ODP Sites 699 and 700 were drilled within the East Georgia Basin primarily to explore the paleoceanographic and sedimentary history of this region during the early stages of separation of South America from Africa and Antarctica. Determination of the timing of the various events represented in the sedimentary record of these sites requires the establishment of a high-resolution stratigraphic framework. This was achieved through combined magnetostratigraphic/biostratigraphic studies of the sediments recovered from Holes 699A and 700B. The magnetostratigraphic data are presented in this paper. They are based on a combination of shipboard whole-core paleomagnetic determinations made at 10-cm intervals on all archive core halves and involving AF demagnetization in fields of 5 and/or 9 mT together with shipboard and post-cruise incremental AF demagnetization analyses of some 450 discrete samples.A generally continuous magnetostratigraphic record has been obtained for the Pliocene-Pleistocene and Oligocene sequences recovered from Hole 699A. A record of the Brunhes, Matuyama, and late Gauss Chrons has been identified in the Pleistocene to late Pliocene age sediments cored in the upper 30-m section of this hole. However, interpretation of the magnetostratigraphic record observed for the Pliocene sediments in the interval from 30 to 70 mbsf is complicated by the possible presence of hiatuses.A well-defined sequence of normal and reverse polarity magnetozones was identified for the Oligocene sequence of Hole 699A in the interval from 85 to 219 mbsf. Although there are few biostratigraphic datums for this interval, the observed polarity sequence shows a good correlation with geomagnetic polarity Chrons C6CR to C11R. As a result of poor core recovery, the magnetostratigraphic sequence for the early Oligocene to early Eocene age sediments from 243 to 468 mbsf in Hole 699A is discontinuous. However, available biostratigraphic datums allow the identification of Chrons C13N and C13R in the depth interval from 270 to 306 mbsf and the Chron sequence C20R to C22R in the interval from 397 to 465 mbsf.The sedimentary sequence recovered from Hole 700B extends from the middle Eocene through to the Coniacian or Turonian stages. The magnetostratigraphic record for the Eocene part of this sequence is fragmentary, but chronal assignments can be made for certain isolated parts of the section. In contrast, a well-defined succession of magnetozones established for the Paleocene to Late Cretaceous age part of the section correlates well with the polarity time scale between Chrons C26R and C34N. Biostratigraphic (nannofossil) data indicate that a hiatus may be present at the Cretaceous/Tertiary boundary. However, the magnetostratigraphic data indicate the probable presence of a reverse polarity magnetozone at this level, which can be correlated with the reverse interval (Chron C29R) known to span the Cretaceous/Tertiary boundary. The record of the preceding Chron C30N is anomalously short at this site. These data indicate that sedimentation may have been continuous across the Cretaceous/Tertiary boundary and that the hiatus is located instead within late Maestrichtian age Chron C30N.

Supplement to: Hailwood, Ernie A; Clement, Bradford M (1991): Magnetostratigraphy of sites 699 and 700, East Georgia Basin. In: Ciesielski, PF; Kristoffersen, Y; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 114, 337-357