Exploring computed tomography in ichnological analysis of cores from modern marine sediments

Abstract

ichnological analysis is considered a very useful tool in several disciplines of earth Sciences, including palaeoenvironmental studies and hydrocarbon exploration. Sediment cores provide excellent records, despite difficulties encountered during study runs due to specific core features. Previous studies using 2D images have proven the benefits of high-resolution image treatment in improving the visibility of ichnological features, but with limitations. 3D computed tomography (CT) techniques were applied to palaeoichnological studies in lithified cores and other disciplines of palaeontology to solve these limitations, but not used for ichnological studies in unconsolidated sediments due to the low density contrast between host sediment and trace fossils. In this study, a CT processing technique, previously tested in coral research, is applied to facilitate the characterisation of the ichnological signature of cores from modern marine soft sediments. This technique allows for the first time the isolation of burrows within these kinds of sediments and the differentiation of intervals based on burrow orientation. Data obtained from the technique are complemented with the ichnological information from conventional core description, thus providing a more complete characterisation of the trace fossil assemblage with additional ichnological properties such as burrow orientation and branching. this will improve palaeoenvironmental interpretations related to changes in energy or oxygenation, and the analysis of reservoir quality given the impact of burrows on porosity and permeability. Therefore, adopting CT to complement visual core description in the ichnological analysis of soft modern marine cores is a very informative approach.Ichnological research is widely recognised as a very useful tool in the study of drilled marine cores in a wide range of fields. Biogenic structures, reflecting the behaviour of trace-makers in response to palaeoenvironmental conditions, provide valuable information into areas such as palaeoecology, facies analysis, palaeoenvironmental reconstructions, sequence stratigraphy and palaeoceanography 1-8 . In recent decades, the study of trace fossils has also become an essential part of reservoir and aquifer characterisation 9 . Numerous studies have proven that bioturbation is an important factor in the study of reservoir properties, affecting parameters such as porosity and permeability 10-18 . The key factors involved would be grain size re-distribution, morphology of trace fossils (e.g., shape, size, orientation, branching), burrow lining, infilling material of trace fossils, and bioturbation intensity 10,19-21 . For all these reasons, ichnology is seen as a powerful tool in Earth Science research and hydrocarbon exploration 4,13 .Initially, ichnological studies were mostly based on outcrops and modern environments 21,22 , but the study of cores has gradually increased as the amount of core material recovered from oceanic expeditions became more abundant 9,23 . Core material makes it possible to...

Magnetic Resonance Imaging as a Novel Method for Elucidating Sediment Burrow Structures and Functions

“…The ammonium ion concentration also increased with depth (Figure b), but biological production and consumption processes also modified the vertical profile. These facts show the validity of the burrow densities calculated from MRI, which are consistent with the reported effects of bioturbation on solute fluxes. ,− In cores with high burrow density, observed ion concentrations ( C z ) were depleted relative to potential C z (Figure S3). We would expect a much depleted Δ C z (= C z – potential C z ) under a substantial water-circulation effect of burrows.…”

“…Three-dimensional (3D) burrow structure analysis based on nondestructive visualization techniques such as X-ray computed tomography (CT) and magnetic resonance (MR) imaging (MRI) would be ideal for elucidating the relationship between the burrow abundance and the water-circulation effect of burrows. Although X-ray CT has been developed and used to analyze burrow structures in various types of sediments, − it could not reveal burrow structures in the soft mud of Lake Kasumigaura, which has a high water content (i.e., 0.89 ± 0.03) and porosity (i.e., 0.95 ± 0.03). Therefore, we wondered whether MRI could be used for the analysis of the burrow structure .…”

Expedition 390/393 methods

“…In addition to characterizing bioturbation intensity (as described in Bioturbation above), Expedition 393 shipboard scientists specified the four most common trace fossils observed (as the 1st, 2nd, 3rd, and 4th dominant ichnofossils), defined ichnofossil diversity as the total number of identified ichnofossils, measured the maximum trace fossil diameter, and added comments in an Ichnofossil comment column for extra observations and details. The most common trace fossils, namely Zoophycos, Chondrites, Planolites, Palaeophycus, Thalassinoides, Skolithos, Nereites/Cosmorhaphe, Phycosiphon, and rarely Arenicolites, Cylindrichnus, and Spirophyton, were defined based on various atlases, books, and scientific papers devoted to ichnological analysis of cores from modern marine sediments (Bromley and Ekdale, 1984;Buatois and Mángano, 2011;Dorador et al, 2020;Bromley, 1984, 1991;Pemberton et al, 2009;Rodríguez-Tovar and Dorador, 2015;Wetzel et al, 2010).…”

CroSSED sequence, a new tool for 3D processing in geosciences using the free software 3DSlicer

“…the Health Sciences, the Arts, and the Earth Sciences) due to their non-invasive revelation of internal structures [1][2][3] . Within the Geosciences, CT techniques, X-ray CT and micro-CT are becoming widely used 4,5 , as reflected by the recent surge in publications [5][6][7][8][9][10][11] . CT enables geoscientists to study internal features (e.g.…”