| Summary: | Supplementary Fig. 4. Foraminifera carbon and oxygen stable isotope cross plot identifying possible diagenetic calcite influence in the basal Oligocene of the NKK-1 borehole. Planktonic foraminifera δ 18 O values ( T. ampliapertura , ‘whole-sparr fill’, ‘empty’ and ‘fragments’) with δ 18 O > 1 ‰ that is negatively offset from the late Eocene ‘base-line’ 1 (i.e. left of the dashed blue vertical line, as defined in Supplementary Fig. 2), and/or having paired sparite infill samples with δ18O that is > 1 ‰ negatively offset from the foraminifera values, are suspected to include a significant diagenetic calcite component. These are excluded from our downhole EOT isotope stratigraphy interpretation. The matching δ 13 C for these samples is also excluded. Benthic foraminifera δ18O from this ‘alteration interval’ should likely also be treated with caution, although the more enclosed tests with smaller internal spaces for diagenetic calcite to form, appear to result in a smaller diagenetic deviations.
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