Sediments of Cores 170-1039B-18X through 1H correspond to Zones N19-N23, which are Pliocene to Pleistocene in age (Fig. F3). From Cores 170-1039B-1H through 18X, a total of 148 samples were examined. Percentages of respective species to the total planktonic foraminiferal assemblage are shown in Table T1. The last occurrence (LO) of Globigerina nepenthes is recognized in Sample 170-1039B-17X-2, 46-49 cm, which indicates an age of 4.2 Ma. The first appearance of Globorotalia tosaensis is recognized in Sample 170-1039B-15X-1, 46-48 cm, which indicates an age of 3.35 Ma, assignable to the base of Zone N21 of the Pliocene. Therefore, the lower sequences, Core 170-1039B-18X through the middle part of Core 15X, are assignable to Zone N19 of the Pliocene. In this interval, occurrences of G. nepenthes, Dentoglobigerina altispira altispira, Globorotalia margaritae, and Sphaeroidinellopsis seminulina are examined. The top of Zone N21 cannot be established; however, the horizon is tentatively assignable to the base of Section 170-1039B-12X-CC. The LO of Globigeinoides extremus is recognized in Sample 170-1039B-11H-5, 46-49 cm, indicating that the sample is approximately correlative with the Pliocene/Pleistocene boundary (1.77 Ma). The LO of G. tosaensis is recognized in Sample 170-1039B-5H-7, 45-47 cm, which indicates an age of 0.65 Ma, correlating to the base of Zone N23. Changes in the coiling direction of Pulleniatina are recognized at three intervals (Fig. F3). The coiling change from sinistral to dextral between Samples 170-1039B-16X-4, 46-49 cm, and 15X-4, 46-48 cm, is estimated at 3.95 Ma (Berggren et al., 1995).
Cores 170-1043A-30X through 18X correspond to Zones N17-N23, late Miocene to Pleistocene in age (Fig. F4). Planktonic foraminifers were obtained from 92 of the 108 samples examined. Percentages of respective species are shown in Table T2.
The base of Zone N18 is recognized in Sample 170-1043A-30X-3, 45-47 cm (276.05 mbsf), in which the first appearance of Globorotalia tumida is examined. The sequences below Zone N18 are, therefore, assignable to Zone N17 of late Miocene age. The Miocene/Pliocene boundary is located in Sample 170-1043A-28X-4, 45-47 cm, based on the occurrence of abruptly decreased Miocene planktonic foraminifers. Samples 170-1043A-28X-4, 45-47 cm, through 26X-CC are assigned to Zone N19 based on the LO of G. nepenthes and the coiling change from sinistral to dextral in Pulleniatina. Samples 170-1043A-26X-CC through 22X-2, 45-47 cm, are assigned to Zone N21, based on the occurrence of G. tosaensis, S. seminulina, and dextral-coiling Pulleniatina. Samples 170-1043-22X-2, 45-47 cm, through 20X-2, 45-47 cm, are assignable to Zone N22, as horizons above this one are assigned to Zone N23 based on the dextral-coiling Pulleniatina and the absence of G. tosaensis. Sample 170-1043A-21X-CC contains well-preserved specimens of G. extremus, of which the LO is 1.77 Ma, corresponding to the Pliocene/Pleistocene boundary. In Cores 170-1043A-30X through 18X, changes in the coiling direction of Pulleniatina are recognized in five intervals (Fig. F4). The coiling change from sinistral to dextral between Samples 170-1043A-27X-CC and 27X-2, 44-46 cm, is estimated at 3.95 Ma (Berggren et al., 1995).