Dating errors in high-resolution stratigraphy: a detailed X-ray radiographand AMS-C-14 study of Zoophycos burrows

Bioturbation in oxic deep-sea settings is often considered (if considered a t all) to consist of a 2-10 cin thick homogenized layer and some easily rec ognizable distinct burrows which could be avoided when sub-sampling the sed iment cores. However, there is one trace that is often difficult to discern in unlithified sediments, that manifests transport of considerable amounts of sediment over lar-e vertical distances, and that is widely spread in de ep-sea sediments in all oceans. This trace, Zoophycos, is therefore predest ined to cause errors and even age reversals in high-resolution dating. In o rder to better estimate the size of these age errors, we have performed AMS -C-14 dating of the trace itself and of directly surrounding material in tw o gravity cores from the Portuguese continental slope. The results show an age falsification of 1110-2525 years at sedimentation rates of 10-20 cra ka (-1). Since Zoophycos burrows are often poorly or not at all visible in fre sh cores, all observations of Zoophycos were made on X-ray radiographs. To avoid dating errors of this kind, an X-ray radiograph study prior to sub-sa mpling is strongly recommended. (C) 2001 Elsevier Science B.V. All rights r eserved.