Samples used for this study came from recovered cores following the rule of 1-3 samples per one core. We treated 122 samples obtained from Holes 1150A and 1150B and 135 samples from Hole 1151A, ranging in age from Holocene to the middle Miocene. The major lithologies of both sites are composed of diatomaceous silty clay with intercalations of minor lithologies such as volcanic ash, sand, and silt layers (Sacks, Suyehiro, Acton, et al., 2000). These lithologies of the present sites gradually become firmer with increasing depth and are identified as four lithologic units (I, II, III, and IV). The sediment samples of the present sites yield abundant siliceous biogenic grains with rare or few calcareous biogenic ones.
Dried sediments (20 cm3) were disaggregated using a sodium sulfate solution and naphtha, and occasionally the sodium tetraphenylborate method (Hanken, 1979) for very hard rocks. After the samples became macerated, each sample was gently wet sieved through a 200-mesh screen (74-µm opening) and oven-dried. Planktonic foraminiferal specimens >125 µm were taken from the dried residues. If a sample contained a large amount of planktonic foraminifers (>500 individuals), the dried residues were split into 2-16 aliquots by using a sample splitter. Semiquantitative estimates of stratigraphically important taxa were made of the relative abundance (very abundant: 
20%, abundant: 10%, common: 5%, rare: <5%) for each sample yielding more than a total of 100 individuals. Stratigraphically important taxa from samples yielding less than a total of 100 individuals were recorded as "+" in occurrence tables. Other taxa were not recorded. Scanning electron microscope (SEM) photographs of some important species were taken by a field-emission-type SEM (JSM-6330F: JEOL Co. Ltd., Tokyo, Japan).
Based on the stratigraphic distributions of selected foraminiferal species, we recognized biohorizons such as the first occurrence (FO) and last occurrence (LO). We recognized each biohorizon between the sample showing the base or top of the occurrence and the nearest sample yielding more than a total of 100 individuals. A biohorizon might have an ambiguous range in its stratigraphic position associated with the distance of the nearest significant sample owing to the sampling interval and the state of the foraminiferal preservation.
