Mathematics – Logic
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997e%26psl.153..251i&link_type=abstract
Earth and Planetary Science Letters, Volume 153, Issue 3-4, p. 251-263.
Mathematics
Logic
5
Scientific paper
U-Th ages of Holocene lacustrine sediments from southern Sweden have been determined to assess the reliability of this technique for dating climatic events from the last interglacial-glacial-interglacial cycle, and for calibration of the 14C dating method. The sediments are organic- and carbonate-rich, and they are shown to be very well suited to high precision 238U-234U-230Th dating by thermal ionisation mass spectrometry (TIMS). Twenty-one samples from 2.58 m of sediment from Lake Igelsjön, southern Sweden, yield ages between 3058 +/- 89 and 9426 +/- 262 yr (2σ error). The sediments consist of hydrogenous calcium carbonate (50-90%), organic matter (5-50%), and siliceous residue (<5%). The high U contents of the lake sediments (between 6 and 76 ppm) are in contrast to the low concentrations in the lake- and groundwater (1.9 and 3.2 ppb, respectively), and mass balance calculations based on U content of water and sediments can be used to calculate a lakewater residence time of 24 days which is close to the residence time calculated using hydrologic data. Recent ground and lakewater ((234U/(238U)) = 0.920) is enriched in 234U compared to soils from the catchment area ((234U/(238U) = 0.587), and (234U/(238U)) in the lake sediments shows a marked decrease with time from 0.958 at 9426 yr BP to 0.919 at 3058 yr BP. This is attributed to progressive leaching of U from soils which have experienced a previous history of recoil-related U loss, and it indicates that the assumption of constant initial (234U/(238U)) ratios may be a source of significant error in the calculation of (234U/(238U)) ages for continental deposits.
Björck Svante
Hawkesworth Chris J.
Israelson Carsten
Possnert Göran
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