During Ocean Drilling Program (ODP) Leg 178 we drilled 23 holes at nine sites on the continental shelf rise (Sites 1095, 1096, and 1101), continental shelf (Sites 1097, 1100, 1102, and 1103), and Palmer Deep (Sites 1098 and 1099) off the Pacific margin of the Antarctic Peninsula. Table T1 presents general information about the sites included in this study. Further details about these sites, holes, and cores can be found in the Leg 178 Initial Reports volume (Barker, Camerlenghi, Acton, et al., 1999) and through the online Janus database. This report presents the final diatom biostratigraphic results of samples examined from Sites 1095, 1096, and 1101 located on the continental shelf rise of the Pacific margin of the Antarctic Peninsula as well as the species data charts for each site. Results from other diatom research from this leg are presented in Iwai (submitted), Sjunneskog and Taylor (in press), and Taylor and Sjunneskog (in press). The species referred to in this study are illustrated and treated systematically in Iwai and Winter (Chap 35, this volume).
Previous Deep Sea Drilling Project and ODP Legs 28, 35, 71, 90, 113, 114, 119, 120, and 177 have built upon each other to increase our understanding of diatom biostratigraphy in the mid- to high-latitude ocean regions of the Southern Hemisphere (Schrader, 1976; Ciesielski, 1983, 1986; Gersonde et al., 1990; Thomas et al., 1990; Harwood and Maruyama, 1992; Gersonde and Bárcena, 1998; Gersonde, Hoddell, Blum, et al., 1999). The Pliocene diatom biostratigraphy of Antarctica shelf sediments have been illustrated (in the Ross Sea area) to closely correspond to the open-ocean record, allowing for direct comparisons with a few regional differences (Harwood, 1986; Winter and Harwood, 1997). The Neogene and Quaternary diatom zonal scheme utilized during Leg 178 was primarily the one proposed by Harwood and Maruyama (1992; Leg 120). The diatom biostratigraphic events, paleomagnetic calibration, and age estimates used during this leg are listed in table T4 and illustrated in figure F10 of the "Biostratigraphy" section of the Leg 178 "Explanatory Notes" chapter (Barker, Camerlenghi, Acton, et al., 1999). This zonation scheme, however, was not fully applicable to the diatom flora present in all the sediment recovered during Leg 178 because of the absence or low abundance of several marker species.
All of the absolute ages for the marker species datums have been recalculated to the timescale of Berggren et al. (1995). The revised ages repositioned some of the boundaries but did not necessitate any major changes in the zonal scheme. The reference ages for species datums are taken from various authors, whereas the ages for datum events within particular samples utilize the magnetostratigraphy determined from this cruise. A new marker species, Thalassiosira oliverana, was adopted for the base of the Fragilariopsis reinholdii Zone. This species is structurally more distinctive than Thalassiosira miocenica, the species used originally for this datum. The boundary age of this zone is not changed by the substitution. The zones in the detailed diatom biostratigraphy of Gersonde and Bárcena (1998) were not incorporated into our initial biostratigraphic scheme, as this data was drawn from more northerly drill cores. Gersonde, Hoddell, Blum, et al. (1999) indicate that the first occurrence (FO) of Thalassiosira vulnifica, which marks the base of the Thalassiosira insigna-T. vulnifica Zone of Harwood and Maruyama (1992), is a diachronous event. They tentatively replaced this zone with one called the T. insigna Zone and divided it into Subzones a-c. This new zone is defined wholly by the FO and last occurrence (LO) of T. insigna (total range zone). It is likely that both species experience diachroneity, particularly between deep-sea and shelf sections. As T. insigna is observed to occur in lower abundance in sites closer to the Antarctic continent, the older zonal definition has been retained for this study. Please refer to the "Explanatory Notes" chapter in the Leg 178 Initial Reports volume for a more detailed discussion of the timescale and chronological framework (Barker, Camerlenghi, Acton, et al., 1999).