Despite that loess records provide a wealth of information on abrupt climatic and environmental changes, almost all such
records have low precision chronologies. Age-depth models of loess sequences have uncertainties reaching thousands of years
thereby rendering proxy interpretations highly ambiguous on millennial/sub-millennial timescales. This is partly because OSL/IRSL
dating techniques, commonly applied to eolian deposits, yield imprecise ages on such timescales. Also, 14C-dating of organic
matter, secondary carbonates and humic acids provide questionable and mostly unreliable dates, for reasons not detailed here.
At the same time, charcoals that are regarded as phases yielding reliable ages rarely occur in loess sequences and 14C-dates of
molluscs are often anomalously old due to dead carbon incorporation during shell formation.
Here we show that some species of molluscs having small (≦ 10 mm) shells incorporate very low amounts of 14C-deficient carbon
into their shells and provide reliable ages as revealed by testing against charcoal ages and against a Bayesian age-depth model.
56 AMS radiocarbon ages were generated from a loess profile at Dunaszekcso (Hungary). Of these ages four originate from charcoals
and are taken as reference. Comparison of mollusc shell ages with those of charcoals reveal that Succinella oblonga and
Vitrea crystallina give statistically indistinguishable ages, while Chondrula tridens and Clausilia sp. shells show age anomalies
ranging from 500 to 900 14C yr. Testing against a Bayesian age model resting on 48 14C ages at different depths (2-3
ages from each depth), highlights that, beyond S. oblonga and V. crystallina, species like Orcula dolium, Discus ruderatus,
Euconulus fulvus, Pupilla muscorum and Vallonia costata yield relatively accurate ages (anomalies mostly within ±300 cal BP
yr). This investigation also demonstrates that Trichia hispida is best avoided in 14C-dating studies and that micrographitization
of shells, in case of low carbon contents after preparation, always results in anomalous ages