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doi:10.2204/iodp.proc.322.212.2016

Results

A total of 86 pore fluid samples were analyzed. Considering the poor core recovery due to RCB drilling during Expedition 322, hard claystones were selected for interstitial water (IW) samples, and careful cleaning prevented extensive drilling fluid contamination (see the “Expedition 322 summary” chapter [Underwood et al., 2010]). At Site C0011, pore fluid samples were affected by seawater contamination ranging from 2% to 14%. At Site C0012, IW shipboard analyses concluded contamination by seawater is minimal, considering the dissolved sulfate profile, which is consistent with the biogeochemical processes at this site (see the “Expedition 322 summary” chapter [Underwood et al., 2010]).

Consequently, no correction for seawater contamination was made on isotopic data for either Site C0011, which leads to underestimating the negative δ¹⁸O signatures by an average value of 6%, or Site C0012, where sulfate distribution precluded any correction for potential contamination.

The data are listed in Table T1. Figure F2 shows the downhole δ¹⁸O depth profiles in the context of the corresponding lithology.

Pore fluids in both sedimentary sequences are depleted in ¹⁸O relative to modern seawater with values ranging from –0.70‰ to –5.66‰. The lower values are obtained in the deeper sediments. At Site C0011, δ¹⁸O values decrease with depth from –0.70‰ (Section 333-C0011D-3H-5; 44.80 mbsf) to –4.66‰ (Section 322-C0011B-16R-2; 478.21 mbsf) and then remain relatively constant with a mean value of –4.7‰ ± 0.4‰ until the deepest sample analyzed (–4.72‰) in Section 322-C0011B-59R-3 (867.50 mbsf) (Fig. F2). The change between the decreasing trend in δ¹⁸O values and the constant trend occurs at the boundary between lithologic Unit II (volcanic turbidite facies) and lithologic Unit III (hemipelagic facies). Similarly, at Site C0012 δ¹⁸O values decrease with depth from –1.58‰ (Section 322-C0012A-5R-2; 89.43 mbsf) to –3.97‰ (Section 322-C0012A-19R-2; 217.58 mbsf) and then remain relatively constant below the Unit II/III boundary with a mean value of –4.5‰ ± 0.5‰. In lithologic Unit V (volcaniclastic turbidite facies), in contrast to what was observed at Site C0011 the δ¹⁸O depth profile at Site C0012 shows a reverse trend with δ¹⁸O values increasing with depth from –4.70‰ (Section 322-C0012A-41R-3; 426.10 mbsf) to –3.15‰ (Section 322-C0012A-52R-2; 529.20 mbsf). Such a reverse trend in concentration profiles of all major cations, chloride, and sulfate was observed in the Site C0012 pore fluids and has been attributed to ion diffusion from fluids in the permeable igneous basement (see the “Expedition 322 summary” chapter [Underwood et al., 2010]; Torres et al., 2015).

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