An age-depth model of Site 1260 was established by combining all available biostratigraphic and magnetostratigraphic datums of Hole 1260A (Fig. F17). The diagram was constructed by plotting highest and lowest possible ages for selected paleontological samples examined shipboard against the depth of those samples (Table T13). In addition, the age and depth of magnetic reversals recognized shipboard (Table T14) are also plotted.
The biostratigraphic resolution is limited in parts of the succession by moderate to poor preservation and/or the absence of certain taxa. In particular, the Turonian–Albian interval was difficult to date by means of shipboard samples. Interpretation of paleomagnetic data was ambiguous throughout much of Site 1260, resulting in reliable magnetostratigraphic datums (boundaries between periods of reversed and normal polarity) only for the middle Eocene and the Maastrichtian–early Campanian intervals (Table T14). The remainder of the recovered succession (the Coniacian–Albian) did not allow a magnetostratigraphic age assignment because of the presence of the Long Normal Polarity Superchron C34n (~38 m.y.).
Linear sedimentation rates (LSRs) in Hole 1260A varied between 4.3 and 20.5 m/m.y. (Table T15). These rates are typical for pelagic chalks, which characterize the early Oligocene–Campanian interval (lithostratigraphic Units II and III) (see "Lithostratigraphy"). Hiatuses separate the section into five intervals, each with approximately constant sedimentation rates (Fig. F17). The Neogene, comprising only 1 m of the section, is not included in this tally. In addition, sedimentation rates were not calculated for the early Oligocene (Biozones P21a–P19 [1–28.8 mbsf]) because of significant reworking, which resulted in age inversions. The five intervals of approximately uniform sedimentation rates are the following:
Mass accumulation rates (MARs) were calculated from LSRs and average dry bulk density data. For these five intervals (see "Physical Properties") (Table T15), MAR calculations may allow for better assessment of the sedimentation processes because the influence of sediment compaction has been taken into account. Middle Eocene–late Paleocene MARs were relatively high and stable with values of 2.1 g/cm2/k.y., the highest values calculated at this site. Early Eocene–late Paleocene values are 1.6 g/cm2/k.y. Rates of 0.7 and 0.8 g/cm2/k.y. were observed for the Maastrichtian–Campanian and Coniacian–Cenomanian intervals, respectively.
With current stratigraphic resolution, the succession seems to reflect intervals of approximately constant sedimentation separated by six distinct hiatuses, periods of slow deposition, erosional events, or a combination thereof (see letters A–F in Fig. F17). Each of these hiatuses comprises at least 1 m.y., based on biostratigraphic dating (see "Biostratigraphy"). Hiatus A spans ~2 m.y. (early Oligocene; Biozone P18), Hiatus B spans ~5 m.y. (late Eocene–middle Eocene; Biozones P14–P15), Hiatus C spans ~1.5 m.y. (early Eocene; Biozone P9), Hiatus D spans ~1 m.y. (late Paleocene; Biozone P3b), Hiatus E spans ~14 m.y. (early Campanian–Coniacian), and Hiatus F spans ~5 m.y. (late Albian).