Record of archaeal activity at the serpentinite‐hosted Lost City Hydrothermal Field

Samples of young, outer surfaces of brucite–carbonate deposits from the ultramafic‐hosted Lost City hydrothermal field were analyzed for DNA and lipid biomarker distributions and for carbon and hydrogen stable isotope compositions of the lipids. Methane‐cycling archaeal communities, notably the Lost City Methanosarcinales (LCMS) phylotype, are specifically addressed. Lost City is unlike all other hydrothermal systems known to date and is characterized by metal‐ and CO₂‐poor, high pH fluids with high H₂ and CH₄ contents resulting from serpentinization processes at depth. The archaeal fraction of the microbial community varies widely within the Lost City chimneys, from 1–81% and covaries with concentrations of hydrogen within the fluids. Archaeal lipids include isoprenoid glycerol di‐ and tetraethers and C₂₅ and C₃₀ isoprenoid hydrocarbons (pentamethylicosane derivatives – PMIs – and squalenoids). In particular, unsaturated PMIs and squalenoids, attributed to the LCMS archaea, were identified for the first time in the carbonate deposits at Lost City and probably record processes exclusively occurring at the surface of the chimneys. The carbon isotope compositions of PMIs and squalenoids are remarkably heterogeneous across samples and show highly ¹³C‐enriched signatures reaching δ¹³C values of up to +24.6‰. Unlike other environments in which similar structural and isotopic lipid heterogeneity has been observed and attributed to diversity in the archaeal assemblage, the lipids here appear to be synthesized solely by the LCMS. Some of the variations in lipid isotope signatures may, in part, be due to unusual isotopic fractionation during biosynthesis under extreme conditions. However, we argue that the diversity in archaeal abundances, lipid structure and carbon isotope composition rather reflects the ability of the LCMS archaeal biofilms to adapt to chemical gradients in the hydrothermal chimneys and possibly to perform either methanotrophy or methanogenesis using dissolved inorganic carbon, methane or formate as a function of the prevailing environmental conditions.     

Upper miocene carbonate ramp deposits from the southernmost part of Maiella Nountain (Abruzzo, Central Italy)

Summary The development of carbonate ramp depositional systems in the Neogene of the Mediterranean Region represents a widespread feature so far analysed in several papers. It is striking to note that the evolution of upper Miocene carbonate ramps, characterized by the presence of coralgal bioherms, highlights the events leading to the Messinian salinity crisis. The coralgal bioherms of preevaporite Messinian age exhibit fossil assemblages indicating marine waters with normal salinity, whereas stromatolitic and microbial encrustations underline the deterioration of the environment during the Messinian salinity crisis. Maiella Mountain is a broad carbonate massif located in Abruzzo (Central Italy). The late lower Oligocene-Messinian part of its stratigraphic succession consists of stacked non-tropical carbonate ramp deposits related to third and higher order sequences. The investigations performed in the southernmost portion of the massif allowed to recognize a complete fourth order carbonate depositional sequence on a homoclinal ramp of pre-evaporite Messinian age. The presence of small coralgal patch reefs and overlaying microbial encrustations is significant. A transect exhibits the stratigraphic framework of the area. The data show how local parameters play a notable role in the development of these deposits.     

Anaerobic and Aerobic Oxidation of Methane at Late Cretaceous Seeps in the Western Interior Seaway,USA

The Late Cretaceous (Campanian) Tepee Buttes represent a series of conical, fossiliferous limestone deposits embedded in marine shales that deposited in the Western Interior Seaway. The previously suggested origin of the Tepee Buttes at methane-seeps was confirmed by this study. δ¹³C values as low as ?50‰ of early diagenetic carbonate phases of two Tepee Buttes near Pueblo (Colorado) reveal that methane was the major carbon source. Molecular fossils released from a methane-seep limestone contain abundant ¹³C-depleted archaeal lipids (PMI, biphytane; δ ¹³C: ?118 and ?102‰), derived from anaerobic methanotrophs. A suite of ¹³C-depleted bacterial biomarkers (branched fatty acids; ?73 to ?51‰) reflects the former presence of sulfate-reducing bacteria, corroborating that a syntrophic consortium of archaea and bacteria mediating anaerobic oxidation of methane already existed in Cretaceous times. Molecular fossils also suggest that methane was not exclusively oxidized in an anaerobic process. A series of unusual C₃₄/C₃₅-8,14-secohexahydrobenzohopanes with low δ¹³C values (?110 and ?107‰) points to the presence of aerobic methanotrophic bacteria at the ancient seep site.     

Paracamelus (Mammalia,Camelidae) remains from the late Messinian of Italy: insights into the last camels of western Europe

In this paper we describe fossil remains of an indeterminate species of the genus Paracamelus (Artiodactyla, Camelidae) from the Messinian post-evaporitic deposits (5.55–5.40 Ma) of Verduno (Piedmont, NW Italy). Camelins dispersed into Eurasia from North America in the late Miocene and almost instantaneously spread in western Europe and Africa. The size and morphology of the fossils found at Verduno are consistent in with those of Paracamelus, the earliest Old World camelin. Up to now, the only fossil camels recovered in the Neogene of Western Europe have been found at Venta del Moro and Librilla in Spain at 6.2 Ma. The remains from Verduno represent the first evidence of a camelin in the Neogene of Italy and they considerably expand the paleobiogeographic range of the Old World early camelins. The presence of a camelid at Verduno reinforces and confirms the importance of the fossiliferous deposits of NW Italy in defining the complex paleobiogeographic patterns of Europe during the Messinian, at the end of the Messinian salinity crisis.     

Records of palaeo‐seawater condition from oxygen‐isotope profiles of early Pleistocene fossil molluscs from the Seoguipo Formation (Korea)

Kim, J.K., Khim, B.‐K., Woo, K.S., & Yoon, S.H. 2009: Records of palaeo‐seawater condition from oxygen‐isotope profiles of early Pleistocene fossil molluscs from the Seoguipo Formation (Korea). Lethaia, Vol. 43, pp. 170–181. High‐resolution δ¹⁸O profiles of early Pleistocene fossil molluscs (Mizuhopecten tokyoensis hokurikuensis) from the shallow‐marine sedimentary Seoguipo Formation (Korea) were found to exhibit distinct annual cycles identified by their unique seasonality (δ¹⁸O amplitude). A direct comparison of fossil δ¹⁸O profiles with that of living shells (Amusium japonicum japonicumi) indicated that the palaeoseawater conditions differed from present‐day seawater. Specifically, the positive δ¹⁸O shift in the isotope profile of the fossil specimens relative to that of the living mollusc shell reflected that palaeotemperature was lower than that today. However, a comparison of the coldest palaeotemperatures (determined from the heaviest δ¹⁸O values of fossil shells), with the present‐day winter temperatures indicates that temperature variation alone cannot account for the entire positive δ¹⁸O offset. These findings indicate that variation in the seawater δ¹⁸O_w values plays a dominant role in the biogenic carbonate precipitation of fossils. Thus, the fossil shells obtained from stratigraphic units suggest different palaeoenvironmental conditions, including lower temperatures and ¹⁸O‐enriched glacial seawater, when compared with the present‐day conditions. The Seoguipo Formation records at least five cycles of relative sea‐level fluctuations, with changes in fossil δ¹⁸O amplitudes separated by sequence boundaries likely to reflect variations of unique palaeoseawater condition, although the oxygen‐isotope profile of fossil molluscs appears to provide a snap‐shot of the palaeoclimatic signature. □Early Pleistocene, mollusc fossils, oxygen isotope, palaeoenvironment, seawater temperature.     

Characterization of a deep-sea microbial mat from an active cold seep at the Milano mud volcano in the Eastern Mediterranean Sea

A white, filamentous microbial mat at the Milano mud volcano in the Eastern Mediterranean Sea was sampled during the Medinaut cruise of the R/V Nadir in 1998. The composition of the mat community was characterized using a combination of phylogenetic and lipid biomarker methods. The mat sample was filtered through 0.2 and 5-microm filters to coarsely separate unicellular and filamentous bacteria. Analyses of 16S rRNA gene sequences amplified from the total community DNA from these fractions showed that similar archaeal populations were present in both fractions. However, the bacterial populations in the fractions differed from one another, and were more diverse than the archaeal ones. Lipid analysis showed that bacteria were the dominant members of the mat microbial community and the relatively low delta(13)C carbon isotope values of bulk bacterial lipids suggested the occurrence of methane- and sulfide-based chemo(auto)trophy. Consistent with this, the bacterial populations in the fractions were related to Alpha-, Gamma- and Epsilonproteobacteria, most of which were chemoautotrophic bacteria that utilize hydrogen sulfide (or reduced sulfur compounds) and/or methane. The most common archaeal 16S rRNA gene sequences were related to those of previously identified Archaea capable of anaerobic methane oxidation. Although the filamentous organisms observed in the mat were not conclusively identified, our results indicated that the Eastern Mediterranean deep-sea microbial mat community might be sustained on a combination of methane- and sulfide-driven chemotrophy.     

Sources of Lipids in Anoxic Lacustrine Sediments Using Stable Carbon Isotopes

The origin of organic matter in recent anoxic sediments of the alpine Lake Bled (NW Slovenia) was determined by analyzing the carbon isotope composition of lipid biomarkers, i.e. alkanes, alcohols, sterols and fatty acids, busing compound specific, carbon isotope analysis. The results indicate that, although biomarker analysis indicated mostly plankton and terrestrial sources for lipids, an important part of sedimentary lipids, especially sterols, are autochthonous, of anaerobic microbial (methanotrophic) origin. Marked differences were observed in δ¹³C values of lipid biomarkers in settling particles collected 2 m above the bottom, and in δ¹³C values determined in surface sediment. These results indicate that even some compounds found in both particulate organic matter and sediments are the same in terms of chemical structures, their sources can be different and thus, isotopic composition should be used as a complementary tool for source identification.     

The archaeal lipidome in estuarine sediment dominated by members of the Miscellaneous Crenarchaeotal Group

The anoxic sediments of the White Oak River estuary comprise a distinctive sulfate–methane transition zone (SMTZ) and natural enrichment of the archaea affiliated with the Miscellaneous Crenarchaeotal Group (MCG). Archaeal biphytanes were generally depleted in ¹³C, with δ¹³C values being less than –35‰, indicative of production by active sedimentary archaeal populations. Multivariate analysis of the downcore distributions of 63 lipid biomarkers identified three major groups of lipids that were enriched in the surface, SMTZ or subsurface depths. Intact polar lipids with phosphatidylglycerol headgroups and glycerol dibiphytanyl glycerol tetraethers containing one, two or three cyclopentane rings were enriched at the base of the SMTZ and likely represent the accumulated product of a small but active ANME‐1 community. The recently identified butanetriol dibiphytanyl glycerol tetraethers (BDGT), which increased relatively to other lipids with depth, were correlated with the relative abundance of MCG in archaeal 16S rRNA clone libraries, and were ¹³C depleted throughout the depth profile, suggesting BDGT lipids as putative biomarkers of an MCG community that may either be autotrophic or feeding on ¹³C‐depleted organic substrates transported by porewater.     

Benthic iron cycling in a high‐oxygen environment: Implications for interpreting the Archean sedimentary iron isotope record

The most notable trend in the sedimentary iron isotope record is a shift at the end of the Archean from highly variable δ⁵⁶Fe values with large negative excursions to less variable δ⁵⁶Fe values with more limited negative values. The mechanistic explanation behind this trend has been extensively debated, with two main competing hypotheses: (i) a shift in marine redox conditions and the transition to quantitative iron oxidation; and (ii) a decrease in the signature of microbial iron reduction in the sedimentary record because of increased bacterial sulfate reduction (BSR). Here, we provide new insights into this debate and attempt to assess these two hypotheses by analyzing the iron isotope composition of siderite concretions from the Carboniferous Mazon Creek fossil site. These concretions precipitated in an environment with water column oxygenation, extensive sediment pile dissimilatory iron reduction (DIR) but limited bacterial sulfate reduction (BSR). Most of the concretions have slightly positive iron isotope values, with a mean of 0.15‰ and limited iron isotope variability compared to the Archean sedimentary record. This limited variability in an environment with high DIR and low BSR suggests that these conditions alone are insufficient to explain Archean iron isotope compositions. Therefore, these results support the idea that the unusually variable and negative iron isotope values in the Archean are due to dissimilatory iron reduction (DIR) coupled with extensive water column iron cycling.     

Lipid and DNA Evidence of Dominance of Planktonic Archaea Preserved in Sediments of the South China Sea: Insight for Application of the TEX86 Proxy in an Unstable Marine Sediment Environment

The marine planktonic archaea are dominated by Thaumarchaeotal Marine Group I, which is characterized by the lipid biomarker thaumarchaeol. The marine benthic archaea are characterized by greater diversity of currently unknown species whose lipid biomarker signatures are uncertain. In this study, a sediment core from the northwestern part of the South China Sea (SCS) (water depth 1474 m) was analyzed using molecular DNA and lipid biomarker approaches. While 16S rRNA gene analysis showed changing archaeal community structures with sediment depth, this change had little impact on the fossil record of archaeal lipids that are characteristic of the planktonic community. As a result, the fossil archaeal lipids recorded paleo sea surface temperature of the SCS since the last glacial maxima by the TEX₈₆ proxy, which agreed generally with the winter temperature recorded by planktonic foraminiferas collected from the same area of the SCS that hosted mass-transported deposits. This suggests that this deep water deposit may have partially preserved paleoclimate record reflecting seasonal temperature variation in a near shore setting, which is in contrast to annual sea surface temperature or sub sea surface temperature variation recorded by TEX₈₆ in the open ocean.     

Acid treatment effects on the stable isotopic signatures of fossils

Abstract: Prior to geochemical analyses, fossil bones and teeth are often extracted from any surrounding lithified sediments using chemical techniques such as immersion in acid. As stable isotope analysis becomes more commonplace in palaeoecological investigations, it is important to consider what effects these chemical preparation techniques may have on any subsequent isotopic data and to constrain these effects as quantitatively as possible. This study aims to elucidate these effects, as it is vital that variability in a data set should not be introduced as a result of protocols used during sample preparation; in addition, it defines the most effective and viable method of carbonate removal for processing bulk fossil samples without causing alteration of their stable isotopic signatures. Various strengths of two weak acids commonly used during palaeontological preparation were tested to evaluate their effects on the δ¹⁵N and δ¹³C_org isotopic signatures of the vertebrae of a large Eocene fossil fish. Changes in the isotopic values occurred over time regardless of which acid was used, each causing a variable response in both δ¹⁵N and δ¹³C_org isotopic values. Without careful monitoring of the acidification process in a controlled environment, any resulting data could therefore confound interpretation. Based on these experiments, it is recommended that 2 m acetic acid be used for the pretreatment of fossils prior to the acquisition of N and C isotope data where carbonate removal is necessary.     

Stable carbon isotope variability associated with taxonomic composition of lotic benthic algae

We examined the relationship between the δ¹³C and taxonomic composition of benthic algae collected from a riffle (fast current habitat) of a non‐shaded mountain stream, which is a tributary of the Kiso River, Japan. The benthic algal δ¹³C ranged from ?20.6 to ?14.2‰ and tended to be ¹³C‐depleted with increasing relative abundance of upright filamentous cyanobacteria and ¹³C‐enriched with increasing relative abundance of prostrate filamentous cyanobacteria. Using isotopic mass balance equations, the relative abundance of the dominant taxa, upright and prostrate filamentous cyanobacteria, small diatoms and others, explained 74% of δ¹³C variability. This study shows a case where the difference in taxonomic composition is a possible source of the isotopic variability of benthic algae, which is a mixture of taxa with distinct isotopic signatures.     

Technical Note: Calcium and carbon stable isotope ratios as paleodietary indicators

Calcium stable isotope ratios are hypothesized to vary as a function of trophic level. This premise raises the possibility of using calcium stable isotope ratios to study the dietary behaviors of fossil taxa and to test competing hypotheses on the adaptive origins of euprimates. To explore this concept, we measured the stable isotope composition of contemporary mammals in northern Borneo and northwestern Costa Rica, two communities with functional or phylogenetic relevance to primate origins. We found that bone collagen δ¹³C and δ¹⁵N values could differentiate trophic levels in each assemblage, a result that justifies the use of these systems to test the predicted inverse relationship between bioapatite δ¹³C and δ⁴⁴Ca values. As expected, taxonomic carnivores (felids) showed a combination of high δ¹³C and low δ⁴⁴Ca values; however, the δ⁴⁴Ca values of other faunivores were indistinguishable from those of primary consumers. We suggest that the trophic insensitivity of most bioapatite δ⁴⁴Ca values is attributable to the negligible calcium content of arthropod prey. Although the present results are inconclusive, the tandem analysis of δ⁴⁴Ca and δ¹³C values in fossils continues to hold promise for informing paleodietary studies and we highlight this potential by drawing attention to the stable isotope composition of the Early Eocene primate Cantius. Am J Phys Anthropol 154:633–643, 2014. © 2014 Wiley Periodicals, Inc.     

Biosignatures in chimney structures and sediment from the Loki’s Castle low-temperature hydrothermal vent field at the Arctic Mid-Ocean Ridge

We investigated microbial life preserved in a hydrothermally inactive silica–barite chimney in comparison with an active barite chimney and sediment from the Loki’s Castle low-temperature venting area at the Arctic Mid-Ocean Ridge (AMOR) using lipid biomarkers. Carbon and sulfur isotopes were used to constrain possible metabolic pathways. Multiple sulfur (δ³⁴S, ?³³S) isotopes on barite over a cross section of the extinct chimney range between 21.1 and 22.5 ‰ in δ³⁴S, and between 0.020 and 0.034 ‰ in Δ³³S, indicating direct precipitation from seawater. Biomarker distributions within two discrete zones of this silica–barite chimney indicate a considerable difference in abundance and diversity of microorganisms from the chimney exterior to the interior. Lipids in the active and inactive chimney barite and sediment were dominated by a range of ¹³C-depleted unsaturated and branched fatty acids with δ¹³C values between ?39.7 and ?26.7 ‰, indicating the presence of sulfur-oxidizing and sulfate-reducing bacteria. The majority of lipids (99.5 %) in the extinct chimney interior that experienced high temperatures were of archaeal origin. Unusual glycerol monoalkyl glycerol tetraethers (GMGT) with 0–4 rings were the dominant compounds suggesting the presence of mainly (hyper-) thermophilic archaea. Isoprenoid hydrocarbons with δ¹³C values as low as ?46 ‰ also indicated the presence of methanogens and possibly methanotrophs.     

Late Miocene biota from the Abad Member of the Carboneras-Nijar Basin (Spain,Andalusia): A bathyal fossil assemblage pre-dating the Messinian salinity crisis

Marly sediments of the early Messinian Abad Member of the Turre Formation from the northeastern sector of the Carboneras-Nijar Basin (southern Spain) have yielded a rich fossil assemblage, of which 60 taxa are documented herein. Besides nannoflora and microfauna, this assemblage includes the first autochthonous macrofauna described from the Abad Member. Based on the calcareous nannofossil assemblage, in particular the occurrence of the zonal index taxon Amaurolithus primus, the sediments are assigned to the Mediterranean calcareous nannofossil zone CNM17, corresponding to the latest Tortonian to earliest Messinian interval. This matches the age range generally reported for the Abad Member. Palaeoecological evidence from calcareous nannofossils (20 autochthonous taxa), planktic and benthic foraminifera (12 taxa), Porifera (3 taxa), Octocorallia (Keratoisis), Serpulidae (4 taxa), Bivalvia (5 taxa), Gastropoda (2 taxa), Brachiopoda (7 taxa), Cirripedia (Faxelepas) and Vertebrata (5 taxa) indicates an upper bathyal environment with an influx of neritic elements for the Abad Member near Carboneras. Additionally, several faunal components may represent allochthonous/parautochthonous elements from adjacent habitats, which were transported into the deep marine setting by turbiditic mass flows. Although similarities exist, the fossil assemblage from the marls is compositionally significantly different from the biota previously documented from a nearby exposed olistostrome, the ‘red breccia’. Similar fossil assemblages from the Mediterranean have so far mainly been reported from the Pliocene-Pleistocene of southern Italy and Greece. The Carboneras fauna thus adds to our knowledge of the development of these habitats and their biota prior to the Messinian salinity crisis. Beyond the novel palaeoenvironmental data, the range of the dyscoliid brachiopod Ceramisia meneghiniana, previously known only from the Pliocene of Italy, is extended to the Miocene of Spain. The cirripede crustacean Pycnolepas paronai De Alessandri, 1895 is transferred to the hitherto monospecific genus Faxelepas Gale, 2015, whereby the range of the latter (previously Maastrichtian to Danian) is extended to the late Miocene.     

Biosignatures present in a hydrothermal massive sulfide from the Mid-Atlantic Ridge

Mid‐ocean spreading and accompanying hydrothermal activities result in huge areas with exposure of minerals rich in reduced chemicals – basaltic and peridotitic rocks as well as metal sulfide precipitates – to the oxygenated seawater. Oxidation of Fe and S present in these rocks provides an extensive long‐term source of energy to lithotrophs. Investigation of lipid biomarkers and their carbon isotope ratios from a massive iron sulfide of an inactive sulfide mound or inactive chimney sampled at the western flank of the Turtle‐Pits hydrothermal field (Mid‐Atlantic Ridge, 5°S) revealed a unique lipid distribution. The bacterial fauna appears to be dominated by chemolithotrophs with a distinct lipid composition mainly comprising of iso‐branched fatty acids and nonisoprenoidal dialkyl glycerol diethers partially including the very rare macrocyclic cores with 30–35 carbon atoms (including 13,16‐dimethyloctacosane and 5,13,16‐trimethyloctacosane). The Bacteria are accompanied by most likely hydrogen/CO₂‐dependent methanogenic Archaea (e.g. Methanococcus) as well as other Archaea with a different life style (e.g. Ferroplasma). Alike some of the bacterial lipids the archaeal lipids predominantly consist of macrocyclic diethers including one C₄₀ and one C₄₁ isoprenoid. Structural homologues of the latter are so far only reported from a methanogenic archaeum and a Pleistocene sulfur deposit. Compound‐specific analyses of the stable isotope ratios revealed δ¹³C values for the majority of bacterial and archaeal lipid components of about 0‰ (vs. VPDB), indicative for chemolithoautotrophically fixed carbon which is, for distinct pathways, accompanied by only negligible fractionations. However, the presence of methanogenic Archaea is indicated by ¹³C‐depleted isoprenoidal lipids (δ¹³C ~ –50‰) characteristic for certain CO₂‐reducing methanogens synthesizing lipids via acetyl CoA.     

Stable carbon isotope composition of bone hydroxylapatite: significance in paleodietary analysis

The stable carbon isotope composition of the structural carbonate derived from animal bone hydroxylapatite (δ¹³C_B-HA) could record an animal’s diet. These records provide critical evidence for different paleontological disciplines, e.g., paleodiet analyses, and paleoclimate reconstructions. Compared to those of other body tissues, such as bone collagen or teeth enamel hydroxylapatite, δ¹³C_B-HA values record information on the whole diet of an animal in its last years. δ¹³C_B-HA can be applied to fossil animals of various body sizes. The δ¹³C analytical instruments available only require that prepared bone samples be approximately 2–5 mg for precise measurement, allowing δ¹³C_B-HA analysis to be feasible on most vertebrate fossils without destructive sampling, especially on small mammals or birds whose teeth are not large enough for sampling or are lost. Moreover, δ¹³C_B-HA can be used from different times or under less than ideal burial environments. For fossils dating back to Devonian or buried in hot and humid regions, dietary information has been completely lost in bone collagen during post-depositional processes but still remained in the δ¹³C_B-HA values because hydroxylapatite is less influenced by diagenetic effects after deposition. In addition, systematic methods such as X-ray diffraction and Fourier transform infrared spectroscopy have been developed to qualitatively or semiquantitatively assess the influence of diagenesis on bone hydroxylapatite to ensure the credibility of the δ¹³C_B-HA values. With the above merits, δ¹³C_B-HA analysis is therefore becoming an increasingly important method in paleodiet-related research. Currently, applications of the δ¹³C_B-HA method on fossil animals are primarily focused on two aspects, namely, paleodietary reconstruction of fossil animals with uncertain diets and paleoenvironmental reconstruction based on the δ¹³C_B-HA values of fossil herbivores. The published researches, combined with our new results from early birds, demonstrate the considerable significance of the δ¹³C_B-HA method in paleontological and paleoenvironmental research. Notably, the δ¹³C_B-HA-based paleodietary analysis of early vertebrates, especially the large number of small birds or mammals discovered in the past decades would be an important work in the near future.     

The Primary Lower Gypsum in the Mediterranean: A new facies interpretation for the first stage of the Messinian salinity crisis

The detailed facies and physical stratigraphic analysis of the Primary Lower Gypsum in the Mediterranean indicates a surprising bed-by-bed correlation at basin-scale (Spain, Italy, Hellenic arc and Cyprus arc), that is tuned to the orbital calibration for the first stage of the Messinian salinity crisis from 5.96 to 5.61 Ma ago. A total of 16, precessionally-controlled, gypsum cycles were deposited rapidly in less than 350 ka, forming sequences up to 300 m thick. The lack of subaerial exposure features and the common facies associations and stacking pattern for sections located thousands of kilometers apart in different geological settings indicates a modest depositional depth, not extremely shallow. Selenite deposition occurred only at the bottom of restricted marginal basins less than 200 m deep, while no gypsum could precipitate in the deeper euxinic Mediterranean portions where only thin and barren shale/dolostone couplets formed. The lowermost selenite beds pass laterally to dolomite-rich limestones interbedded with barren euxinic shales in poorly oxygenated settings, indicating that the gypsum sedimentation was diachronous and did not necessarily mark the onset on the Messinian salinity crisis.Evaporite facies sequences (EF1 to 8) within individual gypsum beds show small-scale, subaqueous sedimentary cycles that mimic regressive-transgressive cycles: a) initial evaporite precipitation at relatively low supersaturation produced the massive selenite (facies EF3) in a relatively deep setting; b) continuous evaporation and drawdown by oscillating brine level formed the banded selenite (EF4) at the aridity acme of the precessionally-controlled cycle; c) general progressive brine level rise with strong brine flow led to the formation of large selenite supercones branching laterally (supercones in Spain and branching selenite, EF5, in the rest of the Mediterranean); and d) flooding by undersaturated continental water terminated gypsum precipitation with the deposition of argillaceous sediments (EF1, Northern Apennines), and/or limestone (EF2, Sicily and Spain) during the humid phase in the precession climate cycle.The stacking pattern and selenite facies associations suggest an overall shallowing-upward trend with a basin-wide hydrologic change starting from the 6th cycle (5.84 Ma), which is marked by the appearance of the branching selenite facies (supercones) in Spain and indicates that the brines became current-dominated. The Sr-isotope stratigraphy suggests that in the Northern Apennines the brines were strongly modified by continental waters (⁸⁷Sr/⁸⁶Sr = 0.708893 to 0.708998), and received direct pulses of Atlantic seawater (⁸⁷Sr/⁸⁶Sr = 0.70900 to 0.709024) only in the upper part of the section. In areas away from the mainland, such as Sicily, the continental input was by far less important.     

Integrated stratigraphy and paleoceanography of the Messinian (latest Miocene) across the North Atlantic Ocean

The Messinian was a time of major climatic and paleoceanographic change during the late Cenozoic. It is well known around the Mediterranean region because of the giant anhydrite/gypsum sequence and the suggested desiccation of the Mediterranean Sea. However, this interval is less constrained outside the Mediterranean region, where several paleoceanographic changes could have taken place because of the desiccation. Hence, we present an integrated stratigraphic framework for future Messinian paleoceanographic studies, determination of the effect of the Mediterranean desiccation on deep-water paleoceanography, and comparison of intra-Mediterranean paleoceanographic changes with those in the open oceans during the Messinian Stage.Four DSDP/ODP Holes (552A, 646B, 608, and 547A) from the North Atlantic Ocean and one land borehole from Morocco have been studied to integrate bio-, magneto-, and stable isotope Messinian stratigraphy with high resolution sampling. Our results produce the best assessment of the Tortonian/Messinian boundaries in all holes because they do not rely on any one signal.In paleomagnetic Subchronozone CSAn.lr in the Salé borehole and DSDP Site 609, a S/D coiling direction change of Neogloboquadrina pachyderma/acostaensis appears to indicate PMOW entering the northeastern Atlantic Ocean, at least reaching 50°N. Diachrony and synchrony of some important Messinian planktic foraminifera from these Atlantic DSDP/ODP holes and the Salé borehole, such as the LO of Gq. dehiscens, the LO of Gt. lenguaensis, the FO and LO of Gt. conomiozea, the FO of Gt. margaritae s.s., the FO of Gt. puncticulata, and the FO of Gt. crassaformis are discussed for understanding some of the paleoceanographic changes. This integrated stratigraphie framework presented here allows much better North Atlantic correlations at this critical point in Messinian geologic history.