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Data report: relative abundance of benthic foraminiferal morphotypes across the Eocene/Oligocene and Oligocene/Miocene boundaries (IODP Expedition 342 Site U1406, North Atlantic)

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      Abstract

      Integrated Ocean Drilling Program Expedition 342 recovered cores from multiple sites with expanded sections of Eocene sediments, often with exceptional carbonate preservation. These cores presented the opportunity to build an Eocene-spanning, orbital-resolution megasplice for refining the Eocene timescale and detailing paleoceanographic change in a high-latitude North Atlantic location. Here we present a sediment coarse fraction record (i.e., a record of the relative portion of >63 µm sized sedimentary particles), considered alongside shipboard estimates of sedimentation rates, from 8,674 of the 10,829 samples of the Eocene megasplice. Weight percent coarse fraction (wt% CF) data were collected in 10 different laboratories, but we find that long-term trends in wt% CF are robust to interlaboratory differences in sample processing. In particular, this record details a progressive decline in wt% CF from around 5%-8% around 50 Ma to lows of less than 1% around 36 Ma. The decline in weight percent carbonate from ∼50-36 Ma is not monotonic; rather, it is interrupted by at least four local highs at around 46.5, 44, 41.7, and 39 Ma. Interestingly, the abrupt onset of drift sedimentation in the early middle Eocene at Site U1409 (∼47 Ma) does not coincide with a step decline in wt% CF. Because the early Eocene section of Site U1409 has lower sedimentation rates (mean = 0.99 cm/ky) compared to the middle Eocene section of Site U1408 (mean = 3.08 cm/ky), the generally lower wt% CaC0<sub>3</sub> in the middle Eocene section of Site U1408 was hypothesized to be driven by clay dilution in shipboard discussions. However, within the sites with variable sedimentation rates (i.e., Sites U1411, U1406, U1408, and U1409), wt% CF exhibited weak covariance with sedimentation rates (highest r<sup>2</sup> = 0.112; significant p-values for Sites U1411 and U1408 on pairwise correlation tests). Precise age models are thus needed to further resolve the relationship between the mass accumulation of clay, nannofossils, and foraminifer-dominated coarse fraction in these sections. Finally, within well-resolved intervals like the middle Eocene section of Site U1408, orbital scale variability is present in the wt% CF record, supporting shipboard observations of pronounced orbital variation in drift lithology (e.g., core color and weight percent carbonate).

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      CaCO3size distribution: A paleocarbonate ion proxy?

       W. Broecker,  E. Clark (1999)
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        Expedition 342 summary

        Integrated Ocean Drilling Program Expedition 342 was designed to recover Paleogene sedimentary sequences with unusually high deposition rates across a wide range of water depths. The drilling area is positioned to capture sedimentary and geochemical records of ocean chemistry and overturning circulation beneath the flow of the Deep Western Boundary Current in the northwest Atlantic Ocean. The expedition was primarily targeted at reconstructing the Paleogene carbonate compensation depth (CCD) in the North Atlantic for reference to recently obtained high-fidelity records of the CCD in the equatorial Pacific. We find evidence of carbonate deposition events following the Cretaceous/Paleogene (K/Pg) boundary mass extinction, the Paleocene/Eocene Thermal Maximum, and the Eocene–Oligocene transition (EOT). These deposition events may reflect the rebalancing of ocean alkalinity after mass extinctions or abrupt global climate change. Expedition 342 recovered sequences with sedimentation rates high enough to enable studies of the dynamics of past abrupt climate change, including both transitions into “greenhouse” and “icehouse” climate states, the full magnitudes of hyperthermal events, and rates of change in the CCD. An unexpected finding was the recovery of a number of Cretaceous “critical boundaries.” These include the K/Pg boundary, the Campanian–Coniacian interval, the Cenomanian/Turonian boundary and Oceanic Anoxic Event (OAE) 2, and the Albian/Cenomanian boundary OAE 1d.
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          Site U1406: Expedition 342

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            Author and article information

            Journal
            10.2204/iodp.proc.342.2014
            Proceedings of the IODP
            Integrated Ocean Drilling Program
            1930-1014
            11 January 2017
            10.2204/iodp.proc.342.203.2017

            This work is licensed under a Creative Commons Attribution 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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