IntroductionThe study of the Messinian salinity crisis (MSC) in the Mediterranean has generated a controversy with a long-term discussion on many aspects. One of the problem faced by the scientists is that the interpretation of evaporite sediments can be very complicated. Evaporite sediments are among the most elusive for facies reconstruction and correlation and most data in the literature were not correctly placed in a reliable stratigraphic framework. Some examples of these difficulties are the following: a) deposits traditionally included in the Lower Evaporites are actually clastic sediments that, as we have shown, derive from the dismantlement of autochthonous Lower Evaporites (Manzi et al., 2005; Roveri et al., 2006);b) many of the Lower Evaporites outcrops in Italy are actually large-scale blocks emplaced by extensive mass-waste movements (Roveri et al., 2003; Roveri et al., 2006); some of these chaotic complexes were interpreted as collapse deposits due to halite dissolution (Caruso and Rouchy, 2006);c) some Lower Evaporites outcrops were commonly considered Upper Evaporites and vice-versa;d) laminated clastic sulphate sediments were commonly mistaken for primary cumulate deposits and vice-versa;e) the significance of halite deposition, which actually bears the only unequivocal sign of exposure found within the Messinian evaporites, has been overlooked;f) the Calcare di Base carbonates show commonly evidence of resedimentation;g) the Calcare di Base is never found at the base of the Lower Evaporites primary in situ selenites;h) lateral transitions between carbonate, gypsum or halite primary evaporites cannot be directly observed and must be considered speculation;For these reasons we devoted our efforts to provide a detailed stratigraphic and facies analyses of all the Messinian evaporites and criteria for distinguishing the Lower from the Upper Evaporites. The main aim was to discuss new possible stratigraphic markers to correlate the elusive evaporite sediments across the Mediterranean during the MSC and to correctly place the Messinian units into a reliable stratigraphic framework.Finally, as the peculiar and restricted setting of evaporite deposition makes the use of geochemical data problematic, we need to integrate the geochemical data in a detailed stratigraphic and facies framework. This because many of the available isotope data are scattered and commonly obtained from sections whose stratigraphy is not well constrained in the regional framework. An extensive study of the literature showed that the majority of the geochemical data were provided without a reliable record even for the local stratigraphy.This presentation illustrates our studies on a new evaporite facies interpretation that may be useful for large-scale correlations. The effort is to provide a new reliable facies, isotope and stratigraphic framework for the understanding of the Salinity Crisis in the Mediterranean.

New facies interpretation of the Messinian evaporites in the Mediterranean / Lugli, Stefano; Manzi, V.; Roveri, M.. - STAMPA. - 33:(2008), pp. 67-72. (Intervento presentato al convegno The messinian salinity crisis from mega-deposit to microbiology - A consensus report tenutosi a Almeria nel 7-10 November 2007).

New facies interpretation of the Messinian evaporites in the Mediterranean

LUGLI, Stefano;
2008

Abstract

IntroductionThe study of the Messinian salinity crisis (MSC) in the Mediterranean has generated a controversy with a long-term discussion on many aspects. One of the problem faced by the scientists is that the interpretation of evaporite sediments can be very complicated. Evaporite sediments are among the most elusive for facies reconstruction and correlation and most data in the literature were not correctly placed in a reliable stratigraphic framework. Some examples of these difficulties are the following: a) deposits traditionally included in the Lower Evaporites are actually clastic sediments that, as we have shown, derive from the dismantlement of autochthonous Lower Evaporites (Manzi et al., 2005; Roveri et al., 2006);b) many of the Lower Evaporites outcrops in Italy are actually large-scale blocks emplaced by extensive mass-waste movements (Roveri et al., 2003; Roveri et al., 2006); some of these chaotic complexes were interpreted as collapse deposits due to halite dissolution (Caruso and Rouchy, 2006);c) some Lower Evaporites outcrops were commonly considered Upper Evaporites and vice-versa;d) laminated clastic sulphate sediments were commonly mistaken for primary cumulate deposits and vice-versa;e) the significance of halite deposition, which actually bears the only unequivocal sign of exposure found within the Messinian evaporites, has been overlooked;f) the Calcare di Base carbonates show commonly evidence of resedimentation;g) the Calcare di Base is never found at the base of the Lower Evaporites primary in situ selenites;h) lateral transitions between carbonate, gypsum or halite primary evaporites cannot be directly observed and must be considered speculation;For these reasons we devoted our efforts to provide a detailed stratigraphic and facies analyses of all the Messinian evaporites and criteria for distinguishing the Lower from the Upper Evaporites. The main aim was to discuss new possible stratigraphic markers to correlate the elusive evaporite sediments across the Mediterranean during the MSC and to correctly place the Messinian units into a reliable stratigraphic framework.Finally, as the peculiar and restricted setting of evaporite deposition makes the use of geochemical data problematic, we need to integrate the geochemical data in a detailed stratigraphic and facies framework. This because many of the available isotope data are scattered and commonly obtained from sections whose stratigraphy is not well constrained in the regional framework. An extensive study of the literature showed that the majority of the geochemical data were provided without a reliable record even for the local stratigraphy.This presentation illustrates our studies on a new evaporite facies interpretation that may be useful for large-scale correlations. The effort is to provide a new reliable facies, isotope and stratigraphic framework for the understanding of the Salinity Crisis in the Mediterranean.
2008
The messinian salinity crisis from mega-deposit to microbiology - A consensus report
Almeria
7-10 November 2007
33
67
72
Lugli, Stefano; Manzi, V.; Roveri, M.
New facies interpretation of the Messinian evaporites in the Mediterranean / Lugli, Stefano; Manzi, V.; Roveri, M.. - STAMPA. - 33:(2008), pp. 67-72. (Intervento presentato al convegno The messinian salinity crisis from mega-deposit to microbiology - A consensus report tenutosi a Almeria nel 7-10 November 2007).
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