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. I and II contain an excellent magnetostratigraphic sequence. The first core of Hole 1179C contains the mudline and is in the Brunhes Chron. The hole was deepened to the approximate end of Hole 1179B before coring resumed.
Sedimentation rates increase upward.
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. Samples from the basaltic basement section of Hole 1179D give mainly negative inclinations consistent with reversed magnetic polarity at a site north of the equator. Reversed polarity was expected because the site is located on magnetic Anomaly M8. We suspect that these seemingly paradoxical trends in density and porosity are caused by a progressive increase in the relative abundance of diatom fragments, which have low grain densities and contain large volumes of intragranular pore space. The contact between Units I and II is marked by small changes in physical properties, but the transition from Unit II to the pelagic clays of Unit III is dramatic.