Hydrogen isotope exchange between clay minerals and sea water

The D/H ratios of separated size fractions of clay minerals in two deep sea sediments taken from depths of 30 and 1100cm in a North Pacific Ocean core were measured to investigate the extent of hydrogen isotope exchange between detrital clay minerals and sea water. The D/H ratio of each size fraction of the shallower sample was compared with that of the corresponding size fraction of the deeper sample. No differences were detected between D/H ratios of corresponding size fractions from the two levels in the core except for the <0.1μm size fraction, which makes up only 5% of the sample. Even in this size fraction only about 8–28% D/H exchange is apparent. This is interpreted as indicating that no significant hydrogen isotope exchange between clay minerals and sea water has occurred during the past 2–3 Myr. Therefore information concerning the provenance and mode of formation of detrital clay minerals can be obtained from the D/H ratios of deep sea sediments younger than 2–3 Myr.