ZONAL CRITERIA

We follow the zonal scheme of Blow (1959, 1969) as emended by Srinivasan and Kennett (1981a, 1981b) and Kennett and Srinivasan (1983), excluding the subdivision of Zone 17, which is not possible due to the truncation of the range of Pulleniatina primalis in Hole 999A (Fig. 2). This species does not appear until the uppermost Miocene at Site 999, as was the case at Site 925 in the western equatorial Atlantic (Chaisson and Pearson, 1997).

Ages for zonal boundaries are those of Berggren et al. (1995a, 1995b), but with some exceptions, which are noted below. The age of the zone base is included in parentheses below.

Zone N22

Age: latest Pliocene to Holocene (2.0-0.0 Ma)
Definition: total range of Globorotalia truncatulinoides
Discussion: The FO of Globorotalia truncatulinoides has been shown to be diachronous between the subtropics and the tropics, but within the tropics this subtropical species seems to have appeared isochronously (Spencer-Cervato et al., 1994).
Occurrence in Hole 999A: Sample 165-999A-1H-2, 42-44 cm, to 8H-2, 42-44 cm (1.92-66.52 mbsf)

Zone N21/N20

Age: middle to late Pliocene (3.6-2.0 Ma)
Definition: interval between the FO of Menardella miocenica and the FO of Globorotalia truncatulinoides
Discussion: Globorotalia tosaensis was found in only one sample (Sample 165-999A-9H-CC). Therefore, Zone N21 cannot be accurately delineated.
Occurrence in Hole 999A: Sample 165-999A-8H-5, 42-44 cm, to 11H-5, 42-44 cm (71.02-99.52 mbsf)

Zone N19

Age: early Pliocene to latest Miocene (5.6-3.6 Ma)
Definition: interval between the FO of Sphaeroidinella dehiscens s.l. and the FO of Menardella miocenica
Discussion: Berggren et al. (1995a) place the first appearance datum (FAD) of S. dehicens s.s. at 3.25 Ma. Malmgren et al. (1996) report the occurrence of specimens with minute supplementary apertures (sensu lato) as old as 6.08 Ma (Malmgren et al. age revised according to Cande and Kent, 1992) at the western Caribbean DSDP Site 502 (see "Taxonomic Notes"). The base of Zone N19 was drawn beneath the lowest S. dehiscens specimen with a secondary aperture visible using light microscopy.
Occurrence in Hole 999A: Sample 165-999A-11H-CC, to 17H-CC (102.58-159.58 mbsf)

Zone N18/17

Age: late Miocene (8.3-5.6 Ma)
Definition: interval between the FO of Globorotalia plesiotumida and the FO of Sphaeroidinella dehiscens s.l.
Discussion: Zone N18 was not delineated at Site 999 because the stratigraphic range of Globorotalia tumida is discontinuous in Hole 999A (as it was at Site 925 in the western tropical Atlantic; Chaisson and Pearson, 1997). It is found in only one sample (Sample 165-999A-18H-2, 42-44 cm) in the late Miocene portion of its range (see "Taxonomic Notes").
Occurrence in Hole 999A: Sample 165-999A-18H-2, 42-44 cm, to 26X-5, 50-52 cm (161.52-236.00 mbsf)

Zone N16

Age: late Miocene (10.0-8.3 Ma)
Definition: interval between the FO of Neogloboquadrina acostaensis and the FO of Globorotalia plesiotumida
Occurrence in Hole 999A: Sample 165-999A-26X-CC, to 29X-5, 41-43 cm (239.08-264.81 mbsf)

Zone N15

Age: middle to late Miocene transition (10.3-10.0 Ma)
Definition: interval between the LO of Paragloborotalia mayeri and the FO of Neogloboquadrina acostaensis
Occurrence in Hole 999A: Sample 165-999A-29X-CC (267.98 mbsf)

Zone N14

Age: late middle Miocene (11.4-10.3 Ma)
Definition: interval between the FO of Globoturborotalita nepenthes and the LO of Paragloborotalia mayeri
Discussion: Zone M13 of Berggren et al. (1995b) is also delineated by the FO of Globoturborotalita nepenthes, but the age of this datum is given as 11.8 Ma. This age is probably derived from work done by Berggren (1993) and Miller et al. (1994) on the Buff Bay section in Jamaica (see Schneider et al., 1997). The datum age in Berggren et al. (1985) is given as 11.3 Ma. When that age is converted using the "Leg 154 time scale" (based largely on the astrochronological time scale of Shackleton et al., 1995) it becomes 11.6 Ma.
Occurrence in Hole 999A: Sample 165-999A-30X-2, 43-45 cm, to 32X-5, 42-44 cm (269.93-293.62 mbsf)

Zone N13

Age: middle Miocene (11.8-11.4 Ma)
Definition: interval between the LO of Fohsella fohsi s.l. and the FO of Globoturborotalita nepenthes
Occurrence in Hole 999A: Sample 165-999A-32X-CC, 37-40 cm, to 33X-1, 41-43 cm (296.68-297.11 mbsf)

Zone N12

Age: middle Miocene (13.5-11.8 Ma)
Definition: the total range of Fohsella fohsi s.l.
Discussion: Specimens of F. fohsi with complete peripheral keels were quite rare at Site 999. In several samples below Sample 165-999A-33X-CC, 18-20 cm, there were specimens that were incompletely carinate. These specimens were considered Fohsella praefohsi to agree with the definition used by Chaisson and Leckie (1993). See "Taxonomic Notes."
Occurrence in Hole 999A: Sample 165-999A-33X-CC, 18-20 cm, and 34X-2, 41-43 cm (306.28-308.21 mbsf)

Zone N11

Age: middle Miocene (14.0-13.5 Ma)
Definition: Interval between the FO of Fohsella praefohsi and the FO of Fohsella fohsi s.l.
Discussion: Chaisson and Leckie (1993) describe F. praefohsi in the western equatorial Pacific (Site 806) with a peripheral keel on the last two or three chambers. At Site 999 the keel is more complete (present on five or six chambers) on many specimens in Core 165-999A-34X, and the top of 35X, but it does not extend 360° around the final whorl. See discussion in "Taxonomic Notes."
Occurrence in Hole 999A: Sample 165-999A-34X-2, 41-43 cm, to 36X-5, 35-37 cm (308.21-331.45 mbsf)

Zone N10

Age: middle Miocene (14.7-14.0 Ma)
Definition: interval between the FO of Fohsella peripheroacuta and the FO of Fohsella praefohsi
Occurrence in Hole 999A: Sample 165-999A-36X-CC, to 37X-CC (335.18-344.78 mbsf)

Zone N9/N8

Age: early to middle Miocene transition (16.4-14.7 Ma)
Definition: interval between the FO of Praeorbulina sicana and the FO of Fohsella peripheroacuta
Discussion: Orbulina universa is not found below Sample 165-999A-37X-CC (the base of Zone N10) and therefore Zone N9 could not be delineated at this site.
Occurrence in Hole 999A: Sample 165-999A-38X-2, 42-44 cm, to 46X-CC, 27-32 cm (246.72-431.38 mbsf)

Zone N7

Age: early Miocene (17.3-16.4 Ma)
Definition: interval between the LO of Catapsydrax dissimilis and the FO of Praeobulina sicana
Occurrence in Hole 999A: Sample 165-999A-49X-5, 115-117 cm, to 49X-2, 42-44 cm (433.80-452.66 mbsf)

Zone N6

Age: early Miocene (18.7-17.3 Ma)
Definition: interval between the FO of Globigerinatella insueta and the LO of Catapsydrax dissimilis. The bottom of Hole 999A is within Zone N6.
Discussion: The definition of Globigerinatella insueta has been called into question by Pearson (1995) and Pearson and Chaisson (1997) (see "Taxonomic Notes"). Pearson and Chaisson (1997) assign a new datum age (17.4 Ma) to the sensu stricto form (with areal apertures) and another age (20.2 Ma) to the sensu lato form (without areal apertures) of this species.
Occurrence in Hole 999A: Sample 165-999A-49X-4, 42-44 cm, to 50X-CC, 37-39 cm (455.62-469.88 mbsf)