At Site 1197, 14 calcareous nannofossil and planktonic foraminifer age-depth control points and two age-diagnostic species ranges were established for the 675-m-thick sequence of early Miocene to Pleistocene age (Fig. F24; Table T7) (see "Biostratigraphy and Paleoenvironments"). The upper ~59 mbsf, corresponding to the hemipelagic lithologic Unit I and seismic Megasequence D, yielded excellent core recovery and abundant and well-preserved nannofossils and planktonic foraminifers. A magnetostratigraphy could be established for this interval, but not for the poorly recovered sequence below it (see "Paleomagnetism") (Fig. F24). The age model is constructed based on the biostratigraphic control points.
Age-depth relationships are ill-constrained for lithologic Unit II (59.6-175 mbsf), which is equivalent to Megasequence C at this site, as well as for the underlying lithologic units of Megasequence B. Core recovery was extremely low over most of that section (a few centimeters per 9.6 m core interval). With the recovery of such small pieces of core, which is associated with grinding and flushing of 99% of the drilled material and borehole instability, downhole contamination becomes likely. In addition, microfossils in the few and small samples were rare and moderately to poorly preserved, and index fossils were difficult to identify. Within Megasequence C, a broad age range (Zones N16-N18; 11-4.8 Ma) defined by an assemblage of planktonic foraminifers is therefore the only age constraint (see "Biostratigraphy and Paleoenvironments") (Fig. F24).
Seismic and lithologic data suggest that two major hiatuses are at 59 and 175 mbsf, the top and bottom of Megasequence C. The age model constrains the total duration of both hiatuses and deposition of Megasequence C to 2-11 Ma; however, it does not constrain the duration of either of the two hiatuses or Megasequence C (Fig. F24). For a rough estimate, it can be argued that the hiatus at 59 mbsf should have lasted ~4 m.y. (6-2 Ma), given the missing section of Megasequence D dated at other sites. Assuming a sedimentation rate of ~60 m/m.y. for Megasequence C for the period of active platform shedding, Megasequence C deposition would have lasted ~2 m.y. (8-6 Ma). This would leave ~3 m.y. for the hiatus at 175 mbsf (11-8 Ma).
Average sedimentation rates at Site 1197 are 60 m/m.y. for the Miocene Megasequence B and 30 m/m.y. for the Pliocene-Pleistocene Megasequence D. Age picks for lithologic and seismic unit boundaries are summarized in Table T8.