Isotope stratigraphy (87Sr/86Sr, δ18O, δ13C) of the Sorbas basin (Betic Cordillera, Spain): Paleoceanographic evolution across the onset of the Messinian salinity crisis

Matteo Reghizzi,Rocco Gennari,Eric Douville,Stefano Lugli,Vinicio Manzi,Paolo Montagna,Marco Roveri,Francisco Javier Sierro,Marco Taviani

doi:10.1016/j.palaeo.2016.12.039

Matteo Reghizzi, Rocco Gennari + Show 7 more

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The Sorbas basin is a reference sector of the Mediterranean basin for the definition of the onset of the Messinian salinity crisis straddling the transition from the open marine deposits (Abad marls) to the Primary Lower Gypsum (Yesares Formation) during the first stage of the crisis, between 5.97 and 5.60Ma. Because of its proximity to the Atlantic gateway, the Sorbas basin is pivotal for the study of the oceanographic evolution that led to the most dramatic environmental event in the Mediterranean Sea. We measured the carbon (δ13C), oxygen (δ18O) and strontium (87Sr/86Sr) isotope ratio of 50 samples of planktonic foraminifera, mollusk shells, gypsum and carbonate sediments from the Abad and Yesares Members (Turre and Caños Formation) in the Perales, Hueli, Los Yesos and Rio de Aguas sections. Our results show a long-term trend with most of the values plotting within the range of the global ocean strontium isotope curve and distinct short-term fluctuations on precessional time scale. The investigated geochemical proxies suggest that these oscillations reflect significant input of continental waters into the basin during the humid phase of a single precessional cycle. This implies that the Western Mediterranean did not experience a main disconnection from the global ocean water before and during the first stage of the Messinian salinity crisis and that different Milankovitch forcings played a significant role in determining the seawater geochemistry.

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The Messinian represents a crucial period for the evolution of the Mediterranean basin, which experienced major geological, hydrological and oceanographic changes with catastrophic consequences on its aquatic ecosystems
According to the three stages evolutionary model proposed by Roveri et al, 2014a (Fig. 1a), during the Messinian salinity crisis (MSC) the Mediterranean was affected by series of climate-induced environmental modifications characterized by the deposition of peculiar geological units in terms of paleoenvironmental, sedimentological and geochemical signatures (Müller and Mueller, 1991; Flecker et al, 2002; Flecker and Ellam, 2006; Roveri et al, 2014a, b)
We used only neogloboquadrinid specimens (Neogloboquadrina acostaensis and, occasionally, Neogloboquadrina humerosa), because of their nearly continuous distribution along the unit and their life habitat. These planktonic foraminifera display the highest abundance in stratified environments of the modern ocean, associated with high-productivity and deep chlorophyll maximum (DCM), where the nutricline and pycnocline are located above the base of the euphotic zone (Sierro et al, 2003)

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Introduction

The Messinian represents a crucial period for the evolution of the Mediterranean basin, which experienced major geological, hydrological and oceanographic changes with catastrophic consequences on its aquatic ecosystems. The Sorbas basin (Betic cordillera, Spain, Fig. 1b) preserves a stratigraphically continuous transition between the pre-evaporitic open marine deposits (Abad marls; Sierro et al, 2001, 2003) and stage 1 evaporites (Yesares Formation; Lugli et al, 2010; Manzi et al, 2013) It represents a key area for understanding the Western Mediterranean paleoceanographic evolution during this crucial period of the Late Miocene history.

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