SSP1.11

Evaporite weathering and deposition are seldom in balance even on million-year time-scales with grand depositional events superimposed against a background of more slowly varying weathering. Despite such imbalance, biogeochemical models generally assume that evaporite weathering and deposition rates are equal on all time scales. Changes in evaporite dynamics through time will likely impact oxidant budgets through the sulfur cycle and we have shown this to have been especially significant during Proterozoic times. Recently, we proposed that imbalances between evaporite weathering and deposition can also affect climate through the process of carbonate sedimentation. Calcium sulfate weathering supplies calcium ions to the ocean unaccompanied by carbonate alkalinity, so that increased carbonate precipitation strengthens greenhouse forcing through transfer of carbon dioxide to the atmosphere. Conversely, calcium sulfate deposition weakens greenhouse forcing, while the high depositional rates of evaporite giants may overwhelm the silicate weathering feedback, causing several degrees of planetary cooling. Non-steady-state evaporite dynamics and related feedbacks have hitherto been overlooked as drivers of long-term carbon cycle change. In this talk, we illustrate the importance of evaporite deposition, in particular, by showing how a series of massive depositional events contributed to global cooling during the mid–late Miocene. Further studies are required to quantify gypsum deposition over time and its possible effects on deoxygenation of the surface environment, especially at times of mass extinction, as well as on climate.

How to cite: Shields, G. and Mills, B.: Evaporite dynamics and their effects on global climate and oxygen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15511, https://doi.org/10.5194/egusphere-egu21-15511, 2021.

Evaporation from porous rock is not only a significant part of the earth-atmosphere water balance but it also plays a crucial role in weathering processes. In the case of salt weathering, the evaporation rate directly influences the amount of precipitated aggressive salts. Evaporation also strongly affects frost, hydric and biogenic weathering, since they are influenced by water content and its temporal changes. Without proper quantification of the evaporation loss, it is not possible to thoroughly explain and/or predict the development of moisture content and its spatial distribution within natural rock outcrops. Despite its importance, the study of evaporation from porous rocks has seen little scientific focus so far. In our study (Slavík et al., 2020), we measured the evaporation rate from bare surfaces of sandstone under field microclimate on a roughly monthly interval for about one year. The measurement was performed using sandstone cores with a set depth of the vaporization plane (i.e. the area where most of the phase change from liquid to vapour occurs in the subsurface) and we used a simple Fick’s law of diffusion for calculations of the evaporation rate from the cores. The calculations required only a laboratory-measured water-vapour diffusion coefficient of the sandstone, in-situ seasonally measured vaporization plane depth, and logs of air humidity and temperature. The analysis of measured and calculated evaporation rate revealed that far the most important single factor influencing the evaporation rate is the depth of the vaporization plane. Other factors such as the microclimate characterised by temperature and relative humidity were of lesser importance and the calculated evaporation rate reasonably follows measured values with Pearson correlation coefficient r > 0.81. The experimental setup of evaporation rate measurement, for its simplicity and price, should find use in studies with high-number measuring sites or even locations with a risk of apparatus damage. Our measurements were performed in a humid continental climate and the suggested approach should be verified in more arid environments.

Figure: Goodness‐of‐fit between measured and calculated evaporation rate. Dashed line represents the identity line (calculated values equal to measured values).

This research was funded by the Czech Science Foundation [GA19-14082S].

References: Slavík, M., Bruthans, J., Weiss, T., Schweigstillová, J. (2020): Measurements and calculations of seasonal evaporation rate from bare sandstone surfaces: Implications for rock weathering. Earth Surface Processes and Landforms 45, 2965–2981.

How to cite: Weiss, T., Slavík, M., and Bruthans, J.: Evaporation rate from bare sandstone surfaces in humid climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15911, https://doi.org/10.5194/egusphere-egu21-15911, 2021.

As the only deep hypersaline, halite‐precipitating lake on Earth today, the Dead Sea is the
single modern analog for investigating the mechanisms by which large‐scale and thick salt deposits,
known as “salt giants”, have accreted in the geological record. We directly measure the hydroclimatic forcing
and the physical limnologic processes leading to halite sedimentation, the vertical thermohaline structure,
and salt fluxes in the Dead Sea. We demonstrate that changes in these forcing lead to strong seasonal
and regional variations in the stratification stability ratio, triggering corresponding spatiotemporal
variations in thermohaline staircase formation and diapycnal salt flux, and finally control the thickness of
the halite layer deposited. The observed staircase formation is consistent with the mean‐field γ instability,
causing layering in double‐diffusive convection. We show that double diffusion and thermohaline staircase
formation drive the spatial variability of halite deposition in hypersaline water bodies, underlying and
shaping “salt giants” basin architecture.

How to cite: Sirota, I., Ouillon, R., Mor, Z., Meiburg, E., Enzel, Y., Arnon, A., and Lensky, N.: Hydroclimatic Controls on Salt Fluxes and Halite Deposition in the Dead Sea and the Shaping of “Salt Giants”, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12510, https://doi.org/10.5194/egusphere-egu21-12510, 2021.

During the first phase of the Messinian Salinity Crisis, massive amounts of sulfate (SO₄^2-) have been sequestred in the form of up to 200m thick gypsum deposits (Primary Lower Gypsum) in Mediterranean marginal basins. The sulfur isotopic composition of the sulfate ion of this unit (δ³⁴S_SO4) (on average 22.3 ‰) strongly suggests that gypsum was formed by concentration of marine sulfate. Interestingly, the preservation of sulfide globules within the gypsum and marls interbeds suggests that the basin sulfate was not only involved in gypsum formation but a fraction was also reduced through microbial sulfate reduction. Moreover, filamentous fossils interpreted to be the remnants of sulfide oxidizing bacterias are entrapped in this gypsum and indicate, together with the occurrence of sulfide globules and dolomite, that an active biogeochemical sulfur cycling was active at the time of Primary Lower Gypsum deposition. To investigate the role of this active sulfur cycling in Mediterranean marginal basins, we analyzed the multiple sulfur isotopic composition of sulfate and sulfide minerals (δ³⁴S andΔ³³S)from Primary Lower Gypsum of the Vena del Gesso basin (Italy). Whereas the isotopic composition of gypsum (δ³⁴S_SO4 from 21 to 24‰ and Δ³³S_SO4 from -0.001 to 0.049‰) display very homogenous values that are close to those of the Messinian ocean (δ³⁴S_MSC ~22±0.2‰ and Δ³³S_MSC~0.039±0.015), the analyzed reduced sulfur compounds display a wide range of variability  with -36 to +9‰ in δ³⁴S and -0.017 to 0.125‰ in Δ³³S. This suggests huge hydrologically-driven redox variations during Primary Lower Gypsum deposition in the Vena del Gesso basin, possibly involving intermittent stratification of the water column and an active microbial cycling of sulfur.

How to cite: Guibourdenche, L., Cartigny, P., Dela Pierre, F., Natalicchio, M., and Aloisi, G.: Microbial sulfur cycling during the formation of Primary Lower Gypsum in Mediterranean marginals basins, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14573, https://doi.org/10.5194/egusphere-egu21-14573, 2021.

Large deposits of gypsum accumulated in the marginal basins of the Mediterranean Sea during the Messinian Salinity Crisis. These form the marginal portions of the Mediterranean Salt Giant (MSG) that also occupies the deep, central Mediterranean basins. Although the marine, evaporitic origin of the MSG is undisputed, the analysis of gypsum fluid inclusions and of gypsum-bound water (d¹⁸O_H2O and dD_H2O) suggest that marginal basin gypsum formed from low- to moderate-salinity water masses (5 - 60 ‰), rather than from high-salinity brines (130 - 320 ‰), as expected during the evaporation of seawater. We present a new set of water isotope and fluid inclusion salinity data that extends the low salinity signature of gypsum to include five Mediterranean Sea marginal basins: Caltanissetta Basin (Sicily), Sorbas Basin (Spain), Piedmont Basin and Vena del Gesso Basin (northern Italy) and Catanzaro Trough (Southern Italy). With a simple geochemical model we explore the salinity-d¹⁸O_H2O-dD_H2O evaporation path and the ^87/86Sr and d³⁴S_SO4 composition of the Mediterranean Sea subject to a variety of evaporation conditions and mixing ratios with continental runoff. This approach suggests that evaporation and mixing with continental runoff - including freshwater transiting via the Paratethys - cannot lead to the observed geochemical signature of MSC gypsum deposits. An alternative process that decouples the saturation state with respect to gypsum from salinity must have been active. We are exploring the possibility that the biogeochemical sulfur cycle leads to spatially and temporally localized gypsum supersaturation conditions via the production of SO₄^2- by the oxidation and disproportionation of reduced sulfur compounds.

How to cite: Aloisi, G., Natalicchio, M., Guibourdenche, L., Caruso, A., and Dela Pierre, F.: Low-salinity Mediterranean gypsum deposits: chemical vs biological products, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12551, https://doi.org/10.5194/egusphere-egu21-12551, 2021.

Recent developments on analytical capabilities in the field of in-situ laser ablation mass spectrometry (LA-ICPMS) have expanded the applications of U-Pb geochronometers in low-U minerals such as carbonates (Roberts et al. 2020) or garnets (Millonig et al., 2020). The rapid development of the technique requires well-characterized, matrix-matched reference materials, which are essential for ion probes or LA-ICPMS due to potential matrix effects. However, given the unavailability of standards for some minerals, the use of non-matrix-matched standards, i.e. reference materials that are different to the sample, have been also addressed (Piccione et al., 2019).

In this contribution, we explored the possibility of using carbonate reference materials for in-situ U-Pb dating of sulphates. For that purpose, we selected samples from the Messinian Salinity Crisis because their ages are well established by cyclostratigraphy and thus can be compared with ages obtained by LA-ICPMS analysis. Data was acquired using a RESOLution 193 nm ArF excimer laser coupled to a (I) sector field ICP-MS (ElementXR) or (II) multicollector ICP-MS (Neptune Plus).

The majority of the samples (27 out of 32) failed due to the elevated common-Pb content and low ²³⁸U/²⁰⁴Pb ratios. Nevertheless, five of the samples showed greater amounts of U and U/Pb ratios of up to 600; therefore, regression lines could be drawn and ages are calculated with 5-10 % of uncertainty. These ages obtained are within error of the cyclostratigraphic ages already published (Vasiliev et al., 2017).

Millonig et al., (2020) Earth Planet. Sci. Lett. 552, 116589; Piccione et al. (2019) Geosphere 15 (6), 1958– 1972; Roberts et al. (2020) Geochronology 2, 33–61; Vasiliev et al. (2017) Palaeogeogr. Palaeoclimatol. Palaeoecol. 471, 120-133.

How to cite: Beranoaguirre, A., Vasiliev, I., and Gerdes, A.: Applicability of carbonate reference materials as matrix-matched standards for in-situ LA-ICPMS U-Pb dating of Sulphates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5791, https://doi.org/10.5194/egusphere-egu21-5791, 2021.

The Messinian Salinity Crisis (MSC) was caused and terminated by changes in the Atlantic-Mediterranean connectivity in the western end of the Alboran Basin, a complex tectonic area affected by the Iberia-Africa collision and the presence of a subducted lithospheric slab beneath the Betic-Rif orogen.

The isostatic, tectonic and erosional effects on surface topography work on different spatial and temporal scales, and their relative contributions to the changes in connectivity and subsequent evaporite deposition and sea-level drop are difficult to constrain.

We perform 2D-planform flexural isostatic modeling using the Messinian Erosion Surface imaged in the Alboran Basin to reconstruct the topography and vertical motions of this region since the end of the MSC. The results constrain the original depth of the Messinian erosional features to test their consistency against the various models proposed for Mediterranean sea-level changes during the MSC.
We apply Glacial Isostatic Adjustment theory to quantify the time response of these vertical motions to the large MSC-related mass shifts (salinification, evaporite deposition and a kilometer-scale sea-level drop),  and their gravitational effects on sea-level in the Mediterranean. In particular, models for the Strait of Gibraltar allowus to identify the potential role of these effects as feedback mechanisms influencing the rates and duration of changes in the Atlantic-Mediterranean connectivity at the straits.  We will explore the possible implications of these for the timing of the closure of the last Atlantic-Mediterranean seaway.

How to cite: Heida, H., Garcia-Castellanos, D., Jiménez-Munt, I., Estrada, F., Ercilla, G., Coulson, S., and Mitrovica, J.: Modelling the vertical motions of the Alboran Sea since the Messinian salinity crisis: Topographic reconstruction and glacial-isostatic sea-level effects, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10081, https://doi.org/10.5194/egusphere-egu21-10081, 2021.

The Nahr Menashe Unit (NMU), which forms the uppermost part of the Messinian succession,  is one of the most cryptic and elusive sedimentary units present in the Levant basin (Eastern Mediterranean). We use a high-resolution 3D seismic dataset from offshore Lebanon to propose a new interpretation for its formation and evolution. The NMU varies laterally across the basin both in thickness and internal seismic characteristics. The variably coherent cyclic seismic packages affected by fracturing, faulting suggests that the NMU represent a reworked, layered evaporite succession interbedded with siliciclastics derived from both the Lebanon Highlands and the Latakia Ridge. Widespread semi-circular depressions, random linear imprints, passive surface collapsing and residual mound features within the NMU suggest that post depositional diagenetic and/or strong dissolution process often affected its evaporite-rich subunits. The well-known extended valley and tributary channel systems characterising the uppermost NMU shows mainly erosional rather than depositional features. Erosion started after deposition of NMU as a consequence of the maximum base level fall during the last phase of the Messinian Salinity Crisis (MSC). The channel and valley system were subsequently infilled by layered sediments here interpreted to represent post-MSC deep water marine reflooding. In conclusion, our analyses suggest the NMU can be interpreted as a mixed evaporite-siliciclastic system deposited in a shallow marine or marginal environment, which subsequently experienced fluvial erosion and later burial by transgressive/high-stand sediments.

How to cite: Kabir, S. M., Iacopini, D., Hartley, A., Maselli, V., and Oppo, D.: The role of the Nahr Menashe in the Messinian Salinity Crisis: formation, dissolution and fluvial incision of the top evaporite unit in the NE Levant Basin, Eastern Mediterranean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10318, https://doi.org/10.5194/egusphere-egu21-10318, 2021.

The Late Miocene has been considered one of the most climatically stable periods of the Cenozoic, time span characterized by minor long-term cooling and ice growth. Especially, the Tortonian-Messinian Transition is recognized as a priority for paleoenvironmental reconstruction and climate modelling due to the significant paleoenvironmental changes preceding the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Here, we present stable oxygen (δ¹⁸O) and carbon (δ¹³C) isotopes measured on benthic and planktonic foraminifera from Potamida section (Crete Island, eastern Mediterranean). The δ¹⁸O results indicate a decoupling between the surface and the bottom water column starting before the Tortonian-Messinian boundary. The difference between planktonic and benthic oxygen isotope signals (Δδ¹⁸O) further provides an estimate of the degree of water column stratification during that time. The δ¹³C data indicate a generally trend towards lighter values as an excellent illustration of the Late Miocene Carbon Isotope Shift (LMCIS; 7.6-6.6 Ma) due to progressive restriction of the Mediterranean basin, with the exception of the 7.38-7.26 Ma time interval where significantly heavier δ¹³C values are documented in both records. Such changes in carbon cycle seem to be most pronounced in the planktonic foraminiferal record (surface waters) through a 6-cycle development indicative of a cyclic productivity pattern during the latest Tortonian. The entire record is substantiated by sea surface temperature (SST) estimates based on TEX₈₆ biomarker based proxy. The reconstructed SST record shows that a warm phase characterized the late Tortonian sea surface (~27⁰C), time followed by a strong, steady cooling starting with earliest Messinian, when the SSTs dropped to values as low as 20⁰C. The outcome of the combined stable isotope and biomarker based SST data hint to increased salinity in the surface waters already before the Messinian, while at the Tortonian-Messinian Transition, the conditions in the surface waters changed towards cooler (~24⁰C) and normal salinity conditions.

How to cite: Besiou, E., Kontakiotis, G., Antonarakou, A., Mulch, A., and Vasiliev, I.: Climate and carbon cycle changes drive the hydrographic configuration of the eastern Mediterranean through the Tortonian-Messinian Transition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8853, https://doi.org/10.5194/egusphere-egu21-8853, 2021.

During the Late Miocene the Mediterranean Sea experienced severe disruption of its connectivity to the Atlantic Ocean, highlighted by a rapid sea-level drop, culminating to the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Such a paleoceanographic change, triggered by the cumulative effect of climate and tectonics, caused high-amplitude fluctuations in the hydrology of the entire basin, and further influenced the geological history of the Mediterranean Sea. Although a consistent pattern of the paleoclimate has started to emerge, we currently lack a continuous sea surface salinity (SSS) record linking the timing of sea surface temperature (SST) variations, sea-level fluctuations, and the overall environmental change, particularly for the pre-evaporitic period. Initial viewpoints of a linear and gradual salinity increase prior to the onset of the MSC have been recently revised and replaced by highly variable salinity-related patterns representative of the stepwise restriction of the Mediterranean Sea. Here we use the combined Tetra Ether (TEX₈₆-) and/or alkenone unsaturation ratio (U^K′₃₇) based SSTs and oxygen isotopes (δ¹⁸O) from the cyclic marl-sapropel sedimentary succession of Agios Myron section (north-central Crete, Greece) to assess hydroclimate changes during that time, and we finally present the first record of SSS in the eastern Mediterranean Sea for the earliest Messinian (7.2–6.5 Ma). The relatively stable marine conditions after the Tortonian/Messinian boundary, expressed through a cool and fresh upper water column, significantly changed at ∼6.9 Ma, when an important reversal in the heart of the Messinian cooling trend supplemented by a coherent hypersaline water column took place. The observed SST and SSS patterns provide context for a two-fold evolution of this event (centered at 6.9–6.8 and 6.72 Ma), which finally led to the onset of a brine pool into the eastern Mediterranean basin. The transitional character of the following time interval (6.7–6.5 Ma) marks another important step in the basin restriction with a wider range of salinity fluctuations from highly saline to diluted conditions and enhanced water column stratification prior to the deposition of evaporites. Overall, this evolution supports the concept of a stepwise restriction of the Mediterranean Sea associated with substantial hydroclimate variability and increasing environmental (thermal and salinity) stress, and further confirms its position as a preferred laboratory for developing new conceptual models in paleoceanography, allowing the investigation and scale assessment of a phenomenon with high chances of representing a future analogue scenario.

How to cite: Kontakiotis, G., Butiseaca, G., Antonarakou, A., Karakitsios, V., Zarkogiannis, S. D., Besiou, E., Agiadi, K., Koskeridou, E., Thivaiou, D., Mulch, A., and Vasiliev, I.: The eastern Mediterranean pre-MSC brine pool as an analogue for future subtropical hydroclimate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8711, https://doi.org/10.5194/egusphere-egu21-8711, 2021.

The fresh new cores 3AGN2S02 and 3AGN2S04 located in the deformed foredeep of the Gela Thrust System, locally known as Caltanissetta Basin, represent an opportunity for a better comprehension of the Messinian events, as well as for the reconstruction of the Sicilian evaporitic Basin architecture. The entire ‘early Messinian stage’ (7.2-5.96Ma) preceding the Messinian Salinity Crisis (MSC) has been already investigated in the Caltanissetta Basin. Even though the Tripoli Formation and ‘Calcare di Base’ (‘CdB’) have been widely studied for a long period of time, many aspects remain unclear. The ‘CdB’ has been commonly considered to represent the first evaporitic unit of the Messinian succession in Sicily. Different ages obtained in the underlying Tripoli deposits from various Sicilian outcrops display a diachronous onset of the MSC (Rouchy & Caruso, 2006). However, Manzi et al. (2011) propose an alternative interpretation for the ‘CdB’, suggesting that it does not belong exclusively to the onset of the MSC, but it is made of three carbonate facies belonging to different MSC stages. A detailed sedimentological, geochemical and petrographic study of the two cores allowed us to evidence the paleoceanographic changes that affected the central Mediterranean Sea during the transition from marine to restricted conditions, up to the onset of the MSC, and to observe the differences between the marginal and the deep basins of the Caltanissetta Basin, enhanced by the ongoing regional tectonics. Facies characterization made it possible to confirm the nature of the sediments of the cores, reflecting distinct depositional environments. A lithological transition passing from the Tripoli Formation to the complex ‘CdB’ carbonates alternating with shales is observed (3AGN2S04). This CdB appears to be laterally equivalent to gypsum and salts at site 3AGN2S02. In the brecciated facies of the ‘CdB’, evaporite pseudomorphs are also present, implying early stage diagenesis. Furthermore, our analyses gave us insights of strong oscillations in hypersaline conditions with freshwater inputs controlled by Milankovitch’s cycles. Moreover, the 3AGN2S04 core is characterized by the repetition of sedimentary successions due to the later development of a thrust system, which can be an important hint concerning the morphological and structural evolution of the Caltanissetta Basin. These new data are fundamental for stratigraphic reconstructions, comparing them with the already well-calibrated reference section of Falconara-Gibliscemi but also with other outcrops located in the various depocenters of the Caltanissetta Basin. The local transition from the uppermost part of the Tripoli cycles to the ‘CdB’ reflects the worsening of the marine connections, implying that during late Messinian broadly constant stressed environmental conditions existed in the central Mediterranean shelves. We conclude that since the onset of the MSC, marine inputs were not important enough to balance the effects of the climate fluctuations and the evaporation/precipitation budget in the individualized semi-closed settings.

How to cite: Tzevahirtzian, A., Caruso, A., Scopelliti, G., and Sulli, A.: The onset of the Messinian Salinity Crisis recorded by a new marginal basin succession in the Caltanissetta Basin (Sicily, IT)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5974, https://doi.org/10.5194/egusphere-egu21-5974, 2021.