The Effects of Bioturbation by Earthworms. Preliminary Results of an Actualistic Taphonomy Experiment

Abstract

The Salado River Depression was inhabited during the Late Holocene (2400-400 14C YBP) by potterymaker societies with a hunting-gathering-fishing lifeway. The archaeological remains are deposited in the A horizon of the modern soil, which constitutes a ?biomantle? as pedogenetic formation processes predominate. These include an intense biological activity produced by the action of roots and edaphic fauna that promote displacements of objects and their sinking to different depths. Hence the archaeological sites of this microregion are shallow. In order to broaden the knowledge about the action of earthworms in these sites, an actualistic taphonomy experiment was designed. The goal was to observe the activity of these invertebrates and to evaluate their possible incidence as a disturbing agent on small bones deposited on a soil. The aim of this paper is to introduce the methodological design of this experimentation and present the preliminary results. For this purpose, two containers with sediment containing humus and earthworms were placed in the open air. Some selected bones of Dasypus hybridus and Gallus gallus were deposited in each container. The activity of earthworms was observed along one year with a weekly record and was detected as deep as 16 cm. Other features associated ?such as burrows? were documented, especially in autumn and winter. No modifications were identified on bone cortical surfaces, though vertical movement of some elements through the sediment is highlighted.