A new facies model for the Upper Gypsum of Sicily (Italy): chronological and palaeoenvironmental constraints for the Messinian salinity crisis in the Mediterranean

Abstract

The Upper Gypsum unit of the Caltanissetta Basin (Sicily) records the last phase of the Messinian salinity crisis comprising the so-called 'Lago Mare' event. A new facies analysis study recognizes nine to ten depositional cycles consisting of seven rhythmically interbedded primary gypsum bodies, and two to three sandstone bodies separated by marly terrigenous horizons showing laterally persistent vertical organization. A basal thin gypsum bed is overlain by a cluster of five thicker gypsum bodies. A marly interval containing two distinct sandstone horizons separates this cluster from the overlying uppermost (seventh) gypsum body. The terrigenous Arenazzolo Formation, in turn followed by the lower Pliocene Trubi Formation, is considered here to form the uppermost part of the Upper Gypsum unit. The rhythmic alternation in the sandy marls and gypsum/sandstone bodies records the response of sediments from shelfal to deltaic systems to precession-driven arid-wet climate fluctuations causing cyclical changes of both base-level and water concentration. During wet climate phases (at insolation maxima) marl and sandstone were deposited in a hypohaline environment as suggested by: (i) the typical Lago Mare faunal assemblage and (ii) the negative d 18 O values. During arid phases (at insolation minima) the reduced meteoric supply, recorded by higher d 18 O values in the carbonate, caused the development of a negative hydrological budget leading to evaporite precipitation. At a basinal scale the Upper Gypsum unit unconformably overlies a mainly clastic evaporite unit containing carbonate breccia (the so-called 'Calcare di Base') and/or clastic gypsum. Towards the basin centres, where the basal contact becomes conformable, a primary gypsum cumulate horizon is present. This layer is interpreted as a possible lateral equivalent of the Halite unit present only in the deepest depocentres. Based on astronomical calibration of the depositional cycles, the Upper Gypsum unit, including the Arenazzolo Formation, spans the interval between 5AE33 and 5AE53 Ma. This new age calibration allows the deposition of the Halite unit to be dated between 5AE6 Ma (top of the Lower Evaporites) and 5AE55 Ma (base of the Upper Evaporites) corresponding to isotopic stages TG12 and/or TG14.

High-Frequency Cyclicity In the Mediterranean Messinian Evaporites: Evidence For Solar-Lunar Climate Forcing

“…Its sedimentary record consists of both clastic deposits, derived from the erosion and resedimentation of stage 1 PLG evaporites (RLG, Resedimented Lower Gypsum; Roveri et al 2008), and of primary evaporites; the latter consisting of thick and extensive primary halite and gypsum cumulate bodies that were mainly deposited in the deeper settings. This stage comprises the TG14 and TG12 glacials and was triggered by a combination of pan-Mediterranean tectonic and climatic factors that caused a significant reduction of the Atlantic connections and the likely blockage of the Mediterranean outflow (Mejier and Krijgsman 2005 Precipitation of UG selenite occurred from a large, residual water body only partially connected with the Atlantic, as suggested by the depleted strontium isotope ratio with respect to the coeval oceanic waters (Flecker and Ellam 2006;Manzi et al 2009). This stage was followed by the return of fully marine conditions in the Mediterranean (Hsü et al 1978;Van Couvering et al 2000).…”

“…(CIESM 2008). The discussion of alternative interpretations supported by other research teams is beyond the aim of this paper; here we simply adopt the stratigraphic framework proposed by CIESM (2008) and its most recent refinements (Roveri et al 2008;Manzi et al 2009;Lugli et al 2010;Manzi et al 2011) that subdivide the Messinian salinity crisis into three main evolutionary stages, each one characterized by peculiar evaporite deposits recording different hydrological and paleoceanographic conditions.…”

“…A consensus has been reached in considering that evaporite deposition was controlled by the variation of Earth's orbital parameters and particularly by precession that drove an , 20 kyr alternation of drier vs. more humid conditions ( Fig. 2; Krijgsman et al 1999;van der Laan et al 2006;CIESM 2008;Roveri et al 2008;Manzi et al 2009;Lugli et al 2010). These mechanisms explain the decameter-scale lithological cyclicity given by the rhythmic alternation of evaporitic and fine-grained terrigenous bodies.…”

“…Deposited during Stage 2, the Resedimented Lower Gypsum unit (RLG) is a complex unit including clastic gypsum (CG), halite, and gypsum primary cumulate deposits (HG); and clastic carbonates derived from evaporitic and microbial limestone (LB, limestone breccia; Calcare di base type 3, sensu Manzi et al 2011). Finally, during stage 3 a further primary gypsum unit was deposited (UG, Upper Gypsum; see Manzi et al 2009). The carbonate unit of the Terminal Carbonate Complex (TCC; Bourillot et al 2009;Roveri et al 2009) are also included: mfs (maximum flooding surface); sb (sequence boundary); 1-4 (transgressive-regressive large-scale sequences, , 100 kyr).…”

Depositional stages of the Eğribucak inner basin (terrestrial to marine evaporite and carbonate) from the Sivas Basin (Central Anatolia, Turkey)

“…Interpretation: Carbonate interlaminae/bands show that evaporite conditions are cut by environmental humidity from time to time, and this reflects the periods of seasonal fluctuations (arid-wet) (Manzi et al, 2009). The sequence with mudstone and carbonate laminae with algal-derived organic contribution of the facies shows that intratidal and intertidal environments were temporarily developed, probably close to evaporite plain precipitated gypsum laminae with the pervasive dolomitization of the carbonate laminae (Warren and Kendal, 1985;Hanford, 1991;Kendal and Harwood, 1996).…”