The principal objectives of Ocean Drilling Program (ODP) Leg 178 were (1) to extract and compare high-resolution records of the past 10 m.y. of continental glaciation of the Antarctic Peninsula Pacific margin contained in topset and foreset beds (paleoshelf) of the same sequence of a glacial prograded wedge and in the hemipelagic sediment drifts on the continental rise; (2) to compile a high-resolution history of grounded ice volume fluctuations and compare it with low-latitude records of sea level change and isotopic estimates of ice volume change over the past 10 m.y.; and (3) to assess the main controls on sediment transport and deposition during glacial intervals and use the insights gained to optimize investigation of the longer, more complicated East Antarctic record of glaciation and glacioeustatic sea level change (Barker, Camerlenghi, Acton, et al., 1999).
More than two decades ago, four sites were drilled on the Bellingshausen Abyssal Plain (Sites 322 and 323) and continental rise (Sites 324 and 325) off the West Antarctic Peninsula (Hollister, Craddock, et al., 1976) during Deep Sea Drilling Project (DSDP) Leg 35. Ice-rafted debris was first recorded in lower to middle Miocene sediments at Site 325 (Hollister, Craddock, et al., 1976). However, poor core recovery at Leg 35 sites limited the glacial and paleoceanographic interpretations that could be made (Barker, Camerlenghi, Acton, et al. 1999). Early drilling on the Antarctic rise and shelf had varying success. DSDP Leg 28 had good core recovery in most holes drilled, with the exception of Site 271 (recovery = 8%), which had difficulty coring through glacial till. ODP Southern Ocean cruises (Legs 113, 114, 119, 120, and 177) greatly improved regional biostratigraphic knowledge (e.g,. Gersonde et al., 1990; Thomas et al., 1990; Barron et al., 1991; Harwood et al., 1992; Gersonde and Barcena, 1998). Although these drilling legs developed biostratigraphy in an open-ocean environment, the resultant diatom zonations (and presumably those of other microfossil groups) are also mostly applicable to the Ross Sea Shelf environment (Winter and Harwood, 1997).
ODP Leg 178 returned to this region in order to refine our understanding of late Neogene West Antarctic Ice Sheet history (Barker and Camerlenghi, 1999). Three sites on the continental rise (Sites 1095, 1096, and 1101) and four sites on the continental shelf (Sites 1097, 1100, 1102, and 1103) were drilled during Leg 178 (Fig. F1; Table T1). Late Miocene to Holocene glacial and interglacial sediments were recovered at the rise and drift sites drilled during Leg 178 (Sites 1095, 1096, and 1101). The upper Quaternary sections of all three sites contained a rare and sporadic record of biosiliceous microfossils with reworked species, a result consistent with other cores taken from around the Antarctic continent. Even though the upper Quaternary assemblage is often sparse, a biostratigraphic signal is obvious. Preservation in general was better in pre-Quaternary parts of the drilled sections, where many samples yielded well-preserved and diverse microfossil assemblages.
Shipboard work was conducted using the magnetochronological calibrations of Berggren et al. (1995). The biochronological framework used during Leg 178 follows that established during ODP Legs 119 (Barron et al., 1991) and 120 (Harwood et al., 1992). The strategy was to establish a biochronological framework at the rise sites and apply it to the shelf sites to investigate the glacial history of Antarctica (Barker, Camerlenghi, Acton, et al., 1999). Here, we link together the multiple stratigraphic and geochronological efforts that have been devoted to Leg 178 sediments, with revised species datum depths and ages as well as data charts for each site. Detailed descriptions of the biostratigraphy of Leg 178 sites are given elsewhere: diatoms of rise sites (Winter and Iwai, Chap. 29, this volume), quantitative diatoms of Site 1095 (Iwai, 2000a, 2000b, 2001, unpubl. data), radiolarians of Hole 1095B (Lazarus, Chap. 13, this volume), nannofossils of Sites 1096 and 1101 (Winter and Wise, Chap. 26, this volume), and nannofossils of Site 1095 (Kameo in Iwai et al., Chap. 28, this volume).
The preliminary magnetostratigraphy proposed for the rise sites during Leg 178 (Barker, Camerlenghi, Acton, et al., 1999) has been revised by Acton et al. (Chap. 37, this volume). Details of the differences in interpretations are discussed in their paper. In essence, their revisions were based primarily on a large number of paleomagnetic observations from U-channel samples and the use of composite depth scales, along with the reevaluation of shipboard data in light of these new constraints. In addition, Acton et al. (Chap. 37, this volume) incorporated the revised biostratigraphic events and datums from this study. Similarly, Williams et al. (Chap. 31, this volume) present a revised interpretation of the magnetic logging data from Sites 1095 and 1096, which is consistent with that from the paleomagnetic measurements on core material. Thus, the paleomagnetic, magnetic logging, and biostratigraphic data from this paper and those of Acton et al. (Chap. 37, this volume) and Williams et al. (Chap. 31, this volume) present a coherent and consistent interpretation of the chronostratigraphy for the Neogene sedimentary sections.