Evaporite Deposits Research Articles

Nature and significance of Late Pleistocene to Holocene thick evaporite deposits of the Danakil Depression, Afar, Ethiopia

Nature and significance of Late Pleistocene to Holocene thick evaporite deposits of the Danakil Depression, Afar, Ethiopia

Architectural development of a land-attached carbonate platform in the African–Arabian Desert Belt: the late Pleistocene to Holocene evolution of the Al Wajh Platform, NE Red Sea, Saudi Arabia

ABSTRACT Carbonate platform architectures are indicators of environmental changes, such as sea level, climatic variations, and tectonic influence, which all control platform evolution. While analog studies on modern carbonate platforms have predominantly focused on tropical settings, limited attention has been given to arid and semiarid environments, although many ancient carbonate sequences were developed under these settings. This study aims to bridge this gap by investigating the Al Wajh carbonate platform lagoon in the NE Red Sea, Saudi Arabia, using geophysical and remote-sensing data to unravel its architecture and development since the last interglacial highstand (MIS 5e). We collected and analyzed sub-bottom profiles extending over 675 km and airborne lidar multibeam bathymetry data covering an area of 1700 km2. Surface sediment samples and vibracores with a maximum penetration of three meters were integrated to strengthen our interpretation. Furthermore, a recently published Red Sea sea-level curve was used to establish an age model and supplemented by available climate data to reconstruct depositional models. The Al Wajh lagoon is a “bucket” structure hosting five distinct depositional units since the late Pleistocene: U0 (pre-MIS 5e and MIS 5e), U1, U2, U3, and U4 (MIS 1), which are composed of five hydroacoustic facies, ranging from mounded to wavy laminated facies. Based on combining climate data, sea-level curves, and platform topography with our geophysical data, we conclude that the lagoon hosts carbonate, siliciclastic (fluvial and eolian), and potentially evaporitic deposits of open-marine and playa-lake origin. Intriguingly, karst architecture (i.e., sinkholes, caves, and collapsed cavities) is absent despite intermittent pluvial episodes and exposure during the late Pleistocene. Data analysis indicates that the Al Wajh lagoon architecture and development since the late Pleistocene are controlled by a combination of antecedent topography, sea-level variation, climate fluctuation, siliciclastic influx, carbonate production, and reef growth and drowning. Finally, insights from this study enhance our understanding of the architecture and sedimentary infill of ancient land-attached carbonate platforms deposited in a mature rift basin under alternating arid and pluvial climate settings.

The role of the Messinian evaporites in the identification of potential gas storage sites: A review of the Adriatic foreland basin system (Italy)

AbstractFocusing on the late Miocene succession stratigraphic successions including the evaporite deposits from the Messinian salinity crisis (MSC) of the Adriatic foreland basin, a revision of available boreholes and seismic data allowed us to recognize the presence of reservoirs and seals systems that can be considered of potential interest for the storage of natural and synthetic gas. Potentially good reservoir sites can be found where porous rocks referable to siliciclastic turbiditites (Marnoso‐arenacea and Laga Fms) or shallow‐water carbonates (Bolognano Fm) preferentially involved in anticlinal structures and covered by thick MSC evaporites, which may represent effective reservoir seals. The integrated reconstruction of porous rocks distribution and facies, thickness, and lateral continuity of the overlying evaporites, allows the identification and zonation of geological settings in the Adriatic foredeep, backbulge and foreland with peculiar stratigraphy and deformations, only partially considered before, that may deserve consideration in the research of potential gas storage sites.

Evaporite sequences as archives for Mg isotope compositions of seawater - Evidence from a Tethys marginal shelf basin in the Anisian

Evaporites have recently been suggested as a potential archive for recording the Mg isotope compositions (δ26Mg) of coeval seawater. However, episodic dolomitization during the deposition of massive evaporites could cause considerable Mg removal and isotopic fractionation. To constrain the hydrological changes and influence of dolomitization on ambient brine δ26Mg, we present petrographic and mineralogical features, as well as Mg-C-O-Sr isotope data extracted from carbonate phases of a middle Triassic (ca. 247 Myr) marine anhydrite-dolostone sequence from a drill core in eastern China. The drilled lithologies are characterized by massive dolostone layers in the lower part, followed by an upward decline in dolomite contents accompanied by a rise in anhydrite. Multiple lines of evidence consistently point to a syn-depositional origin for the dolostones in a marginal basin of the Tethys Ocean and a lack of diagenetic alteration since deposition. We reconstructed the dynamic changes of δ26Mg values of basin waters based on Mg isotope compositions in dolomite leachates. According to our findings, the δ26Mg values of the basin waters were remarkably high (about 0.38 ± 0.05‰) at the onset of evaporation, indicating a significant Mg sink of the massive dolomitization. The δ26Mg of brine in the basin then changed towards the value of coeval seawater (about −0.32 ± 0.05‰) starting with the deposition of evaporites. Concurrently, 87Sr/86Sr ratios of dolomites shift from radiogenic values towards contemporaneous seawater composition. Our results demonstrate that the evaporite basin was not strictly restricted, and water exchange with the open ocean never ceased. Modeling calculation reveals that, even when the seawater exchange rate is far below the average ocean circulation, δ26Mg of brine in the basin will reach the value of open ocean within 1 Myr, completely removing the influence of early dolomitization. We suggested that massive marine evaporite sequences have the potential to record the long-term evolution of seawater Mg isotopes.

Quantitative records of paleotemperature in Qarhan Salt Lake, Qaidam Basin and its relationship with potassium deposits

Qarhan Salt Lake, located in the Qaidam Basin on the Qinghai-Tibet Plateau in northwestern China, is the largest potash production base in China. The main potash deposit in Qarhan Salt Lake is a comprehensive deposit in which the liquid potassium resources dominated by potassium-rich and lithium-rich brine coexist with the low-grade solid potassium salt deposit composed of solid potash minerals (polyhalite, carnallite, sylvite). Polyhalite is one of the representative potassium minerals, widely distributed in the Bieletan area of Qarhan Salt Lake, coexisting with halite, and its deposition indicates that the paleo-temperature of brine in this area once fluctuated obviously. Twenty core samples from two boreholes in the Bieletan area of the Qarhan Salt Lake were subjected to fluid inclusions thermometry, and homogenization temperatures reflecting the brine temperatures during the precipitation of evaporite minerals in the Salt Lake were obtained, ranging from 12.4 to 28.9 °C and 9.2 to 19.8 °C, respectively. By scanning electron microscopy, acicular polyhalite and pompom-like aggregate of polyhalite have been identified in the sampling layer, indicating that evaporite deposition have reached the stage of potassium salt deposition. The temperature fluctuations of the fluid inclusions and the elemental chemical data are compared vertically, and the sections with significant temperature fluctuations are close to the layers where polyhalite were deposited. It shows that the paleo-temperature fluctuation impact the sedimentary environment of brine, and then affected the polyhalite deposition of Qarhan Salt Lake.

Main Characteristics of the Geological Structure of the Evaporite Formation of the Amu Darya Syneclise

The geological structure of the evaporite formation in the Amu Darya syneclise is a complex system that provides valuable insights into the region's geological history and economic potential. The study aims to analyse the main characteristics of the geological structure of the evaporite formation in the Amu Darya syneclise to expand knowledge of the geological and environmental history of the region and to identify the potential of these deposits for various applications. The methods used for this study included geological mapping, mineralogical analysis, stratigraphic analysis and geochemical research. The study identifies three distinct water-bearing horizons within the evaporite complex: Sharaplinsky, Yolotan, and Sakar. These horizons exhibit varying characteristics in terms of composition, water content, and distribution across the basin. Geomorphological manifestations, such as salt lakes and salt marshes, play a crucial role in understanding the ecological and geological history of the region. The evaporite formation holds substantial economic importance, hosting valuable resources including salts, oil, and gas. This geological structure supports regional industrial development, job creation, and overall economic growth. The study also highlights the need for further research into the geology and geomorphology of the Amu Darya syneclise to better understand the formation and dynamics of evaporite deposits and their role in the region’s current environmental and economic sectors. The study emphasizes the need for efficient technologies and methods for resource extraction and management to ensure sustainable development and minimize environmental impact. The research provides crucial data for optimizing mineral extraction strategies and developing effective natural resource management approaches. It underscores the importance of understanding the geological structure for sustainable ecological and economic development in the region. The practical significance of this study is a basis for developing more effective natural resource management strategies based on an understanding of the geological processes of evaporite sedimentation in the Amu Darya syneclise, which is key to the sustainable development of the region’s ecological and economic systems.

The Messinian paleoenvironment in the Mediterranean (Monte dei Corvi, Ancona): A comparison with the modern oceanographic conditions

The Messinian was characterized by peculiar biogeochemical dynamics and climate in the Mediterranean region, testified by widespread deoxygenation events (sapropel) and evaporite deposition. To constrain the Mediterranean response to past perturbation it is crucial to understand the current environmental crisis related to climate change. In this regard, benthic and planktic calcareous fossils provide valuable insights into surface and bottom water conditions during deoxygenation events.Here we studied in high resolution 4 sapropel-bearing cycles of the Monte dei Corvi (Ancona, Italy), which recorded the behavior of the Adriatic Deep-Water formation, a major controlling factor for the oxygenation in the modern Eastern Mediterranean. Our analysis unveils fluctuations in planktic and benthic assemblages driven by variations in insolation parameters. Sapropel interbeds deposited during insolation maxima exhibit warm-oligotrophic and Deep Chlorophyll Maximum taxa, suggesting warming and freshening of surface water, leading to weakened Adriatic Deep-Water formation and reduced oxygen delivery to the bottom. Marly limestone/marlstone interbeds exhibit the dominance of cold-eutrophic taxa and an abundance of fecal pellets with monospecific/oligospecific calcareous nannofossils taxa (Umbilicosphaera jafari and Reticulofenestra perplexa), suggesting moderately high salinity and sustained productivity during phases of strong mixing.Comparisons between Messinian and the present-day setting reveal significant differences in the abundance and distribution of calcareous planktic assemblage, mostly due to heightened productivity during the Messinian, a response to restricted conditions that increased the basin's susceptibility to nutrient-delivering runoff. This circumstance played a significant role in the widespread deoxygenation and accumulation of organic carbon during the Messinian.The uncertain trajectory of primary production in the Mediterranean complicates precise predictions of the future oxygen balance. Insights from the Messinian underscore the crucial role of primary productivity in shaping bottom oxygen conditions, emphasizing the necessity for ongoing investigations.

Hydrochemical and isotopic characteristics of water sources for biological activity across a massive evaporite basin on the Tibetan Plateau: Implications for aquatic environments on early Mars

Covered by vast eolian landforms, gravel deposits, and playas, the worldwide typical evaporite deposit land, Qaidam Basin, in northwestern China is analogous to early Mars when the aridification process had lasted for millions of years since the end of a wetter climate. This study aims to investigate the chemical and isotopic characteristics of waters in an evaporite-rich environment, as well as the habitable conditions therein, that have undergone a transformation similar to early Mars. In May 2023, a total of 26 water samples were collected across the representative central axis of a longitudinal aridity gradient in the Qaidam Basin, including categories of meteoric water, freshwater, standing water accumulated after precipitation, salty lacustrine water, and hypersaline brines to inspect compounds made up of carbon, nitrogen, phosphorus, sulfur, halogen, and metallic elements. As evaporation intensified, the salt types transformed from HCO3-Ca·Na to Cl·SO4-Na or ClMg. The dominance of carbonate will gradually be replaced by sulfate and chloride, leaving much more dilute and less detectable contents. The presence of trace ClO4−, ClO3−, ClO2−, and BrO3− was confirmed in a few of the sampled Qaidam waters, indicating the preservation of oxyhalides in waters within an arid region and possibly the presence of relevant microbial enzymes. The isotopes of water, carbonaceous, and nitrogenous compounds provide valuable references for either abiogenic or biogenic signatures. With undetectable amount, phosphorus was found to be the limiting nutrient in evaporative aquatic environments but not necessarily antibiosignatures. Overall, these results suggest that the paleo-lacustrine environments on Mars are more likely to preserve biosignatures if they feature the dominance of carbonate minerals, bioavailable nitrate, phosphorus, and organic carbon, the presence of thermodynamically unstable oxyhalides, and isotope ratios that point to the involvement of biological activity.

2‐D Geodynamic Modeling of the Central South Atlantic Wide Rifted Margins, Implications for Evaporite Deposition

AbstractThe thick late syn‐ to early post‐rift shallow water evaporites in the most distal part of wide rifted margins is paradoxical with the deep depression at crustal breakup time predicted by isostatically compensated lithospheric thinning. Elevation of the distal margin and water depth during deposition of the late syn‐rift evaporites in the central South Atlantic are not well constrained and remain to be quantified. We use forward 2‐D thermo‐mechanical modeling coupled with melt prediction and surface processes to assess the contribution of lithospheric and mantle processes on the distal margin topography and subsidence history during continental rifting. Models show that (a) counter‐flow of depleted lower lithospheric mantle during rifting explains the magma‐poor nature of these margins and (b) weak crust and syn‐rift sediment control the wide crustal necking and subsidence history of the distal margin. Integration of our modeling results with quantified geophysical and geological observations suggests that (a) base level was down to −600 m below present‐day global sea level (bsl) during distal margin formation in the Aptian before sag and evaporite deposition, (b) base level was about −300/−400 m bsl at the end of evaporite deposition, and (c) scenarios with a fixed shallow base level (−400 m bsl) or with an increasing base level from an initially deep position (−1,600 m bsl) during evaporite deposition can both fit the observed evaporite distribution. However, erosional features along the base of evaporites suggest a deep initial base level.

Hydroclimate of the Messinian Salinity Crisis constrained from paleo-water triple oxygen, hydrogen, and strontium isotopes

Giant evaporite deposits formed during the Messinian Salinity Crisis (MSC) in the Mediterranean Sea during the upper Miocene. The primary cause is a restricted Atlantic-Mediterranean connection, but the detailed hydroclimate evolution of this event is still a matter of debate. Here we reconstruct the triple oxygen and hydrogen isotopic composition of paleo brines from structurally bonded water in Messinian gypsum from Cyprus. A two-stage evaporation model is constructed to best approximate the hydrological conditions at which Messinian gypsum formed in marginal basins of the Mediterranean Sea. Subsequently, hydroclimatic parameters like paleo relative humidity (RH) are modelled using an iterative curve fitting isotope model approach. The results of our limited dataset reveal a slightly lower RH during the third compared to the second stage of the MSC. This apparent drop in RH is consistent with previous observations from the literature.Besides absolute values of RH, our model allows reconstructing the triple oxygen and hydrogen isotopic composition of the open Mediterranean Sea. This provides an estimate for the proportions of continental water vs. Atlantic seawater flowing into the basin, serving as a proxy for the size of the strait of Gibraltar. The model implies a continental water fraction of around 75–81 % both for the second and third stage of the MSC. In addition, we determined the 87Sr/86Sr of our samples to: i) confirm their stratigraphy; and ii) estimate the relative proportion of continental water vs. Atlantic seawater entering the Mediterranean using Sr mass balance calculations. The combined oxygen and Sr isotope records indicate a persistent connection to the Atlantic supporting the hypothesis that the striking drop in 87Sr/86Sr at the beginning of MSC stage 3 is mainly related to an increased contribution of continental water with low 87Sr/86Sr and high Sr concentrations from the Paratethys. Our results show that the combination of triple oxygen, hydrogen, and Sr isotope data provides a powerful tool to disentangle paleo-hydroclimate even in such complicated hydrological settings as the Mediterranean Sea during the MSC.

Modelling sulfate concentrations in the global ocean through Phanerozoic time

Understanding the long-term variations in seawater sulfate concentrations ([SO 4 2− ] sw ) is crucial to our understanding of the dynamic relationships between the sulfur, carbon, calcium and oxygen cycles, and their influence on the habitability of the Earth. Here, we explore how [SO 4 2− ] sw has changed throughout the Phanerozoic and its impact on other elemental cycles. We do this by utilizing the biogeochemical box model GEOCARBSULFOR. The model suggests that [SO 4 2− ] sw increased throughout the Paleozoic, decreased during the Mesozoic and then increased once more in the Cenozoic, generally matching geochemical proxies. Atmospheric oxygen mirrors [SO 4 2− ] sw changes during the Paleozoic and Mesozoic, but, intriguingly, decouples during the Cenozoic. We further explored the controls on [SO 4 2− ] sw by modifying the modelled gypsum fluxes via the incorporation of evaporite data from the geological record. We found that forcing gypsum burial with the observed evaporite deposition data causes the model to better match proxy records at some times, but worsens predictions at others. We also investigated the reliance of the model on a prescribed record of marine calcium concentrations, finding that it is a dominant control on modelled Phanerozoic [SO 4 2− ] sw and that removing this control seriously degrades the model predictions. We conclude that no model can yet simulate a reasonable evolution of both the calcium and sulfur cycles. Supplementary material: Figures S1–S5 are available at https://doi.org/10.6084/m9.figshare.c.7164928 Thematic collection: This article is part of the Sulfur in the Earth system collection available at: https://www.lyellcollection.org/topic/collections/sulfur-in-the-earth-system

Spatial-temporal variability of lacustrine evaporite and carbonate deposits: Effects of tectonics and sediment supply

Little attention has been paid to the nonnegligible effects of fault evolution and basin geometry on lacustrine evaporites in faulted basins. In this study, we focused on the Es4 in the Dongying and Zhanhua sags in Bohai Bay Basin and investigated the effects of faults on the spatial–temporal variability of evaporite deposition based on well data, 3D seismic data. Saline lake deposits, such as gypsum and carbonate rocks, were well developed in the Es4 in Dongying sag, but they were developed mainly in the Es4u in Zhanhua sag. Within the Zhanhua sag, the development pattern of saline lake deposits varied in different sub-sags. Carbonate rocks and gypsum rocks developed in the Es4u of the Bonan sub-sag, but they were rarely seen in the Gubei sub-sag. Different from the typical pattern of carbonate rock development in gentle-slope zones, thick layers of carbonate rocks were deposited in steep-slope zones on the footwall block of the boundary fault in the Bonan sub-sag. Fault evolution and combination controlled the geomorphic variations and sediment supply of the basins, thereby determining the salinity of lake water and uneven spatial–temporal distribution of hydrodynamic conditions. In the Dongying sag, the pre-existing faults in the northern basin connected to the new faults to form a large fault zone with great extension distance and strong activity, and the paleo-lake basin in the Dongying sag had a large area and deep water. The pre-existing faults in the Zhanhua sag were locally reactivated and orthogonally intersected with the new faults, forming a multi-center paleo-lake basin with a small area and a relatively shallow water body. The range and distribution of deep-water zones controlled by the scale of the paleo-lake basins affected the variability of gypsum rock development in the Zhanhua and Dongying sags. The range of deep-water zones, their distribution pattern, and sediment supply jointly influenced the variability of gypsum rock development in the Bonan and Gubei sub-sags. The stepped landform developed in the Yinan fault zone and Mg+ and Ca+ from the Paleozoic carbonate strata in the Yidong bulge jointly caused the deposition of ultra-thick carbonate rocks on the footwall block of the Yidong fault during the sedimentation period of the Es4u.Additionally, in terms of the scale of system tracts, the episodic fault activity affected the supply of terrestrial clastics and freshwater by influencing the formation of basin margin fans, thereby controlling the vertical variation of water salinity in the Bonan paleo-lake basin and thus the periodic evolution of the salt lake. The climate cycle was not the main controlling factor.

A Comparative Study on Speciation and Availability Risk of Toxic and Potentially Toxic Elements in Different Groups of Sediments in the Dar-E-Allo Copper Mine, SE Iran

ABSTRACT The present study has been performed to evaluate the prospective effects of toxic and potentially toxic elements (TPTEs) on different groups of sediments in mining area. Fractionation of metal and metalloid elements (As, Cd, Co, Cu, Fe, Mo and Zn) was studied using a modified Community Bureau of Reference (mBCR) sequential extraction procedure in the sediments collected at five sedimentary systems. Compared to natural background values the enrichment factor (EF) of TPTEs follow the order of Cu > Mo > Cd > Zn > Co > As > Fe. Comparison with sediments quality indicators (including: sediment pollution index (SPI), pollution load index (PLI), and modified contamination degree (mCd)) revealed, that leached sediment containing secondary phases (S5 and S6), sediments containing ferric compounds (S7 and S8) and then evaporitic deposits (S9) are considered as the most contaminated sediment with a high to ultra-high degree of contamination, Subsequently based on the average indices values for sedimentary systems, the descending order is as follows: S5> S4 > S2 > S3 > S1. This issue confirm that sedimentary systems of mining area are heavily contaminated by toxic and potentially toxic elements and were not found within the guideline acceptable values. The potential ecological risk index (PERI) revealed a very high risk level for Cu with a peak in sediments containing sulfide phases. Speciation results in the investigated sediments indicated that the labile form has a considerable role in the release of all TPTEs except for Mo, Fe, and to somewhat As. Accordingly, based on the risk of elements bioavailability, the descending order is as follows: S9 > S4 > S5 > S6 > S7 > S3 > S8 > S2 > S1. X-ray diffraction (XRD) analysis confirmed the presence of lithogenic minerals with low bioavailable elements in the samples (S1, S2, S3, S4, S7 and S8) and secondary minerals with high bioavailable elements in samples (S5, S6 and S9). Multivariate statistical analysis (Pearson’s correlation analysis, PCA, and CA) suggested that the sources of TPTEs contamination were mainly anthropogenic along with the geogenic sources in the study area.

Evidence of huge evaporite mine clusters under extreme arid climatic conditions of Cretaceous to Paleogene in South China: Example of the Huichang large salt deposit

Large amounts of evaporites are distributed throughout all epochs of the Phanerozoic eon, which is closely related to important tectonic activities and extremely arid paleoclimates in specific geological periods. During the Cretaceous-Paleogene period, the Earth's climate was always arid, providing unique conditions for evaporite formation. The large number of evaporites in South China Block is an important part of the puzzle in the study of massive global evaporite deposition. The Huichang typical salt deposit is in the Upper Cretaceous Zhoutian Formation in the Huichang Basin, where the rock salt are interbedded with argillaceous rocks, constituting a rhythmical deposit. Halite was dominant among the saline minerals, followed by gypsum. The homogenization temperatures of halite inclusions ranged from 11.1 ℃ to 24.7 ℃, with a concentration of 15.1–22.2 ℃ and an average of 17.9 ℃. The δEu and δCe of the argillaceous rock studied ranged from 0.84 to 1.14 and 0.96–1.06, respectively, which combined with V/(V + Ni), V/Cr, Ni/Co, and U/Th indicators reflect that the environmental of the sedimentary water body has a weak Redox property. The spore-pollen assemblage is dominated by gymnosperms (Classopollis annulatu and Classopollis minimus) and fern spores (Schizaeoisporites kulandyensis), representing an arid environment in the early stage, and the increase in hygrophilous Taxodiaceaepollenites hiatus in the later stage indicates a shift from an arid to a humid climate. The Milankovitch Earth orbital periods of 401, 93–138, 38–45, 24–27, and 14 kyr were identified by the multiple rhythmic deposition of the rock salt and argillaceous rocks, indicating that the deposition was controlled by climate change, which was driven by the long-and-short eccentricity, obliquity, and precession cycle of the Earth orbit. In addition, the differences in the thickness and alternating frequency of the upper, lower, and middle sediments in the 'Huichang Gypsum-salt Section' also indicated that the intensity and duration of regional tectonic activities and the supply of material sources are important factors that control rock salt deposition. The strong subduction of the paleo-Pacific plate into the Eurasian plate caused the paleogeographic pattern of high in the east and low in the west, in the South China Block during the Cretaceous period, forming a large number of 'high mountain and deep basin' tectonic groups. Under the conditions of an extremely arid climate, combined with the coupling effect of regional tectonic activities and material sources, a large evaporite mineral concentration area was formed in South China, with the Huichang salt basin as a typical representative.

Continental depositional record of climate and tectonic evolution around the Eocene-Oligocene transition in southeast France: perpectives from the Vistrenque Basin (Camargue)

Based on detailed sedimentological analyses of cores, interpretation of well logs and a set of geochemical measurements performed on lacustrine sedimentary rocks, the palaeoenvironmental evolution and the sedimentary architecture of the Paleogene continental Vistrenque Basin (SE France) have been reconstructed. The analysis of sedimentary archives revealed three main stages of basin infill evolution: (1) a deep-lake basin (Priabonian-earliest Rupelian) whose sedimentation was dominated by terrigenous gravity-driven deposits during a period of high subsidence rate and strike-slip fault activity and under a prevailing humid climate; (2) an evaporative deep lake (early Rupelian) characterized by a drastic reduction in lake volume (forced-regression), terrigenous supplies and deposition of evaporites in disconnected sub-basins; (3) an overall long-term normal regressive stage (middle Rupelian to earliest Chattian) of lake infill characterized by an increase in terrigenous supplies and a vertical upward transition from deep-lake gravity-driven deposits to marginal lake and floodplain sedimentation. The onset of lake volume reduction and forced regression during the early Rupelian is associated with (1) the reworking of marginal lake carbonates into the deep lake areas, (2) the deposition of organic-rich sediments (TOC > 10%) coupled with sulphate-reduction processes in the deepest areas of the lake, (3) an important decrease in terrigenous supplies and (4) a long-term increase in δ18O of matrix-supported carbonates. This early Rupelian forced regression of the Vistrenque lacustrine system is interpreted to result from a regional decrease in precipitation in response to global cooling during the Eocene-Oligocene Transition (EOT). The final infill of the Vistrenque lake system (late Rupelian-early Chattian) and the onset of a floodplain occurred in more humid conditions during a stage of decreased activity of the Nîmes Fault, prior to or during an early stage of the Liguro-Provençal rifting.

Calcitized evaporites in the Mesoproterozoic Atar and El Meriti Groups, Mauritania, Africa

One of the most profound byproducts of the Great Oxidation Event (GOE) was the onset of oxidative weathering on land and the riverine delivery of sulfate to marine systems. Although the exact nature of marine oxygenation in the aftermath of the GOE remains uncertain, marine sulfate likely remained below 2 mM until the late Mesoproterozoic and may have remained <10 mM through the Neoproterozoic. Prior to the late Mesoproterozoic, precipitation of sulfate minerals were inhibited by low marine sulfate and possibly by elevated carbonate saturation. By ∼1.1 Ga marine sulfate concentrations were sufficient to sustain the earliest widespread evaporite deposition. Low sulfate concentrations, however, influenced both the deposition and diagenesis of evaporite deposits. Here we investigate unusual limestone deposits in the 1.1 Ga Atar Group, Mauritania, that contain both macroscopic and microscopic features that suggest a primary origin as gypsum. Elevated concentrations of carbonate-associated sulfate (CAS), sodium, and potassium are consistent with primary deposition as a sulfate evaporite and subsequent calcification under low water-rock ratios. Isotope and elemental compositions further indicate diagenetic recrystallization under marine to hypersaline marine conditions. Combined, these observations show the potential for recognizing key evaporite facies in the rock record and support a growing recognition of late Mesoproterozoic evaporite deposits.

Facies distribution and depositional cycles in lacustrine and palustrine carbonates: The Lutetian–Aquitanian record in the Paris Basin

AbstractThe difficulty of correlating continental deposits hinders predicting lacustrine and palustrine carbonate facies variations in time and space. This study aims to understand better the factors governing these facies heterogeneities by measuring carbonate isotopes and conducting facies, petrographic and sequence stratigraphic analyses of the Lutetian–Aquitanian deposits of the Paris Basin, that record the transition from marine to lacustrine environments. Large‐scale correlations enabled the definition of two lacustrine–palustrine carbonate facies models. (1) The coastal lacustrine system (Bartonian to Rupelian), consists of fine‐grained brackish carbonate exhibiting episodic marine inputs during short‐term relative sea‐level maxima and evaporite sedimentation during relative sea‐level minima. Lacustrine sediments differ notably from marine ones with more negative δ13C and δ18O compositions that co‐vary and a biota adapted to low salinity conditions. In the associated palustrine environment, depositional sequences evolve upwards from micritic lacustrine deposits to nodular and then laminar calcretes. Microbial‐coated grains and rhizoliths indicate biological processes during repeated subaerial exposure phases in sub‐tropical to arid climates. (2) The inland lacustrine system (Rupelian and Aquitanian) was disconnected from the marine domain and showed evidence of microbial activity with microbial crusts and oncoidal rudstones. Facies rich in micritic intraclasts composed of palustrine and lacustrine facies indicate the reworking of already lithified sediments along the margins. In the palustrine domain, the calcrete facies are less abundant than breccias formed in‐situ by desiccation, limestones with root traces, or organic‐rich wackestones and marls. This system reflects a more temperate climate with more developed microbial structures and less exposed carbonates than the coastal lacustrine system. The southward migration of the depocentre and the transition from marine environments to (1) coastal and then (2) inland systems are controlled by uplift phases induced by Pyrenean and Alpine orogenesis. Third‐order relative sea‐level variations appear to control only short‐term cycles in coastal systems.

Microfacies analysis and paleoenvironmental interpretation of the late Aptian–Albian (Early Cretaceous) carbonates of the Riachuelo Formation in the Sergipe Sub-basin, northeastern Brazil

The beginning of the drift phase, in the Aptian–Albian transition, marked the development of marine conditions in the South Atlantic Ocean, characterized by the deposition of evaporites, followed by the development of carbonate platforms. The carbonate rocks of this interval were deposited in a passive margin context as part of the Riachuelo Formation in the Sergipe-Alagoas Basin, northeastern Brazil. The objective of present study was to analyze the microfacies of the Aptian–Albian interval in the northern portion of Sergipe State, near the city of Pacatuba. The mainly carbonates of two cores were investigated and five carbonate microfacies were identified: oncoidal rudstone, bioclastic rudstone, oncoidal packstone, peloidal packstone/wackestone, and mudstone with planktonic bioelements that suggest the paleoenvironments were relatively shallow marine. The microfacies were dominated by oncoids in almost every sample, which occurred in association with stromatolites. The biostratigraphic results were based on palynomorphs and calcareous nannofossils. The palynomorphs assemblages indicated a late Aptian age. Paleoecological results of these fossil groups show paleoenvironmental conditions of the shallow waters with proximal characteristics, with the predominance of pollens and spores associated with rare dinoflagellates and ascidians. A striking feature was the presence of authigenic glauconite which filled skeletal cavities and partially replaced the oncoids and their nuclei, mostly in the oncoidal packstone facies. Together, these findings suggest that the samples formed at the basal portion of the Riachuelo Formation in a transgressive systems tract, corresponding to the first depositional stage of the Riachuelo Formation.

Understanding the Deep Structure of the Essaouira Basin Using Gravity Data: Hydrogeological Inferences for a Semiarid Region in Central-Western Morocco

The Essaouira Basin, located in central western Morocco, faces a significant threat of water shortage due to both the substantially reduced rainfall caused by climate change and the continuously increasing demand for this essential resource. Groundwater resources are being increasingly exploited to meet the needs of the population, whether for agricultural or domestic purposes. Therefore, it has become necessary to intensify investigations across the entire basin, particularly through indirect methods such as geophysical techniques, to accurately delineate the productive zones. In this context, the present study was undertaken to investigate the deep structure of this basin with the aim of comprehending the functioning of its aquifer system. This study is based on the interpretation of gravity data covering the Essaouira Basin. In addition to their qualitative analysis, these data underwent a methodological approach involving transformations to extract meaningful insights. The observed anomalies were interpreted in terms of (i) thickness variations within the slightly folded sedimentary series of the basin; (ii) Paleozoic basement topography; and (iii) the presence of salt deposits. In fact, among the negative anomalies, some coincide with evaporitic deposits that are known either from the geological outcrops or the seismic surveys carried out in the Essaouira Basin within the framework of petroleum exploration programs, while others coincide with areas of increased thickness of sedimentary sequences. The latter include synclines and basement depressions, where the accumulation of groundwater tends to occur; as a result, they constitute suitable zones for the drilling of water extraction wells. Groundwater flows observed in some existing wells are consistent with this hypothesis. The results of the contact analysis approach implemented within the framework of the study reveals the Essaouira Basin is affected by a fault network whose main direction is parallel to the Atlantic margin (i.e., NNE–SSW). This implies that the extensional tectonic phase responsible for initiating the rifting of the Central Atlantic in the Triassic era has primarily impacted the structural configuration of this basin. This study demonstrates the strong potential of the gravity method as a tool to delineate the deep structure of sedimentary basins and to identify potentially productive groundwater zones. The final results will provide important support to decision makers in sustainable groundwater management, especially in vulnerable areas.

Structural analysis of the central Tunisian Atlas: Implications for salt-related structures and conjugate strike-slip faults

This scientific study aims to investigate the geological characteristics and tectonic processes of the central Tunisian Atlas region, focusing on the influence of tectonic events related to the Jurassic-Early Cretaceous Tethyan rifting and the subsequent Cenozoic tectonic inversion and uplift. In particular, this research emphasizes the strong control of tectono-sedimentary events on the geology of the central Tunisian Atlas, with specific attention given to the understudied isolated salt-related structures. To gain insights into the relationship between deep-seated faults, salt tectonism, and the conjugate strikes-slip faults, this study is based on subsurface data, including 2D seismic reflection and gravity data. The analysis investigates, the location of salt extrusions in relation to fault intersections. Results derived from subsurface data indicate that diapiric intrusions primarily occur at the junctions of major fault systems likely inherited from the Triassic-Jurassic Tethyan period. Notably, salt migration was remarkably active during the early Cretaceous, as evidenced by halotectonic sequences and salt-related mini-basins. Furthermore, fault blocks display sedimentary infill above tilted blocks, where salt structures appear to occur at their peripheries. During the subsequent tertiary compressions, the structural configurations of the basin (i.e., Z-shape basin) promote the strike-slip movement along pre-existing faults. This new structural interpretation suggests a closely relationship between fault zones inherited from the Jurassic-Early Cretaceous Tethyan Opening and isolated salt-related structures. The subsequent Cenozoic shortening events, including the Atlassic and Alpine events, have led to uplift of the deep-seated faults, facilitating the ascension and deformation of Triassic evaporitic sediments within subcircular isolated structures. Field observations and seismic sections indicate the presence of sedimentary gaps resulting from these processes. The findings of this study contribute to a comprehensive understanding of the deep tectonic framework and shallow salt-related structures in the central Tunisian Atlas.