Messinian Salinity Crisis

L’étude de deux coupes lithologiques à Djebel Aoud Sma (Monts des Ouled Ali, Bordure Sud du bassin du Bas Chélif) a permis d’étudier la série messinienne complète de ce secteur. Les diatomites du Djebel Aoud Sma ont été subdivisées lithologiquement en deux membres. Les résultats ichnologiques ont permis de les placer au sommet du premier membre diatomitique du bassin du Bas Chélif. Les calcaires sus-jacents ont été subdivisés également en unité pré-récifale et unité récifale. Ils ont été le siège d’apports détritiques périodiques, qui ont atteint leur maximum dans l’unité récifale. L’Halimeda-rich beds ; un faciès qui pourrait constituer un niveau index, connu dans toutes les plates-formes carbonatées messiniennes de la Méditerranée occidentale, a été mis en évidence aussi, où il a été découvert pour la première fois dans la plate-forme carbonatée de la bordure Sud du bassin du Bas Chélif (Tessala-Béni Chougrane). L’étude microfaciologique a permis d’interpréter le milieu de dépôt des deux unités carbonatées. L’unité pré-récifale correspond à une plate-forme carbonatée peu profonde, envasée et relativement calme, tandis que l’unité récifale s’est déposée dans un milieu peu profond également, relativement agité, présentant un talus (pente récifale). Aussi, les résultats de la géochimie ont permis d’étudier la composition en éléments majeurs de tous les faciès rencontrés dans les marnes grises, les diatomites et les calcaires. Les diatomites pures peuvent constituer un bon gisement à exploiter, et c’est ainsi pour les calcaires qui peuvent faire une bonne matière première pour la fabrication du ciment gris et blanc.

A new genetic facies model for deep-water clastic evaporites is presented, based on work carried out on the Messinian Gessoso-solfifera Formation of the northern Apennines during the last 15 years. This model is derived from the most recent siliciclastic turbidite models and describes the down current transformations of a parent flow mainly composed of gypsum clasts. The model allows clearer comprehension of processes controlling the production and deposition of clastic evaporites, representing the most common evaporite facies of the northern Apennines, and the definition of the genetic and stratigraphic relationship with primary shallow-water evaporites formed and
preserved in marginal settings. Due to the severe recrystallization processes usually affecting these deposits, petrographic and geochemical analyses are needed for a more accurate interpretation of the large spectrum of recognized
gravity-driven deposits ranging from debrisflow to low-density turbidites.
Almost all the laminar ‘balatino’ gypsum, previously considered a deep-water primary deposit, is here reinterpreted as the fine-grained product of high to low-density gravity flows. Facies associations permit the framing of the distribution of clastic evaporites into the complex tectonically controlled depositional settings of the Apennine foredeep basin. The Messinian Salinity
Crisis occurred during an intense phase of geodynamic reorganization of the Mediterranean area that also produced the fragmentation of the former Miocene Apennine foredeep basin. In this area, primary shallow-water evaporites equivalent to the Mediterranean Lower Evaporites, apparently only formed in semi-closed thrust-top basins like the Vena del Gesso Basin.
The subsequent uplift and subaerial exposure of such basins ended the evaporite precipitation and promoted a widespread phase of collapse leading to the resedimentation of the evaporites into deeper basins. Vertical facies sequences of clastic evaporites can be interpreted in terms of the complex
interplay between the Messinian tectonic evolution of the Apennine thrust belt and related exhumation–erosional processes. The facies model here proposed could be helpful also for better comprehension of other different depositional
and geodynamic contexts; the importance of clastic evaporites deposits has been overlooked in the study of other Mediterranean areas. Based on the Apennine basins experience, it is suggested here that evaporites diffused into
the deeper portions of the Mediterranean basin may consist mainly of deepwater resedimented deposits rather than shallow-water to supratidal primary evaporites indicative of a complete basin desiccation.

The Messinian succession is exceptionally well preserved in the intramontane sedimentary basin of Nijar in the Internal Betic Cordillera (SE Spain). Gypsum-olistostromes and large slabs of the Azagador Member are unconformably overlain by the latest Messinian sediments of the Feos Formation. These deposits, which are studied in detail in the Rambla Los Feos outcrop (basinal area), are characterized by a sedimentary cyclicity and two lithostratigraphic units can be distinguished: (1) a lower one that mainly consists of calcarenitic intervals with laminated pelites and limestone beds (2) an upper unit showing a cyclic alternation of fluvial fan deposits and lacustrine marls, that corresponds to the 'Lago-mare episode'. The sedimentary succession records very precisely the strongly fluctuating environmental conditions during the upper Messinian, as well as the paleomorphological and paleogeographical changes that are likely related to late Miocene and Pliocene tectonic uplift of the Sierra Cabrera (Betic basement). The dominant fossil content, present throughout the upper unit in the lacustrine white marls of the Feos Formation, is represented by ostracods of the Loxocorniculina djafarovi FA, an assemblage of non-marine, aquatic communities which lived in brackish-water bodies (Lago-mare fauna). Extant ostracod faunas, similar to those documented in the Messinian fossil record and characterised by Cyprideis, Tyrrhenocythere, loxoconchids and leptocytherids, occur in hypohaline water bodies, in a salinity range of approximately 5-15‰ (mesohaline water). However, the number of species of Parathetian affinity is low, as observed in other perimediterranean areas (i.e. Apennines). The marine fauna association (foraminifera) present at levels is thought to be partly reworked, even though a marine influence at the end of the Lago-mare stage is not excluded.

The Messinian Salinity Crisis (MSC) was a major ecological crisis affecting shallow and deep-water settings over the entire Mediterranean basin. However, the evolution of the MSC and its ecological impacts have mainly been explained on the basis of sediments from onshore outcrops. Lack of complete and physically connected records from onshore and offshore settings has inhibited comprehensive understanding of basin behaviour during the MSC. Herein we present a continuous record from an intermediate-depth basin on the Balearic Promontory that comprises late Tortonian–Messinian marls and evaporitic beds from the first MSC phase (i.e., Primary Lower Gypsum-PLG stage). Well-log and biostratigraphic data allow us establishing a large-scale calibration to the astronomical solutions, and to correlate pre-MSC sediments with classical rhythmic successions outcropping onshore. Thickness and characteristic sedimentary patterns observed in the offshore evaporitic records resemble those from marginal PLG sequences. Furthermore, seismic reflectors from a Bedded Unit (BU), which corresponds to an evaporitic interval according to well-to-seismic ties, are correlated with the onshore PLG sequences. This correlation constitutes the first attempt to link well-known marginal sequences with intermediate-depth offshore settings, which have previously only been studied through seismic imaging. Our time-calibration provides direct evidence supporting a synchronous onset of the PLG phase between onshore and offshore settings along the southwestern Balearic Promontory margin. Those BU reflectors, which were positively correlated to the PLG, were likely precipitated offshore the continental shelf at Messinian times. These results suggest that gypsum precipitation and/or preservation was not always limited to 200 m water-depths and could occur in non-silled basins. Finally, we only found a major erosion at the top of the PLG sequences, implying that the MSC drawdown occurred after the precipitation of the onshore lower evaporites. Studied sequences provide new insights into the PLG precipitation/preservation settings, as well as into the land-sea correlations of MSC units, and thus could potentially help refine current MSC models.

Dalla pubblicazione online nel 2018 dei tre volumi “La Crisi di Salinità del Messiniano - Il Mistero del Mare Scomparso”, all’indirizzo http://danilobonanni.weebly.com/il-mistero-del-mare-scomparso.html, nuovi, recentissimi articoli su temi di Geologia hanno apportato contributi alla trattazione del tema “Crisi di Salinità del Messiniano”, proponendo alcuni di questi articoli un aggiornamento del modello cronostratigrafico dell’Evento Messiniano con propensione verso lo scenario “bacino profondo disseccato”. I nuovi studi datati 2019-2020 confermano mie puntuali osservazioni espresse ne “Il Mistero del Mare Scomparso” (2018), ivi comprese le inferenze litostratigrafiche e lo scenario paleoambientale che ho avuto modo di ricostruire con deduzione logico-scientifica.

A recently published scenario viewing the Messinian salinity crisis as two evaporitic steps rather than one has led to a search for new indices of the crisis in the Eastern Paratethys. Fluvial processes characterized the southwestern Dacic Basin (Southern Romania, i.e. the Carpathian foredeep) whereas brackish sediments were continuously deposited in its northern part.This is consistent with previously evidenced responses

Neogene intermontane basins in Almería Province, SE Spain, display excellent exposures of Messinian (Late Miocene) sequences. The Sorbas, Almería-Níjar and Vera basins maintained connection with the Mediterranean throughout the Messinian, except during the major desiccation phase leading to the formation of salt in the deep centre of the Western Mediterranean. These basins were part of the Western Mediterranean with no separate link to the Atlantic Ocean. The presence of normal marine sediments in these basins reflects the Western Mediterranean watermass. Messinian pre-evaporitic sediments in the basins of southeastern Almería do not show gradual change towards evaporite deposits. Instead they contain stenohaline invertebrates right up to a major erosion surface that separates them from overlying gypsum deposits. This contradicts suggestion of progressive salinity increase in this part of the Western Mediterranean prior to the Messinian Salinity Crisis (MSC); it also indicates that initiation of evaporite precipitation was not synchronous throughout the Mediterranean Basin. There is no major erosion surface within or at the top of the evaporites in these Almería basins, and the gypsum beds exhibit upward transition to siliciclastic and carbonate deposits. This is inconsistent with a model of Messinian Mediterranean evaporite formation whereby deposition of marginal evaporites was followed by their erosion during drawdown that resulted in formation of evaporites in the centre of the Western Mediterranean. The presence of stenohaline biotas in siliciclastic deposits interbedded with the gypsum and in the Messinian post-evaporitic sediments, challenges the view that a long-standing large body of brackish water (the Lago Mare) filled the Western Mediterranean following the MSC and prior to Early Pliocene flooding. It also contradicts the concept of many relatively small brackish basins spread across an otherwise desiccated Western Mediterranean basin. The basins of southeastern Almería record normal marine Early Messinian sedimentation that was abruptly interrupted by sealevel fall. This drawdown most likely resulted in precipitation of evaporites in the central deep Western Mediterranean basin. Following this episode, final marine reflooding of the Western Mediterranean took place during the Late Messinian, and the Mediterranean Sea rose to a level similar to, or higher than, that preceding the Salinity Crisis.

We present a synthesis of the knowledge on the cholevid fauna of Sardinia, with an annotated checklist and an updated list of both published and unpublished collecting localities. The Cholevidae (Coleoptera, Staphylinoidea) are a group of small to medium-sized beetles, most of which are saprophagous; a significant percentage of Cholevidae are cave-dwellers, and some are highly specialized troglobitic elements. In

The ongoing debate about the Messinian salinity crisis in the Mediternean is fuelled in part by the lack of an adequate time control. The most accurate and, at the same time, detailed constraints are nowadays provided by the astronomical dating technique. Here we present an astronomical age model for the cyclically bedded Tripoli diatomite Formation on Sicily (pre-evaporite Messinian, Italy) based on an integrated stratigraphic study of three key-sections, Falconara, Gibliscemi and Capodarso. Characteristic sedimentary cycle patterns allow (i) the sections to be cyclostratigraphically correlated, the ‘bed-to-bed’ correlations being confirmed by high-resolution planktonic foraminiferal biostratigraphy, and (ii) the Tripoli cycles to be calibrated to the astronomical record. Despite minor misfits the correctness of the tuning is evident from the match between precession-obliquity interference in the astronomical target and its reflection in the sedimentary cycle record. The tuning provides absolute astronomical ages for all sedimentary cycles and planktonic foraminiferal events. The base of the Tripoli is astronomically dated at 7.005 Ma, indicating that the onset of diatomite formation is diachronous in the Mediternean since it started 300 000 years earlier on Sicily than on Gavdos, south of Crete. The top of the Tripoli, and thus the onset of the salinity crisis proper on Sicily, arrives at 5.98 Ma.

The Alba succession (Tertiary Piedmont Basin, NW Italy) preserves the northernmost record of the Messinian salinity crisis (MSC) and was deposited on the southern margin of a wide wedge-top basin, related to the involvement of the Piedmont Basin in the Apennine compressional tectonics. Pre-MSC sediments consist of a cyclic succession of marine euxinic shales and calcareous marls, deposited under the influence of precession-modulated climate changes, and document the progressive restriction of the basin prior to the onset of the MSC. They are followed by the Primary Lower Gypsum unit (PLG), deposited during the first MSC stage (from 5.96 to 5.60 Ma). These sediments show a clear precession-related cyclic stacking pattern and record the lateral transition from a shallow water marginal setting in the SW to a deeper one in the NE. In marginal settings, six PLG cycles are recognised, truncated by an erosional unconformity placed at the base of the post-evaporitic sediments. The lowermost five cycles are composed of massive and banded selenite beds separated by thin shale intervals. A sharp change, evidenced by the appearance of the branching selenite facies, is recorded by the 6th gypsum bed that represents a distinctive marker bed, here called Sturani key-bed, that can be mapped throughout the study area. Basinward, the lower PLG cycles are transitional to decimetre-thick carbonate-rich layers interbedded to euxinic shales, that are overlain by the Sturani key-bed. Above the marker bed, other seven PLG cycles are present. The gypsum beds form thinner bodies compared to the Sturani key-bed and are characterised by a greater amount of fine-grained terrigenous fraction, suggesting an increase of continental runoff related, in turn, to humid climate conditions at the end of the first MSC stage. PLG cycles are followed by slumped mudstones and clastic gypsum beds that correspond to the resedimented and chaotic facies (Resedimented Lower Gypsum), deposited in the Mediterranean basins during the second MSC stage (from 5.60 to 5.55 Ma). They are in turn overlain by continental and brackish water facies with Lago Mare fossil assemblages, recording the final stage of the MSC.The Messinian succession of Alba provides the opportunity to reconstruct the lateral facies transition between marginal and distal settings and to shed new light on the deep water MSC sedimentary record. Moreover, the appearance of the branching selenite facies from the 6th PLG cycle upward provides a tool for properly placing the Piedmont record in the MSC chronostratigraphic framework, allowing us to investigate the influence of climate gradients on the sedimentary response to the Mediterranean salinity crisis.► Updated stratigraphy of the northernmost record of the Messinian salinity crisis ► Reconstruction of the lateral transition between marginal and distal settings ► Influence of climate gradients on the sedimentary response to the salinity crisis

Une description lithostratigraphique et une étude paléoenvironnementale des terrains messiniens affleurant sur la bordure méridionale du bassin du Bas Chélif en Algérie nord-occidentale sont présentées. L’étude est basée sur l’analyse de deux coupes levées au niveau des limites méridionale et septentrionale du Djebel Aoud Sma dans la région de Sig. Trois formations ont été identifiées et interprétées sur le plan environnemental : (i) les Marnes grises, attribuées au Messinien et déposées dans un milieu de vasières profondes ; (ii) les Diatomites, caractérisées par des bancs diatomitiques et des diatomites marneuses à caractères infra- à circalittoraux ; (iii) les Calcaires, correspondant à des calcaires récifaux et péri-récifaux, dans lesquels cinq faciès ont été individualisés.
Le faciès calcaire à Halimeda enregistré dans la coupe de Haoudh el Matmar a été mis en évidence dans le présent papier. Ce faciès, connu dans tous les bassins marginaux de la Méditerranée occidentale, évoque des changements environnementaux importants. Ainsi, il constitue un niveau index permettant la corrélation avec toutes les autres plates-formes carbonatées péri-méditerranéennes.

The rodents from the Upper Messinian deposits of Moncucco Torinese (MCC) (Piedmont, NW Italy) are described. Stratigraphic considerations indicate that the fossiliferous deposits exposed at MCC date back to the post-evaporitic phase of the Messinian Salinity Crisis (5.40–5.33 Ma). Thirteen rodent taxa belonging to the families Cricetidae Fischer, 1817, Muridae Illiger, 1811, Gliridae Thomas, 1897 and Sciuridae Fischer, 1817 are recognized based on 1177 teeth. The occurrence of Centralomys benericettii (De Giuli, 1989), Paraethomys meini (Michaux, 1969) and Apodemus gudruna van de Weerd, 1976 allows to compare MCC with other latest Messinian localities of northern Italy, such as Brisighella and Verduno. The rodent assemblages described herein and, more particularly, the taxa A. gudrunae, Muscardinus vireti Hugueney & Mein, 1965 and Glirulus lissiensis Hugueney & Mein, 1965, suggest that MCC can be referred to the Late Turolian (MN13). Moreover, the presence of taxa commonly found in Pliocene localities of western and central Europe (Occitanomys brailloni Michaux, 1969, Micromys bendai van de Weerd, 1979, Neocricetodon magnus (Fahlbusch, 1969) and Sciurus warthae Sulimski, 1964) indicates that some typical Ruscinian elements were already present at the end of the Miocene at least in southern-central Europe. The rodent assemblages of MCC also include Apodemus atavus Heller, 1936, Eliomys aff. intermedius Friant, 1953, Glis minor Kowalski, 1956, and Pliopetaurista pliocaenica (Depéret, 1897). Overall, the fossil assemblages documented in this paper remarkably expand our knowledge on the Late Miocene rodent communities of Italy, also providing useful data for the interpretation of biogeographic relationships between western and eastern Europe at the end of the Messinian.

The late Miocene evolution of the Mediterranean Basin is characterized by major changes in connectivity, climate and tectonic activity resulting in unprecedented environmental and ecological disruptions. During the Messinian Salinity Crisis (MSC, 5.97-5.33 Ma) this culminated in most scenarios first in the precipitation of gypsum around the Mediterranean margins (Stage 1, 5.97-5.60 Ma) and subsequently > 2 km of halite on the basin floor, which formed the so-called Mediterranean Salt Giant (Stage 2, 5.60-5.55 Ma). The final MSC Stage 3, however, was characterized by a "low-salinity crisis", when a second calcium-sulfate unit (Upper Gypsum; substage 3.1, 5.55-5.42 Ma) showing (bio)geochemical evidence of substantial brine dilution and brackish biota-bearing terrigenous sediments (substage 3.2 or Lago-Mare phase, 5.42-5.33 Ma) deposited in a Mediterranean that received relatively large amounts of riverine and Paratethys-derived low-salinity waters. The transition from hypersaline evaporitic (halite) to brackish facies implies a major change in the Mediterranean's hydrological regime. However, even after nearly 50 years of research, causes and modalities are poorly understood and the original scientific debate between a largely isolated and (partly) desiccated Mediterranean or a fully connected and filled basin is still vibrant. Here we present a comprehensive overview that brings together (chrono)stratigraphic, sedimentological, paleontological, geochemical and seismic data from all over the Mediterranean. We summarize the paleo-environmental, paleohydrological and paleoconnectivity scenarios that arose from this cross-disciplinary dataset and we discuss arguments in favour of and against each scenario.