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doi:10.2204/iodp.proc.342.110.2014 Site U14091R.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 U1409 (proposed Site SENR-22A; 41°17.75′N, 49°14.00′W; ~3500 m water depth) is a mid-depth site (~3050 meters below sea level [mbsl] paleodepth at 50 Ma) (Tucholke and Vogt, 1979) in the upper mid-depth end of the Expedition 342 Paleogene Newfoundland sediment drifts depth transect (Fig. F1). The site was positioned to capture a record of sedimentation ~1.5 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 U1409 were
Secondary objectives included the possible recovery of specific Paleogene hyperthermals such as the Eocene Thermal Maximum 2 (ETM2), Paleocene/Eocene Thermal Maximum (PETM), Danian–Selandian events, and a complete Cretaceous/Paleogene (K/Pg) boundary sequence for comparison with the record of these events elsewhere, particularly Site U1403 at the deep end of the Expedition 342 depth transect. Site U1409 is a companion site to Site U1410 where we employed an offset drilling strategy to obtain advanced piston corer (APC) records through a thicker section of the same sediment drift. Drilling a similar pair of sites (U1407 and U1408) showed that the more expanded Site U1408 record is essentially a record similar to that at Site U1407 but with much more clay and a somewhat younger uppermost sediment record. We found largely the same geometry in the J-Anomaly Ridge sites, where the center of the drift has a massively expanded record of the same geological intervals that are present in relatively condensed sections at the ends of the drift. Hence, we expected that coring at Site U1410 would recover a sequence with more clay but with otherwise similar gross stratigraphy to the more condensed companion Site U1409. The primarily calcareous sequence expected at Site U1409 recorded changes in ocean alkalinity and carbonate production. Sites U1403–U1405 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 K/Pg boundary, the PETM, and the Eocene–Oligocene transition (EOT) (see the “Site U1403,” “Site U1404,” and “Site U1405” chapters [Norris et al., 2014b, 2014c, 2014d). These 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 are recorded at Site U1409 by decreasing carbonate preservation and decreasing carbonate content relative to clay or biosiliceous sediment, as we already observed at Sites U1406–U1408. As an upper mid-depth site on the Newfoundland depth transect at ~3500 mbsl, Site U1409 was positioned to allow us to reconstruct small changes in carbonate content between the records of Sites U1406 (3850 mbsl) and U1407 (3080 mbsl) and should have a few intervals in which the sediment is 100% carbonate but also intervals where carbonate abundance falls in the record. Carbonate content was expected to be generally higher at sites in shallower water depth, such as the majority of the sites located on Southeast Newfoundland Ridge, including Sites U1409 and U1410. The high carbonate contents anticipated in sediment at Site U1409 will 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–U1408 to be exported to the lower ends of the depth transect. Site U1409 assumes greater importance in the depth transect because the early Paleogene and Cretaceous sedimentary sequence was expected to be better preserved and have more complete recovery than at any other Expedition 342 site. Ultimately, the goal was to use the combination of the lower and middle Eocene record at Sites U1407–U1410 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 sites with the sites on Southeast Newfoundland Ridge to create an orbital-resolution record of fluctuations in ocean chemistry and deep water origins. Site U1409 was proposed to test the hypothesis that there are several acoustically transparent drift packages on the Southeast Newfoundland Ridge that correlate to similar but more persistently developed reflector units on the toe of J-Anomaly Ridge (cored at Site U1403). Drilling on J-Anomaly Ridge showed that the uppermost acoustically transparent unit is of middle Eocene to early Miocene age and is separated from a thin, lower acoustically transparent interval by a set of very well developed reflectors of early Eocene to Cretaceous age. In turn, drilling at Site U1407 showed that the lower acoustically transparent interval overlies shallow-marine carbonates of Albian and older ages. At Site U1409, the putative early Paleogene and Cretaceous sequence is represented by a series of discontinuous reflectors, suggesting that the sequence may be more continuous and less plagued by chert formation than at other drill sites. We inferred that Site U1409 would 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 U1409 should provide our highest deposition rate record of the early Eocene to Late Cretaceous as a counterpart to the largely sub-CCD record at Site U1403 and thereby improve age and water depth control on the behavior of the CCD in the North Atlantic during this key interval. Coring at Site U1409 was also expected to recover the most complete and best preserved records of hyperthermal events. |
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