Strontium stratigraphy of the upper MioceneLithothamnionLimestone in the Majella Mountain, central Italy, and its palaeoenvironmental implications

Abstract

The 87Sr/86Sr isotope ratio has been widely used as a physical tool to date and correlate carbonate successions due to the long Sr residence time in comparison with the ocean mixing time. If this method works on oceanic successions, marginal basins may show different Sr isotope records in comparison with the coeval ocean one due to sea‐level variations, continental run‐off and restricted water exchanges. In this work, we present the 87Sr/86Sr isotope record of the upper Miocene carbonate ramp of the Lithothamnion Limestone (Majella Mountain, central Apennines), as an example of the onset of restricted water exchanges between a marginal basin and the ocean water masses. The overall latemost Tortonian–early Messinian Sr isotope record of the Lithothamnion Limestone fits below the global reference line. This deviation has been interpreted as due to the strong control that freshwater input and enhanced continental run‐off, linked to the migration of the Apennine accretionary wedge and foredeep system, have had on the central Adriatic water chemistry. These results imply that an accurate oceanographic and geodynamic framework along with diagenetic overprint investigation has to be taken into consideration prior to apply SIS on carbonate successions on marginal basins, even when facies analyses indicate fully marine conditions. This seems to be the case for the upper Miocene Central Mediterranean carbonate successions, but may have more general validity and be extended to other recent or past marginal basins.

Miocene Oceanographic Evolution Based on the Sr and Nd Isotope Record of the Central Mediterranean

“…Lastly, during the late Miocene, the Atlantic passage gradually narrowed (Popov et al, ). From Tortonian times on, this complex geodynamic evolution led to the isolation of different marginal Mediterranean basins from the larger Central Mediterranean water body (Cornacchia et al, ; Flecker & Ellam, ; Schildgen et al, ; Topper et al, ). It eventually led to the isolation of the entire Central Mediterranean Basin during the Messinian, caused by the tectonic uplift of the Betic corridor and a coeval major sea level fall, leading to the “Messinian salinity crisis” (Krijgsman & Meijer, ; Manzi et al, ; Martín et al, ; Popov et al, ; Roveri et al, ).…”

“…The age model of the La Vedova‐Monte dei Corvi section is from Montanari, Beaudoin, et al (), Hilgen et al (, ), and Hüsing et al (, , ). Age constraints for the Roccamorice sections are referred to by Cornacchia et al (). B 69 = planktonic foraminifera biozones of Blow ().…”

“…The Bolognano Formation consists of sediments deposited on a carbonate ramp in the late Rupelian‐Messinian (Brandano, Cornacchia, et al, ; Brandano et al, ; Mutti, Bernoulli, & Stille, ; Vecsei et al, ) and contains an alternation of shallow‐water carbonate and deeper marly units. The upper unit of the Bolognano Formation, named Lithothamnion Limestone unit, is upper Tortonian‐lower Messinian (Brandano, Tomassetti, et al, ; Cornacchia et al, ). The Turborotalita multiloba marls (Carnevale, Patacca, & Scandone, ) cap the Lithothamnion Limestone unit, and predate the gypsum deposition, representing the lower Messinian interval before the onset of the salinity crisis.…”

“…For the stratigraphy of the Roccamorice section, the reader is referred to Cornacchia et al (), who propose an integrated Sr isotope stratigraphy and biostratigraphy of the Lithothamnion Limestones. The base of the Lithtothamnion Limestone can be ascribed to the upper Tortonian (~8.50 Ma).…”

“…Based on these assumptions, a global reference 87 Sr/ 86 Sr curve, calibrated with biostratigraphy and magnetostratigraphy, has been developed for the entire Phanerozoic (McArthur et al, , ) and has been used extensively to date and correlate carbonate successions (Brandano, Cornacchia, Raffi, et al, ; Brandano & Policicchio, ; Frijia & Parente, ; McArthur & Howarth, ). However, it has become increasingly evident that the Sr isotope signature of marginal basins may deviate from the global ocean signature due to salinity changes, runoff, and local volcanism, coupled with restricted conditions (Cornacchia et al, ; Ingram & Sloan, ; Kocsis et al, ; Schildgen et al, ).…”