Are fluid inclusions in gypsum reliable paleoenvironmental indicators? An assessment of the evidence from the Messinian evaporites

The paleosalinity of water from which the gypsum precipitated during the Messinian salinity crisis is a controversial issue. Recent microthermometry studies on primary fluid inclusions in gypsum provided very low salinity values not compatible with precipitation from seawater, and suggested strong mixing between seawater and nonmarine waters enriched in calcium sulfate. We applied a new microthermometric protocol on gypsum crystals from nine Mediterranean sections that were experimentally stretched to measure a larger population of fluid inclusions. The results show salinities ranging from 9 to 238 wt‰ NaCl equivalent, largely falling within the evaporation path of normal seawater. The data from previous studies were obtained mostly from those fluid inclusions capable of nucleating a stable bubble after a weak stretching, which probably correspond to those having a lower salinity acquired through post-depositional crack-and-seal processes. Our data suggest instead that the primary gypsum precipitated from a marine brine, later modified by post-trapping processes during tectonics and exhumation.

Supplemental Material: Are fluid inclusions in gypsum reliable paleoenvironmental indicators? An assessment of the evidence from the Messinian evaporites

Additional information on the samples (Sr data, geographic and geological settings), a detailed description of the methods, and all microthermometric data obtained in this work.<br>

Supplemental Material: Are fluid inclusions in gypsum reliable paleoenvironmental indicators? An assessment of the evidence from the Messinian evaporites

Additional information on the samples (Sr data, geographic and geological settings), a detailed description of the methods, and all microthermometric data obtained in this work.<br>

On the lack of widespread bottom simulating reflectors in the Mediterranean Basin

&lt;p&gt;In the Mediterranean Basin, gas hydrate bottom simulating reflectors (BSR) are absent, with very few and spatially limited exceptions occurring in Eastern Mediterranean mud volcanoes and in the Nile deep sea fan. This is in spite of widespread occurrence of hydrocarbon gases in the subsurface, mainly biogenic methane, from a wide range of stratigraphic intervals.&lt;br&gt;In this study we model the methane hydrate stability field using all available information on DSDP and ODP boreholes in the Western Mediterranean and in the Levant Basin, including the downhole changes of pore water salinity. The models take into account the consequent pore water density changes and use known estimates of geothermal gradient. None of the drilled sites were located on seismic profiles in which a BSR is present.&lt;br&gt;The modelled base of the stability field of methane hydrates is located variably within, below, or even above the drilled sedimentary section (the latter case implies that it is located in the water column). We discuss the results in terms of geodynamic environments, areal distribution of Messinian evaporites, upward ion diffusion from Messinian evaporites, organic carbon content, and the peculiar thermal structure of the Mediterranean water column. &lt;br&gt;We conclude that the cumulative effects of geological and geochemical environments make the Mediterranean Basin a region that is unfavorable to the existence of BSRs in the seismic record, and most likely to the existence of natural gas hydrates below the seabed.&lt;br&gt;&lt;br&gt;&lt;/p&gt;

The genesis of a giant mud canopy by catastrophic failure of a thick evaporite sealing layer

Three-dimensional seismic imaging and well calibration reveal a large allochthonous mud edifice that is composed of several mud extrusions and covers an area &gt;740 km2 on the outer shelf slope of the Nile Delta. The allochthonous material was sourced from beneath the ∼1-km-thick Messinian evaporites in the Eastern Mediterranean and extruded synchronously as eight large mud volcanoes directly on top of the Messinian evaporites in a catastrophic remobilization event at the end of the Messinian salinity crisis. These large extrusive flows coalesced to form a single edifice with an exceptional volume of ∼292 km3 that is connected to eight widely spaced conduits. We argue that this large mud body represents a new morphological type and scale of mud extrusion. We propose that mud extrusions that coalesce on a surface forming a multi-conduit-fed edifice be referred to as mud canopies, by analogy with salt canopies, with implications for basin reconstruction, paleo–overpressure release events, and fluid migration.

Seismic markers of the Messinian salinity crisis in the deep Ionian Basin

&lt;p&gt;We conduct the seismic signal analysis on vintage and recently collected multichannel seismic reflection profiles from the Ionian Basin to characterize the deep basin Messinian evaporites. These evaporites were deposited in deep and marginal Mediterranean sedimentary basins as a consequence of the &amp;#8220;salinity crisis&amp;#8221; between 5.97 and 5.33 Ma, a basin&amp;#8208;wide oceanographic and ecological crisis whose origin remains poorly understood. The seismic markers of the Messinian evaporites in the deep Mediterranean basins can be divided in two end&amp;#8208;members, one of which is the typical &amp;#8220;trilogy&amp;#8221; of gypsum and clastics (Lower Unit &amp;#8211; LU), halite (Mobile Unit &amp;#8211; MU) and upper anhydrite and marl layers (Upper Unit &amp;#8211; UU) traced in the Western Mediterranean Basins. The other end&amp;#8208;member is a single MU unit subdivided in seven sub&amp;#8208;units by clastic interlayers located in the Levant Basin. The causes of these different seismic expressions of the Messinian salinity crisis (MSC) appear to be related to a morphological separation between the two basins by the structural regional sill of the Sicily Channel. With the aid of velocity analyses and seismic imaging via prestack migration in time and depth domains, we define for the first time the seismic signature of the Messinian evaporites in the deep Ionian Basin, which differs from the known end&amp;#8208;members. In addition, we identify different evaporitic depositional settings suggesting a laterally discontinuous deposition. With the information gathered we quantify the volume of evaporitic deposits in the deep Ionian Basin as 500,000 km3 &amp;#197;} 10%. This figure allows us to speculate that the total volume of salts in the Mediterranean basin is larger than commonly assumed. Different depositional units in the Ionian Basin suggest that during the MSC it was separated from the Western Mediterranean by physical thresholds, from the Po Plain/Northern Adriatic Basin, and the Levant Basin, likely reflecting different hydrological and climatic conditions. Finally, the evidence of erosional surfaces and V&amp;#8208;shaped valleys at the top of the MSC unit, together with sharp evaporites pinch out on evaporite&amp;#8208;free pre&amp;#8208; Messinian structural highs, suggest an extreme Messinian Stage 3 base level draw down in the Ionian Basin. Such evidence should be carefully evaluated in the light of Messinian and post&amp;#8208;Messinian vertical crustal movements in the area. The results of this study demonstrates the importance of extracting from seismic data the Messinian paleotopography, the paleomorphology and the detailed stratal architecture in the in order to advance in the understanding of the deep basins Messinian depositional environments.&lt;/p&gt;

The Messinian Salinity Crisis (MSC) deposits in the Balearic Promontory: An undeformed analog of the MSC Sicilian basins??

&lt;p&gt;The Messinian Salinity Crisis (MSC) is a prominent and still misunderstood event that influenced the Mediterranean basin in the late Miocene leaving behind a Salt Giant (SG) widespread all over the Mediterranean basin. More than 90% of the Messinian Evaporitic deposits are located offshore with reduced access via boreholes, and thus has been studied mainly by seismic imaging. Onshore-Offshore should be considered a key for a better understanding and answering some of the controversies on the MSC.&lt;/p&gt;&lt;p&gt;The Balearic Promontory (BP) contains a series of small perched basins presently lying at different water depths, stepped from the present-day coastline down to the deep basin. These topographic lows trapped sedimentary series up to 500m thick, interpreted as MSC in age.&lt;br&gt;The reduced tectonic movements in the BP since the late Miocene (Messinian) till recent days, favored the conservation of the MSC records in this area. Moreover, recent studies revealed the presence of a Salt layer in the Central Mallorca Depression (CMD).&lt;/p&gt;&lt;p&gt;Considering: 1- the bathymetry of the BP, classified as an intermediate perched basin; 2- the distribution of the MSC records accumulated in a series of sub-basins more or less connected between each other; 3- the geometries of the evaporitic formations, provided by how these records appear on the seismic data; this might recall similarities between the BP records (especially the ones in the CMD) and the MSC reference records outcropping in Sicily (especially in the Caltanissetta Basin).&lt;/p&gt;&lt;p&gt;We perform seismic interpretation of a wide seismic reflection dataset in the study area with the aim of refining the mapping of the Messinian evaporites covering the study area. Four seismic units were identified in the BP based on their seismic facies and their seismo-stratigraphic position. We try to match up these units to the consensus Messinian 3-stages chrono-stratigraphic model proposed during the CIESM in 2008.&lt;br&gt;We also attempt to find similarities in geometries, facies and distribution of the MSC between the sub-basins of the BP and those described in the Sicilian sub-basins.&lt;/p&gt;