Smectites oxygen isotopic data

Table VII. Oxygen Isotope Data for Various Smectites...

The catalytically active, Wyoming-type montmorillonites are inferred to have developed their distinctive, high-Na smectite-rich compositions following deposition of granitic volcanic ash into a shallow, saline ocean during the Late Cretaceous. Oxygen isotopic data from Hadean zircons have been interpreted as indicating that oceans may have been present on the Earth by as early as 4,300-4,400 million years ago (62-63). While current evidence provides no information on the composition of the hypothesized Hadean seawater, the existence of oceans on the Hadean Earth is a necessary environment on the ancient Earth if catalytically active montmorillonites formed. 

Abstract Smectites from the Ishirini bentonite deposit (Libya) were analyzed for their oxygen and hydrogen isotopic ratios. Based on published isotopic fractionation data the results argue for a main meteoric water origin of the fluids responsible for the transformation of pyroclastic rocks to bentonite at temperature range from 30° to 90 °C. 

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