The Eocene-Oligocene transition marks the change in Earth's climate from a "greenhouse" climate to an "icehouse" climate, a theory first postulated by Kennett, Houtz, et al. (1975). This climatic deterioration has been linked to the beginning of circumpolar current flow and the thermal isolation of Antarctica. New Zealand is a prime area to look for evidence of paleoceanographic changes across this transition as it is located downcurrent from the Tasman Seaway, a primary gateway for the evolving Antarctic Circumpolar Current.
Ocean Drilling Program (ODP) Holes 1123C and 1124C penetrated the Eocene-Oligocene transition sequences east of New Zealand (Fig. F1). Site 1123 is located on the Campbell Plateau, 410 km northeast of the Chatham Islands (Shipboard Scientific Party, 1999a). The extended core barrel (XCB) system was used to recover the Oligocene and Eocene sediments. These sediments consist of alternating white clay-bearing nannofossil chalk and light greenish gray clayey nannofossil chalk overlying alternating white and light gray micritic limestone. Clay residues and stylolitic surfaces beginning in Core 181-1123C-30X indicate advanced diagenesis and pressure dissolution (Shipboard Scientific Party, 1999b), which coincides with increasingly poor nannofossil preservation (Table T1).
Site 1124 is located ~600 km due east of the North Island on the Rekohu Drift (Fig. F1), a turbidite overbank deposit southeast of the Hikurangi Channel (Shipboard Scientific Party, 1999a). Oligocene and Eocene sediments were recovered with the XCB and consist of sharply contrasting lithologies including light greenish gray to white nannofossil chalk, red, yellow, pink, and brown mudstone, and nannofossil-bearing mudstone (Shipboard Scientific Party, 1999c). Three distinct disconformities separate these lithologies, and poor nannofossil preservation in the mudstones complicates interpretation of this 20 m sequence.
This study reports the nannofossil biostratigraphy through the Eocene-Oligocene sequences recovered in ODP Holes 1123C and 1124C. Nannofossil datums are used in conjunction with magnetostratigraphic datums to calculate linear sedimentation rates (LSRs) for these sequences.