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

Bioturbation in oxic deep-sea settings is often considered (if considered at all) to consist of a 2-10 cin thick homogenized layer and some easily recognizable distinct burrows which could be avoided when sub-sampling the sediment 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 deep-sea sediments in all oceans. This trace, Zoophycos, is therefore predestined to cause errors and even age reversals in high-resolution dating. In order 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 two 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 fresh 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-sampling is strongly recommended. (C) 2001 Elsevier Science B.V. All rights reserved.