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doi:10.2204/iodp.proc.342.204.2016 Materials and methodsSite studiedSite U1406 (40°21.0′N, 51°39.0′W) was drilled at J-Anomaly Ridge, southeast of Newfoundland in the northern Atlantic (Fig. F1) in a present water depth of 3798.9 m (see the “Expedition 342 summary” chapter [Norris et al., 2014a]). Three holes were drilled at this site, recovering ~310 m of sedimentary sequences. The sequences were divided into lithostratigraphic Units I through IV. Units I and II are composed of foraminiferal sand and/or nannofossil ooze (see the “Site U1406” chapter [Norris et al., 2014c]). Units III and IV mainly consist of nannofossil chalk. The uppermost Unit I is correlated to the Pleistocene (0–2.61 m core composite depth below seafloor [CCSF] in Hole U1406A). Unit II (2.61–205.68 m CCSF in Hole U1406A) is Oligocene through Miocene in age, including the Oligocene/Miocene boundary (88.09 m CCSF). Unit III correlates to the middle Eocene through early Oligocene (206.68–273.84 m CCSF in Hole U1406A) and includes the Eocene/Oligocene boundary (~219 m CCSF). The deepest Unit IV (273.84–310.83 m CCSF in Hole U1406A) represents the Paleocene to middle Eocene time interval with a significant hiatus during the early Eocene. Carbonate content is generally more than 40 wt% in all units, indicating that the site was positioned above the carbonate compensation depth throughout it sedimentary history (Fig. F2) (see the “Site U1406” chapter [Norris et al., 2014c]). Sedimentation rate at Site U1406 is somewhat higher than normal deep-sea sediments because of the site’s position in a drift. Sedimentation rates are especially high within Unit II, where they are estimated to be ~2.8 cm/ky. Downhole, sedimentation rates gradually decrease and are ~0.6 cm/ky across the Eocene/Oligocene boundary, ~0.2 cm/ky in the early Eocene, and somewhat higher at ~0.8 cm/ky within the Paleocene. Mass accumulation rates are ~0.5–1.0 g/cm2/ky in the early Miocene through late Eocene except for the late Oligocene and the Oligocene/Miocene boundary where they reach 1.5–2.0 g/cm2/ky (see the “Site U1406” chapter [Norris et al., 2014c]). Samples analyzedCore composite depth of each core and sample was calculated based on the splice table published by Norris et al. (see Table T21 in the “Site U1406” chapter [Norris et al., 2014c]). All samples analyzed in this study were taken from Hole U1406A. Top core composite depth of each core from Hole U1406A was also calculated and is graphically shown in Figure F2. In addition to the core catcher samples taken on the catwalk, ~5 mL discrete section samples were examined. A list of all samples studied is shown in Table T1. Samples were taken, on average, every 3 m, and 102 samples were analyzed in total from Cores 342-U1406A-1H through 34X. For cores recovered with the extended core barrel, a relatively well preserved solid piece of sediment was chosen for the discrete sampling. Samples were prepared following the procedure described in detail in the “Methods” chapter (Norris et al., 2014b). Sediments were washed with tap water over a 63 µm sieve. If necessary, samples were washed and dried repeatedly until the fine fraction was thoroughly removed. Subsequently, all washed samples were oven-dried at low temperature (~50°C) and examined under a binocular microscope. Benthic foraminifers were hand-picked from the >150 µm size fraction. Relative abundances of benthic foraminiferal morphotypes are based on counts of ~100 individuals from each sample (mean value; maximum 385 individuals, minimum 19 individuals; see Table T1). When the number of benthic foraminiferal specimens was <100 in a given sample, all individuals from the >150 µm size fraction were analyzed. Five benthic foraminiferal morphotypes were identified in this study:
The dominant species for each morphotype are listed in Table T2. Please note that all specimens with an agglutinated test wall are assigned to the agglutinated morphotype. |
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