The oxygen isotopic composition of interstitial waters: evidence for fluid flow and recrystallization in the margin of Great Bahama Bank

Abstract

This study investigates the δ 18 O of pore waters from Sites 1003 through 1007, drilled along the western margin of the Great Bahama Bank during Leg 166 of the Ocean Drilling Program. These pore waters generally show a positive correlation between δ 18 O and the concentration of chloride. The exception to this trend is Site 1006, where the pore waters exhibit nonlinear behavior with respect to chloride. The correlation between the concentration of Cl- and δ 18 O at most of the sites appears to be a coincidence because although the increase in Cl - is a result of diffusion from an underlying source, the increases in δ 18 O result from the recrystallization of metastable carbonates in the presence of a geothermal gradient. The difference in behavior in the δ 18 O of the pore water at Site 1006 is probably a result of the relative reduced rate of carbonate recrystallization at this site. The δ 18 O of the pore waters in the upper portion of the cores shows a pattern similar to the concentration of chloride in that there is an interval of 30-50 m in which neither the δ 18 O nor the concentration of Cl- changes. This interval is consistent with either an interval of very rapid deposition of sediment or the advection of fluid through the platform. Both the δ 18 O and the concentration of Cl-increase toward the platform, suggesting an input of saline and isotopically heavy water from the platform surface.