 |
| Titel |
Establishing chronologies for loess records within 40 ka by AMS 14C-dating of small mollusc shells |
| VerfasserIn |
Gábor Újvári, Mihály Molnár, Ágnes Novothny, János Kovács |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090696
|
| Publikation (Nr.) |
 EGU/EGU2014-4950.pdf |
|
|
|
|
|
| Zusammenfassung |
| The key objective of the INTIMATE project is to determine whether abrupt climatic
changes during the period of 60 to 8 ka, as reflected in a range of proxy records, were
regionally synchronous or whether there were significant ‘leads’ and ‘lags’ between the
atmospheric, marine, terrestrial and cryospheric realms. Such goals require precisely dated
records of paleoenvironmental change for this period. Although wind-blown loess
deposits are regarded as key terrestrial archives of millennial or even centennial scale
environmental changes, these records are mostly poorly dated and/or their age-depth
models have uncertainties of millennial magnitude. This prevents us from addressing
issues like synchroneity of abrupt climatic/environmental events on millennial time
scales.
Two different means of dating are commonly applied for loess sequences: luminescence
and radiocarbon dating. Major problems are low precision of luminescence ages and the
general lack of organic macrofossils (e.g. charcoal) in loess that can reliably be dated using
14C. Other datable phases in loess are mollusc shells, rhizoliths and organic matter. While
organic matter 14C ages are often seriously compromised by rejuvenation in loess sequences,
rhizolites consistently yield very young ages as first demonstrated in German loess profiles.
Indeed, hypocatings (rhizolites) gave Holocene ages from three different depths (4.00 m:
9744-10156 2Ïă age range in cal yr BP, 5.00 m: 8013-8167 cal yr BP and 6.00 m: 9534-9686
cal yr BP) in the DunaszekcsÅ loess record we investigated. Mollusc shells are the only
remaining phases for dating, but these are usually regarded as unreliable material for
14C-dating, as they may incorporate 14C-deficient (or dead) carbon from the local
carbonate-rich substrate during shell formation, thereby producing anomalously old ages
by up to 3000 years. Recent studies, however, indicated that reliable ages can be
obtained by radiocarbon dating of molluscs having comparatively small ( |
|
|
|
|
|
|