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

这是方解石的同位素和地球化学调查 埃尼威托克环礁中新世后层序中的胶结物。 从微量样品中获得的初步碳和氧同位素数据 KAR-1岩芯上新世层序中的方解石胶结物 Enewetak环礁表明，这些水泥是在 陨石潜水透镜体，而87 Sr/86 Sr数据将这些 更新世和上新世的成岩事件。 的位置 与这些胶结物有关的古潜水透镜体 更新世海平面低水位的定量估计。 需要结合稳定同位素和放射性同位素数据 从KAR-1岩芯和年龄相当的岩芯中形成方解石胶结物 岩心OOR-17的沉积物，以区分与 连续的和暂时分离的古潜水透镜体， 评估单个潜水胶结物的地层分布 区界限 这种“化学水泥”地层学将允许多个 要确定的潜水胶结作用及其 分发记录。 因此，这项研究提供了一个机会， 目的是：1）更好地了解大气成岩的动力学 系统在高频率海平面变化期间，以及2） 直接估算更新世海平面低位的大小 通过监测古潜水透镜体的位置。 最终 这个新的海平面记录可以用来校准 层序地层学和有孔虫三角洲18 O地层学， 海拔

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.