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

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.This work is supported by the Spanish Government [Project CGL2015-66835-P, Secretaría de Estado de I + D + I], Andalusian Government [Research Groups RNM-178 and RNM-276], and University of Granada [Scientific Excellence Unit UCE-2016-05]. The research of J.D. is financed by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant Agreement No. 792314 (ICON-SE)

Lateral variability of ichnological content in muddy contourites: Weak bottom currents affecting organisms’ behavior

Although bioturbation is commonly recognized in contourites, only a few studies have analyzed the ichnological content of these deposits in detail. These studies have mainly focused on meso-scale bigradational sequence (a coarsening upward followed by a fining-upward sequence resulting from variations in current velocity). Here we present data from gravitational cores collected along the NW Iberian Margin showing systematic variation in ichnological content across proximal to distal depocenters within a large-scale elongated contourite drift. Data demonstrate that tracemakers’ behavior varies depending on the distance relative to the bottom current core. Trace fossils are already known to be a useful tool for studying of contouritic deposits and are even used as criterion for differentiating associated facies (e.g., turbidites, debrites), though not without controversy. We propose a mechanism by which the distance to the bottom current core exerts tangible influence on specific macro-benthic tracemaker communities in contourite deposits. This parameter itself reflects other bottom current features, such as hydrodynamic energy, grain size, nutrient transport, etc. Ichnological analysis can thus resolve cryptic features of contourite drift depositional settings.European Commission | Ref. H2020, n. 792314Universidad de Granada | Ref. UCE-2016- 05Xunta de Galicia | Ref. ED481B 2016/029-0Junta de Andalucía | Ref. CGL2015-66835-

The complex case of Macaronichnus trace fossil affecting rock porosity

Bioturbation is an important factor for reservoir quality due to the modification of host rock petrophysical properties (i.e., porosity, permeability, and connectivity). However, there is no predictable relationship between bioturbation and its effect on rock properties, due to the variability of the involved ichnological features. A detailed ichnological analysis is necessary to determine how bioturbation affects petrophysical properties in a bioturbated reservoir. Traditionally, ichnological features such as density, tiering, size, orientation, architecture, and fill, have been considered. However, other properties have been undervalued as is the case of lining. Here, we present a detailed study on the effects of Macaronichnus burrows, an ichnotaxon usually related to hydrocarbon exploration due to its high concentration in rock notably affecting petrophysical properties. Macaronichnus, a subhorizontal cylindrical burrow, is characterized by a well-defined and developed outer rim surrounding the tube core. Our data indicates a clear zonation in porosity according to burrow structure, with the lowest porosity in the tube core and higher values associated with the surrounded rim. This duality is determined by the tracemaker grain selective feeding activity and the consequent concentrated cementation. The organism concentrates the lighter minerals in the tube core fill during feeding, favoring post-depositional cementation during diagenesis and this results in lower porosity than the host rock. However, heavy minerals, mainly glauconite, are located in the rim, showing higher porosity. Our results support the view that ichnological analyses are essential to determine reservoir quality in bioturbated reservoirs, evidencing that other ichnological properties in addition to those traditionally considered must be evaluated.EU's Horizon 2020 research and innovation program under the Marie Skodowska-Curie Grant 792314Ministerio de Educación, Cultura y Deporte, SpainSecretaria de Estado de I+D+I, Spain CGL2015-66835-P PID2019-104625RB-100Junta de Andalucía B-RNM-072-UGR18 P18-RT-4074Scientific Excellence Unit (UGR) UCE-2016-0

Trace fossil characterization during Termination V and MIS 11 at the western Mediterranean: Connection between surface conditions and deep environment

This study was supported by the predoctoral FPU contract FPU17/03349 awarded to A. Gonzalez-Lanchas by the Spanish Ministry of Sci-ence, Innovation and Universities. The research by JD was funded through the Juan de la Cierva Program (IJC2019-038866-I) by the Spanish Ministry of Science and Innovation. Essential financial infra-structure was provided by the programs RTI2018-099489-B-100 of the Spanish Ministry of Science, Innovation and Universities granted to GGO (Grupo de Geociencias Oceanicas de la Universidad de Salamanca) and CGL2015-66835-P and PID2019-104625RB-100 of the Spanish Ministry of Science, Innovation and Universities and B-RNM-072-UGR18, P18-RT-4074 of the Andalusian Government granted to Ichnology and Palaeoenvironment RG (University of Granada) . We thank Alessandra Negri and the two anonymous reviewers, whose comments contributed to improve this manuscript.Trace fossil assemblages are studied at Ocean Discovery Program (ODP) Site 977 to characterize the response of the macrobenthic trace maker community to deep paleoenvironmental conditions during the Termination V (TV) and interglacial Marine Isotope Stage (MIS) 11 at the western Mediterranean Alboran Sea. An assemblage composed of Chondrites, Planolites, Scolicia, Thalassinoides and Zoophycos is identified, showing notable variations in ichnodiversity, abundance and Bioturbation Index, that were analyzed in detail. The integration of ichnological information with sediment color and high-resolution coccolithophore records from Site 977, evidenced that variations in macrobenthic trace maker community are primarily controlled by oxygen availability and surface organic productivity patterns. During TV, high surface organic productivity by intense Alboran Upwelling System enhanced the deep organic accumulation that, together with reduced deep-water removal, resulted in a decrease of bioturbation and the formation of an Organic Rich Layer. Moderate and stable surface production through MIS 11c reduced deep food availability, resulting in an oligotrophic and stable deep environment. This is reflected by relatively abundant trace fossils in lighter sediments. Intra-interglacial increase in surface organic production at ~405 ka is evidenced by increased organic matter preservation. Minor impact of western Mediterranean circulation on deep-water removal, but a plausible stronger control by Bernoulli aspiration intensities in the region, is, in overall, observed during these intervals. During the Heinrich-type (Ht) events 3 and 2, increased trace fossil diversity and ameliorated oxygenation is driven by limited surface organic production, but intense western Mediterranean deep-water circulation and enhanced regional deep-water removal.Spanish Government FPU17/03349Juan de la Cierva Program by the Spanish Ministry of Science and Innovation IJC2019-038866-ISpanish Government RTI2018-099489-B-100 CGL2015-66835-P PID2019-104625RB-100Andalusian Government B-RNM-072-UGR18 P18-RT-407

Introducing Fiji and ICY image processing techniques in ichnological research as a tool for sedimentary basin analysis

Some features of trace fossils are not easy to determine due to limited vissibility of trace fossils. Here, we applied two image processing techniques (Fiji and ICY) to ichnological studies and we compare them with the previously used high-resolution image treatment method. , discussing their usefulness for ichnological studies. Then, these are compared with a high resolution image treatment. These techniques are revealed as rapid alternatives for estimation of some ichnological features, being so useful for the first stages of research, when a detailed analysis is not needed

Ichnological characterization of deep-sea muddy deposits: Macrobenthic communities revealing palaeoenvironmental conditions within turbidite systems

Traditionally, studies on turbiditic systems were mostly focused on sedimentological features, but later some other features as bioturbation have been included. Ichnological analysis is probed as a powerful tool for deep-sea sediments studies, revealing accurate information about palaeoenvironmental conditions during deposition. For the first time, a detailed ichnological and sedimentological integrative analysis focused on Miocene muddy turbiditic deposits from the westernmost Mediterranean at the Tabernas Basin (SE Spain) is here presented. The representative Rambla de Tabernas section has been selected to identify dominant palaeoenvironmental conditions before the deposition of the well-known Gordo megabed. The ichnological content reveals a trace fossil association comprising 26 ichnospecies, belonging to 14 ichnogenera ascribed to the Nereites ichnofacies in an overall stable and well oxygenated environment dominated by low-energy conditions. The distribution, and abundance of trace fossils, integrated with sedimentological information, allow to characterize variation in depositional conditions within the turbiditic system. Before deposition of the Gordo megabed, the turbiditic system in the lower part of the studied area had generalized low energy conditions. These conditions are probably linked to distal depositional areas, characterized by the record of the Paleodictyon ichnosubfacies in interbedded sandstones-mudstones, with a common occurrence of Tab/Tabc Bouma intervals. In contrast, higher energy conditions and deposition prevailed in proximal settings (e.g., channels and proximal lobes) in the upper part. They arecharacterized by the Ophiomorpha rudis ichnosubfacies in interbedded sandstones-mudstones with dominant Tab Bouma intervals. Additionally, the low ichnodiversity in comparison with similar deposits from other worldwide areas, is probably caused by the influence of local environmental conditions in the studied basin.This contribution was funded by research projects PID2019-104625RB-100 funded by MCIN/AEI/ 10. 13039/501100011033; by FEDER/Junta de Andalucía-Consejería de Economía y Conocimiento. Projects P18-RT-4074, B-RNM-072-UGR18 and A-RNM-368-UGR20 (FEDER Andalucía); by the Research Group RNM-178 (Junta de Andalucía) and by the Scientific Excellence Unit UCE-2016-05 (UGR). The research by JD was funded through the Juan de la Cierva Program (IJC2019-038866-I) and the Ramón y Cajal fellowship (RYC2021- 032385-I) by the Spanish Ministry of Science and Innovation. Funding for open access charge: Universidad de Granada / CBUA

Trace fossil characterization during Termination V and MIS 11 at the western Mediterranean: Connection between surface conditions and deep environment

[EN] Trace fossil assemblages are studied at Ocean Discovery Program (ODP) Site 977 to characterize the response of the macrobenthic trace maker community to deep paleoenvironmental conditions during the Termination V (TV) and interglacial Marine Isotope Stage (MIS) 11 at the western Mediterranean Alboran Sea. An assemblage composed of Chondrites, Planolites, Scolicia, Thalassinoides and Zoophycos is identified, showing notable variations in ichnodiversity, abundance and Bioturbation Index, that were analyzed in detail. The integration of ichnological information with sediment color and high-resolution coccolithophore records from Site 977, evidenced that variations in macrobenthic trace maker community are primarily controlled by oxygen availability and surface organic productivity patterns. During TV, high surface organic productivity by intense Alboran Upwelling System enhanced the deep organic accumulation that, together with reduced deep-water removal, resulted in a decrease of bioturbation and the formation of an Organic Rich Layer. Moderate and stable surface production through MIS 11c reduced deep food availability, resulting in an oligotrophic and stable deep environment. This is reflected by relatively abundant trace fossils in lighter sediments. Intra-interglacial increase in surface organic production at ~405 ka is evidenced by increased organic matter preservation. Minor impact of western Mediterranean circulation on deep-water removal, but a plausible stronger control by Bernoulli aspiration intensities in the region, is, in overall, observed during these intervals. During the Heinrich-type (Ht) events 3 and 2, increased trace fossil diversity and ameliorated oxygenation is driven by limited surface organic production, but intense western Mediterranean deep-water circulation and enhanced regional deep-water removal.Publicación en abierto financiada por la Universidad de Salamanca como participante en el Acuerdo Transformativo CRUE-CSIC con Elsevier, 2021-202