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T2
Palynostratigraphic alignment chronology versus independent dating methods.
14
C, OSL and tephra: an example from Lake Fimon, northern Italy
S. E. Lowick 1 *, M. Hardiman 2,3 , S. P.E. Blockley 2 , B. Giaccio 4 F. Preusser 5 , P. Reimer 6 , C.
S. Lane 7
1 Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of
Bern, Switzerland
2 Centre for Quaternary Research, Department of Geography, Royal Holloway, University of London,
Egham, Surrey, United Kingdom
3 Department of Geography, University of Portsmouth, Portsmouth
4 Istituto di Geologia Ambientale e Geoingegneria, CNR, Via Salaria km 29,300, 00015 Rome, Italy
5 Department of Physical Geography and Quaternary Geology, Stockholm University, Sweden
6 Centre for Climate, the Environment & Chronology, School of Geography, Archaeology and
Palaeoecology, Queen’s University Belfast, United Kingdom
7 Research Laboratory for Archaeology and the History of Art, University of Oxford, Dyson Perrins
Building, South Parks Road, Oxford OX1 3QY
Independent dating evidence is presented for a lacustrine record for which an age-depth
model had already been derived primarily through the interpretation of a pollen signal. For
the upper part of the core, quartz optically stimulated luminescence (OSL) ages support
radiocarbon ages that were previously considered to suffer an underestimation due to
contamination, and both methods imply a younger chronology than does the pollen. The
successful identification of the Campanian Ignimbrite as a cryptotephra within the core
also validates this younger chronology for the upper part of the core, as well as extending
the known geographical distribution of this tephra layer within Italy. Further down the core,
the OSL ages continue to be younger then the pollen chronology, and underestimate a
pollen assemblage correlated to the Eemian (Marine Isotope Age 5e) by ~ 20 ka. These
new results pose problems for both the pollen interpretation and the OSL in the upper and
lower part of the core respectively. For the upper core, the three independent dating
methods suggest that care should always be taken when building chronologies from proxy
records via alignment techniques, particularly when correlations are made to records
which have themselves been tuned to a target record or global signal (i.e. double tuning).
In the lower part of the core, the OSL quartz signal suggests an underestimation around
the age range that has already been shown to be problematic by some other studies,
although no indication of a problem has so far been found with the Fimon quartz. No
definitive chronology is offered here for Lake Fimon, although multiple lines of dating
evidence show that there is sufficient reason to seriously consider it within MIS 3. This
data is presented to encourage debate and further investigation of such issues. The
Quaternary dating community should always have all age information available, even
when significant temporal offsets are apparent between various lines of evidence, to be: 1)
better informed when they face similar dilemmas in the future, and 2) allow multiple
working hypotheses to be considered.
Keywords: independent dating; proxy records; tuning; luminescence; radiocarbon;
cryptotephra