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The global strontium isotopic composition of the World’s oceans through the past few tens of millions of years. Sea shells and evaporites that precipitate from ambient sea water record the Sr isotopic ratio of the sea water at the time. Generally the curve is used to estimate the age of rocks. But if you know the age of the strata (e.g. on Sicily) independently, we can use the Sr isotopic composition to see if the strata were deposited in normal marine conditions for the time.
The material analysed from Messinian basins on Sicily. Shells from the " congieri" fauna have intact shell structure (so have not been later altered). The gypsum has intact fluid inclusion structure so have not been altered since primary precipitation.
Strontium isotopic data for Messinian samples on Sicily. First cycles gypsum form a distinct population from the stratigraphically younger (but lower 87/86 ratio) Second Cycle materials (gypsum and shells). These data were obtained from a range of mini-basins and clearly indicate that while the First Cycle represents evaporation from normal World Ocean water, the Second Cycle water-body must have been isolated from World’s Ocean.
A mixing model to explain the Sr isotopic composition of Second Cycle materials on Sicily. If these individual samples (from distinct mini-basins) were filled from local run-off then we would expect wide variety in the Sr composition. Because they are consistent ikt suggests that the basins were supplied from a larger- well-mixed reservoir, yet this is notr World’s Ocean water. Consequently it must be the main Mediterranean (or a large part of it), which itself must be isolated from World Ocean and have a significant component of other water in it (e.g. Nile run-off).
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