A thick Neogene section was recovered in the upper ~300 m of Ocean Drilling Program Hole 1138A, drilled on the Central Kerguelen Plateau in the Indian sector of the Southern Ocean. Sediment lithologies consist primarily of mixed carbonate and biosiliceous clays and oozes, with several thin (1-3 cm) tephra horizons. The tephras are glass rich, well sorted, and dominantly trachytic to rhyolitic in composition. Volcaniclastic material in these horizons is interpreted to have originated from Heard Island, 180 km northwest of Site 1138, and was likely emplaced through both primary ash fall and turbiditic, submarine flows.
A Neogene age-depth model for Hole 1138A is constructed primarily from 36 diatom biostratigraphic datums. Nannofossil and planktonic foraminifer biostratigraphy provides supporting age information. Additionally, four high-precision 40Ar-39Ar ages are derived from ash and tephra horizons, and these radiometric ages are in close agreement with the biostratigraphic ages. The integrated age-depth model reveals a reasonably complete lower Miocene to upper Pleistocene section in Hole 1138A, with the exception of a ~1-m.y. hiatus at the Miocene/Pliocene boundary. Another possible hiatus is also identified at the Oligocene/Miocene boundary. High Neogene sedimentation rates and the presence of both calcareous and siliceous microfossils, combined with datable tephra horizons, establish Site 1138 as a suitable target for future drilling legs with paleoceanographic objectives. This report also proposes two new diatom species, Fragilariopsis heardensis and Azpeitia harwoodii, from Pliocene strata of Hole 1138A.
1Bohaty, S.M., Wise, S.W., Jr., Duncan, R.A., Moore, C.L., and Wallace, P.J., 2003. Neogene diatom biostratigraphy, tephra stratigraphy, and chronology of ODP Hole 1138A, Kerguelen Plateau. In Frey, F.A., Coffin, M.F., Wallace, P.J., and Quilty, P.G. (Eds.), Proc. ODP, Sci. Results, 183 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/183_SR/016/016.htm>. [Cited YYYY-MM-DD]
2Earth Sciences Department, University of California, Santa Cruz, Santa Cruz CA 95064, USA. sbohaty@es.ucsc.edu
3Department of Geological Sciences, 4100, Florida State University, Tallahassee FL 32306-4100, USA.
4College of Oceanic and Atmospheric Sciences, Oceanography Administration Building 104, Oregon State University, Corvallis OR 97331, USA.
5Earth and Land Science, University of Canberra, Canberra ACT 2601, Australia.
6Department of Geological Sciences, University of Oregon, Eugene OR 97403, USA.
Initial receipt: 29 April 2002
Acceptance: 29 January 2003
Web publication:
30 May 2003
Ms 183SR-016