Search

The onshore–offshore correlation of sedimentary successions is a common problem in basin analysis, but it becomes critical for the full understanding of the Messinian salinity crisis (MSC), a complex array of palaeoenvironmental events which affected the Mediterranean basin at the end of the Miocene. The outcrop records show that the Messinian stratigraphic architectures may be highly complex as the deposits of the different MSC evolutionary stages can be lithologically similar and separated by erosional surfaces and/or morphostructural highs. The correct definition of the nature and stratigraphic position of Messinian deposits in offshore areas through seismic data may be almost impossible, especially where core data are sparse. To bridge the gap between onshore and offshore records, we have built synthetic seismic sections from well‐constrained outcrop successions. Our results provide useful insights and warnings for the interpretation of offshore data, pointing out that MSC units having different age, nature and depositional settings, may show similar seismic facies and geometries. Conversely, the same deposit may result in different seismic facies, either with parallel and high‐amplitude reflections or even transparent or chaotic due to interference patterns of seismic reflections related to dominant frequency. It follows that a correct interpretation of the nature and age of deep‐seated Messinian deposits can only be obtained through the integration of seismic and core data, and considering the onshore record. The application of our approach to the Balearic Promontory results in an alternative interpretation with respect to previous models. We show that this offshore area has good analogues in the onshore of the Betic Cordillera and includes both shallow and intermediate depth sub‐basins that underwent a strong post‐Messinian subsidence. [ABSTRACT FROM AUTHOR]

The salt giant beneath the deep Mediterranean seafloor is the impressive record of the "Messinian salinity crisis," a dramatic event that occurred about 6 Ma ago following the reduction of the connections with the Atlantic Ocean. According to the shallow-water deep-basin model, developed for these deposits (Hsü and others, 1973a, 1973b, 1978a, 1978b), the Messinian evaporites formed in a deep. but desiccated Mediterranean, while shelves and slopes underwent subaerial erosion due to fluvial rejuvenation triggered by a 1500 m sea level drawdown. Deeply incised Messinian canyons in the continental slopes surrounding the Mediterranean are the main argument supporting this scenario. Using a state of the art model and idealized but realistic numerical simulations, here we demonstrate that the activation of downslope flows of hypersaline, dense waters, in a process similar to present-day "dense shelf water cascading," but much more energetic, may account for both slope erosion and progressive salinity rise leading to the formation of deep-seated supersaturated brines. Our findings support a deep-water deep-basin model (Schmalz, 1969, 1991; De Benedetti, 1976, 1982; Dietz and Woodhouse, 1988), thus implying that evaporite deposition may have occurred in a non-desiccated basin with strongly reduced ocean connections. [ABSTRACT FROM AUTHOR]

We present a basin-wide correlation of the pre-evaporitic succession across the deep Levant basin, based on integrated bio- and cyclostratigraphy. The onset of Messinian salinity crisis (MSC) can be placed in all studied wells where foraminifers suddenly disappear and normal marine calcareous nannofossils are replaced by opportunistic assemblages. These changes mark the base of the Foraminifers Barren Interval (FBI), a 10s-of-m-thick (below seismic resolution), evaporite-free, shale unit that records the entire duration of the first stage. Moving towards the basin margin the FBI is progressively truncated on top by the Messinian erosional surface (MES), a regional-scale discontinuity sealed by a thin clastic evaporite units overlain by thick halite deposits. Our results confirm previous hypothesis suggesting that the crisis started in deep- as well as in shallow-water settings at 5.97 Ma and pointing to a synchronous onset of the MSC but diachronous deposition of evaporites. During stage 1 of the crisis, coeval with gypsum deposition in marginal basins, the salinity in deep basins progressively increased (with possible oxygen reduction) hindering the life of marine organisms. Then, at 5.60 Ma, when salinity in deep basins exceeded halite saturation, massive halite precipitation started, and a nearly 2-km-thick salt sequence accumulated in deep basins within a short period of 60 kyr. At that time (stage 2), sedimentation rate jumped by an order of magnitude reaching a few cm/yr. Similar sedimentation rates are inferred for the Realmonte salt mine (Sicily) and observed in the modern Dead Sea and artificial salinas. • The onset of the Messinian salinity crisis was synchronous at 5.97 Ma. • In the deep Levant basin the onset is marked by the disappearance of marine biota. • Evaporite-free shales barren in foraminifers record stage 1 of the crisis. • The evaporite succession started to accumulate in deep settings only since stage 2. • A regional-scale unconformity marks the base of the evaporites. [ABSTRACT FROM AUTHOR]

Abstract: The importance of the sedimentary record of Messinian events in the Apennines foredeep is due to its geological and structural settings, which allow the reconstruction of the relationships between marginal and basinal settings and provide fundamental insights into some important issues. A geologic–stratigraphic model of the Messinian Apennine foredeep indicating a possible solution for closing the last ‘Messinian gap’ is here presented. Moreover, the establishment of a preliminary high-resolution stratigraphy for the terminal Lago Mare stage allows us to attempt Mediterranean-scale correlations across different structural settings. The Messinian evolution of the Apennine foredeep and some considerations of adjacent areas suggest the great importance of tectonic deformation in controlling Messinian events. The intra-Messinian unconformity is a common feature of the marginal basins of the Mediterranean, and it is associated in many cases to the collapse and resedimentation of primary evaporites. The genesis of such unconformity seems to be strictly related to a general tectonic reorganization of the Mediterranean area. Preliminary observation on the stratigraphy of the Lago Mare stage suggest that the high-frequency lithological cyclicity observed in the non-marine deposits of this stage, as well as the superimposed transgressive trend, are common to many Mediterranean basins. These characteristic features might reflect the interplay between a longer-term tectonic trend and higher-frequency, precession-related, climatic changes; this could represent a fundamental tool for establishing a high-resolution stratigraphic framework of the latest Messinian allowing long-distance correlations between terrestrial and marine ecosystems and hence more accurate palaeoenvironmental studies. [Copyright &y& Elsevier]

Abstract: We present the Messinian evaporite suite (Mediterranean region) and the Solfatara hydrothermal system (Phlegraean Fields volcanic province, Italy), discuss their implications for understanding the origin of sulfates on Mars and show preliminary sets of VNIR laboratory and in situ reflectance spectra of rocks from these geologic systems. The choice was based on a number of evidence relative to Mars: (1) the chemistry of the Martian sulfates, suggesting fluid interactions with possibly alkali-basaltic rocks and/or regolith; (2) close range evidence of sulfates within sedimentary formations on Mars; (3) sulfate spectral signatures associated to large-scale layered patterns interpreted as thick depositional systems on Mars. The Messinian evaporites comprise three units: primary shallow-water sulfates (primary lower gypsum: PLG), shallow- to deep-water mixed sulfates and clastic terrigenous deposits (resedimented lower gypsum: RLG), and shallow-water associations of primary sulfates and clastic fluvio-deltaic deposits (upper evaporites: UE). The onset of the Messinian evaporites records the transition to negative hydrologic budget conditions associated with the Messinian Salinity Crisis, which affected the entire Mediterranean basin and lasted about 640kyr. The Solfatara is a still evolving hydrothermal system that provides epithermal deposits precipitated from the interaction of fluids and trachybasaltic to phonolitic rocks. Thermal waters include alkali-chloride, alkali-carbonate and alkali-sulfate endmembers. The wide spectrum of sedimentary gypsum facies within the Messinian formation includes some of the depositional environments hitherto identified on Mars and others not found on Mars. The PLG unit includes facies associations correlated over long distances, that could be a possible analog of the stratified rock units exposed from Arabia Terra at least as far as Valles Marineris. The facies cycles within the UE unit can be compared to the sequences of strata observed in craters such as Holden and Eberswalden. The UE unit records paleoenvironmental changes which are ultimately controlled by terrestrial climatic variations. They can be considered as a reliable climatic proxy and may be useful for the reconstruction of climatic events on Mars. The intermediate Messinian RLG unit has not, at present, a well-defined depositional counterpart on Mars, although there are some similarities with the northern lowlands and Vastitas Borealis Formation. The dramatic variation of hydrologic budget conditions at the onset of the Messinian evaporites may provide criteria for the interpretation of similar variations on Mars. The volcanic rocks at the Solfatara bear some similarities with the “alkaline magmatic province” observed at the Gusev crater on Mars, and the assemblages of hydrothermal phases resulting from the Solfatara''s parent rocks could be analogues for processes involving Gusev-type rocks. The Messinian sulfates have a prevalent Ca-sulfatic composition and wide textural variability. Preliminary laboratory reflectance spectra of rock samples in the VNIR region reveal the signature of sulfates and mixtures of several Fe-bearing phases. At the Solfatara, in situ reflectance measurements of epithermal minerals close to active fumaroles showed the presence of Fe-bearing sulfates, hematite, Al- and K-sulfates and abundant amorphous fraction. XRD analysis supported this interpretation. The range of depositional facies observed in the Messinian units and the variety of minerals detected in the Solfatara will be useful for the interpretation of close range data of Mars. The spectral characterization at various scales of the Messinian sedimentary facies and the Solfatara hydrothermal minerals will both help in the exploration of Mars from orbit and with close range inspection. [Copyright &y& Elsevier]