Evolution of the Late Miocene Mediterranean–Atlantic gateways and their impact on regional and global environmental change

Abstract

Marine gateways play a critical role in the exchange of water, heat, salt and nutrients between oceans and seas. As a result, changes in gateway geometry can significantly alter both the pattern of global ocean circulation and associated heat transport and climate, as well as having a profound impact on local environmental conditions. Mediterranean-Atlantic marine corridors that pre-date the modern Gibraltar Strait, closed during the Late Miocene and are now exposed on land in northern Morocco and southern Spain. The restriction and closure of these Miocene connections resulted in extreme salinity fluctuations in the Mediterranean, leading to the precipitation of thick evaporites. This event is known as the Messinian Salinity Crisis (MSC). The evolution and closure of the Mediterranean-Atlantic gateways are a critical control on the MSC, but at present the location, geometry and age of these gateways is still highly controversial, as is the impact of changing Mediterranean outflow on Northern Hemisphere circulation. Here, we present a comprehensive overview of the evolution of the Late Miocene gateways and the nature of Mediterranean-Atlantic exchange as deduced from published studies focussed both on the sediments preserved within the fossil corridors and inferences that can be derived from data in the adjacent basins. We also consider the possible impact of evolving exchange on both the Mediterranean and global climate and highlight the main enduring challenges for reconstructing past Mediterranean-Atlantic exchange.

The Tell-Rif orogenic system (Morocco, Algeria, Tunisia) and the structural heritage of the southern Tethys margin

“…3B and 8) and the north Rifian corridor basins (Flecker et al, 2015;Wernli, 1988) do share a similar structural position within the belt. They are all localized in the western parts of the belt, the latter being characterized also by the presence of the EMM and frontal flexural basins.…”

Estuarine Lago Mare fauna from the Tertiary Piedmont Basin indicates episodic Atlantic/Mediterranean exchange during the final stage of the Mediterranean Salinity Crisis

“…Otolith 87 Sr/ 86 Sr values clearly exceed typical values from Lago Mare deposits ( Fig. 5; Roveri et al, 2014a;Flecker et al, 2015). The geological setting of the Mediterranean generally favors low 87 Sr/ 86 Sr river waters (e.g.…”

“…However, as the gypsum and otolith values are merely identical, we consider its contribution minor. Mixing with Paratethys waters cannot be entirely excluded; however, 87 Sr/ 86 Sr of Paratethyan waters from this time interval is largely unknown, the location of a potential gateway is unclear, and Moncucco mollusks show no clear relation to Paratethys faunas (Vasiliev et al, 2010;Flecker et al, 2015;Harzhauser et al, 2015). Tables 1, 3).…”

“…The hypothesis of a brackish lake during the final stage of the MSC is largely based on the widespread Lago Mare biofacies (i.e., brackish mollusks and ostracods) and depleted 87 Sr/ 86 Sr values (McCulloch and De Deckker, 1989;Roveri et al, 2014a;Flecker et al, 2015). The existence of genuine estuarine paleobiotopes in the TPB challenges this hypothesis and supports previous arguments for at least one major ingression of Atlantic waters into the Mediterranean basins during the final MSC stage, strong enough to affect even remote areas like the TPB (e.g., Carnevale et al, 2008b;Bache et al, 2012;cf.…”

“…The range of data from evaporitic deposits are indicated for each MSC stage by shaded boxes. MO = mollusk samples of the present study; OT = otolith samples of the present study.The compilation of data is based onRoveri et al (2014a) andFlecker et al (2015). Maximum error for individual data-points of the compiled data-set is c. ± 0.000035 (indicated at the bottom left corner; seeFlecker et al, 2015).…”