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Organic-rich deposits are valuable paleo-archives, recording significant paleoceanographic changes linked to past climate variations and marine deoxygenation events. The deposition of organic-rich sediments stops when bottom-water reventilation/oxygenation occurs. This impedes organic matter preservation, enabling macro and micro burrowing-organisms to recover and bioturbate the seafloor. In this sense, highly bioturbated sediments require particular attention when sampling is done for geochemical analyses, as sediments can be considerably mixed. While avoiding trace fossils during sampling for geochemical analyses is easy for large traces (e.g. Planolites, Thallasinoides, and Zoophycos), it becomes challenging for smaller and complex traces (< 0.5 cm), as is the case with Chondrites. Chondrites-producers have an opportunistic behavior, being one of the first organisms to colonize the seafloor after an anoxic event. As a result, Chondrites are commonly and sometimes abundantly found in the upper layers of organic-rich sediments, including sapropels and black shales. This study focuses on sapropel S7, which was deposited between ∼198.5 and 191.9 ka at the top of Eratosthenes Seamount and exhibits abundant Chondrites. For this sapropel, we demonstrated that Chondrites-producers can bioturbate significant volumes of organic-rich sediments (over 35%), introducing oxic/dysoxic material downward into anoxic sediments enriched in redox-sensitive trace metals and organic matter. This process can dilute up to 18% the original concentration of redox-sensitive trace metals (e.g. Mo, U and V). This dilution is especially important to consider when calculating trace metals and organic matter burial flux from bulk sediment data. Therefore, Chondrites-producers can play a crucial role in altering the sediment texture and distribution of minerals and organic matter at sub-cm scale, and may thus impact paleoenvironmental and paleoceanographic reconstructions based on geochemical sig

Contourite depositional systems (CDS) represent the sedimentary records of paleoceanographic circulation and paleoclimatic changes throughout the geological timescale. These records offer expanded but contingent information relative to their adjacent marine gateways, documenting changes in the intensity and the direction of modern-day and paleo-current pathways on multicentennial, millennial and million-year timescales. This study investigates the late Miocene to Quaternary CDSs from the Gulf of Cadiz towards the West Iberian margin after the exit of the past Betic and Rifian corridors and most recent Strait of Gibraltar, the key gateways for the Mediterranean – Atlantic exchange trough time. A summary of the key results is presented as a representative study case for decoding the long- and short-term behaviour of oceanographic processes related to gateways and their associated overflows.

The Last Glacial Cycle is one of the most interesting periods for environmental studies, presenting some of the most complete records of climatic and environmental changes that can be analogous to the current anthropogenic climate change. In addition, the Mediterranean area presents a highly interesting setting for palaeoceanographic, paleoclimatic and palaeoenvironmental studies, situated and impacted by both the north, middle and equatorial latitudes climate systems and presenting al the oceanographic characteristics of a big ocean with much faster reaction times. The layers rich in organic carbon, such as the sapropels in the Eastern Mediterranean Sea and their counterparts in the Western Mediterranean, the Organic Rich Layers (ORL), represent one of the most interesting phenomena within the recent geological record of the Mediterranean Sea Basin. These events have occurred over the past 3 million years as a consequence of the restriction of the waters of deep parts of the Mediterranean basins in response to climatic changes. This doctoral thesis presents a comprehensive analysis of these layers during the Last Glacial Cycle, with a particular focus on the ORLs, which have received less attention in past works, with the objective of deciphering the environmental changes and oceanographic and climatological triggers of these events in the Mediterranean. Additionally, a comparative examination between events in the West and East Mediterranean Sea basins is conducted, elucidating the temporal evolution of both basins and differences in the external factors leading to the deposition of these layers. In the present thesis, a multiproxy approach is employed to assess the stated objectives, integrating inorganic geochemistry and palaeontological proxies, in particular, the ichnological features observed on core surfaces. Novel ichnological analysis tools have been developed through image analysis, which have been applied in conjunction with traditional ichnological and

Bottom currents and a series of secondary oceanographic processes interact frequently at different scales to form distinct sedimentary deposits referred to as contourite and mixed (turbidite-contourite) depositional systems. These systems represent major depositional systems along the continental margins and abyssal plains of the world¿s oceans. A recent proliferation of both academic and industry research on deep-water sedimentation has revealed significant advances in the understanding of these systems, but non-specialists remain unaware of their sedimentary features and how they were formed. A paucity of examples in the ancient record and a lack of consensus regarding the diagnostic criteria used to characterise and differentiate them from other deep-water deposits limits our understanding of how they may record past processes, such as global oceanic circulation, tectonic events, gateway evolution, among others. In this work, examples of deep-marine deposits from onshore (Cyprus, Morocco, Spain, Italy and Angola) and offshore (Gulf of Cadiz, West Portugal, Mozambique, Antarctica, etc.) areas have been studied through a multidisciplinary approach to discriminate the main deep-water facies as contourites, pelagites/hemipelagites, turbidites, reworked turbidites and mass-transport deposits and determine why, when and how these deposits were formed in response to long-term tectonic history. The results described here highlight the importance of using primary sedimentary structures, microfacies and ichnological features as the best diagnostic criteria to distinguish reworked turbidites from contourites at the sedimentary facies scale. Diagnostic criteria for discriminating bottom current deposits include sedimentary condensation, reworking, reactivation surfaces, smaller grain-size variations, small-scale hiatuses, and omission surfaces. All of these vary according to the paleoenvironmental conditions, especially current velocities and sedimentation rates. Petrophysic

The influence of bottom-water oxygenation on sapropel deposition has been thoroughly studied since sapropels represent exceptional examples of deoxygenation events linked to past climate changes. Most of the studies have used the concentration of redox sensitive trace metals (RSTMs) to assess the evolution and dynamics of past large-scale deoxygenations. Sapropel deposition is interrupted when reventilation oxygenates bottom-waters preventing the accumulation/preservation of organic matter (OM) and allowing macro and micro burrowing-organisms to repopulate and bioturbate the seafloor. Bioturbation is an important aspect to be considered when assessing RSTMs concentrations obtained from bulk sediment samples. Bioturbated sediments should be avoided during sampling for geochemical analyses, this is easy for big and visible traces, however it is difficult for small traces, as is the case of Chondrites. Chondrites-producers have an opportunistic behavior, being one of the first organisms to colonize the seafloor after an anoxic event, therefore they are very abundant in organic-rich sediments. Because of this behavior, Chondrites-producers can introduce great volumes of oxic sediments into anoxic sediments (enriched in OM and RSTMs). Consequently, the derived signal from bulk sediment geochemical analyses will have a mixed signature between Chondrites infill and host sediments. As a case study, this work assesses the influence of Chondrites on RSTMs enriched in sapropel S7 deposited ~195ka at Eratosthenes Seamount (Levantine Basin, Easter Mediterranean). ICP-OES, ICP-MS and Pyrolysis-Rockeval were used to obtain major and trace elements concentration and TOC content. Moreover, thin sections from resin embedded sediments were prepared for LA-ICP-MS analyses in order to compare the RSTMs concentration in the host sediments and Chondritesinfills. After statistical analyses of the geochemical data and quantification of bioturbation using image treatments, the data supports

Interactions between deep-water sedimentary processes are responsible for building a large variety of features and deposits across mixed turbidite-contourite depositional systems, from <5 cm thick beds to >200 km long sedimentary drifts. Investigations of the spatial and temporal variability of their sedimentary facies and facies associations are therefore crucial to reveal the dynamics between along-slope bottom currents and gravity-driven flows, as well as their impact on drift construction and channel erosion. This study focuses on a large modern mixed (turbidite-contourite) system developed across the continental rise of the Antarctic Peninsula Pacific margin. Nine sediment cores were sampled and analysed, through granulometric and geochemical methods, to study the sedimentary facies at a high-resolution scale (ca. 1 to 20 cm). Three main sedimentary facies associations have been identified across distinct morphological features (i.e., mounded drifts and trunk channels), comprising intercalations of hemipelagites, bottom current reworked sands (which include reworked sand-rich turbidites and fine- to coarse-grained contourites) and gravitational facies (such as turbidites and mass-transport deposits). These sedimentary facies associations appear to reflect fluctuations in the background sedimentation and oscillations of both the bottom-current velocity and the frequency of gravity-driven transport processes. The sedimentary record features cyclic alternations during the Late Quaternary (>99 kyr), suggesting that variations between along-slope bottom currents and down-slope gravity-driven flows are strongly linked to glacial¿interglacial cycles, such as those of Marine Isotope Stages 1 to 6. Sedimentary records affected by bottom currents on polar margins are essential to decipher the facies and facies sequences of bottom-current deposits, as the low degree of bioturbation throughout most of the sediments, especially those deposited during glacial periods, allows

Process-based, mechanistic research of mineral authigenesis has been progressively utilized to understand the biogeochemical processes taking place at the sediment¿water interface (SWI), and to capture long-term sedimentary (biogeochemical) records of paleoenvironments. A better understanding of mineral authigenic sedimentary processes directly beneath the SWI in Arctic continental shelves is thus fundamental as Earth¿s polar regions are at greatest risk of future climate change. This is in part due to disturbances in the benthic¿pelagic coupling related to changes in ocean circulation and sea ice dynamics. In this study, we aim at focusing on the Holocene period by investigating sedimentary archives recovered from the NE Greenland shelf during the NorthGreen17 Expedition. Here we combined a suite of sedimentological (e.g., detailed ichnological analysis and taphonomic features of the benthic foraminifera Cassidulina neoteretis), mineralogical (bulk and clay mineralogy) and geochemical (major, trace and rare earth elements, and ¿13C and ¿18O stable isotope signatures recorded in Cassidulina neoteretis) proxies with bulk organic matter parameters (¿13C, TOC, TN). The first results of this study, presented during the EGU General Assembly 2023 in Vienna, Austria, focus on several important points such as: (1) changes in sedimentation (geochemical characteristics) over the NE Greenland sediment profiles; (2) evolutionary characteristics of terrigenous influx, redox conditions and productivity; and (3) controlling factors and modes of organic matter accumulation.

The oscillatory behaviour of the climate system on decadal timescales before the instrumental record is hard to quantify. However, knowledge of this variability is important for putting current changes in context and for supporting reliable future predictions. Here we investigate the recurrent component of Holocene climate variability in the North Atlantic sector from 10,500 to 2,000 years ago by conducting a frequency analysis of both an annually laminated climate record from a lake in England and outputs from a long transient simulation of the Atlantic meridional overturning circulation. We find consistent decadal variability over the past 6,700 years and before 8,500 years before present, probably reflecting predominance of solar and ocean forcings. Between these dates, climate variability was dampened on decadal timescales. Our results suggest that meltwater discharge into the North Atlantic and the subsequent hydrographic changes, from the opening of the Hudson Bay until the final collapse of the Laurentide Ice Sheet, disrupted the decadal cyclic signals for more than a millennium. Given the current acceleration of the Greenland Ice Sheet melting in response to global warming, this study provides long-term evidence of potential challenges predicting future patterns of the climate system.

Modern marine settings are experiencing rapid deoxygenation mainly forced by global warming and anthropogenic eutrophication. Therefore, studies that assess the role of climate variability in large spatiotemporal deoxygenations during past climate changes are needed to better comprehend the consequences of the current global warming and ocean deoxygenation. In this respect, deep marine sediments associated to past oxic-to-anoxic transitions are useful palaeoarchives for understanding the interplay between climate variability, deep-water dynamics and large-scale deoxygenation. Moreover, they can offer long-term perspectives to modern marine settings that are suffering oxygen depletion due to climate change and anthropogenic pressure. In particular, sapropel layers from the Middle Pleistocene to the Holocene are excellent palaeoarchives of past large-scale deoxygenation events, since (i) they occurred during a similar Mediterranean hydrogeographic configuration to the present, (ii) have a robust chronological control, and (iii) previous studies have reconstructed the climate conditions that ruled during their deposition. In this work, we have applied empirical palaeoceanographic conceptual models to five sapropels (S1, S5, S6, S7 and S8) in three Eastern Mediterranean (EM) settings. The models suggest that the hydrographic regimes of all studied sapropels can be considered as analogues to those observed in certain modern marine restricted settings. The results obtained support the idea that climate and the degree of surface-water freshening are the primary factors that influence deep-water dynamics in marine restricted settings, that in turn control the frequency and intensity of bottom-water deoxygenation and the stability and depth of the chemocline. The deepest EM sites are the most vulnerable locations to develop bottom-water restriction and deoxygenation. Local hydrogeographic factors play an essential role in the extent and frequency of bottom-water deoxygenatio

Deoxygenation in marine systems is globally increasing due to anthropogenic pressures and climate change impacts, leading to significant ecological and environmental consequences. Understanding past deoxygenation events is crucial for assessing the response of ocean stressors to climate variability and for predicting and managing the impacts of current and future changes. Deep-marine basins with organic-rich deposits serve as valuable palaeo-archives, preserving evidence of profound palaeoceanographic changes involving deoxygenation events. Such events have been broadly studied and reconstructed using redox-sensitive trace metals (RSTMs) as proxies for oxygenation conditions. Assessing these proxies is therefore crucial for further understanding deoxygenation events. To do so, this study focuses on RSTMs distribution across the most recent sapropel, S1, which is a well-preserved organic-rich sediment layer that represents the most recent large-scale deoxygenation event in the Eastern Mediterranean. High-resolution geochemical microanalyses, including Laser Ablation ICP-MS and SEM-EDX, were conducted to investigate sub-mm scale geochemical signals and post-depositional remobilization of RSTMs within S1 and surrounding sediments. Statistical analyses have also helped to identify the geochemical fractions within S1, including detritic, carbonate, and authigenic, enriched in RSTMs and organic matter. The study revealed distinct specific geochemical intervals, such as the marker bed, oxidized interval, unoxidized interval, and synsapropel interval. These intervals provided insights into the diagenetic processes and post-depositional reactions occurring within and across sapropel S1 boundaries. The enrichment of RSTMs within pyrite aggregates in the synsapropel interval was primarily attributed to post-depositional processes rather than the initial syndepositional conditions of S1. Large pyrite surfaces below S1 and the precipitation of Mn-oxyhydroxides over S1 played a s

Despite carbon-cycle perturbations at a global scale during the early Toarcian, the extent of anoxia during the ∼182-Ma Toarcian Oceanic Anoxic Event (T-OAE) remains in debate. A common factor in the development of oceanic anoxia is watermass restriction, which is thought to have been important in the NW European Seaway, but whose influence elsewhere is relatively unstudied. Here, we analyze Mo/TOC (a proxy for watermass restriction) and redox proxies (e.g., C/P) in two sections of the Asturian Basin (northern Iberian Paleomargin), and we integrate these results with data from a suite of global Toarcian sections in order to reassess the relationship of euxinia and local hydrographic restriction during the T-OAE. The Asturian Basin study sections accumulated in oxic to dysoxic waters, punctuated by two episodes of intermittently euxinic bottomwaters or porewaters around the Tenuicostatum/Serpentinum zonal boundary. This area was an unrestricted carbonate ramp during the T-OAE that was not sufficiently reducing for its Mo/TOC ratios (2.3–4.5) to accurately record the degree of watermass restriction. Regionally, Lower Toarcian black shales exhibit elevated Mo and TOC concentrations (21–42 ppm Mo, 12–18% TOC) along with exceptionally low m (e.g., ∼0.3 in the Paris Basin, ∼0.4 in the Cleveland Basin, and ∼ 2.0 in the Qiangtang Basin), providing evidence of highly restricted, euxinic bottomwaters in Northwestern (epicontinental intrashelf troughs) and Eastern (barrier-lagoon) Tethyan settings. In contrast, in other basins across the SW Tethys and Panthalassic oceans, low contents of Mo and TOC (mostly <5 ppm Mo, <3% TOC) indicate unrestricted watermass conditions and at most intermittent bottomwater or porewater euxinia in pelagic to hemipelagic environments, although intermittently euxinic bottomwaters developed also in deep open-marine settings. The results of our analysis support both (1) a major role for hydrographic restriction in modulating the local expression of t

To fully assess the resilience and recovery of life in response to the Cretaceous–Paleogene (K-Pg) boundary mass extinction ~ 66 million years ago, it is paramount to understand biodiversity prior to the Chicxulub impact event. The peak ring of the Chicxulub impact structure offshore the Yucatán Peninsula (México) was recently drilled and extracted a ~ 100 m thick impact-generated, melt-bearing, polymict breccia (crater suevite), which preserved carbonate clasts with common biogenic structures. We pieced this information to reproduce for the first time the macrobenthic tracemaker community and marine paleoenvironment prior to a large impact event at the crater area by combining paleoichnology with micropaleontology. A variable macrobenthic tracemaker community was present prior to the impact (Cenomanian–Maastrichtian), which included soft bodied organisms such as annelids, crustaceans and bivalves, mainly colonizing softgrounds in marine oxygenated, nutrient rich, conditions. Trace fossil assemblage from these upper Cretaceous core lithologies, with dominant Planolites and frequent Chondrites, corresponds well with that in the overlying post-impact Paleogene sediments. This reveals that the K-Pg impact event had no significant effects (i.e. extinction) on the composition of the macroinvertebrate tracemaker community in the Chicxulub region., SCOPUS: ar.j, info:eu-repo/semantics/published

Organic rich layers (ORLs), deposited in the westernmost Mediterranean over the Last Glacial Cycle, have been studied integrating sedimentological and ichnological information from sediment records recovered at Ocean Drilling Program Leg 161 Sites 976 and 977. The conducted study has served to redefine the ORLs initially differentiated in sediment records from Sites 977 and 976, with seven new ORLs recognized, as well as extensions and subtraction of some parts in the ORLs previously defined. In addition, three different ORL types are distinguished according to sedimentological and ichnological features. Type 1 with intermediate thickness is highly bioturbated, mainly consisting of abundant Scolicia and Planolites, frequent Chondrites, and possible Thalassinoides in the base, which are interpreted as supporting dysoxic conditions during deposition. Type 2, corresponding to thicker intervals, shows alternance of highly to moderately bioturbated parts, revealing variable oxygen conditions —from moderate to extreme dysoxic or even suboxic. Type 3 consists of short, laminated intervals characterized by the absence of bioturbation, indicating anoxic or suboxic conditions and determining unfavourable macro benthic habitat. The amended ORLs show a correlation between the Sea Surface Temperatures and established climatic events over the Last Glacial Cycle in the Western Mediterranean.

Despite numerous efforts to properly differentiate between contourites and other deep-water deposits in cores and outcrops, reliable diagnostic criteria are still lacking. The co-occurrence of downslope and along-slope sedimentary processes makes it particularly difficult to differentiate these relatively homogeneous deposits. The main aim of this paper is to identify differences in deep-water sediments based on Principal Component Analysis of grain size and geochemistry, sedimentary facies, and reinforced by microfacies and ichnofacies. The sediments studied were obtained from two International Ocean Drilling Program Expedition 339 sites in mounded and sheeted drifts in the Gulf of Cadiz. The statistical approach led to the discernment of hemipelagites, silty contourites, sandy contourites, bottom current reworked sands, fine-grained turbidites and debrites over a range of depositional and physiographic elements. These elements are linked to contourite drifts, the drift-channel transition, the contourite channel and distal upper slope. When bottom currents or gravity-driven flows are not the dominant depositional process, marine productivity and continental input settling forms the main depositional mechanism in deep-water environments. This is reflected by a high variability of the first principal component in hemipelagic deposits. The stacked principal component variability of these deposits evidences that the contourite drift and the adjacent contourite channel were influenced by the interrelation of hemipelagic, gravitational and bottom current induced depositional processes. This interrelation questions the paradigm that a drift is made up solely of muddy sediments. The interrelation of sedimentary processes is a consequence of the precession-driven changes in the intensity of the Mediterranean Outflow Water related to Mediterranean climate variability, which are punctuated by millennial-scale variability. Associated vertical and lateral shifts of the Mediterr

Detailed bed-by-bed ichnological and sedimentological analysis of the early Toarcian Oceanic Anoxic Event (T-OAE) in two sections from the Asturian Basin – Rodiles and Lastres – reveals changes in the macrobenthic tracemaker community mainly induced by oxygen fluctuations. Ichnological analysis enabled us to document an abundant and diverse trace fossil assemblage, with ten ichnogenera, probably corresponding to alternations between the Zoophycos ichnofacies and the distal expression of the Glossifungites ichnofacies: Arenicolites, Chondrites, Diplocraterion, Halimedides, Palaeophycus, Planolites, Rhizocorallium, Thalassinoides, Trichichnus and Zoophycos. Six ichnofabrics were differentiated: laminated?, Diplocraterion–Thalassinoides, Chondrites-mottled, Chondrites–Palaeophycus–Planolites, Chondrites–Halimedides–Planolites and Chondrites-laminated. Ichnological features (including ichnodiversity, distribution of traces and cross-cutting relationships) allowed us to characterise a well-developed multi-tiered macrobenthic tracemaker community, as well as distinguish different tiering models associated with variations in bottom- and pore-water oxygenation. Anoxic conditions associated with the T-OAE corresponded mainly, but not exclusively, to black shale facies. Minor-order oxygen fluctuations from suboxic/anoxic to disoxic/oxic conditions developed during the middle part of the T-OAE. Laminated intra-T-OAE dark and light grey marls show lithological features similar to those of bioturbated pre- and post-event marls; thus, the ichnological information provides evidence that the T-OAE had a larger effect on biota than on depositional features.

Recent ichnological analysis conducted in two sections (Rodiles and Lastres) of the Asturian Basin revealed the presence of Halimedides Lorenz von Liburnau 1902, which occurs just above the black shales related to the end of the Toarcian Oceanic Anoxic Event (T-OAE). Halimedides is associated with recovery of the trace-maker community after the re-establishment of favourable, oxic, conditions. The appearance of Hal- imedides after the T-OAE event, previously not registered, supports the close relationship of the trace maker with oxygen conditions, as occurs in other anoxic events including the Cretaceous OAE-1a and OAE-2. Also, a relationship between morphometric and palaeoenvironmental parameters is observed: occurring larger and densely chambered specimens in darker, weakly oxygenated facies, while smaller and sparsely chambered forms are registered in lighter, better oxygenated sediments.

Image analysis has been succesfully applied in core research, especially in studies from modern deposits, to enhance the visibility of ichnological features and characterize ichnoassemblages and ichnofabrics. Its application to ichnological research provides useful information for marine core studies, hence sedimentary geology, but also for hydrocarbon exploration. Here we develop a new methodology, using Python programming language, which significantly improve the ichnological analysis. The method automatizes the process of obtaining continuous ichnological information, in this case about the percentage of bioturbation as a key aspect of the ichnofabric approach. The method affords the possibility of automatically generating continuous percentage and other index records using pixel counts in previously treated images. The resulting data sets are easy to correlate with the information usually obtained from cores (e.g., geochemical and mineralogical data). Such an integration of different proxies for to the field of sedimentary geology especially in the use of ichnological analysis, making it easier for the researcher, less time consuming, and more likely to be undertaken. The coding and sharing of open software tools allow for great flexibility, giving researchers in ichnology or related fields the option to implement new features, develop more complex tools to improve the package, and share findings with the scientific community.