Ocean Drilling Program (ODP) Leg 167 represents the first deep drilling since 1978 to study ocean history in the North American Pacific margin. During Leg 167, more than 7000 m of middle Miocene to Holocene sediments were recovered at 13 sites (Sites 1010 to 1022) in the California margin of the northwest Pacific Ocean (Fig. 1; Table 1). The primary objective of this leg was to collect sediments to study the links between the evolution of North Pacific climate and the evolution of the California Current system, with respect to both long-term climate history and high-frequency climatic variability.
One of the basic requirements for this purpose is the availability of an accurate chronology. Biostratigraphy remains a necessary step in establishing such a chronology (Shackleton et al., 1995). Because the onboard calcareous nannofossil biostratigraphy was based only on analyses of core-catcher samples, it was deemed necessary to study supplementary samples, particularly at those sites where detailed paleoclimatic and paleoceanographic studies were being conducted.
The first goal of the present study is, therefore, to present a more complete data set on the calcareous nannofossil biostratigraphy for Leg 167 to supplement the Initial Reports volume (Lyle, Koizumi, Richter, et al., 1997).
The study area covers a large latitudinal transect (from 29°N to 40°N) and is strongly affected by the California Current system; therefore, the environmental conditions are highly variable. Subtropic and subarctic flora and fauna mix along this zone, and, as noted by Wise (1973) and Bukry (1981), the calcareous nannofossil "standard" zonal schemes of Martini (1971) and Okada and Bukry (1980; Fig. 2) cannot be easily applied. Hence, to get intersite correlations and age estimates, the reliability of the biohorizons used in the standard zonations and proposed in the existing literature is evaluated. As a result of this analysis, a regional biostratigraphic scheme is proposed that is correlated with the global chronostratigraphic scale (GCS) and, to a large extent, is calibrated to the geomagnetic polarity time scale (GPTS). This integrated time frame has been used for the dating and correlation of Leg 167 sites.