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doi:10.2204/iodp.proc.320321.216.2014

Results

One of the important uses of XRF scanning is to be able to produce high-resolution data sets, such as the >19 m.y. sediment records from Sites U1335 and U1337. The Site U1336 sediment record spans ~12.12 to 20 Ma. Figure F6 shows the NMS time series of CaCO₃ NMS data at all three sites examined in this study. Also shown are biostratigraphic and magnetostratigraphic tie lines used to compare the records at each site to one another. Table T5 provides the depths, ages, and types of stratigraphic tie points shown in the figure. The upper section of the Site U1337 splice is expanded when compared with that of the Site U1335 splice because Site U1337 has been in closer proximity to the Equator since 12 Ma (1.1°–3.8°N) versus 2.4°–5.3°N for Site U1335. The closer proximity to the Equator exposed Site U1337 to higher sediment deposition. As the sites moved further from the Equator, they received less sediment deposition, as illustrated in the extreme by the hiatus from ~0 to 12 Ma at Site U1336.

Figure F7 shows all three sites, again with bio- and magnetostratigraphic tie lines, focusing on a very prominent CaCO₃ low that peaks at ~17 Ma and begins at ~17.7 Ma. The age is earlier than the usually assumed start of the Monterey carbon isotope excursion (16.9–13.7 Ma; Holbourn et al., 2007) but older than that of the Columbia River basalt flood basalt eruption (~16.8–5.5 Ma; Reidel and Tolan, 2013), which could have released significant amount of deep CO₂ that potentially could have caused added carbonate dissolution in the oceans. The peak CaCO₃ dissolution occurs at or slightly after the onset of the southeast Oregon eruptions that began the deposition of the Columbia River basalts in North America (16.8–16.6 Ma; Barry et al., 2013). The flood basalt deposition and the equatorial Pacific dissolution event can only be linked if volatile degassing is associated with the emplacement of the magma in the crust, not the eruption.

The 17 Ma carbonate dissolution event lasted ~1 m.y. and is strongly influenced by orbital insolation changes. The CaCO₃ analyses indicate cyclicity on an approximately 100,000 y timescale.

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