P.M. Hull , S.M. Bohaty , A. Cameron , H.K. Coxall , S. D<߰>haenens , D. De Vleeschouwer , L.E. Elder , O. Friedrich , K. Kerr , S.K. Turner , W.E.C. Kordesch , K. Moriya , R.N. Norris , B.N. Opdyke , D.E. Penman , H. Pälike , P.A. Wilson , P.F. Sexton , M. Vahlenkamp , F. Wu , J.C. Zachos
11 January 2017
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).