N.J. Shackleton2 and M.A. Hall2


A continuous and record in bulk fine-fraction carbonate has been obtained for the late Miocene and late middle Miocene (5-14 Ma) at 10-cm intervals (corresponding to an average 6 k.y.). Continuous data are presented for benthic foraminifers over the interval 5–7.3 Ma as well as over intervals from ~9.5 to 9.8 Ma and 11 to 13 Ma. Limited data are also available for planktonic foraminifers over the same intervals. There is strong orbital-frequency covariance between in bulk fine fraction and in benthic foraminifers, suggesting that both parameters reflect variability in the of dissolved CO2 in the ocean. Spectral analysis of the whole record for bulk fine fraction shows strong power in the 400-k.y. and 100-k.y. eccentricity bands. Benthic shows variability that probably reflects the temperature of the deep (3.6 km) Atlantic Ocean water. Bulk fine-fraction displays very little high-frequency variability, possibly due to an original signal having been reduced through isotopic equilibration with pore water. The origin of the long-term variability in bulk fine-fraction , which apparently implies a cooling centered on about 9.5 Ma, is enigmatic, since this feature is not evident in the data for G. sacculifer.

1Shackleton, N.J., Curry, W.B., Richter, C., and Bralower, T.J. (Eds.), 1997. Proc. ODP, Sci. Results, 154: College Station, TX (Ocean Drilling Program).
2University of Cambridge, Godwin Laboratory, Free School Lane, Cambridge, CB2 3RS, United Kingdom. njs5@cam.ac.uk