Paleogeographic reconstructions of the Western Mediterranean are often based on the present location of sedimentary outcrops. However, most geodynamic and biogeographic models for the region have highlighted the importance of up-to-hundreds of km of horizontal displacements of the terrains forming the western Mediterranean orogenic arcs since the early Miocene until the Pliocene. Here we update the known paleogeographic evolution for the westernmost Mediterranean, considering published biogeographic and recent new geological constraints, including paleontological, stratigraphic, tectonic kinematic data, seismic reflection lines, low-temperature thermochronological dating, detrital zircon age populations, among others. During the Burdigalian to Langhian the rocks of the Betic hinterland, corresponding to the Alboran domain, where exhumed in a forearc setting as far East as Mallorca, now located 450 to 700 km of their present outcrops. Those exhuming rocks floored sedimentary basins among an island archipelago. The land connection between Mallorca and Alboran domains continued until the Serravallian as attested by the shared fossils of vertebrate insular fauna and biogeographic data of different taxa including trap-door spiders, beetles and fresh-water planarians. The westward migration of the Alboran forearc archipelago and its overlying basins (currently forming the Betic intramontane and western Alboran basins) was concomitant to the Langhian to Tortonian opening of the Algero-Balearic back-arc basin and the retreat of the Betic-Rif subducted slab. At a smaller scale, the Granada supra-detachment intramontane basin moved > 100 km between the Tortonian and Present, implying that previously interpreted, emerged domains, like the Sierra Nevada island where either inexistent or in a different location during the Tortonian. Sediment interpreted to represent marine gateways around and through the Alboran archipelago in the westernmost Mediterranean, may have being partially deposited as far East as Mallorca, and probably migrated westwards from the Langhian to the late Pliocene in the Gibraltar straits. Of particular interest, is the Late Messinian to Late Pliocene westward migration of the Gibraltar straits documented by sedimentary onlap over erosive channels in the Western Alboran basin and marine terraces along its Betic and Rif shores. The above proposals are evolving questions concerning the Neogene paleogeographic evolution of the Western Mediterranean that may be tested by future work and drilling.

How to cite: Booth-Rea, G., Ranero, C., Azañón, J. M., Garrido, C. J., and García-García, F.: Migrating straits, basins and archipelagos: open questions about the Neogene paleographic evolution of the Westernmost Mediterranean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15310, https://doi.org/10.5194/egusphere-egu23-15310, 2023.

Neoichnology of high energy deep-sea environments: A tool to improve gateways characterization

Olmo Miguez-Salas¹, Francisco J. Rodríguez-Tovar²

1Department of Marine Zoology, Senckenberg Research Institute and Natural History Museum, 60325 Frankfurt, Germany.

2 Department of Stratigraphy and Paleontology, University of Granada, 18071 Granada, Spain

Evolution of ocean gateways determines significant changes in deep-water dynamics affecting depositional and ecological conditions. Particularly, variations in deep-water circulation associated to closing and opening gateways induce changes in hydrodynamic energy, rate of sedimentation, organic matter availability, salinity, oxygenation, etc., affecting benthic community. Modern biogenic structures (lebensspuren), as reflecting the behavior of the tracemaker to environmental conditions (i.e., depositional and ecological) reveal as a useful tool to interpret processes affecting deep-sea depositional settings. The exploration of these deep-sea environments and the in-situ observation of tracemakers require the expensive and time-consuming deployment of short-range observation gear, in many cases with inherent limitations, such as restricted fields of view in both spatial and temporal scales. However, in recent years neoichnological information from marine epibenthic lebensspuren (i.e., traces on the seafloor) has been obtained from videos or still images captured by cameras on autonomous and remotely operated underwater vehicles transiting on or above the seafloor. This new information reveals of major interest, especially in high-energy deep-sea environments, which can be correlated with those related to gateways and paleo-gateways.

In this study we present three cases that exemplify how lebensspuren features are related to deep-sea environments that have high-energy conditions: 1) Rosette-shape traces (RST) related to echiuran feeding activities. We study two locations of the Porcupine Abyssal Plain (NE Atlantic) where the seafloor consistency is different due to sporadic high energetic gravity flows as well as the local dominant megabenthos feeding group (e.g., suspension vs. deposit feeders). The seafloor consistency appeared not to affect RST morphology while the dominant feeding group seemed to control rosette areal coverage. 2) At an abyssal site in the NE Pacific ('Station M'), high-energy periods associated with benthic storms have been related to the impoverishment of lebensspuren abundance and diversity. The local-scale erosion and re-suspension of unconsolidated surface sediment inhibits the formation of previous softground traces and led to the redistribution of organic matter resources but the trace maker remained in the deep-sea station. These findings offer a new perspective where absence of traces may not imply tracemakers absence during quick (<1 day) energetic episodes at the deep-sea. 3) At an abyssal site with a dune field in the Bering Sea, lebensspuren abundance and diversity varies from the abyssal area to the dune field. Changes in the abundance of dwelling structures seem to be related to the high energetic conditions typical of deep-sea dunes.

How to cite: Miguez Salas, O. and Rodríguez Tovar, F.: Neoichnology of high energy deep-sea environments: A tool to improve gateways characterization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7273, https://doi.org/10.5194/egusphere-egu23-7273, 2023.

During the early and middle Miocene, the Mediterranean became a restricted marginal sea with the contraction of the Mesopotamian Gateway and ultimate loss of connectivity to the Indian Ocean. Leading to the transformation of the Mediterranean into a restricted marginal marine sea . Low latitude circumglobal circulation through the basin characterized the basin for most of the Cretaceous and Paleogene. With the loss of this supply of surface and subsurface waters, dramatic changes occurred to the heat, energy, and nutrient budgets across the Mediterranean. The most affected area was the eastern basin. , As is well evidenced by the onset of sapropel formation, many other aspects of the sedimentary system changed in response to this ocean circulation rearrangement. Hemipelagic successions in southwestern Cyprus offer a window into the changes in the subsurface waters occurring in the Eastern Mediterranean through the closure of the gateway to the Indian Ocean. Dated to the late Aquitanian to the early Serravallian (22.5–14.5 Ma), this sequence is carbonate-dominated and overall continues. It exhibits sedimentation with mass transport contribution from shallow water carbonates to deeper facies. The succession exhibits fluctuation of bottom current activity, which was disrupted in the early Burdigalian by mass transports and temporarily halted during the Langhian. Phosphates are present through the entire succession, but most notably in the Langhian. Combined, these lithological characteristics indicate changes in bottom current energy and seafloor ventilation that point to two key intervals of connectivity restriction through the Mesopotamian gateway.

How to cite: Bialik, O. M., Reolid, J., Kulhanek, D. K., Hincke, C., Waldmann, N. D., and Betzler, C.: The impact of Indian Ocean - Mediterranean gateway closure on the current and nutrient regime in the Eastern Mediterranean during the early to middle Miocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12101, https://doi.org/10.5194/egusphere-egu23-12101, 2023.

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 multi-centennial, 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.

In the study area, it is well known that the Mediterranean Outflow Water (MOW) has generated a complex CDS since the full opening of the Strait of Gibraltar in the early Pliocene (5.3 Ma). Recently, an ancient CDS has also been discovered in the late Miocene, which is separated from the Pliocene-Quaternary CDS by a period of quiescence representing the restriction of bottom water circulation across the Mediterranean-Atlantic exchange during the late Messinian (~6.4 - 5.3 Ma). The late Miocene CDS was established after the final closure of the Indian Gateway (IG) and the Neo-Tethys Ocean in the Middle Miocene, followed by the inception of the Mediterranean Sea (~13.8 - 11 Ma). The final closure of the IG conditioned a wide gateway configuration for the connection between the Mediterranean Sea and the Atlantic Ocean, with the full establishment of an anti-estuarine circulation similar to the present day as opposed to its previous situation.

Interestingly, both the late Miocene and the Pliocene-Quaternary CDSs have a long common evolution that could be simplified into two stages, with an initial- and growth-drift stages. The late Miocene CDS is then buried under dominantly hemipelagic late Messinian (~6.4 - 5.3 Ma) deposits, whereas the buried-drift stage is absent for the Pliocene-Quaternary system due to the ongoing nature of the CDS’s evolution. The long-term development of these CDSs can be correlated with a coeval shallowing of sills, which determined a change from an outflow to an overflow setting across the gateways through time. These long-term variations (>5-10 My) in paleo-circulation are thus driven by the by the tectonic control on the evolution of oceanic gateways. The internal sedimentary architecture of the late Miocene and Pliocene-Quaternary CDSs indicates a complex stratigraphic stacking pattern of deposits bounded by internal discontinuities and hiatuses in response to the intermittent behaviour of the MOW at different temporal scales, which have been attributed to tectonic pulses, climatic and eustatic changes and oceanographic processes that have caused deepening/shoaling or weakening/strengthening of bottom currents through time, exerting a major effect on deepwater sedimentation and the benthic habitat.

This project was funded by the JIP#1 within the framework of “The Drifters” Research Group at Royal Holloway University of London and related to the projects, CTM2016-75129-C3 (INPULSE) and PID2021-123825OB-I00 (ALGEMAR).

How to cite: Hernández-Molina, F. J., Ng, Zhi. L., Duarte, D., Llave, E., Roque, C., Sierro, F. J., de Weger, W., de Castro, S., Rodrigues, S., Rodríguez-Tovar, F. J., Fernández-Salas, L. M., García, M., Arnaiz, Á., Roque, D., Bruno, M., and Sánchez-Leal, R. F.: Late Miocene to Quaternary Contourites Depositional Systems in the Gulf of Cadiz and West Portugal related to the Mediterranean - Atlantic exchange evolution: decoding bottom currents behaviour and oceanographic processes associated with gateways, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15668, https://doi.org/10.5194/egusphere-egu23-15668, 2023.

The extreme Mediterranean sea-level drop during the Messinian salinity crisis has been known for >50 years, but its amplitude and duration remain a challenge. Here we estimate its amplitude by restoring the topography of the Messinian Nile canyon and the vertical position of the Messinian coastline by unloading of post-Messinian sediment and accounting for flexural isostasy and compaction. We estimate the original depth of the geomorphological base level of the Nile River at ~600-m below present sea level, implying a drawdown 2-4 times smaller than previously estimated from the Nile canyon and suggesting that salt precipitated under 1-3-km deep waters. This conclusion is at odds with the nearly-desiccated basin model (>2 km drawdown) dominating the scientific literature for 50 years. Yet, a 600-m drawdown is ca. five times larger than eustatic fluctuations and its impact on the Mediterranean continental margins is incomparable to any glacial sea-level fall.

How to cite: Gvirtzman, Z., Heida, H., Garcia-Castellanos, D., Bar, O., Zucker, E., and Enzel, Y.: Limited Mediterranean sea-level drop during the Messinian salinity crisis inferred from the buried Nile canyon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7864, https://doi.org/10.5194/egusphere-egu23-7864, 2023.

At the end of the Miocene, the restriction of the Atlantic-Mediterranean seaway led to the deposition of a basin-wide salt giant (of up to 2.5km in thickness) in the Mediterranean. Drawdown(s) of the water level of the Mediterranean during this Messinian Salinity Crisis (MSC) have been proposed to have occurred. However, their number, timing and amplitude are still largely debated, with estimates ranging from 200m to 2km. While an important sea level fall could have efficiently blocked the Mediterranean outflow to the Atlantic Ocean, a limited drawdown would have allowed huge export of salt from the Mediterranean to the Atlantic Ocean, and in turn to the global ocean.  These two scenarios would thus have had opposite effects on thermohaline circulation and consecutively on climate. It is therefore crucial to estimate the water level of the Mediterranean during the MSC to understand its climatic and environmental effects both on a regional and global scale.

Here we investigated the deposits drilled by ODP and DSDP expeditions that characterize the terminal phase of the MSC in deep basins of the Mediterranean.  We measured the sulfur isotopic composition (both in sulfide and sulfate bearing minerals) in these deposits to constrain the maximal depth under which they formed, building on the observation that sea level is an important factor controlling sedimentary sulfur isotopic composition. We then used these maximal depths of deposition in a paleo-bathymetric reconstruction to constrain the amplitude of the base level fall that characterized the end of the Messinian Salinity Crisis. The result of this approach suggests a minimal water level drop of 1.1km in the western Mediterranean and a 1.7km drawdown at least in the eastern Mediterranean. This imply that these two basins were disconnected at the end of the MSC, and supports the findings of studies using independent seismic markers.

How to cite: Guibourdenche, L., Heida, H., Andreetto, F., and Aloisi, G.: Late Messinian Mediterranean base level fall : insights from sulfur isotopic variations coupled with isostasy-based paleo-depth estimates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16940, https://doi.org/10.5194/egusphere-egu23-16940, 2023.

The boron isotope composition of the ocean is homogeneous, but varies on multi-million year time scales, given its residence time of approximately 10 million years. To date, the secular evolution of the oceanic boron isotope budget has been difficult to constrain. The lack of knowledge on past boron isotope composition of seawater (δ¹¹B_sw) poses a major uncertainty for reliable boron-based pH and CO₂ reconstructions from Earth’s geologic past and critically limits our understanding of the global biogeochemical cycling of this important element through time. Evaporitic minerals bearing fluid inclusions – and halites in particular – present a highly appealing archive for reconstructing δ¹¹B_sw given their direct origin from seawater. However, the interpretation of their boron isotope signatures is not straightforward due to the possibility of fractionation during evaporation and crystallisation. Here we present first insights into boron isotope evolution during evaporite formation from laboratory experiments and natural modern evaporitic settings. These data enable us to place constraints on boron fractionation in ancient evaporites, offering new insights into δ¹¹B_sw during some of the key periods of the Phanerozoic.

How to cite: Jurikova, H., Gázquez, F., Branson, O., Evans, D., Dumont, M., Sendula, E., Bodnar, R., Weldeghebriel, M., Lowenstein, T., and Rae, J.: Secular evolution of boron isotope composition of seawater archived in evaporites?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9969, https://doi.org/10.5194/egusphere-egu23-9969, 2023.

In the Mediterranean region, the end of the Miocene is marked by the Messinian Salinity Crisis (MSC; 5.97 - 5.33 Ma), a peculiar event that governed environmental modifications in the region, causing the deposition of large thicknesses of evaporitic rock units, dramatic hydrological and ecological crises that affected both water and land-based habitats. The onset of the MSC has been proven to be synchronous over the Mediterranean basin as demonstrated by astronomical tuning of the pre-evaporitic sedimentary successions. Among these, the Sorbas Basin plays a pivotal role for the understanding of the palaeoceanographic evolution of the Western Mediterranean Sea before the onset of the MSC. Its location within proximity of the Atlantic gateway renders the Sorbas Basin an exceptional recorder of palaeoceanographic changes just prior to the MSC. The pre-evaporitic sequence starts with Tortonian calcarenites (belonging to the Azagador Member) followed by early Messinian clays and diatomites (belonging to the Abad Member). The Lower Abad Member, consists of indurated whitish marls and softer grey marls which contrast sapropel and diatomite alterations of the Upper Abad Member. Here, we present biomarker-based sea surface temperatures (SST) using TEX₈₆ paleotemperatures recorded in the Sorbas basin for the time interval between 7.3 and 6.1 Ma. The TEX₈₆ SST estimates show a generally decreasing trend, with a 7.26 Ma to 7.11 Ma warm phase (averaging 27 °C). This warm phase is followed by ~5°C cooling (to values averaging 22 °C) after 7.11 Ma, with two distinct colder peaks, one centred around 7.09 Ma and one around 6.95 Ma. The cooling after 7.11 Ma follows shallowing and restriction in the Betic and Rifian marine gateways and is most likely controlled by global cooling characterizing the latest Miocene. In a second step, we couple the TEX₈₆ SST estimates with oxygen stable isotope ratios (δ¹⁸O) measured on the surface-dwelling planktonic foraminifera Orbulina universa to reconstruct sea surface salinity (SSS) variations at the corresponding stratigraphic levels for the study interval. The newly acquired SST and SSS data from the Sorbas Basin provide a previously unavailable record of changed environmental conditions recorded in the Western Mediterranean Basin that permit direct comparison across the Mediterranean Basin with the recently acquired Messinian Eastern Mediterranean SST and SSS changes.

How to cite: Lanterna, F., Vasiliev, I., Sierro, F. J., and Mulch, A.: Sea Surface Temperatures variations during the Messinian in the Sorbas Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9065, https://doi.org/10.5194/egusphere-egu23-9065, 2023.

At present, the Mediterranean is connected to the Atlantic Ocean through the narrow Strait of Gibraltar (only 13 km wide). The latter, in the late Miocene, most probably did not exist, and the Mediterranean – Atlantic water exchange took place through the Betic (Southern Spain) and Rifian (Northern Morocco) corridors. Studying the evolution of such gateways is fundamental when investigating the extraordinary event known as the Messinian Salinity Crisis (5.96 – 5.33 Ma), when the connection between the Mediterranean Sea and Atlantic Ocean significantly diminished or even ceased. In this work we present a new high resolution geochemical (XRF and stable isotope) record of the Tortonian – Messinian interval of the Montemayor-1 and Huelva-1 cores located in the Betic corridor, current Guadalquivir Basin. Our new data enabled in the first place the high-resolution tuning of the 7.4 – 5.8 Ma time interval, and consequently to precisely date environmental changes and relate them to Mediterranean and global events.

Our results indicate that, at 7.17 Ma and in concomitance with a shallowing of the basin, the bottom water residence time, temperature and salinity increased. These changes have been associated with a reduction of the Mediterranean Outflow Water reaching the Guadalquivir Basin as a consequence of the restriction of the last strand of the Betic corridor connecting the Mediterranean and the Atlantic. This hypothesis is in line with the analogous changes observed in several Mediterranean Sea locations, where from 7.17 Ma a reduced Mediterranean – Atlantic connection is visible. Nonetheless, even if such reduction of the connection was feasible, the same changes in isotope record and analogous cyclicity observed both in the Guadalquivir and Alboran Basin record imply that the Mediterranean signal was still reaching the Betic gateway to some degree. In addition, the significant offset present between our and North Atlantic oxygen stable isotope records entails how the signal in the Guadalquivir basin could not have been purely Atlantic. Consequently, we conclude that a significant Mediterranean signal was still present in the Betic corridor during the Messinian.

How to cite: Bulian, F., Jiménez-Espejo, F. J., Andersen, N., Larrasoaña, J. C., and Sierro, F. J.: Evidence of Mediterranean water in the Atlantic margin during the Messinian, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2922, https://doi.org/10.5194/egusphere-egu23-2922, 2023.

Restricted basins are susceptible to develop anoxia because these land-locked basins can trap nutrients and the water column can easily become stratified. The Mediterranean basin has a limited connection to the open ocean and became increasingly restricted over time, making it suitable to study effect of basin configuration on anoxia development. Enhanced runoff, related to increased North-African monsoon intensity, regularly resulted in increased productivity and/or deep-water anoxia and deposition of organic-rich sediments, the so-called sapropels. Most depositional models for sapropel formation focus on the most recent sapropels (e.g. S1 and S5), outcrop samples or individual Pliocene sapropels from ODP leg 160. Until recently, continuous and high-resolution records were lacking, whereas such records can provide important constraints on the relationship between sapropel deposition and its environmental driving forces, such as climate and basin configuration. Here we present newly acquired XRF-scanning data of redox-sensitive trace elements and estimates for total organic carbon (TOC) from a 5 Myr record of the Eastern Mediterranean Sea (ODP Site 967), where reoccurring sapropels are recorded from 3.2 Ma onwards. Based on our geochemical proxies, we reconstruct (de)oxygenation and associated basin restriction over the last 5 Myr. This record allows us to elucidate which primary processes drove sapropel formation in this basin and whether these processes changed over time. We show that the first preserved Pliocene sapropels (~3.2-3.0 Ma) are highly enriched in redox-sensitive trace elements and have TOC values up to 25%, and likely formed in a much more open (i.e. with increased water renewal) depositional environment. Such a model of Mediterranean sapropel deposition differs significantly from that of the more recent sapropels, which are deposited in a much more restricted environment. Hence, the depositional model for recent sapropel formation cannot be directly extrapolated to these older sapropel deposits.

How to cite: van der Hoeven, I., Grant, K., Rohling, E., Liebrand, D., Lourens, L., Reichart, G.-J., and Hennekam, R.: A 5-million-year record of (de)oxygenation and associated changes in basin restriction in the Mediterranean Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8524, https://doi.org/10.5194/egusphere-egu23-8524, 2023.