Lateral variability of ichnofabrics in marine cores: Improving sedimentary basin analysis using Computed Tomography images and high-resolution digital treatment

摘要

Major ichnofabric attributes may be related to a number of limiting marine parameters for tracemakers with paleoenvironmental significance, including ocean/atmosphere dynamics. This is why ichnofabric analysis has proven to be a very useful tool in sedimentary basin analysis - as well as in other Earth Science disciplines - although it is a comparatively recent approach in ichnological research. Ichnofabric characterization is usually based on 2D visual observations of a single view in both outcrops and cores. Yet ichnofabric features can vary vertically and laterally within a very short-distance, which may lead to misinterpretations. Here, a new methodological approach is presented, allowing for a more objective evaluation of ichnofabric features, based on the high-resolution digital treatment of Computed Tomography images on marine sediments cores. The method evaluates variations in ichnoassemblages, cross-cutting relationships, and the degree of bioturbation structures in nearby selected images pertaining to several sections of the same interval of a core. Average values of the obtained data imply a significant improvement of the resolution than 2D observations, and therefore a more precise and objective characterization of ichnofabrics. The usefulness of the method and its differences with respect to traditional ichnofabric analysis are exemplified by a study of the gravity core FSG09-10 (Galicia Bank domain, NW Iberian Peninsula), showing as a very significant tool to interpret paleoenvironmental changes (i.e., sedimentation rate, nutrient availability, and bottom water oxygenation) from the Last Glacial Maximum (LGM) to Heinrich Event 1 (HE1). This example reveals the importance of proposed methods in order to characterize the ichnofabrics, including their lateral variability, with clear implications for future research on basin analysis.