Fluid inclusions in halite from marine salt deposits: are they real micro-droplets of ancient seawater?

Evaluation of data sets on inclusion brine compositions in halite from the Phanerozoic marine evaporite deposits used for the reconstruction of ancient seawater chemistry shows that brine analysis of primary inclusions from primary marine halite (in the case of proper genetic type determination) undoubtedly indicate two megacycles in secular variation of seawater chemistry during the Phanerozoic. It is also shown that inside primary halite, inclusions formed at later stages of deposit formation locally occur. Erroneous attribution of such inclusions to primary ones is the main reason for deviations observed in most data sets. It is also obvious that fluid inclusions in clear (recrystallized) halite are unsuitable for the reconstruction of ancient seawater chemistry. Brines from inclusions properly determined as primary in primary bedded halite are micro-droplets of concentrated ancient seawater.