Precipitation and lithification of magnesian calcite in the deep‐sea sediments of the eastern Mediterranean Sea*

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Abstract
Magnesian calcite is an important sedimentary component in the deep‐sea sediments of the eastern Mediterranean Sea, comprising an average of 20–50% of the carbonate fraction in most areas. The lack of any obvious biogenic source, plus similarities with magnesian‐rich lutites from the Red Sea and deep‐sea cements from other areas suggest that this magnesian calcite was precipitated inorganically.Although the exact mode of precipitation is not understood at present, it probably occurred at the water‐sediment interface under elevated salinity and temperature conditions, such as those present in the modern eastern Mediterranean. Precipitation did not occur during periods of lower temperatures and/or salinities such as during the stagnant conditions caused by the influx of fresh waters from melting Pleistocene glaciers.The eastern Mediterranean magnesium‐rich sediments appear to represent an intermediate stage between normal deep‐sea sediments and those from the warm hpyersaline Red Sea. Normal deep‐sea carbonates are composed almost entirely of biogenic calcite, whereas the Red Sea magnesian calcite alternates with layers of aragonite that were precipitated under elevated salinity and temperature conditions brought about by lowered stands of sea level.