Interstitial Water and Bulk Calcite Chemistry, Leg 130, and Calcite Recrystallization

Abstract

We investigated minor element ratios (Sr/Ca and Mg/Ca) in bulk sediment samples from Sites 803-807 using a recently optimized sample treatment protocol for calcium-carbonate-rich sediments consisting of sequential reductive and ion exchange treatments. We evaluated this protocol relative to bulk sediment leaching using samples from Sites 804 and 806, the two end-member sites in the depth transect, reporting as well Mn/Ca and Fe/Ca ratios for sediments from these two sites processed by means of both methods. The Sr/Ca ratios were only slightly affected by the sample treatment, with an average reduction of 6%-7% caused primarily by the ion exchange step. The reductive sample treatment, designed to be effective at removing Mn-rich oxyhydroxides, has a major effect on Mg/Ca ratios, with up to 50% reduction, whereas little effect occurred in ion exchange alone on Mg/Ca ratios. The Mn/Ca and Fe/Ca ratios were not consistently offset by the sample treatment, and these ratios do not appear to be representative of calcite geochemistry reflecting either ocean history or diagenetic overprinting.Celestite solubility appears to be an important control on interstitial water Sr concentrations in these sites, and it must be considered when constructing Sr mass balance models of calcite recrystallization. Calcite Sr/Ca ratios (range 1-2 mmol/mol) are similar from site to site when plotted vs. age, with a pattern comparable to that for well-preserved foraminifer tests over the past 40 Ma. Interstitial water Mg and Ca gradients appear to reflect basement character and the intensity of alteration; they can vary substantially over a small area. Calcite Mg/Ca ratios (range 1.5-4.5 mmol/mol) differ from site to site, with generally higher ratios for sites at a shallower water depth. Increasing calcite Mg/Ca ratios correlate with decreasing Sr/Ca ratios in the treated samples. No consistent pattern exists for calcite Mg/Ca ratios vs. age or depth, nor is any direct correlation to interstitial water Mg/Ca ratios present.

Stylolites, porosity, depositional texture, and silicates in chalk facies sediments. Ontong Java Plateau – Gorm and Tyra fields, North Sea

“…9). Delaney & Linn (1993) suggested that the formation of celestite could explain the concurrent decline in sulphate and stabilization of Sr in the pore water, but no celestite was observed in the present study, so at least the main part of the dissolved Sr is taken up by barite. Cronan (1974) cited authors reporting up to 3% Sr in solid solution in microcrystalline barite in deep-sea sediments.…”

“…During recrystallization, calcite releases Sr (Baker et al, 1982;Delaney & Linn, 1993) and approaches stable crystal shape, a process which is largely over for sediments of Palaeogene age (Figs 4, 6 and 9). The released Sr precipitates as a component in barite (Fig.…”

Sr isotopes and pore fluid chemistry in carbonate sediment of the Ontong Java Plateau: Calcite recrystallization rates and evidence for a rapid rise in seawater Mg over the last 10 million years

“…The average calcite Mg content of deep samples (>800 mbsf) is 0.032 ± 0.002 molal while the Mg content of the entire section at 807A ranges between 0.022 and 0.048 molal. The Mg contents of calcite at 807 show no significant or systematic changes with depth that would support the use of a model in which the solid Mg content varied (Delaney and Linn, 1993). For each of the reference K Mg values, we calculate K Mg as a function of pore fluid Ca concentration in each time step of the model (Fig.…”

“…The maximum r-error in the Sr concentration measurements is 2% (Delaney and Linn, 1993); thus the r value assigned for the minimization of v 2 is equal to the maximum error, or 0.02 AE y i . In order to match the model data to measured data prior to minimization, the measured data are linearly interpolated to the 25-meter grid spacing of the model.…”

Data Report: Geochemistry of Fine Fraction Carbonate Sediments, Shatsky Rise (ODP Leg 198)

“…Although much of past research has focused on isotopic records, a growing literature on elemental variation has led to a better understanding of variability of elements like Sr (e.g., Graham et al, 1982;Renard, 1986;Delaney and Boyle, 1988;Baker et al, 1990;Delaney and Linn, 1993;Hampt and Delaney, 1997;Andreasen and Delaney, 2000a). Despite the effort focused on Sr, as pointed out by Andreasen and Delaney (2000b), significant scatter and differences exist in these records.…”