Sedimentation rates at Site 1179 have been calculated from paleomagnetic and biostratigraphic data.
Figure F37 shows a depth vs. age curve for sedimentation at Site 1179 derived from magnetic stratigraphy and the magnetic polarity reversal time scale (See "Paleomagnetism" in the "Explanatory Notes" chapter). Cores 191-1179C-24H through 26X have been excluded, because no magnetic stratigraphy has been defined in these cores. The sedimentation rate curve can be divided into three segments. There are three sedimentation rates that correspond to the first three lithostratigraphic units (see "Sedimentology"). Cores 191-1179C-22H and 23H, which consist of pelagic brown clay, display a slow sedimentation rate of 1.56 m/m.y. for the upper part of Unit III. Sedimentation rates increase upward. Unit II, a massive diatom-bearing radiolarian ooze, which spans Cores 191-1179C-20H through 22H, has a sedimentation rate of 7.56 m/m.y. Unit I, consisting of radiolarian-bearing diatom oozes with ash layers and zeolitic clays, has a sedimentation rate of 29.29 m/m.y. The curve implies either that Site 1179 drifted into an area of increased productivity in the late Miocene and Pliocene or that oceanographic conditions changed in such a way as to lead to a 200-fold increase in sedimentation.
Sediment ages derived from biostratigraphic datums (radiolarians, dinoflagellate cysts, benthic foraminifers, and calcareous nannofossils) in the upper Miocene to Holocene sequence at Site 1179 are plotted against depth in Figure F38. Except for one Lower Cretaceous sample at 358 mbsf, sediments below 240 mbsf are barren of biostratigraphically useful microfossils. Biostratigraphic resolution is highest in Pleistocene sediments and lowest in the upper Miocene-lower Pliocene sediments. The shaded area encompasses the minimum and maximum ages for each sample, constraining sediment accumulation rates. Sedimentation rates were high and increased gradually throughout the late Cenozoic, averaging between ~19 and ~30 m/m.y. during the late Miocene and ~35 m/m.y. during the Pliocene-Pleistocene.