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doi:10.2204/iodp.proc.342.108.2014 Site U14071R.D. Norris, P.A. Wilson, P. Blum, A. Fehr, C. Agnini, A. Bornemann, S. Boulila, P.R. Bown, C. Cournede, O. Friedrich, A.K. Ghosh, C.J. Hollis, P.M. Hull, K. Jo, C.K. Junium, M. Kaneko, D. Liebrand, P.C. Lippert, Z. Liu, H. Matsui, K. Moriya, H. Nishi, B.N. Opdyke, D. Penman, B. Romans, H.D. Scher, P. Sexton, H. Takagi, S.K. Turner, J.H. Whiteside, T. Yamaguchi, and Y. Yamamoto2Background and objectivesIntegrated Ocean Drilling Program (IODP) Site U1407 (proposed Site SENR-20A; 41°25.5′N, 49°48.8′W; 3073 m water depth) is a mid-depth site (~2600 meters below sea level [mbsl] paleodepth at 50 Ma) (Tucholke and Vogt, 1979) in the upper end of the Expedition 342 Paleogene Newfoundland sediment drifts depth transect (Fig. F1). The site is positioned to capture a record of sedimentation ~1.9 km shallower than the largely sub–carbonate compensation depth (CCD) record drilled at Site U1403 (Figs. F2, F3). The location above the average late Paleogene CCD should be sensitive to both increases and decreases in carbonate burial, whether these reflect variations in dissolution related to changes in the CCD, changes in carbonate production, or variations in background noncarbonate sedimentation. Our primary scientific objectives for drilling Site U1407 were
The secondary objective included dating acoustic horizons to better constrain regional sedimentation during the Paleogene and Cretaceous and allow us to anticipate the likely age of the sedimentary sequence at the remaining Expedition 342 sites. The primarily calcareous sequence expected at Site U1407 should record changes in ocean alkalinity and carbonate production. Sites U1403 and U1404 were mainly positioned to capture large-amplitude CCD deepening events such as the carbonate budget “overshoots” that are thought to be associated with the most extreme climate perturbations of the Cenozoic such as those involved with the Cretaceous/Paleogene (K/Pg) boundary, the Paleocene/Eocene Thermal Maximum (PETM) and the Eocene–Oligocene transition (EOT) (see the “Site U1403” and “Site U1404” chapters [Norris et al., 2014c, 2014d). Those events are recorded at deepwater sites as stratigraphically thin intervals of calcareous sediment in otherwise noncalcareous sediment. In contrast, transient shoaling of the CCD in generally carbonate rich sequences should be recorded at Site U1407 by decreases in carbonate preservation and decreasing carbonate content relative to clay or biosiliceous sediment, as we have already observed at Site U1406. As an upper to mid-depth site on the Newfoundland ridges depth transect, Site U1407 should have a few intervals in which the sediment is 100% carbonate but also intervals where carbonate content decreases in the record. Carbonate content is expected to be generally higher at sites in shallower water depth, such as the majority of the sites located on Southeast Newfoundland Ridge, including Site U1407. The high carbonate contents anticipated in sediment at Site U1407 should permit the construction of detailed stable isotope records and calcareous microfossil biostratigraphy that can be tied by physical property records and magnetochronology to Sites U1403–U1406 further downslope. Ties between sites on Southeast Newfoundland Ridge and those on J-Anomaly Ridge will allow the isotope stratigraphy and biochronology developed for Sites U1406 and U1407 to be extended to the entire lower half of the depth transect. Site U1407 assumes greater importance in the depth transect because the lower and middle Eocene sedimentary sequence at Site U1406 was relatively condensed and incompletely recovered. Ultimately, the goal is to use the combination of the lower and middle Eocene record at Site U1407 and the younger Paleogene record at Site U1406 to produce composite records of stable isotope and carbonate content and mass accumulation rate (MAR) variability that can be tied to the more intermittent geochemical records at Sites U1403–U1405. Our aim is to match carbonate-rich intervals across all of the J-Anomaly Ridge sites with the sites on Southeast Newfoundland Ridge to create an orbital-resolution record of fluctuations in ocean chemistry and deepwater origins. Site U1407 was proposed in response to our discovery that there is a subtle but recognizable internal stratigraphy to the acoustically transparent sequence on J-Anomaly Ridge. Seismic data show an intermittent fuzzy reflector near the middle of the J-Anomaly Drift as well as a zone of fuzzy, slightly less transparent reflections in the lower half of the drift. Drilling on J-Anomaly Ridge showed that these two fuzzy reflector packages correspond to the Eocene/Oligocene boundary and lower and middle Eocene sediment. We used those interpretations of the seismic stratigraphy to propose sites that would preferentially target the lower half of the acoustically transparent seismic package. Site U1407 and its upslope companion, Site U1408, were designed to recover advanced piston corer (APC) records of the lower and middle Eocene sequence. The seismic stratigraphy of Site U1407 shows a complex array of reflectors below the presumed Eocene sedimentary sequence. We proposed to drill into this reflector-rich section in order to help bridge our seismic stratigraphic interpretations from J-Anomaly Ridge across Southeast Newfoundland Ridge. As at Site U1403, the primary goal was to date the reflector package and to recover intervals of calcareous sediment that could be useful for paleoceanographic studies of Paleogene and, potentially, Cretaceous events. Targets of particular interest included the early Paleogene hyperthermals, the K/Pg boundary, and an Upper Cretaceous sequence that could be matched in a depth transect with the Maastrichtian–Campanian sequence at Site U1403. We also expected that the sequence at Site U1407 includes, at depth, shallow-marine reef carbonates and possibly overlying black shale of various oceanic anoxic events such as those cored in the deep Newfoundland Basin during Ocean Drilling Program (ODP) Leg 210. We hypothesized that Site U1407 should provide a record of primarily calcareous ooze and chalk of rough age-equivalence to sites in deeper water on J-Anomaly Ridge. In particular, Site U1407 should provide a carbonate-rich record through the early and middle Eocene as a counterpart to the largely sub-CCD record drilled through this interval at Sites U1403 and U1404 and thereby improve age and water depth control on the behavior of the CCD in the North Atlantic during this key interval of the Cenozoic when the CCD in the equatorial Pacific was at its most dynamic (Lyle, Wilson, Janecek, et al., 2002; Pälike et al., 2012). |
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