Among the groups of oceanic microfossils, only Radiolaria occur in abundances and preservation states sufficient to provide biostratigraphic control for restricted intervals within sediments recovered in Hole 1223A. The distribution of these microfossils has been divided into four major intervals, A–D. Radiolaria distribution Interval A occupies the depth range 0–3.0 meters below seafloor (mbsf), where the abundance of specimens is very low and preservation is poor. Radiolaria distribution Interval B occupies the depth range 3.02–7.1 mbsf. Radiolaria in Interval B are locally rare to abundant and well preserved, and assemblages range in age from pure early Eocene to early Eocene admixed with late Neogene taxa. Radiolaria distribution Interval C occupies the depth range 7.1–36.99 mbsf and is characterized by sediments either barren of microfossils or containing extremely rare early Eocene specimens. Radiolaria distribution Interval D occupies the depth range 36.99–38.7 mbsf (base of the recovered sedimentary section), where early Eocene Radiolaria are present in rare to common frequencies, but opal-A to opal-CT recrystallization has degraded the preservation state.
The late Neogene assemblage of Radiolaria distribution Interval B is dated at 1.55–2.0 Ma, based on occurrences of Eucyrtidium matuyamai, Lamprocyclas heteroporos, and Theocorythium trachelium trachelium. The early Eocene assemblage of Radiolaria distribution Intervals B and D is somewhat problematically assigned to the Buryella clinata Zone.
1Popova-Goll, I.M., and Goll, R.M., 2006. Cenozoic Radiolaria biostratigraphy of Hole 1223A in the North Pacific: ODP Leg 200. In Kasahara, J., Stephen, R.A., Acton, G.D., and Frey, F.A. (Eds.), Proc. ODP, Sci. Results, 200 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/200_SR/007/007.htm>. [Cited YYYY-MM-DD]
2Integrated Ocean Drilling Program, Texas A&M University, College Station Texas 77845-9547, USA. Correspondence author: goll_i@iodp.tamu.edu
Initial receipt: 8 June 2004
Acceptance: 28 March 2006
Web publication: 17 July 2006
Ms 200SR-007