Magnetoblostratigraphic chronology and palaeoenvironmental history of Cenozoic sequences from ODP sites 1165 and 1166, Prydz Bay, Antarctica

A transect of three sites was drilled during Leg 188 of the Ocean Drilling Program (ODP), proximal to the East Antarctic Ice Sheet (EAIS) across the Prydz Bay continental shelf (Site 1166), slope (Site 1167), and rise (Site 1165). We present results of a palaeomagnetic and rock magnetic Study of sediments recovered at sites 1165 and 1166. Magnetostratigraphic interpretations are presented for both holes and are mainly constrained by diatom and radiolarian biostratigraphies, interpreted in the light of recent refinements to Southern Ocean zonal schemes and datum calibrations for these microfossil groups. Site 1165 records a history of sedimentation on the continental rise extending back to earliest Miocene times (about 22 Ma). Several long-term changes characterise this record, including an overall trend of decreasing sedimentation rates from the bottom to the top of the hole. There is a progressive decrease in the sedimentation rate above about 308 mbsf (meters below sea floor), which is marked by a transition from dark-grey fissile claystones to greenish-grey diatom-bearing clays. At this transition, ice-rafted debris, sand grains, and total clay content also increase. The chronology presented here indicates a middle Miocene age (similar to 14.3 Ma) for the lithological transition. Correlation to ODP Hole 747A from the Kerguelen Plateau suggests that this lithological transition coincides with the base of the Mi-3/3a delta(18)O event, which suggests palaeoclimatic control on middle Miocene sedimentation changes at Site 1165. Core recovery was poor at Site 1166. Consequently, the magnetostratigraphic data are of limited value. The deepest cores recovered at Site 1166 record brief intervals in the early history of the EAIS for the Prydz Bay region, extending back through the early stage of glaciation to pre-glacial times. An Early Cretaceous fluvio-lacustrine unit, lagoonal deposits and sandy fluvio-deltaic units of mid-late Eocene age contain a sporadic record of the transition from humid and mild conditions to cool temperate conditions. (C) 2003 Elsevier B.V.. All rights reserved.