Potassium, illite and the ocean

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Not only do clays extract material from the ocean but they also contribute. Sufficient clay has passed through the ocean to exert a significant influence on its chemical composition. The extraction of potassium by the formation of illite is considered by some to be one of the more important processes operative in the sea. Some of the assumptions on which this idea is based are critically evaluated. Clay minerals are presently adsorbing from the ocean more Na +and Mg 2+than K +. Younger sediments have relatively more Na + and montmorillonite and less K and illite than older sediments. This change occurs near the end of the Paleozic and appears to be world wide. The change is believed due to an increase in the Na, and perhaps Mg, content of the oceans, caused by the rapid development of plant life and an increase in soil acidity. Montmorillonite, rather than illite, was formed in the Cenozoic and Mesozoic oceans. Much of the Paleozoic and Precambrian illite was formed on the land rather than in the ocean. Primitive biota may have aided in concentrating K in the early terrestial environment. Less than 10 % of the K + carried to the ocean today is in solution. This value may have been even smaller in the past. Considerably less K, in solution, has been cycled through the ocean than has been assumed. Since the late Paleozoic a major portion of the K removed from the ocean has been removed in the interstitial waters trapped in marine and deltaic muds. Only after deep burial is this K fixed in the illite lattice.