the age range from decades to ~900 ka. Some remaining challenges also will be mentioned.