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doi:10.2204/iodp.proc.342.112.2014
Site U14111
R.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. Yamamoto2
Background and objectives
Integrated Ocean Drilling Program (IODP) Site U1411 (proposed Site SENR-11A; 41°37.1′N, 49°00′W; ~3300 m water depth) is a mid-depth site (~2850 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 ~1.65 km shallower than the largely sub–carbonate compensation depth (CCD) record drilled at Site U1403 (Figs. F2, F3). The location, well 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 U1411 were
To obtain an expanded record of the upper half of a Miocene–lower Eocene sediment drift to compare directly to the timing and nature of drift development at the Site U1407 and U1408 drift and the Site U1409 and U1410 drift; To recover an expanded record of the Eocene–Oligocene transition (EOT) in a clay-rich sequence where we expect unusually well preserved microfossil records for geochemical and faunal analysis; To capture fine-scale variations in carbonate preservation and lysocline shifts in Miocene–Eocene carbonate-rich sediment that is ~550 m shallower than the Site U1406 Oligocene–Miocene section; and To evaluate the history of deep water and the CCD on sediment chemistry, grain size, and provenance.
Secondary objectives include the possible recovery of the Oligocene/Miocene boundary and events in the later Eocene for comparison with the record of these events elsewhere, particularly at Sites U1404–U1406 along the Expedition 342 depth transect.
Site U1411 was drilled to date the fourth and last Paleogene sediment drift of Expedition 342. Previous drilling demonstrated that all of the drifts were initiated in the middle early Eocene, but their times of termination vary from the early Miocene (J-Anomaly Ridge) to late middle Eocene (the two Southeast Newfoundland Ridge drifts). Drilling at Site U1411 aimed to refine our ideas of drift stratigraphy, particularly to test the time of cessation of drift growth. The end of drift growth is likely to record the time when the supply of clay and other noncarbonate components largely ceased or to indicate when currents became too strong to deposit fine-grained sediments around the volcanic seamounts on Southeast Newfoundland Ridge. Sedimentation rates fall in the J-Anomaly Ridge drift in the late Eocene and again in the middle Oligocene, so we expect that these times could represent hiatuses or times of the cessation of drift sedimentation at Site U1411.
The calcareous sequence targeted at Site U1411 was expected to capture 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 Paleocene/Eocene Thermal Maximum (PETM), the late middle Eocene, and the EOT (see the “Site U1403” and “Site U1404” chapters [Norris et al., 2014b, 2014c]). Transient shoaling of the CCD in generally carbonate-rich sequences should be recorded at Site U1411 by decreases in carbonate preservation and decreasing carbonate content relative to clay or biosiliceous sediment, as we have already observed at Sites U1405–U1410. As a mid-depth site on the Newfoundland depth transect at ~3300 mbsl, Site U1411 was positioned to allow us to reconstruct small changes in carbonate content between the records of Sites U1406 (3850 mbsl), U1410 (3400 mbsl), and U1408 (3022 mbsl) and should have a few intervals in which the sediment is 80%–90% carbonate and also intervals in which carbonate abundance falls 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, but less than our shallowest depth Sites U1407 and U1408.
The mix of high clay and carbonate contents anticipated in sediment at Site U1411 should produce unusually good microfossil preservation, as seen in other Expedition 342 sites. In turn, well-preserved fossils should permit construction of detailed stable isotope records and a calcareous microfossil biostratigraphy that can be tied by physical property records and magnetochronology to Sites U1403–U1406, U1409, and U1410 further downslope and Sites U1407 and U1408 upslope. Ties between sites on Southeast Newfoundland Ridge and those on J-Anomaly Ridge will allow the isotope stratigraphy and biochronology developed for Sites U1406–U1410 to be exported to the lower ends of the depth transect.
Ultimately, the goal is to use the combination of the middle Eocene record at Sites U1407–U1411 and the younger Paleogene record at Site U1406 to produce composite stable isotope and carbonate content records that can be tied to the more intermittent geochemical records at Sites U1403–U1405. Our aim was 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 deep water origins.
We conclude that Site U1411 should provide an expanded record of primarily calcareous ooze and chalk of rough age-equivalence to sites in deeper water on J-Anomaly Ridge. In particular, Site U1411 should provide a high–deposition rate record of the Miocene, Oligocene, and Eocene as a counterpart to the largely sub-CCD record at Site U1403 and the shallower records at Sites U1405 and U1406. The combination of these records will improve age and water depth control on the behavior of the CCD in the North Atlantic during this key interval.
Publication: 3 March 2014
MS 342-112
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