For late Quaternary records, most tephra horizons in sediment cores are dated by (linear) interpolation of 14C dates of carbonates, bulk sediment or organic remains. However, lakes are especially prone to a reservoir effect, due to dissolution of ancient carbonates and/or old organic matter that is washed into the lake from the catchment and incorporated into the sediment. Both phenomena can result in anomalous 14C ages and an offset from the real age of the dated material, which is not necessarily constant through time in the sediment section (Geyh et al., 1998; Yu et al., 2007). This offset from the real age can be of the order of several hundred or even more than a thousand years if bulk sediment or carbonates are dated, and can thus lead to misleading or erroneous age models if it is not taken into account (Geyh et al., 1998; Bertrand et al., 2012). Sediment sections spanning time intervals with multiple tephra layers could therefore easily be miscorrelated if the tephra is not adequately characterised to back up correlations. Appropriate tephra characterisation can potentially also help in evaluating the reservoir effect in a sediment section by providing a tie-point in the age model, provided the age of the tephra is well known from one or more independent sources (e.g., 14C dating on charcoal incorporated in terrestrial deposits, for example the well-constrained 3.00–3.05 ka cal BP Alpehué Pumice (So-A) eruption from Sollipulli; Supplementary Table 1; Naranjo et al., 1993b).
real age
offset from
several hundred or even more than a thousand years
years
cal BP Alpehué Pumice (So-A) eruption
3.00–3.05 ka
ka