A 288.9-mcd-thick (256.0 mbsf) middle Miocene to Holocene sequence was recovered at Site 1242. A major hiatus near the base of the sequence (281 mcd) spans the tie from ~12 to ~2.5 Ma. Biostratigraphic datums (see "Biostratigraphy") from the upper 280 mcd were used to construct an age-depth model for this site (Table T17; Fig. F29). Linear sedimentation rates (LSRs), total MARs, and carbonate MARs were calculated at 0.4-m.y. intervals (see "Age Models and Mass Accumulation Rates" in the "Explanatory Notes" chapter).
We relied primarily, although not exclusively, on calcareous nannofossil datums to define the age-depth model for Site 1242 (Fig. F29). The abundance of calcareous nannofossils was low, planktonic foraminifers were poorly preserved and rare in the lower part of the record, and diatoms were generally rare and poorly preserved (see "Biostratigraphy"). The age-depth profile shows no major inflections, reflecting the rather homogeneous lithology in this sediment sequence (see "Lithostratigraphy").
LSRs range between ~0 and 138 m/m.y., and total MARs range between 0 and 11 g/cm2/k.y. The rates all show the same general pattern of a broad peak characterized by an initial, rapid increase in values from 2.8 to 1.6 Ma, maximum values between 1.6 and 1.2 Ma, and a gradual decline in the values after 1.2 Ma. LSRs deviate from the MARs by a gradual relative increase with time, reflecting the general trend of increasing porosity with decreasing overburden combined with a general trend of decreasing carbonate concentrations (decreasing grain density). The interval 100-150 mcd (0.8-1.2 Ma) has a significantly higher relative diatom abundance and reduced relative nannofossil abundance (see "Lithostratigraphy"), but this lithologic change has no apparent effect on the MARs.
Although total MARs and carbonate MARs show the same general trend, carbonate MARs are significantly lower than total MARs because of the high terrigenous content of this sediment.