Miocene Planktonic Foraminiferal Biostratigraphy of Sites 1143 and 1146, ODP Leg 184, South China Sea

Abstract

The biostratigraphy of Miocene-age sediment samples recovered from Ocean Drilling Program Sites 1143 and 1146, South China Sea, is presented. The preservation of the planktonic foraminifers recovered from both sites varies widely, from poor to very good. The volume of biogenic sediment in the >63-μm size fraction also varies considerably, with many samples being dominated by mud. In comparison to shipboard biostratigraphy, based on core catcher analyses with a depth resolution of ~10 m, we analyzed samples from the two stratigraphic columns every 2–3 m (~45to 93-k.y. resolution). The placement of planktonic foraminifer zonal boundaries was made at a resolution of ~1.5 m at Site 1146 and ~3.0 m at Site 1143. The higher resolution has resulted in significant changes in biostratigraphic zonal boundary locations compared to shipboard results. For the time interval of 5.54–10.49 Ma, the changes in zonation reveal similar age-depth models at both sites, with three segments of changing sedimentation rate through the upper Miocene, though the differences in sedimentation rates at Site 1146 are subtler than those at Site 1143. The boundary between lithologic Units II and III at Site 1146 corresponds to a sharp change in sedimentation rate (58 to 21 m/m.y.) at 15.1 Ma (the first occurrence of Orbulina suturalis). At this site, the interval from 16.4 to 15.1 Ma is characterized by very high mass accumulation rates in the noncarbonate fraction. Above this interval the carbonate fraction becomes increasingly important in the sediment flux to the South China Sea. At Site 1143, sedimentation rates increase from 8 to 99 m/m.y. at 8.6 Ma. This corresponds to a dramatic increase in 1Nathan, S.A., and Leckie, R.M., 2003. Miocene planktonic foraminiferal biostratigraphy of Sites 1143 and 1146, ODP Leg 184, South China Sea. In Prell, W.L., Wang, P., Blum, P., Rea, D.K., and Clemens, S.C. (Eds.), Proc. ODP, Sci. Results, 184, 1–43 [Online]. Available from World Wide Web: . [Cited YYYYMM-DD] 2Department of Geosciences, University of Massachusetts, 611 North Pleasant Street, Amherst MA 01003, USA. Correspondence author: snathan@geo.umass.edu Initial receipt: 6 September 2002 Acceptance: 12 February 2003 Web publication: 20 June 2003 Ms 184SR-219 S.A. NATHAN AND R.M. LECKIE MIOCENE PLANKTONIC FORAMINIFERAL BIOSTRATIGRAPHY 2 both carbonate and noncarbonate mass accumulation rates at the site, but no change in lithology.