Fig. 1. Geographic location of the cores used in this study. ● indicates the successions studied, * indicates the successions considered for discussion.

Fig. 2. Location of sampled intervals in the successions used in this study. Investigated sections are plotted relative to δ¹⁸O stratigraphy of DSDP Site 677 (Shackleton et al., 1990) and polarity time scale. Hatched AREAS=published data; gray COLOR=intervals sampled in this study; WHITE=intervals not studied.

Fig. 3. Intrageneric relative abundances of different size-classes of Gephyrocapsa at DSDP Site 607 (showing the biohorizons , , and ), abundance (number of specimens per unit area) of Calcidiscus macintyrei and Reticulofenestra asanoi (showing the biohorizons and ) and δ¹⁸O stratigraphy. Data on samples from the composite section (mcd=meters composite depth). Interglacial stage numbers are indicated (Ruddiman et al., 1989). Acronyms: , base medium-sized Gephyrocapsa spp.; , base large Gephyrocapsa spp.; , top large Gephyrocapsa spp.; , re-entrance medium-sized Gephyrocapsa spp.; , top C. macintyrei; , base R. asanoi.

Fig. 4. Intrageneric relative abundances of different size-classes of Gephyrocapsa at ODP Site 926 (showing the biohorizons , , and ), abundance (number of specimens per unit area) of Calcidiscus macintyrei and Reticulofenestra asanoi (showing the biohorizons and ) and δ¹⁸O stratigraphy (Curry and Bickert, unpublished), plotted versus mcd. Acronyms: as in Fig. 3.

Fig. 5. Abundances of nannofossil markers plotted versus mbsf and compared with HCGR log results at ODP Site 1063. Polarity reversal boundaries are shown. Isotope stage numbers are tentatively placed in correspondence with peaks in γ-ray counts (=peaks in clay content) (see text and Fig. 6). Acronyms: as in Fig. 3; , top Olduvai; , base Cobb Mountain; , base Jaramillo; , top Jaramillo.

Fig. 6. Comparison of HCGR log results from Site 1063 and δ¹⁸O low-latitude stack, from δ¹⁸O stratigraphies of Core MD900963 of Bassinot et al. (1994) and DSDP Site 677 of Shackleton et al. (1990). Isotope stage numbers are tentatively placed in correspondence with fluctuations in γ-ray counts by correlation with the diagram of δ¹⁸O measurements (see text). Nannofossil and paleomagnetic data are referred to ODP Hole 1063A. Acronyms: as in Fig. 3; LO P. lac., last occurrence of Pseudoemiliania lacunosa; , base Olduvai; , top Olduvai; , base Cobb Mountain; , base Jaramillo; , top Jaramillo; , Brunhes/Matuyama boundary. (Modified from Keigwin et al., 1998, fig. 58.)

Fig. 7. Sapropel pattern, nannofossil biostratigraphic data in the lower-middle Pleistocene interval of ODP Site 967, showing the biohorizons , , , , , tRa, and δ¹⁸O stratigraphy (from Kroon et al., 1998) plotted versus r_mcd (revised meters composite depth). Glacial stage numbers are indicated. Numbers at the right side of the lithologic column indicate sapropels; shaded segments are less distinct sapropels. Position of biohorizons and correlation with sapropel layers of the reference section of Vrica (arrows and lower case letters ‘b’ to ‘v’) are also indicated, together with some of the corresponding i-cycles (from Lourens et al., 1998). Acronyms: as in Fig. 3.

Fig. 8. Sapropel pattern and nannofossil biostratigraphic data in the lower Pleistocene interval of ODP Hole 969D, showing the biohorizons , , and . Numbers at the right side of the lithologic column indicate sapropels. Shaded segments are less distinct sapropels. Correlation with sapropel layers of the reference section of Vrica (arrows and lower case letters ‘e’ to ‘v’) are also indicated, with some of the corresponding i-cycles (from Lourens et al., 1998). Acronyms: as in Fig. 3.

Fig. 9. Lithologic log with sapropel pattern and nannofossil biostratigraphic data in the lower Pleistocene interval of Venezia 1 well, showing the biohorizons and . Sapropels are marked by numbers at the right side of the lithologic column and tentatively correlated with sapropel layers of the reference section of Vrica (lower case letters ‘e’ to ‘p’) and Site 967 (numbers 47–38) (from Massari, Rio, Raffi et al., unpublished). Acronyms: as in Fig. 3.

Fig. 10. Intrageneric relative abundances of different size-classes of Gephyrocapsa (showing the biohorizons , , and ), abundance (number of specimens per unit area) of medium-sized Gephyrocapsa spp., Calcidiscus macintyrei and Reticulofenestra asanoi (showing the biohorizons , , , tRa) at ODP Site 1014. Nannofossil data, spliced record of color reflectance (Lyle et al., 1997), and δ¹⁸O stratigraphy (deMenocal and Baker, 2000) are plotted versus mcd. Acronyms: as in Fig. 3.

Fig. 11. Intrageneric relative abundance of large Gephyrocapsa spp., and abundance (number of specimens per unit area) of Calcidiscus macintyrei at ODP Site 758, showing the biohorizons and , and δ¹⁸O stratigraphy, plotted versus mcd. Interglacial stage numbers are indicated (Farrell and Janecek, 1991). Acronyms: as in Fig. 3.

Fig. 12. Comparison of gephyrocapsid biochronologic data and δ¹⁸O records of DSDP Site 607, ODP Site 926 and Mediterranean ODP Site 967 and Hole 969D, in the early Pleistocene time interval (up to 1.2 Ma). Age models from Ruddiman et al. (1989) for Site 607, Bickert et al., 1997 for Site 926, and Lourens et al. (1998) and Kroon et al. (1998) for ODP Sites 967 and 969. Notations as in Fig. 3, Fig. 4 and Fig. 8.

Fig. 13. Comparison of gephyrocapsid biochronologic data and δ¹⁸O records of DSDP Site 607, ODP Site 926 and ODP Site 967, in the lower part of the middle Pleistocene interval. Age models from Ruddiman et al. (1989) for DSDP Site 607, Bickert et al., 1997 for ODP Site 926, and Kroon et al. (1998) for ODP Site 967. Notations as in Fig. 3, Fig. 4 and Fig. 8.

Fig. 14. Comparison of biochronologic data on Calcidiscus macintyrei and δ¹⁸O records of DSDP Site 607, ODP 926 and ODP Sites 967 and 969. Age models from Ruddiman et al. (1989) for ODP Site 607, Bickert et al., 1997 for ODP Site 926, and Kroon et al. (1998) and Lourens et al. (1998) for ODP Sites 967 and 969. Acronym: , top C. macintyrei.

Fig. 15. Comparison of biochronologic data on Reticulofenestra asanoi and δ¹⁸O records of DSDP Site 607and ODP Site 967. Age models from Ruddiman et al. (1989) for Site 607, and Kroon et al. (1998) for Site 967. Acronyms: , base R. asanoi; tRa, top R. asanoi.

Fig. 16. Summary of the position of the biohorizons considered in this study, in the different sections (a–g), relative to δ¹⁸O low-latitude stack (from δ¹⁸O stratigraphies of Core MD900963 of Bassinot et al., 1994, and DSDP Site 677 of Shackleton et al., 1990) and to polarity time scale. A=Site 607; B=Site 926; C=Sites 967 and 969; D=Site 1014; E=Site 1063; F=Site 758; G=Site 677. Acronyms: , base medium-sized Gephyrocapsa spp.; , top Calcidiscus macintyrei; , base large Gephyrocapsa spp.; , top large Gephyrocapsa spp.; , base Reticulofenestra asanoi; , re-entrance medium-sized Gephyrocapsa spp;.; , top Reticulofenestra asanoi.

Table 1. Summary of successions investigated in this study

Table 2. Comparison of various subdivisions used in Gephyrocapsa taxonomy

Table 3. Summary of biohorizons considered in this study

Table 4. Positions of nannofossil biohorizons investigated in the studied sections

Table 5. Summary of age estimates of biohorizons and correlation with MIS