The response of water column and sedimentary environments to the advent of the Messinian salinity crisis: insights from an onshore deep-water section (Govone, NW Italy)

Abstract

During Messinian time, the Mediterranean underwent hydrological modifications culminating 5.97 Ma ago with the Messinian salinity crisis (MSC). Evaporite deposition and alleged annihilation of most marine eukaryotes were taken as evidence of the establishment of basin-wide hypersalinity followed by desiccation. However, the palaeoenvironmental conditions during the MSC are still a matter of debate, chiefly because most of its sedimentary record is buried below the abyssal plains of the present-day Mediterranean Sea. To shed light on environmental change at the advent and during the early phase of the MSC, we investigated the Govone section from the Piedmont Basin (NW Italy) using a multidisciplinary approach (organic geochemical, petrographic, and carbon and oxygen stable isotope analyses). The Govone section archives the onset of the crisis in a succession of organic-rich shales and dolomite-rich marls. The MSC part of the succession represents the deep-water equivalent of sulphate evaporites deposited at the basin margins during the first phase of the crisis. Our study reveals that the onset of the MSC was marked by the intensification of water-column stratification, rather than the establishment of widespread hypersaline conditions. A chemocline divided the water column into an oxygen-depleted, denser and more saline bottom layer and an oxygenated, upper seawater layer influenced by freshwater inflow. Vertical oscillations of the chemocline controlled the stratigraphic architecture of the sediments pertaining to the first stage of the MSC. Accordingly, temporal and spatial changes of water masses with different redox chemistries must be considered when interpreting the MSC event.

Sedimentology and depositional environment of the Late Eocene marine siliciclastic to evaporite transition in the Sivas Basin (Turkey)

“…By analogy with dolomitic muds reported during the Messinian salinity crisis, part of the dolomite content in this facies may be of diagenetic origin and result from sulphate-reduction processes in deepwater anoxic condition (e.g. de Lange et al, 2010;Sabino et al, 2020). Part of the gypsum probably also grown displacively in the mud through saline fluid-flow during burial and/or exhumation (e.g.…”

“…Despite increasing aridity, continental runoffs carrying very fine-grained material were maintained in FA3 and probably contributed to intensify the water-column stratification and related bottom anoxic-conditions (e.g. Sabino et al, 2020).…”

“…Such interval probably records a coeval period during which resedimentation events were highly reduced and the basin became again starved with anoxic bottom water conditions, possibly because of a freshening event (increasing marine or meteoric water inputs; e.g. Sabino et al, 2020;Dela Pierre et al, 2014).…”

Architecture and sequence stratigraphy of the Upper Coralline Limestone formation, Malta—Implications for Eastern Mediterranean restriction prior to the Messinian Salinity Crisis

“…Baldassini and Di Stefano ( 2017 ) inferred that the age of the base of the UCL is at ca 8 Ma and the top of it lies within the MNN11 nanofossil zone. Dolomitisation appears to have occurred wherever such interaction took place (de Lange & Krijgsman, 2010 ; Manzi et al, 2011 ; Sabino et al, 2020 ). This relationship appears to be the result of vigorous reflux circulation with extensive microbial activity.…”

Supplemental Material: Carbon isotope excursions during the late Miocene recorded by lipids of marine Thaumarchaeota, Piedmont Basin, Mediterranean Sea

“…of 57 total lipid extracts (TLE) from a sub-set of samples from Natalicchio et al (2019; Pollenzo: 43 samples) and Sabino et al (2021; Govone: 14 samples) was used to obtain isoprenoid and branched glycerol dialkyl glycerol tetraethers (iGDGTs and bGDGTs; Fig. S2) according to the method reported in Sabino et al (2021). Briefly, after dissolution in n-hexane, an internal standard (C 46 GDGT; 12 mg/L) was added and 10 µL for each sample were analyzed using a Varian MS Workstation 6.91 HPLC system coupled to a Varian 1200L triple quadrupole mass spectrometer.…”