High sedimentation rate (~4-7 cm/k.y.) sites in the North Atlantic drilled with the hydraulic piston corer on Leg 94 (Ruddiman, Kidd, Thomas, et al., 1987) have provided particularly useful biostratigraphic and magnetostratigraphic data for calibration of many important datum levels to the GPTS. In particular, calibration of several planktonic foraminiferal datum levels at these sites has demonstrated synchroneity and diachroneity for several species in the mid-latitude North Atlantic from ~37ºN-53ºN (Weaver and Clement, 1986, 1987; Raymo et al., 1989).
An integrated magnetostratigraphy (Channell and Lehman, Chap. 8, this volume) and calcareous nannofossil biostratigraphy for Leg 162 drill sites (Jansen, Raymo, Blum, et al., 1996) allows independent calculation of planktonic foraminiferal datum level ages for subpolar North Atlantic Sites 981-984 (~55ºN-61ºN). Ages were calculated by linear interpolation between age control points. Polarity reversals were used as age control points from core top to the Matuyama/Gauss boundary at Sites 981 and 982. Calcareous nannofossil datum levels were used below the Matuyama/Gauss boundary, with the working hypothesis that they are nearly synchronous (e.g., Backman and Shackleton, 1983). Datum levels include the FO of Pseudoemiliania lacunosa at 3.7 Ma, the LO of Amaurolithus primus at 4.7 Ma, the FO of Discoaster surculus at 7.3 Ma, the LO of Calcidiscus miopelagicus at 10.9 Ma, the LO of Sphenolithus heteromorphus at 13.6 Ma, and the FO of S. heteromorphus at 18.2 Ma (Shipboard Scientific Party, 1996b, 1996c). At Site 983, polarity reversal age control points were used down to the base of the Olduvai Chron. At Site 984, polarity reversals were used down to the base of the Reunion Event; the FO of P. lacunosa at 3.7 Ma was not reached, so the age of the LO of N. atlantica cannot be accurately determined using biostratigraphy at this site.
Planktonic foraminiferal datum levels from Sites 981 to 984 are located to the section level. This resolution is insufficient to resolve glacial-interglacial variations; high-resolution, quantitative data are needed to refine the placement of datum levels. However, resolution is adequate to address broad-scale synchroneity/diachroneity. Several Pliocene-Pleistocene planktonic foraminiferal datum levels judged synchronous in the mid-latitude North Atlantic (Weaver and Clement, 1986; Raymo et al., 1989) are found to be within 5% of their published ages in at least two subpolar sites (Table 12). These include the start of the Acme Zone N. pachyderma (sinistral), the FO of Gr. inflata, and the FO of Gr. puncticulata. However, the LO of N. atlantica (sinistral) somewhat lags its mid-latitude age (2.41 Ma), by ~200 k.y. at Site 981 and by ~100 k.y. at Site 982. Interestingly, the LO of Gr. puncticulata coincides with the LO of N. atlantica (sinistral) at Site 981 (~2.2 Ma) but precedes it at Site 982 (by ~500 k.y.). The LO of Gr. puncticulata is clearly time-transgressive, generally (but not entirely) disappearing earlier at the more northerly sites, consistent with its preference for subtropical/temperate latitudes (Kennett and Srinivasan, 1983; Raymo et al., 1989).
Based on nannofossil biostratigraphy, three Miocene datum levels at Site 982 (Table 12) are found to be within 5% of their published ages (Berggren et al., 1995): the LO of N. acostaensis (5.29 Ma), the FO of O. suturalis (15.1 Ma), and the LO of C. dissimilis (17.3 Ma). Diachroneity is observed for other species datum levels. The dextral to sinistral transition in N. atlantica precedes its published age (6.4 Ma, Weaver and Clement, 1986) by ~700 k.y. The LO of P. mayeri and FO of N. acostaensis pair are both somewhat younger than their published ages. Factors such as sample resolution and preservation complicate the interpretation of these results, and more work is needed to address patterns of diachroneity related to climate.