Author's personal copy The Primary Lower Gypsum in the Mediterranean: A new facies interpretation for the first stage of the Messinian salinity crisis Lugli Stefano a, ⁎, Manzi Vinicio b , Roveri Marco b , Schreiber B. Charlotte c a Dipartimento di Scienze della Terra, Universitá degli Studi di Modena e Reggio Emilia, Piazza S. Eufemia 19, 41100 Modena, Italy b Dipartimento di Scienze Geologiche, Università di Parma Dipartimento di Scienze della Terra, Parco Area delle Scienze 157/A 43100, Parma, Italy c Department of Earth and Space Sciences, University of Washington, PO Box 351310, Seattle, WA 98195, USA abstract article info Article history: Received 8 April 2010 Received in revised form 15 July 2010 Accepted 18 July 2010 Available online 23 July 2010 Keywords: Primary Lower Gypsum Mediterranean Messinian salinity crisis Selenite Evaporites Astrochronology The detailed facies and physical stratigraphic analysis of the Primary Lower Gypsum in the Mediterranean indicates a surprising bed-by-bed correlation at basin-scale (Spain, Italy, Hellenic arc and Cyprus arc), that is tuned to the orbital calibration for the first stage of the Messinian salinity crisis from 5.96 to 5.61 Ma ago. A total of 16, precessionally-controlled, gypsum cycles were deposited rapidly in less than 350 ka, forming sequences up to 300 m thick. The lack of subaerial exposure features and the common facies associations and stacking pattern for sections located thousands of kilometers apart in different geological settings indicates a modest depositional depth, not extremely shallow. Selenite deposition occurred only at the bottom of restricted marginal basins less than 200 m deep, while no gypsum could precipitate in the deeper euxinic Mediterranean portions where only thin and barren shale/dolostone couplets formed. The lowermost selenite beds pass laterally to dolomite-rich limestones interbedded with barren euxinic shales in poorly oxygenated settings, indicating that the gypsum sedimentation was diachronous and did not necessarily mark the onset on the Messinian salinity crisis. Evaporite facies sequences (EF1 to 8) within individual gypsum beds show small-scale, subaqueous sedimentary cycles that mimic regressive–transgressive cycles: a) initial evaporite precipitation at relatively low supersaturation produced the massive selenite (facies EF3) in a relatively deep setting; b) continuous evaporation and drawdown by oscillating brine level formed the banded selenite (EF4) at the aridity acme of the precessionally-controlled cycle; c) general progressive brine level rise with strong brine flow led to the formation of large selenite supercones branching laterally (supercones in Spain and branching selenite, EF5, in the rest of the Mediterranean); and d) flooding by undersaturated continental water terminated gypsum precipitation with the deposition of argillaceous sediments (EF1, Northern Apennines), and/or limestone (EF2, Sicily and Spain) during the humid phase in the precession climate cycle. The stacking pattern and selenite facies associations suggest an overall shallowing-upward trend with a basin-wide hydrologic change starting from the 6th cycle (5.84 Ma), which is marked by the appearance of the branching selenite facies (supercones) in Spain and indicates that the brines became current-dominated. The Sr-isotope stratigraphy suggests that in the Northern Apennines the brines were strongly modified by continental waters ( 87 Sr/ 86 Sr = 0.708893 to 0.708998), and received direct pulses of Atlantic seawater ( 87 Sr/ 86 Sr = 0.70900 to 0.709024) only in the upper part of the section. In areas away from the mainland, such as Sicily, the continental input was by far less important. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The study of huge evaporite deposits, the saline giants, has generated profound controversies in the scientific community. The reason for disagreement among scientists is that great parts of the sequences are buried and it is very difficult to assess their internal facies relationships. This is mostly because we have no clues to determine water depth in such extreme environments and particu- larly because no modern analogues for very large and relatively deep deposits are available for comparison. These problems are greatly amplified in the study of the Mediterranean evaporite giant that formed during the late Miocene (Messinian). First, because the data on the Messinian salinity crisis (MSC) were not provided within a reliable stratigraphic framework (Roveri et al., 2008b) and thus different interpretations for the chronology of the depositional phases have been proposed (see Rouchy and Caruso, 2006 and CIESM, 2008 Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010) 83–99 ⁎ Corresponding author. E-mail address: lugli.stefano@unimore.it (L. Stefano). 0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.07.017 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo