Average LSRs at Site 1216 are based primarily on paleomagnetic reversals and radiolarian zonal boundaries as defined in Hole 1216A (Tables T5, T6, respectively). Because only one core was taken at the top of Hole 1216B, no composite depth for the site was calculated. LSR values are combined with the dry bulk density (DBD) data (from porosity measurements on individual samples, averaged over the intervals reported) (see "Physical Properties") (Table T11) to determine the mass accumulation rates (MARs) of the sediments.
The paleomagnetic inclination data (see "Paleomagnetism") (Fig. F7) show one comparatively long normal event at the top of Hole 1216A. The base of this event at 10 mbsf, if it represents the base of Subchron C1r.1n (Jaramillo), would have an age of ~1 Ma. The magnetic reversal data are very compressed because of the low sedimentation rates in the pelagic clay facies; thus, it is difficult to recognize the standard magnetic reversal chronology. However, based on the presence of radiolarians from Zone RP13 in Core 199-1216A-6H (see "Biostratigraphy") (Table T3), it is thought that the reversal near the base of Core 199-1216A-5H (see "Paleomagnetism") (Fig. F7) may be the top of Chron C20n, and the base of the long normal section above the overlying reversed interval may be the base of Chron C19n. These very tentative magnetic reversal identifications are used together with three identified radiolarian zonal boundaries (Tables T5, T6) to establish the sedimentation rates for Site 1216 (Fig. F10).
By combining LSR values with DBD data, we determined the MAR of the total sediment (Table T7). Sediment with an LSR of 1.0 cm/k.y. and a DBD of 1.0 g/cm3 will have a 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.).
Lithologic Subunit IA, pelagic clay, is characterized by two LSR values. DBD values range from 0.3 to 0.55 g/cm3 in this unit. Fluxes are high at the top, averaging ~500 mg/cm2/k.y. for this uppermost 1-m.y. interval, if the uppermost normal paleomagnetic interval does represent Chron C1n through Subchron C1r.1n. These values are significantly higher than MAR values reported elsewhere for this facies (J.D. Gleason, et al., unpubl. data; Kyte et al., 1993; Janecek and Rea, 1983). MAR values for the bulk of the pelagic clay unit range from 20 to 40 mg/cm2/k.y., a more normal range for pelagic "red" clays.