A Messinian Gypsum Deposit in the Ionian Forearc Basin (Benestare, Calabria, Southern Italy): Origin and Paleoenvironmental Indications

: This study reports the ﬁrst accurate record of the Messinian Resedimented Gypsum in the forearc and back-arc basins connected to the Calabrian-Peloritan orogen. A multidisciplinary approach has been used to investigate a gypsum deposit located in the Benestare’s area (Calabria, Southern Italy). Such deposit is made of bedded gypsrudites displaying clastic selenite with chaotical textures. On the top, the gypsrudites are interspersed with gypsum lenses belonging to the branching-like facies. Despite these two facies seem different macroscopically, they show petrographic features, ﬂuid inclusions, organic matter and Strontium isotopic values very similar to each other. On the other hand, both facies show fractured and folded crystals. Crystals are only locally corroded and preserve primary structure relict as well as allochthonous (organic debris) and autochthonous putative microbial remains. All crystals are rich in ﬂuid inclusions but these are visibly affected by stretching and leaking (re-equilibration processes) suggesting a moderate plastic deformation during re-sedimentation and subsequent burial. Minimal transport of the deposit is testiﬁed by subangular shapes of the gypsum crystals. The gypsrudite and branching-like facies reveal an 87 Sr/ 86 Sr average value of 0.709045 and 0.709082, respectively. These values suggest a strong connection with the global Ocean and reduced freshwater input. The Benestare’s deposit originated from the partial to complete dismantling of selenite crystals related to the ﬁrst stage (5.97–5.60 Ma) of the Messinian Salinity Crisis through gravitational collapse due to local controlling factors. tion, Writing—review and Editing. A.C.: curation, Investigation, Methodology, Supervision, Val-idation, Writing—review and Editing. M.D.: Data curation, Investigation, Methodology, Validation, Writing—review and Editing, Supervision. A.G.: Conceptualization, Data curation, Investigation, Methodology, Supervision, Validation, Visualization, Writing—review and


Introduction
The Messinian Salinity Crisis (MSC), which occurred approximately 6 Ma ago, is a complex geological event which transformed the Mediterranean Sea into a giant saline basin, causing a catastrophic hydrological and biological crisis [1]. This event is one of the most important and controversial topics being debated in the scientific community. The MSC triggered the formation of extensive evaporite deposits known as Lower Evaporites, Halite and Upper Evaporites which, in less than 640 ka, accumulated on the bottom of the Mediterranean basin [2][3][4][5]. During the CIESM workshop (Almeria, 7-10 November 2007), it was proposed a new MSC scenario involving three phases [2]. Stage 1 (5. 97-5.60 Ma) is the first evaporitic stage associated with the deposition of Primary Lower Gypsum (PLG). Stage 2 (5. 60-5.55 Ma) is the MSC acme where the Resedimented Lower Gypsum (RLG) and Salt Unit formed. RLG, consisting of large blocks of the Primary Lower Gypsum unit emplaced by gravity flows and it is considered as the best candidate for a possible equivalent of the deep Mediterranean Basin's Lower Evaporites unit. Stage 3 (5.  is represented by the Upper evaporites and Lago Mare event (s) and defines the end of MSC. The environmental conditions controlling the deposition of Messinian gypsum are still debated, especially due to the lack of modern analogues [6].
Each of the three Messinian units show a characteristic 87 Sr/ 86 Sr signature, which records changes in the hydrological balance of the Mediterranean. Indeed, Sr isotope ratio is a function of the balance between ocean and riverine input, which are characterized by strong variations in Sr concentration and 87 Sr/ 86 Sr signature, thus providing a valuable proxy of its hydrological structure and may thus have a good chronostratigraphic value [2,4,7]. An extensive 87 Sr/ 86 Sr database has been established for the Messinian onshore and offshore evaporitic deposits [7][8][9][10][11]. The compiled data show that the Mediterranean 87 Sr/ 86 Sr values progressively diverged from the global ocean at the dawn of the MSC [11][12][13][14]. This change has been related to the progressive isolation of the Mediterranean Sea and the consequent gradual decrease of the oceanic input into the basin and/or to the increase of freshwater input from rivers [15,16] and/or the Paratethys [11][12][13][14][15][16][17][18][19][20]. These factors allowed the development of a distinct Sr isotopic signature for the Mediterranean basin during the MSC, which significantly differs from the coeval global ocean signal. According to the revised version of the Sr isotope curve proposed by Roveri et al. [11], the three phases of the crisis are characterized by well-defined non-overlapping 87  Moreover, an important role in the study of evaporites and facies analyses is played by the fluid inclusions and the ancient microbial remains hosted in the crystals. Fluid inclusions represent multicomponent brines trapped during crystal growth. They are a common feature in evaporitic minerals and provide important information on the composition of ancient seawater. They are a key component for the reconstruction of environmental changes [11,[21][22][23][24][25][26][27]. However, they provide microthermometric data that can be used to infer trapping conditions only if the inclusion satisfies several criteria referred to as "Roedder's Rules" [28,29]: (a) the inclusion must trap a single, homogeneous phase; (b) the inclusion must remain a constant volume system after trapping (excluding reversible elastic volume changes); (c) nothing has been added to, or removed from, the inclusion following trapping. If the inclusion volume changes, or if anything is added to or lost from the inclusion following trapping, the inclusion is said to have re-equilibrated.
Another important aspect of the evaporitic minerals is the entrapped organic matter as sourced by putative microbial organisms. The presence of traces of ancient microbial life in different salt-saturated environments (shallow and deep) may provide information about salinity, depth of the basins, light penetration, oxygen and nutrient availability. Recent studies described a diversified and well-preserved body and molecular fossil assemblage within Messinian selenites, confirming that gypsum evaporites represent an excellent archive of microbial life [6,30,31].
Over the years, numerous scientific studies have been carried out on several deposits of the Mediterranean basin (e.g., Spain, Central-Northern Italy, Sicily, Turkey, Cyprus) contributing to a better understanding of their formation mechanisms. These studies agree with the new MSC scenario proposed during the CIESM workshop [1], however the environmental interpretations of the depositional systems during the three steps remain unresolved.
Among the overall basins studied, evaporite basins of the Calabria region (Southern Italy) are the least investigated. Indeed, they were the subject of only preliminary stratigraphic and petrographic studies [32][33][34][35][36][37]. The research is aimed at settling the origin of the gypsum deposit in order to add a new element on the MSC scenario and implement the paleo-environmental data of the Calabrian forearc.

Geological Setting
The Cattolica Formation represents the southernmost Messinian evaporitic stratigraphic unit of the Ionian forearc basin [38]. The Ionian forearc basin represents a sedimentary succession that covers unconformably the plutonic and metamorphic tectonostratigraphic unit of the Calabria-Peloritani Orogen (CPO). The Calabria-Peloritani Orogen is made up of two different fragments of continental plates separated by the fault systems of the Catanzaro Trough [39][40][41]. The northern sector of the CPO has been subjected to a continental collision since the Oligocene, while in the southern sector, the subduction of the Tethyan ionian oceanic crust is active since the Cretaceous [42][43][44]. In the study area (Figure 1), located south of Catanzaro Trough, in the central part of the Ionian forearc, the sedimentary succession is >2000 m thick. The basement is the result of stacking of three tectonostratigraphic units involving Palaeozoic crustal rocks: the Africo-Madonna di Polsi Unit (phyllites, marbles, schists), the Aspromonte Unit (gneiss, granitoids) and the Stilo Unit (phyllites, marbles, schists, granitoids), [37,45,46]. On top lies a Palaeozoic metasedimentary succession of Cambrian-to-Carboniferous age, constituted of phyllites, metarenites, metalimestones and metasiliceous rocks intruded by a late Variscan large plutonic body [46][47][48][49][50][51]. This Unit is largely covered by Late Triassic-earliest Jurassic continental to marine deposits [52]. The Oligocene to Middle Miocene succession is represented by the Stilo-Capo d'Orlando Formation [53][54][55][56][57][58][59]. This Formation has been interpreted as continental deposit passing to shelf and slope deposits [54,55,[57][58][59] and as submarinecanyon deposits passing upward and laterally to overbank and slope deposits [53,58]. The Variegated Clays rest on the Stilo-Capo d'Orlando Formation and are characterized by a predominant mélange type internal structure [37,39,60]. The Serravallian to Messinian sequences rest unconformably on the oldest units and start with Serravallian-to-Tortonian marine strata (conglomerates, sandstones and pelites) and continue with the Messinian Gessoso-Solfifera Group (MGSG) of the Cattolica Formation. Critelli et al. [37] and Tripodi et al. [61,62] describe the MGSG in the Benestare area as made up of limestone (Calcare di Base Formation-GTL 1 ), massive or laminated, vacuolar, brecciated, microcrystalline limestone passing upward to selenite crystals and gypsrudite (GTL 2 ) and interbedded olistoliths of Variegated Clays Formation (ob).

Materials and Methods
The sampling was preceded by a stratigraphic analysis of the selenite outcrop (38°11′17.65″ N, 16°8′15.93″ E) and a macroscopic facies analysis to describe the principal elements of the gypsum deposit. Fifteen samples from the gypsrudites facies and branching-like facies were sampled at the bottom and top of the quarry, respectively.
The sampling has been carried out following the criteria to prevent external contaminations see [74]. All samples were cleaned and studied to determine the best orientation for the cutting. Samples were cut parallel to the crystal growth direction to preserve the trapped fluid inclusions. Ten gypsum samples were sent to the ALS Petrophysics Laboratory (Normandy) to obtain fluid inclusion wafers (~200 μm in thickness).

Petrography and Mineralogy
Petrographic and fluid inclusions study was carried out in the Geofluids Research Laboratory at the National University of Ireland in Galway. Petrographic investigations have been carried out using transmitted light microscopy on a Nikon Eclipse E200 polarizing microscope, at various magnifications (4×, 10×, 40×, 60×) to determine the presence and types of fluid inclusions and their suitability for microthermometric analyses.
Macroscopically, crystals from the gypsrudite and branching-like facies are not well developed and show chaotical distribution. Petrographic investigations were performed on five wafers cut longitudinally to the crystal growth direction.  [73] and stratigraphy of the Ionian forearc basin (modified after Tripodi [62]). The abbreviation of the stratigraphic legend refers to [73]. Red circle indicates Benestare's quarry.

Materials and Methods
The sampling was preceded by a stratigraphic analysis of the selenite outcrop (38 • 11 17.65 N, 16 • 8 15.93 E) and a macroscopic facies analysis to describe the principal elements of the gypsum deposit. Fifteen samples from the gypsrudites facies and branching-like facies were sampled at the bottom and top of the quarry, respectively.
The sampling has been carried out following the criteria to prevent external contaminations see [74]. All samples were cleaned and studied to determine the best orientation for the cutting. Samples were cut parallel to the crystal growth direction to preserve the trapped fluid inclusions. Ten gypsum samples were sent to the ALS Petrophysics Laboratory (Normandy) to obtain fluid inclusion wafers (~200 µm in thickness).

Petrography and Mineralogy
Petrographic and fluid inclusions study was carried out in the Geofluids Research Laboratory at the National University of Ireland in Galway. Petrographic investigations have been carried out using transmitted light microscopy on a Nikon Eclipse E200 polarizing microscope, at various magnifications (4×, 10×, 40×, 60×) to determine the presence and types of fluid inclusions and their suitability for microthermometric analyses.
Macroscopically, crystals from the gypsrudite and branching-like facies are not well developed and show chaotical distribution. Petrographic investigations were performed on five wafers cut longitudinally to the crystal growth direction.
Further analysis was carried out through the Laser Raman Spectroscopy (Horiba Scientific LabRam, Lille, France) to investigate the mineralogy of the samples. The technical specifications consist of confocal system, 600 slit grating (~1 cm −1 spectral resolution), spectral range (100-400 cm −1 , laser excitation (−785 nm NIR) and spatial resolution of 2 mm.

Microthermometry
Fluid inclusion microthermometric studies were performed on doubly polished wafers using a Linkam THM&-600 heating-freezing stage mounted on a Nikon Labophot transmitted light microscope equipped with a range of objective lenses including a 100× lens. The phase behaviour of fluid inclusions was analysed over the temperature interval −80 • to +50 • C in gypsum samples. The estimated accuracy of measurements is ±0.2 • C during freezing runs and ±1.0 • C during heating runs. The rate of heating and freezing experiments varied as a function of the velocity of phase transitions in the inclusions and ranged from 0.1 to 10 • C/min. The error in estimating salinity using the depression of freezing point methods of NaCl equivalent is ± 0.05 wt% at all temperatures [75].

Organic Matter
A Zeiss Axioplan optical microscope, outfitted with a Hg vapor lamp and highperformance wide band pass filters (BP 436/10 nm/LP 470 nm for green light; BP 450-490 nm/LP 520 nm for yellow light) was utilized to observe mineral epifluorescence, in order to reveal the distribution of organic matter [76,77].
The wafers were examined under ultraviolet (UV) light using a Nikon Eclipse E200 microscope with an epi-fluorescence attachment. This technique was used to record the fluorescence emitted by the organic material trapped in the gypsum-hosted fluid inclusions.

87 Sr/ 86 Sr Analyses
The procedure to determine 87  Sr samples were loaded on previously degassed 99.98% pure rhenium filaments and introduced in the source of a Thermo Scientific TM Triton Plus ® (Thermo Fisher Scientific Inc., Waltham, MA, USA) solid-source nine-collector mass spectrometer for Sr-isotope ratio determination. Possible mass interference on 87 Sr by 87 Rb was checked and corrected throughout all measurements. 87 Sr/ 86 Sr was normalized for within-run isotopic fractionation to 88 Sr/ 86 Sr = 8.37520 using an exponential low for correction. The final 87 Sr/ 86 Sr value is reported as the mean of 150 single runs (15 blocks of 10 cycles each; integration time 16.777 s) at 2σ confidence level according to Goldstein et al. [78]. Replicate measurements of the NIST SRM 987 international standard in the period of samples anal-ysis provided an average value of 87 Sr/ 86 Sr = 0.710243 ± 0.000006 (2σ, N = 29; external reproducibility according to Goldstein et al. [78]. Therefore, a correction of + 0.000005 has been applied to the measured 87 Sr/ 86 Sr values to normalize them to the recommended value (0.710248 ± 0.000012; [78]). The Sr blank has been on the order of 100 pg during the period of chemical processing of the samples, thus negligible.

Field Observations and Sampling
In the Benestare's quarry, located north of the homonym village, outcrops the most important gypsum deposit of the Cattolica Formation passing upward to Upper Messinian conglomerates and sandstones (NTO) and pliocenic marls of Trubi Formation (TRB) (Figure 2). At field observation scale, the gypsum deposit is massive with thickness of 15 metres. At mesoscale, the strata are characterized by two facies: (i) clastic (gypsrudites) and (ii) branching-like selenite deposits.
The gypsrudite strata, from 1 to 10 cm thick, are interbedded by thin argillaceous/ calcareous laminae (from 0.5 and 3 cm thick), (Figure 2a,b). The boundary on the laminae shows dissolution or mechanical reworking.
The branching-like facies is arranged in lenses made of clastic gypsum recognizable within thin argillaceous/calcareous laminae (Figure 2c). They are located at the top of the gypsrudites and show "nodular" features composed of millimetre-sized crystals.  [78]. Therefore, a correction of + 0.000005 has been applied to the measured 87 Sr/ 86 Sr values to normalize them to the recommended value (0.710248 ± 0.000012; [78]). The Sr blank has been on the order of 100 pg during the period of chemical processing of the samples, thus negligible.

Field Observations and Sampling
In the Benestare's quarry, located north of the homonym village, outcrops the most important gypsum deposit of the Cattolica Formation passing upward to Upper Messinian conglomerates and sandstones (NTO) and pliocenic marls of Trubi Formation (TRB) (Figure 2). At field observation scale, the gypsum deposit is massive with thickness of 15 metres. At mesoscale, the strata are characterized by two facies: (i) clastic (gypsrudites) and (ii) branching-like selenite deposits.
The gypsrudite strata, from 1 to 10 cm thick, are interbedded by thin argillaceous/calcareous laminae (from 0.5 and 3 cm thick), (Figure 2a,b). The boundary on the laminae shows dissolution or mechanical reworking.
The branching-like facies is arranged in lenses made of clastic gypsum recognizable within thin argillaceous/calcareous laminae (Figure 2c). They are located at the top of the gypsrudites and show "nodular" features composed of millimetre-sized crystals.

Petrographic Observations
The observation on the wafers reveals that crystals belonging to the gypsrudites facies have two types of morphologies: (1) fractured and folded crystals (>1 cm in size) showing elongated shape ([120] and [111] faces) and chaotic orientation (Figure 3a-d), and (2) hexagonal and tabular crystals (<1 cm in size) immersed in a clear brown-orange matrix occurring either in groups or as isolated crystals (Figure 3e-h). In most of the crystals, relicts twin planes are recognised.
Wafers from the branching-like facies display gypsum crystals of few millimetres in size (Figure 3i-k). Wafers confirm the irregular shape and chaotical orientation of the crystals observed during the observation at mesoscale.

Petrographic Observations
The observation on the wafers reveals that crystals belonging to the gypsrudites facies have two types of morphologies: (1) fractured and folded crystals (>1 cm in size) showing elongated shape ([120] and [1̅ 11] faces) and chaotic orientation (Figure 3a-d), and (2) hexagonal and tabular crystals (<1 cm in size) immersed in a clear brown-orange matrix occurring either in groups or as isolated crystals (Figure 3e-h). In most of the crystals, relicts twin planes are recognised.
Wafers from the branching-like facies display gypsum crystals of few millimetres in size (Figure 3i-k). Wafers confirm the irregular shape and chaotical orientation of the crystals observed during the observation at mesoscale.
Raman spectroscopy was carried out on all crystals to investigate the mineralogy of the samples and to exclude the presence of anhydrite. All crystals show peaks distinctive of gypsum. The main vibration bands (cm −1 ) are 492-494, 1006-1008 and 3405 [79].  Raman spectroscopy was carried out on all crystals to investigate the mineralogy of the samples and to exclude the presence of anhydrite. All crystals show peaks distinctive of gypsum. The main vibration bands (cm −1 ) are 492-494, 1006-1008 and 3405 [79].

Fluid Inclusions Study
All crystals from the analysed facies contain primary and secondary fluid inclusions (FIs). Primary FIs are two-phase liquid rich (L+V) and occur in trails along the crystal growth direction (Type 2 FIs). Secondary FIs are monophase liquid (L) or monophase vapour (V) and they are distributed in trails along annealed microfractures that display networks of crosscut-ting trails to the crystals (Type 1 FIs).
Type 1 and Type 2 inclusions show tabular to irregular shape (from 5 to 20 µm in size, rare 50 µm), (Figure 4a). At room temperature, the FIs within a fluid inclusions assemblage (FIA) do not show the same phases, volume proportions and shape. These petrographic differences suggest that the FIs are re-equilibrated (change of pressure and temperature post-entrapment).
In the studied samples, the type of re-equilibration process is not easily recognizable; however, no fluid inclusions affected by decrepitation have been observed.
Probably, these inclusions have likely undergone post-entrapment processes, such as stretching and leaking, associated with gradual plastic and low deformation [80][81][82]. Moreover, some FIs are affected by necking down phenomena. These inclusions are distributed alongside trails of Type 1 and Type 2 FIs (Figure 4b,c).
Rare larger inclusions show microtubules or microfractures, which radiate from the walls inferring an irregular appearance (Figure 4d).

Fluid Inclusions Study
All crystals from the analysed facies contain primary and secondary fluid inc (FIs). Primary FIs are two-phase liquid rich (L+V) and occur in trails along the growth direction (Type 2 FIs). Secondary FIs are monophase liquid (L) or monoph pour (V) and they are distributed in trails along annealed microfractures that disp works of crosscut-ting trails to the crystals (Type 1 FIs).
Type 1 and Type 2 inclusions show tabular to irregular shape (from 5 to 20 size, rare 50 μm), (Figure 4a). At room temperature, the FIs within a fluid inclusi semblage (FIA) do not show the same phases, volume proportions and shape. The rographic differences suggest that the FIs are re-equilibrated (change of pressure an perature post-entrapment).
In the studied samples, the type of re-equilibration process is not easily recogn however, no fluid inclusions affected by decrepitation have been observed.
Probably, these inclusions have likely undergone post-entrapment processes, stretching and leaking, associated with gradual plastic and low deformation [ Moreover, some FIs are affected by necking down phenomena. These inclusions a tributed alongside trails of Type 1 and Type 2 FIs (Figure 4b,c).
Rare larger inclusions show microtubules or microfractures, which radiate fr walls inferring an irregular appearance (Figure 4d).
Microthermometric analysis has been conducted on Type 1 and Type 2 FIs ho crystals belonging to the gypsrudite and branching-like facies to obtain paleoenviro tal information (salinity, temperature of trapping, chemical composition). Unfortu during microthermometric analyses, Type 1 inclusions did not nucleate the bubble cooling step, while in Type 2 inclusions the bubble did not show any volume chan did not disappear during heating. The lack of any change during the analyses d strates that all fluid inclusions are re-equilibrated and not suitable for microthermo studies. Microthermometric analysis has been conducted on Type 1 and Type 2 FIs hosted in crystals belonging to the gypsrudite and branching-like facies to obtain paleoenvironmental information (salinity, temperature of trapping, chemical composition). Unfortunately, during microthermometric analyses, Type 1 inclusions did not nucleate the bubble during cooling step, while in Type 2 inclusions the bubble did not show any volume change and did not disappear during heating. The lack of any change during the analyses demonstrates that all fluid inclusions are re-equilibrated and not suitable for microthermometric studies.

Preliminary Organic Matter Data
Organic material can be subdivided in allochthonous and autochthonous remains. Allochthonous organic matter is present as fine debris filling the inter-crystalline spaces and crystal fractures. This debris shows variable sizes and morphologies (Figure 5a-d).
Autochthonous organic matter is present as amorphous materials strictly related to the crystal lattice (Figure 5e-h) Under plane polarized observations, the organic material shows four different colours: (a) transparent, (b) red, (c) brown and (c) black. All materials are fluorescent when exposed to UV light suggesting their organic nature.
Transparent materials are widespread among the crystals. They display tubular morphologies (<60 µm) and emit blue fluorescence under UV light (Figure 5a,b). Most of these organic debris show internal segmentation.
Red materials display irregular shape (<10 µm) and emit red fluorescence under UV excitation (Figure 5c,d). They do not show internal segmentation or specific morphologies.
Brown autochthonous materials are very abundant. They are located mainly in the core of the crystals belonging to the gypsrudites facies. In some crystals, this material follows the crystallographic planes of the hosting crystals. The morphologies are similar to those observed by Lugli et al. [3] and called "dark core". Under UV-excitation this material exhibits a variable distribution of green epifluorescence. The core of the crystals, showing brown material, is characterized by bright fluorescence, while the limpid rim of the crystal is not fluorescent (Figure 5e,f).
Black material is arranged in aggregates and observed in the fractures, between the crystals or in the matrix and under UV light show a bright fluorescence (Figure 5g,h). Transparent (abundant) and red (rare) materials are observed only in the -branchinglike facies, on the contrary, brown and black materials (abundant) are recognised in all samples.

Preliminary Organic Matter Data
Organic material can be subdivided in allochthonous and autochthonous remains. Allochthonous organic matter is present as fine debris filling the inter-crystalline spaces and crystal fractures. This debris shows variable sizes and morphologies (Figure 5a-d).
Autochthonous organic matter is present as amorphous materials strictly related to the crystal lattice (Figure 5e-h) Under plane polarized observations, the organic material shows four different colours: (a) transparent, (b) red, (c) brown and (c) black. All materials are fluorescent when exposed to UV light suggesting their organic nature.
Transparent materials are widespread among the crystals. They display tubular morphologies (<60 μm) and emit blue fluorescence under UV light (Figure 5a,b). Most of these organic debris show internal segmentation.
Red materials display irregular shape (<10 μm) and emit red fluorescence under UV excitation (Figure 5c,d). They do not show internal segmentation or specific morphologies.
Brown autochthonous materials are very abundant. They are located mainly in the core of the crystals belonging to the gypsrudites facies. In some crystals, this material follows the crystallographic planes of the hosting crystals. The morphologies are similar to those observed by Lugli et al. [3] and called "dark core". Under UV-excitation this material exhibits a variable distribution of green epifluorescence. The core of the crystals, showing brown material, is characterized by bright fluorescence, while the limpid rim of the crystal is not fluorescent (Figure 5e,f).
Black material is arranged in aggregates and observed in the fractures, between the crystals or in the matrix and under UV light show a bright fluorescence (Figure 5g,h). Transparent (abundant) and red (rare) materials are observed only in the -branchinglike facies, on the contrary, brown and black materials (abundant) are recognised in all samples.

87 Sr/ 86 Sr Isotopic Study
A reliable hydrologic indicator to study the salinity crisis appears to be the strontium ( 87 Sr/ 86 Sr) isotope ratio because it is not influenced by salinity change and evaporation conditions [4,6,12].

87 Sr/ 86 Sr Isotopic Study
A reliable hydrologic indicator to study the salinity crisis appears to be the strontium ( 87 Sr/ 86 Sr) isotope ratio because it is not influenced by salinity change and evaporation conditions [4,6,12].
The gypsrudite facies displays 87 Sr/ 86 Sr average value of 0.709045 ± 0.000002, while branching-like facies show 87 Sr/ 86 Sr average value of 0.709082 ± 0.000001. Plotting these values on the global ocean field [1], it appears that both facies formed between 5.9 and 5.6 Ma, during the deposition of the Lower Gypsum Unit. These data strengthen the petrographic observations which attribute the gypsum origin of the Benestare's deposit to primary selenite.
Moreover, these values fall in the range of the global ocean field and suggest an evaporite basin with limited freshwater input and strongly influenced by seawater ingressions. Figure 6 shows the isotopic values of the samples from the gypsrudite and branchinglike facies collected from the Benestare's quarry; horizontal red line defines theoretically the max and min age that the Benestare's sample could have in relationship with isotopic values of the samples reported by Roveri et al. [11]. The gypsrudite facies displays 87 Sr/ 86 Sr average value of 0.709045 ± 0.000002, while branching-like facies show 87 Sr/ 86 Sr average value of 0.709082 ± 0.000001. Plotting these values on the global ocean field [1], it appears that both facies formed between 5.9 and 5.6 Ma, during the deposition of the Lower Gypsum Unit. These data strengthen the petrographic observations which attribute the gypsum origin of the Benestare's deposit to primary selenite.
Moreover, these values fall in the range of the global ocean field and suggest an evaporite basin with limited freshwater input and strongly influenced by seawater ingressions. Figure 6 shows the isotopic values of the samples from the gypsrudite and branchinglike facies collected from the Benestare's quarry; horizontal red line defines theoretically the max and min age that the Benestare's sample could have in relationship with isotopic values of the samples reported by Roveri et al. [11].

Gypsrudites Facies
The selenite clasts of gypsrudite are slightly corroded. Microscopic analyses revealed the presence of fractured crystals with chaotical distribution and variable sizes. No crystals show the typical structure made of a single selenite crystal (swallow-tail) with the twin plane perpendicular to bedding and the re-entrant angle pointing upwards [3,36]. Only a few scattered relict crystals show twin plane [120] and [1̅ 11] faces. Field and petrographic observations suggest a local massive erosion and a rapid deposition of primary selenite (probably of massive and/or banded facies). During sediment deposition and reworking abundant autochthonous and allochthonous organic materials were trapped.
No information on crystal chemistry (salinity, brine type, temperature) was obtained from fluid inclusions study due to re-equilibration phenomena. However, the absence of anhydrite, suggest that the Benestare gypsum deposit, upon sedimentation, was not subjected to significant changes in pressure and temperature (low deformation and burial).

Gypsrudites Facies
The selenite clasts of gypsrudite are slightly corroded. Microscopic analyses revealed the presence of fractured crystals with chaotical distribution and variable sizes. No crystals show the typical structure made of a single selenite crystal (swallow-tail) with the twin plane perpendicular to bedding and the re-entrant angle pointing upwards [3,36]. Only a few scattered relict crystals show twin plane [120] and [111] faces. Field and petrographic observations suggest a local massive erosion and a rapid deposition of primary selenite (probably of massive and/or banded facies). During sediment deposition and reworking abundant autochthonous and allochthonous organic materials were trapped.
No information on crystal chemistry (salinity, brine type, temperature) was obtained from fluid inclusions study due to re-equilibration phenomena. However, the absence of anhydrite, suggest that the Benestare gypsum deposit, upon sedimentation, was not subjected to significant changes in pressure and temperature (low deformation and burial). Moreover, the presence of relict twin plane, crystals not rounded in shape and remains of autochthonous organic materials could testify limited transport.

Branching-Like Facies
Samples from the branching-like facies display fractured crystals with chaotic arrangement. The millimetres gypsum grains are separated by thin fine-grained carbonate or gypsum laminae. Abundant autochthonous and allochthonous organic materials have been observed within, between and on the top of the crystals, in the fractures and in the matrix.
The branching-like facies have been described as "nodular and lenticular selenite" commonly displaying flaser bedding [83], "wavy, needle-like selenite layers" [84,85], or "hemi-radial to radial textures" [86]. They consist of clear selenite crystals, a few centimetres in diameter, with their long axis inclined or oriented horizontally. They are grouped into decimetre-large irregular nodules and lenses separated by thin fine-grained carbonate or gypsum laminae. This facies was originally interpreted as deriving from previous anhydrite nodules formed in a sabkha-like environment [85]. However recently, Lugli et al. [3] and Natalicchio et al. [87] have re-interpreted this gypsum facies as primary formed through two different mechanisms: crystals formed by an initial nucleation zone (into a matrix) and subsequently growing laterally, with crystals grouped in branches projecting outward and crystals grew in the subsurface at the expenses of pelagic gypsum crystals.
From a petrographic point of view, the branching-like facies from the Benestare's quarry is something between the branching facies described by Lugli et al. [3], Natalicchio et al. [87] and, Vai and Lucchi [83]. According to Vai and Lucchi [83], we consider this facies as re-sedimented and not primary due to the fact that: (1) the crystals observed are fractured and show a chaotical orientation, they do not grow laterally and they are not grouped in branches projecting outward from an initial nucleation zone, and (2) the crystals do not show relict twin plane of primary crystallographic textures. However, the studied facies show differences from those observed by Vai and Lucchi [83], mainly: (1) absence of recrystallized gypsum or re-hydrated secondary anhydrite, and (2) presence of autochthonous organic materials in the crystals core.

Putative Source of Organic Matter
The crystal core of the gypsrudites show brown organic materials under optical microscopy. The morphologies of this material are similar to the "dark core" observed in the crystals from the Vena del Gesso basin (Northern Apennines) [3]. Our hypothesis is that the presence of brown matter is strictly related to the crystal growth because it follows the crystallographic morphologies of the hosting crystals. The nature of this autochthonous organic matter was not identified but it is believed it may have derived from putative benthic microbial assemblage or organic-rich peloids, like those described by Natalicchio et al. [87]. The relation between microbial communities and primary gypsum has been recently evidenced by Dela Pierre et al. [30] and Natalicchio et al. [6] which detected interwoven filaments in the Messinian gypsum and interpreted them as remains of colourless sulphide-oxidizing bacteria. Microbial mats dominated by these large prokaryotes are found also in coastal upwelling areas [88,89], in stratified basins [90], as well as in sulphide-rich marine sediments associated with methane seepage [91,92].
The allochthonous organic materials, visible as organic debris, is located in fractures between the crystals and in the inter-crystalline matrix. In our opinion, this material is not related to the crystal growth but that was trapped among the crystals after their formation, probably during the processes of erosion and re-sedimentation.
Similar organic matter has also been detected in the lenses of the branching-like facies. A biotic attribution of allochthonous remains is hampered by the absence of specific morphologies. They could represent plant-derived debris or rests of cyanobacteria, diatoms or other prokaryotes [74,83,93,94]. Green-blue microalgae have been suggested to live in shallow lakes, influenced by solar irradiation and affected by continuous mixing of the water column [95]. Other components of the allochthonous materials show irregular shape, red colour under optical microscopy and emits red fluorescence (UV light). A putative attribution of this material to red algae remains could be suggested. These organisms contain a variety of pigments but the most important is the phycoerythrin, which provides these algae with their red pigmentation by reflecting red light and absorbing blue light [96,97]. Red algae are found all over the world, from polar waters to the tropics, and are commonly found in tide pools and in coral reefs [96,97].
Autochthonous organic matter of the branching-like facies is similar to that found in the gypsrudites. It appears as amorphous and cloudy, and it is strictly linked with crystal lattice. When excited with UV irradiation, the crystals show bright fluorescence in the area occupied by amorphous materials. Even in this case, it is plausible to hypothesize the presence of organic matter in close genetic association with the crystals, but more specific analyses (i.e., characterization of the lipidic fraction through gas chromatography) are needed to assess their nature.
In general, the organic matter content suggests a double source of the biological material. The allochthonous material could represent extrabasinal-derived debris, whereas autochthonous material could represent intrabasinal planktic and benthic remains that were entrapped within the crystals during primary gypsum formation.

Inferences from Sr-Isotope Geochemistry
The gypsrudite and branching-like facies recognised in the Benestare's quarry show very similar isotopic values (0.70904 and 0.70908) suggesting a deposition in an evaporite basin with limited freshwater input and strongly influenced by seawater ingressions. Recently, studies [3,7] carried out on Primary Lower Gypsum of the Vena del Gesso, documented the seawater ingression starting from the 6th (5.84 Ma) gypsum bed where the branching-like facies appear for the first time in the section. These data suggest a global change in hydrology at 5.84 Ma (100 ka eccentricity minimum), when the brine became current-dominated for all the Mediterranean marginal basins [3].

Conclusions
A multidisciplinary approach allowed to improve the knowledge about the evaporitic deposits of the Benestare's quarry in the Calabrian forearc basin (Calabria, Southern Italy). The gypsrudite and the detrital nature of the branching-like facies allow to suggest a clastic nature for the Benestare's deposit. Considering the presence of relict structures (i.e., twin plane), the absence of recrystallization (anhydrite), angular crystals and remains of autochthonous organic materials in addition to the stretching and leaking re-equilibration of the fluid inclusions, it is plausible a limited transport and low to very low deformation grade and burial diagenesis of the primary gypsum.
The 87 Sr/ 86 Sr values attribute the gypsum crystals to the first Messinian evaporitic phase, widening the poor dataset of the 87 Sr/ 86 Sr curve for the period subsequent to the onset of the MSC in the Mediterranean basin. The Benestare's deposit represents a unicum in the MSC sedimentary successions of the Calabrian arc. It is the first record of clastic selenite deposit in the Ionian forearc basin. Furthermore, this work confirms that gypsum evaporites have great potential to preserve the autochthonous and allochthonous organic materials, providing important information on the paleoecology of ancient evaporitic environments.