Vena Del Gesso Research Articles

Isoprenoidal GDGTs and GDDs associated with anoxic lacustrine environments

We examined membrane-spanning archaeal lipids using ultra high pressure liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) in a suite of sediment samples from both cored sequences (Messel oil shale and Lake Chala) and surface sediments (Azorean lakes) encompassing ancient and modern (Eocene to Present) lacustrine environments. Additionally we compared the lacustrine data to those of marine (Mediterranean cored sequences, Arabian Sea surface sediments and Monterey outcrop sediments) and hypersaline sediments (Vena del Gesso marls) as well as marine suspended particulate matter (SPM) from the Black Sea. Regular isoprenoidal glycerol dialkyl glycerol tetraethers (GDGTs) and glycerol dialkyl diethers (GDDs) were the most abundant membrane-spanning lipids in all investigated settings (>90 % and 84 % respectively). Interestingly, GDGTs with a cyclohexyl ring (S-GDGTs) were also present in almost all investigated lake sediments, in relative abundances of ca. 2–7 % and, for the first time, also their S-GDD counterparts were detected (2–10 %). The producers of S-GDGTs are still unknown, however our results show that it is likely that bottom water anoxia (both seasonally induced or permanent) is the driving factor for the production of these lipids, whereas previous studies suggested euxinia was required for production. Unsaturated GDGTs (uns-GDGTs, ca. 2 %) were only detected in Lake Chala sediments and surface sediments from Azorean lakes, but without accompanying uns-GDDs. GMGTs, glycerol monoalkyl glycerol tetraethers, were present in Messel oil shale and marine samples, while GMDs were only found in Messel oil shale.

Messinian bottom-grown selenitic gypsum: An archive of microbial life.

Primary gypsum deposits, which accumulated in the Mediterranean Basin during the so-called Messinian salinity crisis (5.97-5.33Ma), represent an excellent archive of microbial life. We investigated the molecular fossil inventory and the corresponding compound-specific δ13 C values of bottom-grown gypsum formed during the first stage of the crisis in four marginal basins across the Mediterranean (Nijar, Spain; Vena del Gesso, Italy; Heraklion, Crete; and Psematismenos, Cyprus). All studied gypsum samples contain intricate networks of filamentous microfossils, whose phylogenetic affiliation has been debated for a long time. Petrographic analysis, molecular fossil inventories (hydrocarbons, alcohols, and carboxylic acids), and carbon stable isotope patterns suggest that the mazes of filamentous fossils represent benthic microbial assemblages dominated by chemotrophic sulfide-oxidizing bacteria; in some of the samples, the body fossils are accompanied by lipids produced by sulfate-reducing bacteria. Abundant isoprenoid alcohols including diphytanyl glycerol diethers (DGDs) and glycerol dibiphytanyl glycerol tetraethers (GDGTs), typified by highly variable carbon stable isotope composition with δ13 C values spanning from -40 to -14‰, reveal the presence of planktic and benthic archaeal communities dwelling in Messinian paleoenvironments. The compound inventory of archaeal lipids indicates the existence of a stratified water column, with a normal marine to diluted upper water column and more saline deeper waters. This study documents the lipid biomarker inventory of microbial life preserved in ancient gypsum deposits, helping to reconstruct the widely debated conditions under which Messinian gypsum formed.

Terrestrial laser scanning, geomorphology and archaeology of a Roman gypsum quarry (Vena del Gesso Romagnola area, Northern Apennines, Italy)

Roman-period extractive sites in gypsum outcrops are very rare, and most have become very degraded by later weathering or quarrying activities. This paper describes, using laser scanning, photogrammetry and survey using a UAV-based survey, the uniquely well-preserved Roman-period gypsum quarry of Ca’ Castellina (Northern Apennines, Italy). This site was excavated only in the last few years and the excavations have brought to light some gypsum blocks and the ancient quarry benches showing excavation marks, the remains of a rectangular building and a great number of artefacts that range between the Protohistoric Period and the modern times. The size of the extracted blocks, the extraction methodologies and the age of a charcoal fragment (361 – 178B CE) found immediately at the contact between the gypsum quarry floor and the infilling sediments date the quarry back to the Roman age. Archaeological evidences demonstrate the building to have been used for a short period of time during the XVI-XVII century. Immediately after its abandonment most of the quarry floor has been covered with a thick detrital layer, protecting it from dissolution (fossilizing this floor and leaving it as if it was abandoned very recently), whereas the naked or poorly covered floor of this quarry has been subjected to dissolution phenomena of the exposed gypsum rocks, with a lowering of the surface, the smoothening of the corners and the formation of a set of deeply carved karren features.A 3D survey using both a laser scanning instrument and a drone-mounted photo camera have allowed to get precise measures on the size of the blocks that were extracted in this quarry, the traces of pick axe marks, and on the dissolution morphologies that have developed on the bare gypsum rock. These typical gypsum landforms show how fast these solution forms can develop where concentrated runoff flows on bare gypsum. To prevent this exceptional archaeological extractive site of being further dissolved, it will be important to plan some measures to be put in place in order to protect this delicate historical landmark.

Diazotrophy Drives Primary Production in the Organic-Rich Shales Deposited Under a Stratified Environment During the Messinian Salinity Crisis (Vena del Gesso, Italy)

Density stratification between freshwater and brine is periodically formed during massive evaporation events, which often associates deposition of organic-rich sediments. Here, we investigated phototrophic communities and nitrogen cycle during the deposition of two organic-rich shale beds of gypsum–shale alternation, representing the initial stage of the Messinian salinity crisis (Vena del Gesso, Northern Apennines, Italy). The structural distributions and the carbon and nitrogen isotopic compositions of geoporphyrins show a common pattern in the two shales, indicating the predominance of a particular phototrophic community under freshwater–brine stratified conditions. The ~6‰ difference in δ13C of total organic carbon between PLG 4 and 5 shales was associated with similar shift in δ13C of the porphyrins derived from chlorophyll c, suggesting that the eukaryotic algae producing chlorophyll c were the major constituent of the phototrophic community. Importantly, these porphyrins show δ15N values (−7.6‰ to −4.7‰) indicative of N2-fixation. We suggest that nitrate-depletion in the photic zone induced the predominance of diazotrophic cyanobacteria, which supplied new nitrogen for the chlorophyll c-producing eukaryotic algae. The large difference in the δ13C values of porphyrins and total organic carbon between PLG 4 and 5 shales are interpreted to reflect the depth of the chemocline, which fluctuates in response to changes in the regional evaporation–precipitation balance. Such variation in the chemocline depth may have dynamically changed the mode of the nitrogen cycle (i.e., nitrification–denitrification–N2-fixation coupling vs. phototrophic assimilation of ammonium) in the density-stratified marginal basins during the Messinian salinity crisis.

Orbitally Forced Hydrological Balance During the Messinian Salinity Crisis: Insights From Strontium Isotopes (87Sr/86Sr) in the Vena del Gesso Basin (Northern Apennines, Italy)

AbstractThe 87Sr/86Sr ratio is a proxy of the hydrologic structure of marginal basins characterized by the mixing between marine and continental waters. This reliable paleoceanographic and paleoclimatic tool is considered a key to the reconstruction of high‐amplitude hydrologic changes that governed the evolution of the Mediterranean region during the Messinian salinity crisis (MSC), when reduced connections with the global ocean resulted in the deposition of the most studied Earth's salt giant. Paleohydrological dynamics leading to the deposition of the Primary Lower Gypsum during the first stage of the MSC were revealed by the study of the 87Sr/86Sr composition of 114 samples from the Vena del Gesso basin (Northern Apennines, Italy). The analysis of seven high‐resolution 87Sr/86Sr profiles from individual gypsum beds suggests a climatic influence of precessional‐scale orbital parameters during evaporite deposition. The variations of Sr isotope ratios over time indicate that gypsum precipitation started from a seawater body dominated by continental contributions, followed by a relative increase of marine input. The overall results show a gradual upward detachment from the global ocean 87Sr/86Sr curve, with crucial steps corresponding to the most extreme eccentricity minima, suggesting an orbital influence on the hydrological balance of the basin. Given the sedimentological and geochemical analogies shared by the Mediterranean marginal basins that hosted the Primary Lower Gypsum deposition, the 87Sr/86Sr evolution of the Vena del Gesso basin may be considered as indicative of Mediterranean‐scale hydrologic dynamics, driven by gradual reduction of exchanges with the Atlantic and variable freshwater input.

Precessional control of Sr ratios in marginal basins during the Messinian Salinity Crisis?

AbstractBased on 87Sr/86Sr data of the Primary Lower Gypsum (PLG) deposits in the Vena del Gesso basin—a marginal basin of the Mediterranean during the Messinian Salinity Crisis—a correlation between 87Sr/86Sr values and precessional forcing has recently been proposed but not yet confirmed. In this study, a box model is set up to represent the Miocene Mediterranean deep basin and a connected marginal basin. Measurements of 87Sr/86Sr in the Vena del Gesso and estimated salinity extrema are used to constrain model results. In an extensive analysis with this model, we assess whether coeval 87Sr/86Sr and salinity fluctuations could have been forced by precession‐driven changes in the fresh water budget. A comprehensive set of the controlling parameters is examined to assess the conditions under which precession‐driven 87Sr/86Sr variations occur and to determine the most likely setting for PLG formation. Model results show that precession‐driven 87Sr/86Sr and salinity fluctuations in marginal basins are produced in settings within a large range of marginal basin sizes, riverine strontium characteristics, amplitudes of precessional fresh water budget variation, and average fresh water budgets of both the marginal and deep basin. PLG deposition most likely occurred when the Atlantic‐Mediterranean connection was restricted, and the average fresh water budget in the Mediterranean was significantly less negative than at present day. Considering the large range of settings in which salinities and 87Sr/86Sr fluctuate on a precessional timescale, 87Sr/86Sr variations are expected to be a common feature in PLG deposits in marginal basins of the Mediterranean.

Age refinement of the Messinian salinity crisis onset in the Mediterranean

AbstractWe propose a revised age calibration of the Messinian salinity crisis onset in the Mediterranean at 5.971 Ma based on the recognition of an extra gypsum cycle in the transitional interval of the Perales section (Sorbas basin, Spain) and the revision of the magnetostratigraphy of the Monticino section (Vena del Gesso basin, Italy). This age re‐calibration allows to state more accurately that: (i) the interval encompassing theMSC‐onset is continuous, thus ruling out any erosional feature or stratigraphic hiatus related to a major sea‐level fall affecting the Mediterranean; (ii) the first gypsum was deposited during the summer insolation peak at 5.969 Ma associated with an eccentricity minimum and roughly coincident with glacial stageTG32; (iii) theMSC‐onset was preconditioned by the tectonically‐driven reduction of the hydrological exchanges with the Atlantic Ocean and finally triggered by glacial conditions in the northern hemisphere and by arid conditions in northern Africa.

Hypogeal geological survey in the “Grotta del Re Tiberio” natural cave (Apennines, Italy): a valid tool for reconstructing the structural setting

Abstract As karst systems are natural windows to the underground, speleology, combined with geological surveys, can be useful tools for helping understand the geological evolution of karst areas. In order to enhance the reconstruction of the structural setting in a gypsum karst area (Vena del Gesso, Romagna Apennines), a detailed analysis has been carried out on hypogeal data. Structural features (faults, fractures, tectonic foliations, bedding) have been mapped in the ”Grotta del Re Tiberio” cave, in the nearby gypsum quarry tunnels and open pit benches. Five fracture systems and six fault systems have been identified. The fault systems have been further analyzed through stereographic projections and geometric-kinematic evaluations in order to reconstruct the relative chronology of these structures. This analysis led to the detection of two deformation phases. The results permitted linking of the hypogeal data with the surface data both at a local and regional scale. At the local scale, fracture data collected in the underground have been compared with previous authors’ surface data coming from the quarry area. The two data sets show a very good correspondence, as every underground fracture system matches with one of the surface fracture system. Moreover, in the cave, a larger number of fractures belonging to each system could be mapped. At the regional scale, the two deformation phases detected can be integrated in the structural setting of the study area, thereby enhancing the tectonic interpretation of the area (e.g., structures belonging to a new deformation phase, not reported before, have been identified underground). The structural detailed hypogeal survey has, thus, provided very useful data, both by integrating the existing information and revealing new data not detected at the surface. In particular, some small structures (e.g., displacement markers and short fractures) are better preserved in the hypogeal environment than on the surface where the outcropping gypsum is more exposed to dissolution and recrystallization. The hypogeal geological survey, therefore, can be considered a powerful tool for integrating the surface and log data in order to enhance the reconstruction of the deformational history and to get a three-dimensional model of the bedrock in karst areas.

Calcareous nannofossils and foraminifers herald the Messinian Salinity Crisis: The Pollenzo section (Alba, Cuneo; NW Italy)

During the Messinian, the Mediterranean area experienced fast and prominent paleoenvironmental changes, culminating in the so-called Messinian Salinity Crisis, with the deposition of the evaporitic series. This work investigates the micropaleontological assemblages in the pre-evaporitic sediments of the Sant’Agata Fossili Marls (SAF) of the Pollenzo section (Cuneo area, North Western Italy). A semiquantitative analysis is carried out on the upper part of the marly and pelitic sediments of the SAF underlying the first gypsum bed, ascribed to the Vena del Gesso Fm. (VDF). The studied interval belongs to the planktonic foraminifer Globorotalia conomiozea Zone and “non distinctive Zone” of Iaccarino and to the calcareous nannofossil MNN11b/c Zone of Raffi et al. (1998, 2003) ( Raffi et al., 1998; Raffi et al., 2003). Decrease of diversity and abundance of the foraminifer and calcareous nannofossil assemblages is recorded 12 m below the VDG and clearly reflects environmental stress. From bottom to top, six paleoecological events are recorded: (1) the first peak abundance of “small” Reticulofenestra and the last recovery (LR) of planktonic foraminifers; (2) the peak abundance of Pontosphaera japonica and the last recovery of warm water taxa Discoaster spp.; (3) the last recovery of benthic foraminifers; (4) the co-occurring peak abundances of Helicosphaera carteri and Sphenolithus abies, and the last recovery of warm water taxa Amaurolithus spp.; (5) the second peak of “small” Reticulofenestra; (6) the definitive disappearance of calcareous nannofossils. These paleoecological events describe a progressive isolation of the basin from the world ocean and increasingly stressed environment (LR planktonic foraminifers; LR Discoaster spp.), increasing dysoxic to anoxic conditions at the sea floor (LR benthic foraminifers), shallowing of the water column (peak of H. carteri), increasing salinity in surface waters (peak of S. abies), and enhanced nutrient concentration in surface waters (peak of “small” Reticulofenestra); these are related to paleoenvironmental changes predating gypsum deposition at Pollenzo and affecting the whole Mediterranean basin.

Osservazioni sul giacimento del Bronzo Antico della Grotta dei Banditi

The Grotta dei Banditi is a cave located in the Vena del Gesso Romagnola (a Miocenic Gypsum Geological Formation) near Brisighella. Excavations made in 1973 have revealed a thick stratum (from 1,30 to about 3 meters), in which have been found stratified hearths and abundant finds of the Early Bronze Age. The pottery may be assigned to an advanced – but probably not final – stage of this period, according with a 14C date (1890-1750 BC 1 ?).

Occurrence and biomarker potential of 23-methyl steroids in diatoms and sediments

23-Methyl sterols have been reported to be synthesized by a few marine algae, but unambiguous identification of 23-methyl steroids in sediments and petroleum is lacking. We report the presence of 23-methylcholesta-5,22E-dien-3β-ol in 14 out of 106 diatom cultures, thereby showing that diatoms, together with dinoflagellates, may be an important environmental source for such steroids. Synthesis of authentic 23-methylcholestanes showed that their mass spectra are identical to those of 24-methylcholestanes, but that they elute earlier on apolar stationary phases during gas chromatography (GC) analysis. Co-injection of the authentic standards with sediment extracts revealed the presence of these compounds in the Skole unit of the Oligocene Menelite Formation, the Miocene Monterey Formation and the Messinian Vena del Gesso Formation. In addition, we tentatively identified 23,24-dimethyl-27-norcholestanes in some of these sediments. Molecular clock calculations suggest that diatoms are a possible source for 23-methyl steroids in sediments and petroleum from the late Jurassic onwards.

Microbial communities in Messinian evaporite deposits of the Vena del Gesso (northern Apennines, Italy)

The Vena del Gesso (Northern Apennines) is a 230 m-thick succession consisting of up to 16 gypsum-shale cycles belonging to the “Lower Evaporites” formed during the Messinian salinity crisis in theMediterranean. The study of the microbial communities preserved in the gypsum crystals of one complete cycle (6 th cycle at Monte Tondo quarry) showed abundant, regularly arranged filamentous forms that resemblemorphologically modern obligate phototrophes, cyanobacteria colonizing modern photic, shallow-water gypsum basins. At least four different bacterial populations have been recognized: a) filamentous type cyanobacteria with characteristic inserted funnel shaped structure resembling the modern Scytonematacean; b) Type 1 organisms consisting of filamentous structures impregnated by clay minerals containing pyrite grains in the outer sheath; c) Type 2 filaments filled by clay minerals with dolomite in the outer sheath; d) Type 3 filamentous organisms with a central hollow tube and an encrusted outer sheath mainly composed of calcium carbonate. These organisms were probably associated with other heterotrophic bacteria as suggested by the presence of dolomite and pyrite structures. The size and preservation suggest that most of these cyanobacteria were likely conducting oxygenic photosynthesis as presently observed in modern solar salt works. It follows that they were living in shallow water settings or settled down from the water column to the bottom of a relatively deep evaporite basin.

Novel functionalised chlorins in sediments of the Messinian Vena del Gesso evaporitic sequence: Evidence for a facile route to reduction for biomarkers

Fossil pigment distributions from sediments of the Messinian Vena del Gesso, Italy, include two novel sedimentary chlorins as revealed by high performance liquid chromatography and liquid chromatography multistage mass spectrometry. The two novel chlorin components are meso-derivatives of chlorophyllone a and represent early stage diagenetic intermediates in the formation of bicycloalkano chlorin and porphyrin structures that occur in these and other carbonaceous sediments. Their presence indicates the operation of a facile route to reduction during early diagenesis.

Passive‐roof thrusting in the Messinian Vena del Gesso Basin (Northern Apennines, Italy): constraints from field data and analogue models

AbstractWe present the results of a study of the Vena del Gesso Basin (Romagna Apennines, Italy) integrating field analyses and analogue modelling. This basin represents one of the best‐preserved top‐thrust basins in the Northern Apennines foreland and is one of the few examples where primary evaporites, related to the Messinian salinity crisis of the Mediterranean, widely crop out. The structural style affecting the Messinian gypsum is examined to get insights into the mechanism responsible for the overall deformation features recognizable in the area. The evaporites are completely detached at the base and widespread back‐thrusts, repeatedly doubling these deposits, strongly contrast with the regional forelandward vergence of structures in the Apennines. On the basis of the comparison between field data and experimental results, the features characterising this area can be described as the result of the deformation linked to the sequential activation of an obliquely propagating passive‐roof duplex. Analogue models evidenced the major role played (1) by syntectonic erosion that promoted the development of passive‐roof duplex style, as well as (2) the role of décollement level pinch‐out that determined an oblique progression of deformation. Finally our data lead to reconsider the palaeoenvironmental reconstruction concerning the onset of the Messinian salinity crisis in the Mediterranean. Copyright © 2007 John Wiley & Sons, Ltd.

The Messinian ‘Vena del Gesso’ evaporites revisited: characterization of isotopic composition and organic matter

Abstract The ‘Vena del Gesso’ (Gessoso-Solfifera Fm, Messinian) is a 227 m-thick ridge along the western Romagna Apennines (Italy) consisting of up to 16 selenite cycles separated by shales and minor carbonate. The total organic carbon values of these deposits range between 0.087–0.016% (gypsum) and 3% (shales). Organic matter is dominated by black debris associated with continental debris. Algae and dynocysts are rare (<1%). The amount of amorphous organic matter is low but it may reach up to c. 40%. The 87 Sr/ 86 Sr of gypsum and carbonate vary from 0.708890 to 0.709024, yielding non-oceanic values with several exceptions that plot within error of coeval oceanic values only in the upper part of the section (from the 6° bed). The sulphur isotope composition of gypsum range between δ 34 S =+21.8 and +23.7‰ and may represent precipitation of δ 34 S-enriched gypsum due to the fractionation effect or recycling of coeval gypsum with contributions of brine-sediment redox variations. The isotope values of carbonates show a large variability (−6.4<δ 18 O<+6.05‰; −14.68<δ 13 C<+2.5‰), suggesting a complex origin by mixing of marine and non-marine waters with a significant contribution of reduced organic matter. These data point to an evaporite basin dominated by continental waters which received significant phases of marine recharge in the upper part together with a marked facies change. Because seawater recharges and a similar facies change are present in other Messinian sections, it follows that we have new possible geochemical and facies markers to correlate the Lower Evaporites across the Mediterranean.

The Northern Apennines palynological record as a contribute for the reconstruction of the Messinian palaeoenvironments

The Messinian stage has long been associated with an overall warm and dry climate whereas recent researches indicate either a warm and humid or a cool and dry climate. The integrated stratigraphic record of vegetation and climatic changes from Northern Apennines sites provides the solution to this apparent contradiction. Its integration with the updated geological and sedimentological studies provides additional data for the reconstruction of the depositional palaeoenvironments in both marginal and deeper sub-basins of the Apennines foredeep. The onset of the Mediterranean salinity crisis (MSC) is recorded in the Gessoso–Solfifera of the Vena del Gesso (marginal sub-basin). Cyclical humid conditions, corresponding to precession minima, developed during the deposition of the shales interbedded with the gypsum (5.9 to 5.6 Ma); some cooler events took also place under the effects of global (glacial stadials) and regional factors (Apennines uplift). At present no major changes from moist to dry conditions are attested to just before the salinity crisis, as well as in Sicily. So climate did not play a major role in the onset of the MSC despite the favourable context provided by inferred thermo-xeric conditions in southern Italy. A drier episode indicated by the expansion of the open vegetation including the northward migration of Lygeum postdates the onset of the salinity crisis of about 400 kyr, in the lower post-evaporitic deposits of Maccarone (deeper sub-basin). It falls within a period of global warming whereas at a regional scale it could correlate p.p. to the evaporite deposition in deeper basins and to hiatuses in the marginal basins of Sicily and of the western sector of Northern Apennines. Its sudden end, about 100 kyr later, in coincidence with a significant increase of Pinaceae, indicates a turnover in the terrestrial setting not linked to major climate changes but possibly to a complex interaction between other palaeoenvironmental factors (e.g., tectonics and eustatism). In contrast organic-walled dinoflagellate cysts exclude significant modifications in aquatic settings (insaturation of either open marine or brackish conditions). In the latter, a later change is marked by the arrival of Impagidinium (?) sp. 1., a species here referred instead to Caspidinium rugosum, about 7 m below the first colombaccio. This occurrence together with the spread of Pediastrum indicates a freshwater dilution i.e. the “Lago-Mare” event during wetter climatic conditions on the adjacent landmass (increase of Tsuga and Cedrus). The successive arrival and/or dominance of other “Paratethyan” taxa such as I. (?) sp. 2, I. (?) sp. 3 and Galeacysta etrusca indicate highly variable water environments (marine vs. continental water inputs) during the deposition of the uppermost post-evaporitic deposits. The Lago-Mare is stratigraphically sandwiched between an ash layer (130 m below) dated at 5.5 Ma and the beginning of the Pliocene where a peak of Impagidinium patulum marks the onset of open marine conditions. The dominant humid, subtropical to warm temperate climate indicates differences in both temperature and moisture values with respect to the coeval southern sections, revealing climatic gradients within the Mediterranean, at least from the Messinian. No dramatic vegetation and climate changes have been recorded during the MSC; major changes occurred later as indicated by the palynological record from 2.6 Ma. This palynostratigraphic record is a good reference for more recent models of the development of the MSC and for establishing time-relationships between the Apennine and Sicilian successions.

Deep‐water clastic evaporites deposition in the Messinian Adriatic foredeep (northern Apennines, Italy): did the Mediterranean ever dry out?

AbstractA 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 downcurrent 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 deep‐water resedimented deposits rather than shallow‐water to supratidal primary evaporites indicative of a complete basin desiccation.

Identification of carotenals in sediments

High performance liquid chromatography with photodiode array UV–Vis detection and atmospheric pressure chemical ionization mass spectrometry was used to analyze sediment samples from the meromictic Ace Lake (Antarctica), as well as a Pliocene sapropel from the Mediterranean Sea and a Miocene marl from the Vena del Gesso formation (Italy). The Ace Lake samples contained intact chlorobactene, isorenieratene, γ- and β-carotene and two series of carotenoid breakdown products. The first and more abundant series was identified as aryl (ϕ)-carotenals of increasing chain length (C 13, C 15, C 18, C 20, C 22, C 25, C 27, C 30, and C 32) on the basis of their UV–Vis and mass spectra. They appear to be formed from chlorobactene through oxidative cleavage of the double bonds of the polyene chain. The minor series (β-carotenals) was also identified, and may be formed from γ-carotene in a similar manner. Intact isorenieratene and the ϕ-carotenal series were also found in the Mediterranean Sea sapropel. Only a trace of the C 32 ϕ-carotenal could be detected, suggesting isorenieratene as the predominant source of these ϕ-carotenals. Additionally, intact β-carotene and C 13–C 30 β-carotenals were found in the sapropel. The absence of the C 32 β-carotenal strongly suggests these breakdown products are derived from β-carotene. The Vena del Gesso marl contained both intact isorenieratene and the C 13–C 25 ϕ-carotenals. The absence of the longer chain length ϕ-carotenals from this sample may indicate more advanced oxidation of isorenieratene. The carotenals are likely formed during storage of samples and/or extracts under non-ideal conditions, i.e., not frozen and exposed to oxygen although they may also be formed by diagenetic processes. They can be relatively abundant and sometimes be an order of magnitude higher in concentration than the parent carotenoid. Hence, not including the ϕ-carotenals could lead to an underestimation of the persistence of photic zone euxinia.

Sedimentary and tectonic evolution of the Vena del Gesso basin (Northern Apennines, Italy): Implications for the onset of the Messinian salinity crisis

The integration of field and subsurface data permits a substantial revision of the sedimentary evolution of the Vena del Gesso basin, a thrust-top basin in the Northern Apennines where shallow-water primary gypsum deposits related to the Messinian salinity crisis were well developed and preserved. As inferred from lateral and vertical facies changes within the underlying deep-marine turbidites of the Marnoso-arenacea Formation, evaporite precipitation occurred in a basin bounded to the north and to the east by a thrust-related anticline actively growing since the late Tortonian. Both gypsum deposition and subsequent deformation were strongly controlled by evolving paleobathymetry driven by tectonics. Primary gypsum precipitated in a shallow, silled basin, while in the adjacent deeper and larger foredeep basin, organic-rich shales were deposited. Gypsum deposits underwent severe postdepositional deformation related to large-scale gravitational collapse, as a result of a regional uplift event, also coincident with the end of the evaporitic phase. Along the inner, shallower-dipping limb of the anticline bounding the basin, large-scale, poorly deformed gypsum slabs moved downslope along a detachment surface developed at the contact with the underlying euxinic shales, forming both extensional and compressional features and showing an overall southwestern vergence. The identification of a south-southwest–dipping paleoslope, here pointed out for the first time, suggests that the deformational features affecting the gypsum unit were probably driven by gravity and not by active thrusting, as thought up to now. The steeper frontal limb of the anticline promoted the transformation of gypsum slides into debris flows and turbidite currents that deposited their load in the adjacent deeper basin. This gravitational deformation was sealed by postevaporitic upper Messinian Lagomare deposits. The sedimentary history of the Vena del Gesso basin suggests that the Messinian salinity crisis in the Apennine foredeep, as well as in the Balearic, Tyrrhenian, Sicily, and Eastern Mediterranean Basins, was tightly linked to tectonic processes. The large-scale, postdepositional collapse of primary evaporitic deposits is a widespread feature in the Mediterranean basins, and it may have altered the original stratigraphic relationships in some places. This finding has potentially important implications for a correct paleoenvironmental reconstruction of the onset of the Messinian salinity crisis.

Clues to early diagenetic sulfurization processes from mild chemical cleavage of labile sulfur-rich geomacromolecules

Macromolecular fractions, isolated from the solvent extract of sulfur-rich Recent (Siders Pond, USA; Lake Cadagno, Switzerland; Walvis Bay, Namibia) and immature sediments (Gibellina, Messinian of Sicily; Vena del Gesso, Messinian of Italy), were investigated by chemical degradation using sodium ethanethiolate/methyliodide. This mild reagent which cleaves polysulfide bonds to yield methylsulfides has the advantage over other methods of leaving intact other functionalities (like double bonds) and preserving sulfur atoms at their incorporation site. The method is, therefore, well-suited to the molecular level investigation of sulfur-rich macromolecules from Recent sediments containing highly functionalized polysulfide-bound subunits. In Recent anoxic sulfur-rich sediments, the release of various methylthioethers clearly demonstrates that intermolecular sulfurization of organic matter does occur at the earliest stages of diagenesis. Steroids and phytane derivatives are the major sulfurized lipids, a feature also observed in more mature sulfur-rich sediments. Several phytene derivatives, such as cis and trans 1-methylthiophyt-2-enes, as well as methylthiosteroids, including 5α- and 5β-3-(methylthio)-cholest-2-enes, were identified by comparison with synthesized standards. Steroid methylthioenolethers are released from polysulfide-bound steroid enethiols present in the macromolecular fractions. The latter, which correspond to thioketones, can be considered as intermediates in the reductive sulfurization pathway leading from steroid ketones to polysulfide-bound saturated steroid skeletons and are characterized for the first time in the present study. Thus, it could be shown that the major part of the polysulfide-bound lipids occurring in Recent sediments is apparently the result of sulfurization processes affecting carbonyls (aldehydes and ketones). The unsaturated methylthioethers obtained from Recent sediments were not present in more mature evaporitic samples, which suggests that polysulfide-bound unsaturated thiols are intermediates formed during the first sulfurization steps occurring soon after deposition and that they are rapidly transformed by various processes taking place during early diagenesis, notably to yield their saturated counterparts.