REAL

High-precision loess chronologies by 14C-dating of small molluscs

Újvári, Gábor and Molnár, Mihály and Páll-Gergely, Barna (2015) High-precision loess chronologies by 14C-dating of small molluscs. In: XIX INQUA Congress, 2015.07.26-08.02., Nagoya, Japán.

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Abstract

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.

Item Type: Conference or Workshop Item (Poster)
Subjects: Q Science / természettudomány > QE Geology / földtudományok > QE02 Geochemistry / geokémia
Depositing User: Dr. Gábor Újvári
Date Deposited: 03 Sep 2015 08:39
Last Modified: 03 Sep 2015 08:39
URI: http://real.mtak.hu/id/eprint/26020

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