A total of 77 radiolarian events were recognized within the examined sequences: 26 Bms, 5 evolutionary transitions (e), and 46 Tms (Table T1). Of the 77 events, 67 events were recognized in all holes and 9 were recognized in two holes. The distribution of Bms and Tms demonstrates that the interval from the late Eocene to early Oligocene is characterized by Tms rather than Bms (Figs. F5, F6, F7, F8; Table T1).
Paleomagnetic events were assigned in Holes 1219A and 1220A (Shipboard Scientific Party, 2002c, 2002d). In this study, the Hole 1220A paleomagnetic events that were confirmed from the Chron C11r/C12n to C17n/C17r boundaries throughout the sequence examined were applied for age calibration of the radiolarian events. Ages of radiolarian events were calibrated to the global paleomagnetic timescale of Berggren et al. (1995) and are noted in the right-hand columns in Table T1. Ranges of stratigraphically valuable species and species groups in Hole 1220A are shown in Figure F5.
In Hole 1218A, 25 Bms and 46 Tms were identified (Fig. F6; Table T1).
In Zones RP18, RP19, and RP20, 12, 22, and 9 Tms are distributed, respectively (Fig. F6; Table T1). Three intervals featuring concentrations of Tms were distinguished. Ten Tms are observed in the middle–upper part of Zone RP18 from Samples 199-1218A-25X-1, 75–77 cm, to 24X-5, 71–73 cm (225.45–221.41 mbsf), and form an interval of Tm concentration. Across the Eocene/Oligocene boundary from the upper part of Zone RP19 to the lowermost part of Zone RP20 between Samples 199-1218A-24X-2, 118–120 cm (217.38 mbsf), and 23X-4, 118–120 cm (211.18 mbsf), 25 Tms are concentrated. In Zone RP20, 5 Tms are situated within an interval from Sample 199-1218A-22X-4, 75–77 cm, to 22X-1, 120–122 cm (201.15–197.10 mbsf).
In Zones RP18, RP19, and RP20, 4, 10, and 10 Bms are observed, respectively (Fig. F6; Table T1). One interval characterized by concentration of Bms is recognized around the Eocene/Oligocene boundary from the upper part of Zone RP19 (Sample 199-1218A-24X-3, 29–31 cm; 217.99 mbsf) to the lower part of Zone RP20 (Sample 23X-3, 107–109 cm; 209.57 mbsf), in which 17 Bms are located.
In the examined sequence from this hole, 22 Bms and 44 Tms were identified (Fig. F7; Table T1).
In Zones RP18, RP19, and RP20, 11, 14, and 16 Tms are identified, respectively (Fig. F7; Table T1). In the uppermost part of Zone RP18 between Samples 199-1219A-18H-1, 30–32 cm, and 17H-7, 130–132 cm (158.30–157.65 mbsf), 10 Tms and 2 Bms are concentrated. Because these events are scattered from the middle to upper part of Zone RP19 in Holes 1218A and 1220A (Figs. F6, F8), a possible hiatus covering part of upper Zone RP19 is indicated in this hole. According to age calibration of radiolarian events in Hole 1220A, the estimated age of the lower limit of the hiatus is ~36.1 Ma and that of the upper limit is ~34.7 Ma.
Across the Eocene/Oligocene boundary from the upper part of Zone RP19 to lowermost part of Zone RP20 between Samples 199-1219A-17H-4, 130–132 cm (153.15 mbsf), and 16H-7, 30–32 cm (148.30 mbsf), a total of 25 Tms are situated. In Zone RP20, 6 Tms are located in the interval from Sample 199-1219A-16H-1, 78–80 cm, to 15H-5, 130–134 cm (139.78–136.80 mbsf).
In Zones RP18, RP19, and RP20, 2, 10, and 8 Bms are distributed, respectively (Fig. F7; Table T1). Sixteen Bms are situated around the Eocene/Oligocene boundary from the upper part of Zone RP19 (Sample 199-1219A-17H-4, 130–132 cm; 153.15 mbsf) to the lower part of Zone RP20 (Sample 16H-5, 78–80 cm; 145.78 mbsf).
In the examined interval from this hole, 26 Bms and 45 Tms were identified (Fig. F8; Table T1).
In Zones RP18, RP19, and RP20, 10, 16, and 14 Tms are distributed, respectively (Fig. F8; Table T1). In an interval from the upper part of Zone RP18 (Sample 199-1220A-9H-2, 125–127 cm; 78.75 mbsf) to the lowermost part of Zone RP19 (Sample 8H-5, 125–127 cm; 73.75 mbsf), 12 Tms are concentrated. Across the Eocene/Oligocene boundary from the upper part of Zone RP19 to the lowermost of Zone RP20 between Samples 199-1220A-8H-3, 127–129 cm (70.77 mbsf), and 8H-1, 77–79 cm (67.27 mbsf), a total of 22 Tms are distributed.
In Zones RP18, RP19, and RP20, 4, 9, and 10 Bms are observed, respectively (Fig. F8; Table T1). From the upper part of Zone RP19 (Sample 199-1220A-8H-3, 127–129 cm; 70.77 mbsf) to the lower part of Zone RP20 (Sample 7H-7, 35–37 cm; 66.35 mbsf), 16 Bms are distributed; this interval is characterized by Bms.