Ichnological analysis: A tool to characterize deep-marine processes and sediments

The deep-marine environment is a complex setting in which numerous processes —settling of pelagic and hemipelagic particles in the water column, sediment gravity flows (downslope density currents; turbid flows), and bottom currents— determine sediment deposition, hence a variety of facies including pelagites/hemipelagites, contourites, turbidites and hyperpycnites. Characterization and differentiation among deep-sea facies is a challenge, and numerous features may be highlighted to this end: sedimentary structures, geochemical data, micropaleontological information, etc. Ichnological information has become a valuable, yet in some cases controversial, proxy, being in most of cases understudied. This paper gathers the existing ichnological information regarding the most frequent deep-sea facies —from those in which ichnological analyses are numerous and detailed (e.g. pelagites/hemipelagites and turbidites), to those for which ichnological information is lacking or imprecise (hyperpycnites and contourites). This review analyses palaeoenvironmental (i.e., ecological and depositional) conditions associated with deep-sea sedimentary processes, influence of these changes on the tracemaker community, and associated ichnological properties. A detailed characterization of trace fossil assemblages, ichnofabrics and ichnofacies is presented. Special attention is paid to variations in trace fossil features, approached through sedimentary facies models and the outcrop/core scale. Similarities and differences among deep-sea facies are underlined to facilitate differentiation. Pelagic/hemipelagic sediments are completely bioturbated, showing biodeformational structures and trace fossils, being characterized by composite ichnofabrics. The trace fossil assemblage of muddy pelagites and hemipelagites is mainly assigned to the Zoophycos ichnofacies, and locally to the distal expression of the Cruziana ichnofacies. Turbidites are colonized mostly from the top, determining an uppermost part that is entirely bioturbated, the spotty layer; below it lies the elite layer, characterized by deep-tier trace fossils. Turbidite beds pertain to two different groups of burrows, either “predepositional”, mainly graphogliptids, or “post-depositional” traces. Turbidite deposits are mostly characterized by the Nereites ichnofacies, with differentiation of three ichnosubfacies according to the different parts of the turbiditic systems and the associated palaeoenvironmental conditions. There are no major differences in the trace fossil content of the hyperpycnite facies and the classical post-depositional turbidite, nor in the pelagic/hemipelagic sediments, except for a lower ichnodiversity in the hyperpycnites. Trace fossil assemblages of distal hyperpycnites are mainly assigned to the Nereites ichnofacies, while graphogliptids are scarce or absent. Ichnological features vary within contourites, largely related to palaeoenvironmental conditions, depositional setting, and type of contourite. Ichnodiversity and abundance can be high, especially for mud-silty contourites. The ichnological features of mud-silty contourites are similar to those of the pelagic/hemipelagic sediments (the tiering structure probably being more complex in pelagic/hemipelagic) or to the upper part of the muddy turbidites (contourites probably being more continuously bioturbated). No single archetypal ichnofacies would characterize contourites, mainly assigned to the Zoophycos and Cruziana ichnofacies

Eocene to middle Miocene contourite deposits in Cyprus: A record of Indian Gateway evolution

Acknowledgements This work was funded through the Joint Industry Project (JIP) supported by BP (United Kingdom), ENI (Italy), TOTAL (France), ExxonMobil (United States), Wintershall Dea (Germany) and TGS (United Kingdom) within the framework of “The Drifters” Research Group at Royal Holloway University of London (RHUL), and it is related to the projects CTM 2012-39599-C03, CGL2016-80445-R and CTM2016- 75129-C3-1-R. Financial support of the Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged (HU 804/11-1). We thank the Cyprus Geological Survey for scientific collaboration and support, in particular Costas Constantinou and Efthymios Tsiolakis. We thank A. Creaser, L. Hyslop (RHUL), D.A.W. Stow (Heriot-Watt University) and A. Viana (PETROBRAS) for valuable help and discussions during field campaigns. We are also grateful to S. Suklap and B. Docherty for their analysis on microfacies during their MSc. in 2016. Thanks to Dr. G. Blackbourn (Blackbourn Geoconsulting) for his petrographic analysis; F. Sierro (Univ. Salamanca, Spain), RPS Energy Ltd and PalaeoVision Ltd for their biostratigraphic analysis of the samples and A. Maestro (IGME, Spain) for the basemap in Fig. 1. A. de la Vara’s contribution is based on work done during her PhD at Utrecht University, supervised by Paul Meijer. We thank the editor, Gabriel Tagliaro and one anonymous reviewer for their positive comments which helped us to improve considerably our manuscript.Bottom current deposits (contourites) form in association with modern-day or ancient oceanic gateways. A paucity of examples in the ancient record and the lack of consensus on diagnostic criteria for differentiating them from other deepwater deposits limit our understanding of how they may record past global oceanic circulation, tectonic events and gateway evolution. This work describes an exceptional example of Eocene to middle Miocene deep-marine deposits located both onshore and offshore deepwater environments around the island of Cyprus. Multidisciplinary approaches were used to discriminate contourite facies associations, propose a sedimentary model, and interpret the relations with regional tectonics and the evolution of the nearby Indian Gateway. Contourite deposits appear in late Eocene to middle Miocene intervals interstratified with pelagic/hemipelagic sediments, turbidites and mass-transport deposits (MTDs). These deepwater deposits developed along a slope basin located on the upper plate of an active margin, evolving from a wide basin formed during a period of tectonic quiescent into a series of shallowing-upward, segmented sub-basins affected by compressional stress. The present study proposes a sedimentary model in which two contourite depositional systems developed: first in the Eocene (dominated by finer-grained contourites), and then during the latest Oligocene to middle Miocene (dominated by coarser-grained contourites). Both systems were buried by extensive marl deposits and record the respective influence of deep (circulating NW) and intermediate (circulating SE) water masses. The long-term evolution of the contourites reflects tectonic events that enhanced subduction processes south of Cyprus as well as exchange between the Neotethys Ocean and the Indian and Atlantic Oceans —until the final closure of the Indian Gateway by the end of the middle Miocene, when a new circulation pattern was established with the formation of the Mediterranean Sea. The contourites described here represent bi-gradational sequences that normally form in association with contouritic drifts, sometimes having the asymmetric top-cut sequence characteristics of plastered drifts and contourite terraces. The coarser (sandy) contourites, formed from the latest Oligocene to middle Miocene, consist of three packages associated with compressive and flexural phases. They pertain to I) Chattian (late Oligocene); II) Aquitanian/Burdigalian (early Miocene) and III) Langhian (middle Miocene). Evidence of enhanced bottom current episodes occurs toward the top of these packages before they are buried by later dominant marl deposits. The sandy contourites thus formed during the compressive phases, whereas the predominately finer-grained units formed during later flexural phases. The intermittent turbidites and MTDs (developed during compressional phases in combination with pelagic/hemipelagic sediments) represent the sediment supply for the contourite deposits after their winnowing and / or reworking. Our research found that the diagnostic criteria for discriminating ancient bottom current deposits from other deepwater deposits are related primarily to variations in sedimentary processes, current behaviour and its velocity, sedimentation rates and paleoenvironmental conditions. This highlights the importance of primary sedimentary structures, microfacies and ichnological features in making determinations at the sedimentary facies scale. Due to their common occurrence, sedimentary thickness (30-40 m), potential porosity and permeability, sandy contourites can form deepwater reservoirs for energy geosciences. In summary, this work demonstrates the role of plate tectonics and oceanic gateways in driving the paleo-oceanic circulation that, in turn, controls sedimentary processes and shapes the morphology of oceanic basins and continental margins. It also allows for comparison with other present-day and ancient continental margin deposits. Future high-resolution approaches and analyses of other geological settings could help resolve the sedimentary architectures of similar deepwater systems in terms of episodic tectonic processes —involving compressive-flexural stress variations. They control the Earth’s surface environment (sea-level, climate and oceanic circulation) over time by influencing sediment supply, packages of strata and types of contourite deposits.Joint Industry Project (JIP) supported by BP (United Kingdom), ENI (Italy), TOTAL (France), ExxonMobil (United States), Wintershall Dea (Germany) and TGS (United Kingdom) within the framework of “The Drifters” Research Group at Royal Holloway University of London (RHUL), and it is related to the projects CTM 2012-39599-C03, CGL2016-80445-R and CTM2016- 75129-C3-1-RDeutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged (HU 804/11-1

Northernmost (Subarctic) and deepest record of Paleodictyon: paleoecological and biological implications

The data were collected in the framework of the AleutBio project of BMBF grant 03G0293A to Prof. Dr. Angelika Brandt, Senckenberg Research Institute and Natural History Museum Frankfurt, Germany. The research of O. Miguez-Salas was funded by a Humboldt Postdoctoral Fellowship from the Humboldt Foundation and a Margarita Salas Fellowship from the Ministry of Spain and EU Next Generations projects. The research of F.J. Rodríguez-Tovar was supported by grant PID2019- 104625RB-100 funded by MCIN/AEI/ https://doi.org/10.13039/501100011033.The online version contains supplementary material available at https://doi.org/10.1038/s41598-023-34050-wPaleodictyon is one of the most iconic and widespread of trace fossils in the geological record. However, modern examples are less well known and restricted to deep-sea settings at relatively low latitudes. Here, we report the distribution of Paleodictyon at six abyssal sites near the Aleutian Trench. This study reveals for the first time the presence of Paleodictyon at Subarctic latitudes (51°–53°N) and at depths over 4500 m, although the traces were not observed at stations deeper than 5000 m suggesting that there is some bathymetric constraint for the trace maker. Two small Paleodictyon morphotypes were recognized (average mesh size of 1.81 cm), one having a central hexagonal pattern, the other being characterized by a non-hexagonal pattern. Within the study area, Paleodictyon shows no apparent correlation with local environmental parameters. Finally, based on a worldwide morphological comparison, we conclude that the new Paleodictyon specimens represent distinct ichnospecies that are associated with the relatively eutrophic conditions in this region. Their smaller size may reflect this more eutrophic setting in which sufficient food can be obtained from a smaller area in order to satisfy the energetic requirements of the tracemakers. If so, then Paleodictyon size may provide some assistance when interpreting paleoenvironmental conditions.EU Next Generations PID2019-104625RB-100Ministry of SpainWolfgang BorchertAlexander von Humboldt-Stiftung AvHBundesministerium für Bildung und Forschung 03G0293A BMBFMinisterio de Ciencia e Innovación MICINNAgencia Estatal de Investigación AE

Macaronichnus ‘co-occurrence’ in offshore transition settings: Discussing the role of tidal versus fluid muds influence

We thank the Associate-Editor, Emmanuel Fara, and the reviewer, Alfred Uchman, for their detailed and useful comments that significantly contributed to improve the manuscript. This research was funded by Grants PID2019-104625RB-100 funded by MCIN/AEI/10.13039/501100011033, and Grants BRNM-072-UGR18, A-RNM-368-UGR20 and P18-RT-4074 funded by Consejería de Universidad, Investigación e Innovación and by “ERDF A way of making Europe”. Research Group RNM178 (Junta de Andalucía), as well as the “Ichnology and Paleoenvironmental Research Group” (UGR). Funding for open access charge: Universidad de Granada / CBUA.Macaronichnus is a key trace fossil in palaeoceanographic, palaeoclimatic, and petroleum exploration research. Small ichnosubspecies such as Macaronichnus segregatis segregatis, M. s. lineiformins, M. s. maeandriformis and M. s. spiriformis, typically occur in wave-dominated foreshore sands where large M. s. degiberti was never found. The latter shows a wide environmental distribution, occurring in sandy deposits of tidal channels, tidal bar sand sandridges, tidal-flat sand sheets, shorefaces, bioturbated sandy shelf, shelf storm-sheets, shelf sand ridges, and upper slopes. Small M. segregatis and large M. s. degiberti have not been observed to date due the ecological segregation of the tracemakers. An abundant record of large M. s. degiberti in a Tortonian (Late Miocene) mixed carbonate-siliciclastic unit from the Betic Cordillera (southern Spain) has been studied. Occurrence of M. s. degiberti is the result of the interaction of tidal and waves, storm influenced environment determining high-energy conditions and associated palaeoenvironmental parameters as shifting substrates, organic matter availability, and oxygenated pore and bottom-waters. Locally, associated to M. s. degiberti appear small, sinuous traces infilled by light material that were originally assigned to M. s. maeandriformis, and very rare M. s. spiriformis. However, the absence of the typical rim of Macaronichnus avoid a conclusive assignment. The coexistence of both small traces (?M. s. maeandriformis) and large M. s. degiberti is identified in the deposits underlying mudstone layers, revealing the importance of mud deposition during tidal slack water intervals or linked to fluid mud events favouring the co-occurrence of the trace makers of both Macaronichnus ichnosubespecies. This fact would have significant palaeobiological and palaeoecological implications, and could be the first record of both ichnosubspecies in the same intervals.MCIN/AEI/10.13039/501100011033: PID2019-104625RB-100Consejería de Universidad, Investigación e Innovación BRNM-072-UGR18, A-RNM-368-UGR20, P18-RT-4074“ERDF A way of making Europe”Junta de Andalucía: Research Group RNM178“Ichnology and Paleoenvironmental Research Group” (UGR)Universidad de Granada / CBU

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

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

Ichnological record of the Frasnian-Famennian boundary interval : two examples from the Holy Cross Mts (Central Poland)

The Frasnian-Famennian (Late Devonian) boundary interval within the carbonate-siliciclastic series in the Kowala and Płucki sections (Holy Cross Mts, Central Poland) has been analysed to evaluate the influence of the Kellwasser event on the macrobenthic tracemaker community. The Upper Kellwasser event has a lithologically variable record, as horizons of flints (Kowala) and as a bed of bituminous, black, cephalopod limestone (Płucki). Both sections show mostly laminated, unbioturbated beds of marlstones or shales just above the Frasnian-Famennian boundary, which point to events of anoxia on the sea floor. However, the first anoxic horizon occurs below the Frasnian-Famennian boundary. The trace fossils and bioturbational structures are uncommon and poorly diversified. Trichichnus and Multina are the only frequent trace fossils in some beds. Moreover, one horizon above the Frasnian-Famennian boundary contains numerous Multina and a single? Planolites. Such poorly diversified trace fossil assemblage suggests an unfavourable environment for most of burrowing organisms and fluctuations in oxygenation from anoxic, to dysoxic conditions. The occurrence of the trace fossils and bioturbational structures as spotted and mottled ichnofabrics from the 1.3 m above the Frasnian-Famennian boundary is interpreted as an improvement in bottom water oxygen conditions after the Upper Kellwasser event

Changes in the composition of trace fossil assemblages across the Paleocene-Eocene transition in the north-western Tethys (Untersberg section, Austria)

The Untersberg section (Northern Calcareous Alps, Austria) provides an expanded and biostratigraphically well constrained deep-sea record of the Paleocene-Eocene transition in the north-western Tethyan realm. At the base of the Eocene, massive carbonate dissolution and a shoaling of the calcite compensation depth (CCD) by at least 1 km is recorded by 5.5 m-thick red claystone, which is intercalated into a grey marlstone succession. Previous studies documented the benthic foraminifera extinction event (BEE) in this claystone. Now biodeformational structures and trace fossils were investigated in this interval to evaluate the impact of the extinction event on the macrobenthic tracemaker fauna. Using the stratigraphic distribution pattern of trace fossils, the lowermost Eocene claystone can be subdivided into three parts: (1) the lower part shows a trace fossil assemblage consisting of Chondrites isp., Planolites isp., Thalassinoides isp., and Zoophycos isp., (2) the middle part is characterized by primary sedimentary lamination and exceedingly rare ichnofossils, and (3) the upper part shows a less abundant and less diverse trace fossil assemblage than the lower part, indicating a slow recovery of the macrobenthic tracemaker community. This pattern demonstrates that macrobenthic communities were severely affected by the ecological perturbations in the earliest Eocene. The change in sediment colouration towards red colour in the middle part of the Paleocene-Eocene transition at the Untersberg section, together with decrease in bioturbation degree indicate that oxygen consumption was rather reduced during the PETM, and the loss in bioturbation is thus unrelated to oxygen limitation. Trace fossils can be used to improve the resolution of the benthic extinction interval and provide an excellent proxy for the precise determination of timing of the climax of this global event

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)