The onset of the Messinian Salinity Crisis in the central Mediterranean recorded by pre‐salt carbonate/evaporite deposition

Abstract

The Calcare di Base is a carbonate/evaporitic unit formed before the deposition of the massive halite bodies in the main depozones of the Mediterranean region, and has been at the centre of a fiery debate between different 'schools of thought' about its genesis, environmental conditions and timing of deposition. It crops out extensively in Southern Italy, across Neogene basins located on the Tyrrhenian and Ionian margins of northern Calabria, where it was studied through a detailed facies and stratigraphic analysis that revealed the presence of a continental/shallow-marine to slope system, active during the onset of the Messinian Salinity Crisis. During the Calcare di Base deposition, an arid climate regime with intermittent humid phases occurred with a precession forced cyclicity, facing an overall generally cold climatic period. During arid periods, stressed environmental conditions permitted the establishment of widespread microbial-mediated carbonate production, frequently associated with evaporitic (gypsum-dominated) deposition, along a sabkha-type environment with extensive salinas and hypersaline coastal lagoons grading seaward into a carbonate/evaporite shallow-marine shelf. This is testified to by microbial boundstones and dissolution breccias commonly associated with nodular gypsum and arenites affected by desiccation, typically forming metre-scale shallowing-upward peritidal cycles. Seaward, gravity flow deposits are interpreted as re-sedimented shelf limestones, defining a slope apron. Mixed carbonate/evaporite megabreccias and disorganized floatbreccias were deposited along the upper slope, whereas soft deformation with slides, slumps and channelized turbidites further developed along the lower slope to basin. During the humid climate episodes, that affected the platform system with a precession-forced cyclicity, the carbonate production was reduced together with the evaporitic deposition, leading to the widespread deposition of marlstones and fine to coarse siliciclastic deposits.

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

“…Early interpretation, based on sedimentary components and modern coralline algae, described the deposition of the UCL as a shallowing upward sequence (Pedley, 1978 ; Table 1 ). The UCL does not exhibit any of the extreme stress features reported in the Calcare di Base (Borrelli et al, 2020 ), which marks the onset of the MSC in Sicily. Thus, it probably represents more moderate temperature/salinity conditions.…”

A bio-chronostratigraphic study of the upper Miocene from the northern Caltanissetta Basin, Sicily (core 3AGN2S04). Implications for dating the Messinian Salinity Crisis onset

“…The Tripoli Formation is followed by the "Calcare di Base" (CdB) member. Most authors (Caruso et al, 2015;Perri et al, 2017;Gindre-Chanu et al, 2020;Borrelli et al, 2020;Tzevahirtzian et al, 2022) argue that the CdB consists of a 'microbial boundstone' commonly observed as 'autobrecciated' due to the interplay of diagenesis and brecciation processes and formed in situ. The CdB corresponds to the Lower Evaporites (LE) unit, and therefore marks the MSC onset (i.e.…”

The transition from normal marine to evaporitic conditions recorded in a cold seep environment: The Messinian succession of Northern Italy

“…Some authors argued that these carbonates precipitated during evaporitic and hypersaline conditions as suggested by some positive δ 18 O values and laminated-stromatolitic structures (Ziegenbalg et al, 2012;Birgel et al, 2014), originally interpreted as remains of benthic algae (Vai and Ricci Lucchi, 1977) and later as generated by cyanobacteria consistent with a relatively shallow water depositional environment (Natalicchio et al, 2013). According to Borrelli et al (2021) during the CDB deposition, an arid climate regime alternated with intermittent humid phases and conditioned the establishment of microbial-mediated carbonate production along a sabkha-type environment with extensive hypersaline coastal lagoons. This interpretation is also supported by the recognition that carbonate lamination in CDB is associated with faecal pellets of brine shrimps (Natalicchio et al, 2013), J o u r n a l P r e -p r o o f confirming shallow and hypersaline depositional conditions.…”