Investigating optical dating of carbonate-rich cobbles from a river terrace: A pilot study from the Mula Valley, Spain

Rock surface luminescence dating has emerged as a powerful geochronological tool; however, the method requires lithologies containing sufficient amounts of quartz or feldspar grains. The application of burial dating to fluvial cobbles, containing only sparse amounts of feldspars, is evaluated in calcarenite cobbles collected in the Mula valley, Spain. Two sampled cobbles demonstrated sufficient luminescence sensitivity. We extracted three or more drill cores from each cobble surface and subsequently measured the sensitivity-corrected luminescence signal with depth using an IRSL/pIRIR protocol to target feldspar grains in calcarenites. We observed significant luminescence-signal depth variations between the cores collected from the same rock surface, suggesting the value of measuring several cores. None of the top surfaces has been significantly bleached; therefore, they convey no relevant age data. Cores from the bottom surfaces show evidence of bleaching in the first 1 to 3 mm, but generally, only the surface slices can be used for dating. One core from each cobble displays a short, non-saturated dose plateau near the surfaces; the modelling demonstrates that the surface slices from these cores contained negligible doses before burial. The age estimate for the bottom surfaces mainly falls into two groups: 24–38 ka and 11–16 ka. The older age group is within the expected age range, previously dated with radiocarbon on another outcrop of the same terrace system. However, the signal-depth profiles indicate that the younger date is more reliable than the older date. Currently, no geomorphological explanation exists to explain the younger-than-expected ages.