Large-scale mass-transport deposits recording the collapse of an evaporitic platform during the Messinian salinity crisis (Caltanissetta basin, Sicily)

• Published in: Sedimentary geology 2021-10, Vol.424, p.106003, Article 106003
• Main Authors: Manzi, Vinicio, Roveri, Marco, Argnani, Andrea, Cowan, Darrel, Lugli, Stefano
• Format: Article
• Language: English
• Subjects: Caltanissetta basin; Evaporites; Mass transport complex; Messinian; Sicily
• ISSN: 0037-0738; 1879-0968
• DOI: 10.1016/j.sedgeo.2021.106003

The Messinian primary gypsum sequence, formed during the first stage of the salinity crisis in the Caltanissetta basin (Sicily), is characterized by a high degree of disruption and deformation. The primary gypsum occurs as huge (up to 3 km large and up to 250 m high) tilted blocks, detached from their stratigraphic base, floating within a matrix of folded shales and clastic gypsum. This association represents a giant chaotic unit lying unconformably on the Gela Nappe, the youngest structural unit of the Maghrebian fold-and-thrust belt. The origin of the deformations affecting the Primary Lower Gypsum unit is still debated; in the past they have been related to intra-Messinian tectonics or to the collapse of primary gypsum platforms due dissolution of interbedded to halite. Our study on the distribution, size and bedding of the gypsum blocks reveals a pattern similar to that of modern giant submarine mass-transport deposits, which may have been triggered by a combination of active tectonics and sea-level change, and favored by the strong mechanical contrasts of the involved units. The chaotic unit shows a downslope evolution from the south, characterized by elongated blocks with their main axes parallel to the inferred slide headwall (NW-SE oriented), to intermediate and distal areas, where the blocks become progressively smaller in size with their main axes parallel to the flow (SW-NE). We identify the source area as either a shallow evaporitic basin above the Gela Nappe or on the Pelagian foreland ramp. A general implication for the Messinian salinity crisis is that no primary gypsum was deposited in deep water basins during the first stage; instead, during the second stage, large gypsum blocks collapsed from the basin margin and were mass-transported into a deeper water setting, where halite was depositing. •mass-transport deposits with giant gypsum blocks occur in Caltanissetta basin;•Primary Lower Gypsum blocks are allochthonous slabs transported by gravity flows;•primary selenite gypsum did not precipitate in deep basins during the first stage;•PLG-bearing MTDs were emplaced during stage 2 of the Messinian salinity crisis;•Mechanisms of purely tectonic or halite dissolution collapses can be ruled out.