Cross dating (Th/U-14C) of calcite covering prehistoric paintings in
Borneo

Quaternary Research, September 2003, vol. 60, no. 2, pp. 172-179
(8)

Plagnes V.[1]; Causse C.; Fontugne M.; Valladas H.; Chazine J.-M.;
Fage L.-H.

[1]Laboratoire des Sciences du Climat et de l'Environnement, UMR
CEA/CNRS 1572, avenue de la Terrasse, 91198 Gif/Yvette , Cedex,
France

Abstract:

We present the first application of cross-dating (Th/U measured by
thermo-ionization mass spectrometry (TIMS) and 14C measured by
accelerator mass spectrometry (AMS)) of calcite covering prehistoric
paintings. Th/U age estimates of cave drapery range from 9800 to
27,300 yr B.P. while conventional 14C age is estimated between 9900
and 7610 yr B.P. depending on the dead carbon correction. The age
discrepancy is attributed to a disturbance of Th/U and/or 14C
geochemical systems, showing the limits of the geochronological
approach applied to this kind of material. For the Th/U system, the
poor consistency of U data (U content, 234U/238U activity ratios)
and apparent ages argue for open system conditions. For 14C system,
variation of the dead carbon fraction (dcf) and a possible mixing of
successive generations of calcite could account for age discrepancy.
Nevertheless, one sample shows concordant ages for the two methods.
Compatible ages through corrections for open system conditions are
assumed for other samples. Then, the cross-dating suggests 9900 yr
as the minimum age of the piece of drapery; the underlying painting
must be older. This study of rock art demonstrates the presence of a
Pleistocene population before 9900 yr in the southeast of Borneo,
whereas previously the only population in evidence in this area was
of Austronesian type from ~5000 to 6000 yrs ago.