A Semiquantitative Field Method for Evaluating Bioturbation on Bedding Planes

Abstract

Amount of bioturbation on bedding planes records the relationship between physical and chemical depositional conditions and biological activity. We propose a simple and easy-to-use method for field estimation of horizontal disruption using bedding-plane bioturbation indices that allow rapid generation of large data sets. Photographs of a representative subset of observations can be evaluated in the laboratory using image analysis and statistical analysis programs, providing a check on accuracy and potentially yielding additional information on the size, shape, and distribution of burrows and bioturbated patches. Extent of bioturbation on bedding planes can be integrated with other sedimentologic and ichnologic characteristics to interpret the infaunal community paleoecology and to reconstruct the history of the depositional, erosional, and burrowing events. Furthermore, use of the bedding-plane bioturbation indices and ichnofabric indices on vertical surfaces facilitates comparison of the extent of bioturbation through time, within and between facies, and across and between basins. It therefore enhances recognition of significant changes in physical processes, chemical conditions, and biological activity, and is a powerful tool in identifying long-term biological trends.