The radiolarian stratigraphy, together with a set of 21 paleomagnetic reversals, is defined in Holes 1222A and 1222B (Tables T7, T8). These stratigraphies are used to calculate the average linear sedimentation rates (LSRs) for Site 1222 through the section, with dependence on two nannofossil events providing age constraints near the base of the Oligocene and the base of the section (Fig. F10; Table T8). The paleomagnetic stratigraphy extends through the section recovered by APC coring (0-81 mcd). At the base of the Oligocene in Core 199-1222A-7H, there is a marked hiatus as the radiolarian assemblage (although poorly preserved and containing reworked older specimens) shows a transition from the lower Oligocene Zone RP20 in Section 199-1222A-7H-5 through a poorly preserved upper Eocene interval in Section 7H-6, to a well-preserved middle Eocene assemblage (Zone RP15) in Section 7H-7 (see "Biostratigraphy"). The age of the base of the hole is based on the identification a nannofossil assemblage from Zone NP10, recovered from the crust of a piece of chert in Section 199-1222A-12X-CC (Tables T7, T8).
There is no site survey piston core from Site 1222; however, the piston Core EW9709-14P (Lyle, 2000), taken at the next closest site (Site 1221), can be correlated to the density record of Site 1222 (Fig. F11). This correlation is consistent with radiolarian biostratigraphy in the piston core and at Site 1222. Unlike Site 1221, Site 1222 has a fairly thick interval of siliceous clays overlying the high-amplitude density variations found in the lower Oligocene section of lithologic Units II and III (see "Lithostratigraphy"). The section in the piston core equivalent to lithologic Unit I in Site 1222 is represented by 4.5 m of pelagic red clay showing none of the density variations seen in Site 1222 (Fig. F11; see "Lithostratigraphy").
Based on a simple linear interpolation through the uppermost stratigraphic events (Tables T7, T8), the siliceous clays of the upper part of lithologic Subunits IA (see "Lithostratigraphy") have an LSR of about 5.5 m/m.y. Below this relatively high LSR of the Pliocene-Quaternary section, the rates decrease markedly through the Miocene (Fig. F10). Starting in the Oligocene (top of Chron C7n; Tables T7, T8), the LSR generally increases, reaching 3-6 m/m.y. in the Oligocene. Part of the base of the Oligocene may be missing in the hiatus interval that spans the E/O boundary, giving rise to the relatively low LSR (1.75 m/m.y.) in the lower Oligocene. Below the hiatus zone down to the base of the section, the LSR is estimated to be ~1.45 m/m.y.
LSR values may be combined with the dry bulk density (DBD) data from porosity measurements on individual samples (see "Physical Properties") (Table T12) to determine the bulk mass accumulation rates (MARs) of the sediments (Table T9). Sediment with an LSR of 1.0 cm/k.y. and a DBD of 1.0 g/cm3 will have an MAR value of 1.0 g/cm2/k.y. The observed values are rarely this high, so we report the data in milligrams per square centimeter per thousand years (mg/cm2/k.y.) (Fig. F12). MAR values are relatively high in the Pliocene sediments of Subunit IA (>250 mg/cm2/k.y.). These are the highest MAR values for the young part of the section seen at any of the Leg 199 sites. The lower portion of Subunit IA has lower flux values of 60-80 mg/cm2/k.y. The radiolarian clays of Subunit IB accumulated at a modest rate of ~150 mg/cm2/k.y. The lower Oligocene nannofossil ooze of Unit II displays flux values of only 50-100 mg/cm2/k.y., although data are few for this horizon. Unit III, a clay layer, accumulated quite slowly and may contain, or record, a significant hiatus. There are no data relevant to determination of fluxes in the chert horizon of Unit IV.