Isotopic and Chemical Signatures of Paleophreatic Lenses at Enewetak Atoll: Constraints on Pleistocene Sea Level

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This is an isotopic and geochemical investigation of calcite cements in the post-Miocene sequence of Enewetak Atoll. Preliminary carbon and oxygen isotope data from microsamples of calcite cements within the Pliocene sequence of Core KAR-1 at Enewetak Atoll indicate that these cements were emplaced in meteoric phreatic lenses, while 87Sr/86Sr data places these diagenetic events in the Pleistocene and Pliocene. The position of paleophreatic lenses associated with these cements can provide quantitative estimates of Pleistocene sea-level lowstands. A combination of stable and radiogenic isotope data are needed form calcite cements from Core KAR-1 and from age-equivalent sediments of Core OOR-17 to discriminate cement phases related to successive and temporally separate paleophreatic lenses and to assess the stratigraphic distribution of individual phreatic cement zones. This "chemical cement" stratigraphy will allow multiple episodes of phreatic cementation to be identified and their distribution documented. Thus, this study offers an opportunity to: 1) better understand the dynamics of the meteoric diagenetic system during times of high frequency sea-level change, and 2) directly estimate the magnitude of Pleistocene sea-level lowstands by monitoring the position of paleophreatic lenses. Ultimately this new sea level record can be used to calibrate the records of sequence stratigraphy and foraminiferal delta 18O stratigraphy to sea level.