BIOSTRATIGRAPHY OF LEG 182 SITES

At Site 1126, Miocene sediments were recovered in Samples 182-1126D-7R-CC, 15-16 cm, through 182-1126B-8H-3, 76-78 cm, between 204.61 and 67.3 meters below seafloor (mbsf), and Pliocene sediments were recovered in Samples 182-1126B-8H-2, 76-78 cm, through 6H-6, 75-77 cm, between 65.8 and 52.8 mbsf (Fig. F3). Hiatuses were identified in the early Miocene through Pliocene, and several layers of slumped sediments are present in the upper Miocene and lower Pliocene sections.

The lower Miocene resides in Samples 182-1126D-7R-CC, 15-16 cm (204.61 mbsf), through 182-1126B-19H-5, 73-75 cm (154.53 mbsf), an interval with poor core recovery. Zone SAN3 cannot be positively identified, and Zones SAN4 to SAN6 are strongly condensed between 154.53 and 159.55 mbsf, indicating hiatuses at ~155 and between 170 and 180 mbsf. The planktonic foraminiferal assemblage consists mainly of G. woodi, G. bulloides, Globorotaloides suteri, and tenuitellids in the lower part and G. trilobus, G. woodi, G. praescitula, and G. zealandica in the upper part. Species typical of early Miocene to older ages occur sporadically, including Paragloborotalia semivera and C. dissimilis (Fig. F3).

Middle Miocene Zone SAN7 is recognized by the FO of P. sicana in Sample 182-1126B-19H-3, 74-76 cm (151.54 mbsf). It was overshadowed in abundance upward in Cores 182-1126B-18H and 19H by numerous Globigerinoides mitra and frequent G. trilobus, G. quadrilobatus, and G. falconensis (Fig. F4). A short interval between 131.04 and 136.82 mbsf with P. glomerosa indicates that the 1-m.y. Zone SAN8 is probably hiatus-bound if not condensed between Samples 182-1126B-17H-2, 74-76 cm (131.04 mbsf), and 17H-CC, 13-16 cm (136.82 mbsf). An assemblage characterized by F. peripheroronda and Orbulina spp. denotes Zones SAN9-SAN10 in Samples 182-1126B-14H-6, 74-76 cm (117.74 mbsf), through 17H-1, 75-77 cm (129.76 mbsf). P. mayeri is rare or absent. The uppermost middle Miocene is not present at Site 1126, as the F. peripheroronda assemblage was overlain by upper Miocene sediments.

Zones SAN14-SAN19 of late Miocene age were identified in Samples 182-1126B-8H-3, 76-78 cm (67.26 mbsf), through 14H-4, 75-77 cm (114.75 mbsf). They contain G. bulloides, G. falconensis, G. woodi, G. nepenthes, G. conoidea-G. miotumida, O. suturalis-Orbulina universa, G. dehiscens, Globorotalia scitula, and, in the upper part, Globorotalia cibaoensis, G. conomiozea, and G. pleisiotumida (Fig. F3). A major reduction in the abundance of Globigerinoides and globorotaliids occurs from Zone SAN15 into Zone SAN16 in Hole 1126B (Fig. F4), probably indicating climatic cooling and low sea level. Slumped sediments fall in between Zones SAN17 and SAN18, and the contemporary assemblages were mixed with specimens of older species such as P. glomerosa s.l. in Sample 182-1126C-9H-5, 120-125 cm (82.2 mbsf). Many aggregates of the fairly to poorly preserved specimens from this and the underlying sample (Sample 182-1126C-9H-CC, 20-23 cm) at 84.59 mbsf are believed to have been cemented in a process of diagenesis. Frequent Globoconella sphericomiozea, G. margaritae, and G. crassaformis indicating Subzone SAN19b of the latest Miocene are present in Sample 182-1126B-8-CC, 13-16 cm (72.96 mbsf), but the latter taxon fails to present in other Miocene samples from above, Samples 182-1126B-8H-3, 76-78 cm, through 8H-6, 75-77 cm, between 67.26 and 71.75 mbsf.

The entire lower Pliocene is missing and the upper Pliocene is condensed between Samples 182-1126B-6H-CC, 0-5 cm (53.18 mbsf), and 8H-2, 76-78 cm (65.76 mbsf). A major biotic change across the Miocene/Pliocene boundary saw the extinction of many middle to late Miocene species including G. conoidea and G. sphericomiozea and the appearance of Globoconella puncticulata and G. crassaformis, as well an increased abundance of G. ruber and G. falconensis (Fig. F4). Zones SAN23 and SAN24 can be recognized based on the LO of D. altispira (3.09 Ma) in Sample 182-1126B-7H-6, 75-77 cm (62.25 mbsf), within a slump. Therefore, the slump at 60-63 mbsf likely bears an age of ~2.5-3.2 Ma.

A 45-m-thick Neogene section recovered at this deepwater site is represented only by the upper Miocene and Pliocene (Fig. F5). Hiatuses were identified between the lower Oligocene and upper Miocene and between the lower and upper Pliocene. A slumped debrite overlying the lower Oligocene ooze contains species of various ages: Subbotina angiporoides and Chiloguembelina cubensis (early Oligocene), G. suteri and P. semivera (late Oligocene to early Miocene), F. peripheroronda and P. mayeri (middle Miocene), G. cf. lenguaensis and G. juanai (late Miocene), and G. crassaformis (Pliocene), suggesting a multiple slumping process (Fig. F5). A late Miocene age assemblage referable to Zones SAN17-SAN18 can be recognized in the upper part of the debrite. Although the youngest slumping episode appears to have taken place during the late Miocene-Pliocene, a conclusive age needs further studies (see Finn Surlyk et al., pers. comm., 2002).

An undistorted Subzone SAN19a with G. conomiozea, G. conoidea, and rare G. margaritae is recorded overlying the debrite in Samples 182-1128B-6H-5, 78-80 cm (50.48 mbsf), through 182-1128C-7H-1, 75-77 cm (56.25 mbsf). Abundant Globoconella sphericomiozea (5%-70%) is present in Samples 182-1128B-6H-2, 74-76 cm (45.94 mbsf), through 6H-4, 74-76 cm (48.94 mbsf), indicating Subzone SAN19b of the uppermost Miocene (Fig. F5). Rare G. conoidea and G. sphericomiozea range into the lower Pliocene in Hole 1128B, although both are last found in the Miocene of Hole 1128C in Sample 182-1128C-6H-3, 75-77 cm (49.75 mbsf). Planktonic foraminifers decline to a minimum across the Miocene/Pliocene boundary between 44.4 and 46.75 mbsf in Samples 182-1128B-6H-1, 70-72 cm, and 182-1128C-6H-1, 75-77 cm, accompanied by an increase in benthic species, glauconite, and weathered grains.

The early Pliocene age assemblage with Globoconella puncticulata, G. crassaformis, and G. margaritae is present between 28.45 and 42.45 mbsf in Samples 182-1128B-4H-3, 75-77 cm, through 5H-6, 75-77 cm. Zone SAN20 tops at the LO of G. cf. cibaoensis at ~34 mbsf. As Zone SAN21 cannot be positively identified because of the rarity of the zonal marker G. nepenthes, a hiatus close to ~34 mbsf is then suggested. The LO of G. margaritae at 28.45 mbsf indicates the top of Zone SAN22. Another hiatus probably lies at this level, as it also coincides with the LOs of Globorotalia menardii and N. acostaensis and is only one sample below the LOs of G. extremus and G. trilobus s.l at 27 mbsf in Hole 1128B. Dissolution is also apparent, with up to 50% broken tests found in the assemblage from Samples 182-1128C-3H-3, 75-77 cm (21.25 mbsf), through 182-1128B-4H-1, 75-77 cm (25.45 mbsf). The coincidence of these events likely indicates the responses to the mid-Pliocene global cooling and a major ice-cap growth on Antarctica (e.g., Kennett, 1977). The overlying assemblage belongs in upper Pliocene Zones SAN23-SAN25, with abundant Globoconella inflata, G. puncticulata, G. crassaformis, and frequent G. ruber in Samples 182-1128B-3H-3, 76-78 cm (18.96 mbsf), through 4H-2, 75-77 cm (26.95 mbsf). The absence of D. altispira in samples above 28.45 mbsf also indicates that upper Pliocene sediments are mainly of Zone SAN24 age.

The Neogene at Site 1130 is similar to that at Site 1128 in comprising mainly the upper Miocene and Pliocene, but the section is expanded between 225 and 328 mbsf in Holes 1130A and 1130B (Fig. F6). The upper Miocene ooze is mainly of Zones SAN17-SAN19 age, unconformably overlying the upper Oligocene chert-carbonate sequence. Zone SAN17 with G. plesiotumida and G. extremus extends from 327.05 to 309.15 mbsf in Samples 182-1130A-35X-4, 85-87 cm, to 33X-5, 75-77 cm. Upsection, Zone SAN18 is marked at base by the FO of G. conomiozea in Sample 182-1130A-33X-4, 85-87 cm (307.75 mbsf), Subzone SAN19a by the LO of G. lenguaensis in Sample 32X-1, 75-77 cm (293.55 mbsf), and Subzone SAN19b by the FCO of Globoconella sphericomiozea in Sample 31X-1, 75-77 cm (283.85 mbsf). It is noteworthy that G. dehiscens is not present in any upper Miocene samples from these two holes, although its LO has been recorded in Zone SAN18 at Site 1126 (Fig. F3) and in Subzone SAN19a at Site 1128 (Fig. F5). A steady decrease in the abundance of G. woodi from the upper Miocene to Pliocene was matched by an increase in globorotaliids (Globorotalia, Globoconella, and Menardella) and Globigerinoides (Fig. F7).

The Miocene/Pliocene boundary lies between the LCO of Globoconella sphericomiozea in Sample 182-1130A-29X-5, 75-77 cm (270.65 mbsf), and the FO of G. puncticulata in Sample 29X-CC, 36-39 cm (273.71 mbsf). Only in Holes 1130A and 1130B did we observe an overlap between these two datums. The FO of G. crassaformis, which was found coeval with the FO of G. puncticulata and both together indicating the Miocene/Pliocene boundary in other holes, is present within Subzone SAN19b in Sample 182-1130A-30X-5, 76-78 cm (280.26 mbsf). The concurrence of these species probably resulted from sediment mixing, and the lowermost Pliocene (Zone SAN20) is likely missing. Nevertheless, the population of G. crassaformis from Cores 182-1130B-29X and 30X is dominated by sinistrally coiled specimens, similar to those recorded in the lower Pliocene of New Zealand (Hornibrook et al., 1989, fig. 28). The LO of G. nepenthes in Sample 182-1130A-29X-4, 85-87 cm (269.25 mbsf), defines the upper limit of the undivided Zone SAN21. The lower/upper Pliocene boundary falls at the FO of Globoconella inflata in Sample 182-1130A-28X-3, 75-77 cm (258.05 mbsf), ~1 m below the slump zone between 256.5 and 257.3 mbsf.

As from other holes, the upper Pliocene in Hole 1130A contains a less diverse assemblage predominated by G. inflata, G. puncticulata, G. crassaformis, and G. ruber, and its upper boundary lies close to 240.25 mbsf with the LO of G. extremus in Sample 182-1130B-26X-5, 75-77 cm. The LO of G. woodi in Sample 182-1130A-26X-3, 75-77 cm (238.75 mbsf), can also be used as a proxy. The Zone SAN23 marker D. altispira was observed only in the uppermost Miocene (278.85mbsf) but not in any Pliocene samples from Holes 1130A or 1130B, suggesting that the upper Pliocene section could be mainly of Zones SAN24-SAN25 age. Consequently, the FO of G. truncatulinoides in Sample 182-1130A-25X-1, 75-77 cm (226.15 mbsf), is probably not a true FO record but represents a younger local occurrence of that species at ~1 Ma.

Only ~3% of the cored Neogene section was recovered at this shallow-water site, with the core catcher samples the only material available. About 90% of this material is represented by middle Miocene chert-carbonates, which attain 190 m out of the 210-m Neogene section between 240 and 450 mbsf. The lower and upper Miocene are both thin and incomplete, and the Pliocene is missing (Fig. F8). Planktonic foraminifers are rare and poorly preserved. Hiatuses are suspected at the early/middle Miocene boundary, within the middle Miocene, at the middle/late Miocene boundary, and at the late Miocene/Pleistocene boundary.

The lower Miocene is represented by a single sample, Sample 182-1132C-23R-CC, 18-21 cm (441.68 mbsf), with rare G. suteri, G. dehiscens, Tenuitella spp., and G. bulloides. The absence of G. woodi, G. trilobus, and other younger species suggests a Zone SAN1 assemblage. The contacts of this thin unit with the underlying upper Oligocene (mid to lower Zone P22) and overlying middle Miocene are therefore unconformable.

P. sicana, indicating middle Miocene Zone SAN7 is present in Samples 182-1132C-21R-CC, 23-26 cm (423.13 mbsf), and 22R-CC, 10-13 cm (432.3 mbsf). The latter sample also contains the FO of F. peripheroronda. In Sample 182-1132C-20R-CC, 22-25 cm (413.82 mbsf), the coexistence of P. sicana, P. glomerosa, and O. suturalis-O. universa indicates Zone SAN9. Farther upsection, however, core catchers from Cores 182-1132C-15R to 19R are in such a poor state that neither P. glomerosa nor O. universa was observed. The undifferentiated Zones SAN9-SAN10 interval extends up to Sample 182-1132B-29X-CC, 23-26 cm (257.43 mbsf), because of the persistent occurrence of F. peripheroronda (LO 13.5 Ma). Sample 182-1132C-3R-CC, 7-8 cm (255.87 mbsf), contains P. mayeri but without F. peripheroronda, probably representing Zones SAN11 to SAN13.

The upper Miocene is represented only by Samples 182-1132B-27X-CC, 34-37 cm (241.8 mbsf), and 28X-CC, 32-35 cm (250.73 mbsf). Globoconella cibaoensis, G. extremus, and (in the latter sample) G. conomiozea indicate that these two samples fall, respectively, in Zones SAN17 and SAN18. Rare specimens similar to P. mayeri are likely representatives of Paraglorotalitia challengeri if they are not the reworked P. mayeri.

A good recovery, especially in the upper parts of Holes 1134A and 1134B, allows a better biostratigraphic resolution by planktonic foraminifers. Neogene sediments comprise the interval between ~50 and 235 mbsf, including a relatively complete Miocene section (Fig. F9). Hiatuses occur mainly in the middle Miocene to Pliocene. The abundance variations of species in Hole 1134A (Fig. F10) are comparable with those in Hole 1126B (Fig. F4).

Lower Miocene Zone SAN2 with G. dehiscens and later with G. woodi and G. connecta is present between Samples 182-1134A-27X-1, 75-77 cm (234.35 mbsf), and 23X-CC, 32-35 cm (197.83 mbsf). The FO of Globoconella incognita in Sample 182-1134A-23X-1, 75-77 cm (195.85 mbsf), denotes Zone SAN3, in which P. semivera is also characteristic. G. trilobus first occurs in Sample 182-1134A-19X-CC, 29-32 cm (162.84 mbsf), whereas the FO of G. praescitula is observed ~5 m below, in Sample 20X-1, 75-77 cm (167.05 mbsf). Both datums are close to the base of Zone N6 ( SAN4), but unlike those previously reported from other southern Australian localities (e.g., Li and McGowran, 2000), they are here inverse in the order of distribution. This pattern suggests that G. trilobus was rare in its early transition from G. connecta and its FO could have been slightly diachronous between regions if they are not obscured by hiatuses. The boundary between Zones SAN5 and SAN6 cannot be defined without C. dissimilis, a species last observed below 189 mbsf in Zone SAN3. The upper Zone SAN6 appears to be missing, as the diagnostic species Globoconella miozea first occurs together with and above the Zone SAN7 marker P. sicana in Samples 182-1134B-16X-5, 75-77 cm (145.35 mbsf), and 17X-1, 75-77 cm (148.95 mbsf). G. mitra here is not as characteristic as in Zone SAN7 of Hole 1126B, although it ranges up to Zone SAN13 in Hole 1134A. Therefore, the mixing between the Zone SAN5-lower SAN6 species G. praescitula and G. zealandica and Subzone SAN7a P. sicana without significant G. mitra suggests that a hiatus is probably present at least in the upper Zone SAN6-SAN7 interval.

Farther upsection, a middle Miocene assemblage with P. glomerosa and O. suturalis indicating Zone SAN9 or younger is present in Samples 182-1134B-16X-3, 75-77 cm (142.35 mbsf), and 182-1134A-17X-CC, 31-34 cm (144.17 mbsf). Accordingly, Zone SAN8 (15.1-16.1 Ma) as a whole is likely hiatus-bound, if it is not condensed in the 1.2-m unsampled interval between 144.17 and 145.35 mbsf. Zone SAN10 with O. universa and F. peripheroronda extends up to Sample 182-1134A-14H-5, 75-77 cm (125.13 mbsf). P. mayeri is also present in this interval. An overlap in the ranges of F. peripheroronda and G. lenguaensis s.l. was recorded at 125.13-129.75 mbsf, and their transitional morphologies appear to support a predecessor-descendant relationship between them as implied by Kennett and Srinivasan (1983). However, many studies indicate that the FO of G. lenguaensis is in Zone N12 (= mid-SAN12) and the LO of F. peripheroronda in Zone N10 (= SAN10-SAN11) and there is even a gap within Zone N12 between the former and an advanced form of the latter, the LO of F. peripheroacuta (Chaisson and Leckie, 1993), a species rarely recorded from southern Australia. Therefore, the overlap between the ranges of G. lenguaensis and F. peripheroronda likely reflects a sediment disturbance resulting from events such as a hiatus or slump. Reworking also caused the presence of other older species such as P. glomerosa s.l. (Zones SAN8-SAN9). Sample 182-1134A-14H-5, 75-77 cm (125.13 mbsf), not only contains the LOs of F. peripheroronda and P. mayeri but also the FOs of M. menardii and G. nepenthes, indicating Zone SAN13. Therefore, Zone SAN12 is probably missing, representing a hiatus of at least 1 m.y.

The middle/late Miocene boundary is also unconformable, overlain by a Zones SAN17-SAN18 assemblage comprising Globorotalia cibaoensis, G. cf. conomiozea, N. acostaensis, and Sphaeroidinellopsis seminulina in Samples 182-1134A-13H-5, 75-77 cm (115.75 mbsf), through 14H-1, 75-77 cm (119.25 mbsf). Subzones SAN19a and SAN19b, respectively, are defined at the base by the FO of G. margaritae in Sample 182-1134A-12H-3, 75-77 cm (103.25 mbsf), and by the FCO of Globoconella sphericomiozea in Sample 11H-1, 75-77 cm (90.75 mbsf). The LO of G. lenguaensis is present in Sample 182-1134A-10H-5, 75-77 cm (87.28 mbsf), and the FO of Globoconella pliozea in Sample 9H-5, 78-80 cm (77.78 mbsf). As at Site 1130, G. crassaformis first occurs within Subzone SAN19b in Sample 182-1134A-9H-3, 77-79 cm (74.77 mbsf).

The lower Pliocene Zone SAN21 is defined by the coexistence of Globoconella puncticulata and Globorotalia cibaoensis in Samples 182-1134A-8H-3, 75-77 cm (65.25 mbsf), and 8H-5, 78-80 cm (68.28 mbsf). G. crassaformis and G. falconensis are most abundant (Fig. F10). Almost the entire Pliocene section is occupied by a slump between 49.25 and 62.25 mbsf with displaced specimens of such older species as G. suteri, G. dehiscens, and G. conomiozea. However, several diagnostic datums recognized are in the correct order for determining zones. Zones SAN21 and SAN22 were then justified at the top, respectively, by the consistent LO of G. nepenthes in Sample 182-1134A-8H-1, 75-77 cm (62.25 mbsf), and the FO of Globoconella inflata in Sample 7H-3, 75-77 cm (55.75 mbsf). The coexistence of the LO of D. altispira and the FO of G. inflata at 55.75 mbsf indicates that Zone SAN23 is likely missing. The LCO of G. extremus in Sample 182-1134A-7H-1, 77-79 cm (52.77 mbsf), denotes lower Zone SAN24. One sample above the latter datum contains the Zone SAN25 marker G. truncatulinoides in Sample 182-1134A-6H-5, 75-77 cm (49.25 mbsf). Another slumped assemblage with Pliocene and older species is present in the lower part of the Pleistocene, coinciding with the consistent occurrence of G. truncatulinoides (Fig. F9).

Figure F11 summarizes the planktonic foraminiferal results, emphasizing the new SAN zones and their correlated N zones. The following generalizations can be made.

1. The most complete Neogene sections were recovered from intermediate depths at Sites 1126 and 1134.
2. Sediments are dated to planktonic foraminiferal zones and subzones, although uncertainties exist, especially for the lower Miocene at Sites 1126 and 1134 and middle Miocene at Site 1132, with low core recoveries.
3. Most Neogene units are bounded by hiatuses, numbered 1-11 for the Miocene and 12-15 for the Pliocene and basal Pleistocene (detailed below and in Figs. F12 and F13). The lower and middle Miocene are missing from Sites 1128 and 1130, and at least part of the middle and upper Miocene are absent from all sites studied.
4. The entire Pliocene is missing from Site 1132, and the section at Sites 1126, 1128, 1130 and 1134 is condensed.
5. Slumps occur mainly in the uppermost Miocene and Pliocene, largely concurring with hiatuses. A congestion of these events in this interval may reflect stronger fluctuations at generally lower sea levels, probably conjoined with tectonic activities in the region (Dickinson et al., 2001).
6. The abundance variations of planktonic foraminifers in Holes 1126B, 1130A, and 1134A (Figs. F4, F7, F10) reveal a cool-temperate regime in the early Miocene with abundant G. woodi, a warm-temperate middle Miocene with abundant G. trilobus s.l and Orbulina, a fluctuating cool- to warm-temperate late Miocene with abundant G. conoidea and Menardella spp., and a temperate Pliocene with abundant G. crassaformis and Globoconella puncticulata.
7. An influx of Globoconella inflata and G. ruber in the late Pliocene was probably related to a period of high productivity induced by cooling and northward expansion of the fertile Subantarctic Water (Hodell and Warnke, 1991).
8. Species diversity was low, ~20 species, in the Eocene-Oligocene, although the number could have been obscured by poor preservation (Li et al., this volume). Thirty or more species were present in two periods: the early middle Miocene and latest Miocene. Diversity gradually declined to ~20 species in the Pliocene, and only about 15 species were recorded in recent sediments (Li and McGowran, 1998).
9. Subtropical species are rare and are mainly present in the upper lower Miocene and younger intervals, indicating climatic warming and a stronger flow of the Leeuwin Current (McGowran et al., 1997a). They include G. quadrilobatus, G. sacculifer, G. mitra, G. conglobatus, P. glomerosa s.l., G. lenguaensis, G. margaritae, G. plesiotumida, M. menardii, S. seminulina, and G. nepenthes.
10. The local assemblages responded to global warmings and coolings with speciations and extinctions as well as changing abundances. There is also faunal evidence of other paleoceanographic events, such as the development of the circum-Antarctic Current (Kennett, 1977) and glaciations defined isotopically during the Miocene and Pliocene (Miller et al., 1991, 1998) (Fig. F12).

A plot of planktonic foraminifer datum levels from Tables T2, T3, T4, T5, and T6 revealed the duration and position of hiatuses, as well as changes in sedimentation rates at these five sites (Fig. F12). The numbered hiatuses 1-15 fall mostly at the major third-order boundaries recognized by Hardenbol et al. (1998) and correspond to major falls in sea level (Haq et al., 1987) (Fig. F13). Longer gaps in the sedimentary column indicate erosion and/or nondeposition for at least 3 m.y., probably related to repeated erosional events concurring with the hiatuses. The hiatuses are described below in ascending order.

1. Hiatus 1, between Zones P22 and SAN1 or SAN2, is equivalent to Oligocene/Miocene boundary Ch4/Aq1 at 23.8 Ma (Hardenbol et al., 1998). Upper Oligocene Zone P22 sediments unconformably underlie upper Miocene Zone SAN17 in Hole 1130A. At Site 1128, the hiatus is subsumed in a debrite representing a gap between the lower Oligocene and upper Miocene. Zone P22 in Holes 1126B, 1132C, and 1134A is condensed, although because of poor recovery planktonic foraminifers cannot resolve how much of it is missing. The estimated duration of hiatus 1 is ~0.5 m.y. Within the limit of our biostratigraphic resolution, sedimentary accumulation resumes coevally after the event at two slope sites and one shelf site.
2. Hiatus 2, between Zones SAN2 and SAN3, is equivalent to lower Miocene boundary Aq2 at 22.2 Ma. The coexistence of the FOs of G. woodi (~23 Ma) and G. connecta (~22.2 Ma) in Holes 1126B and 1134A indicates the upper part of Zone SAN2 is probably missing (Fig. F12), although poor core recovery hinders a firm conclusion. The hiatus is subsumed in the gap between Zones SAN2 and SAN7 in Hole 1132C, in the gap between Zones P22 and N17 in Hole 1130A, and in the debrite at Site 1128. Its duration is estimated to be <0.5 m.y.
3. Hiatus 3, within Zone SAN3, lower Miocene boundary Aq3/Bur1 at 20.5 Ma, is equivalent to the second-order TB1/TB2 boundary of Haq et al. (1987). This hiatus is subsumed in the gap between Zones SAN2 and SAN8 in Hole 1132C, in the gap between Zones P22 and SAN17 in Hole 1130A, and in the debrite at Site 1128. It is also suspected in Holes 1126B and 1134A, but the poor recovery hampers a proper resolution. At least 1 m.y. is estimated for its duration.
4. Hiatus 4, lower Zone SAN4, is equivalent to lower Miocene boundary Bur3 at 18.7 Ma. In Holes 1126B and 1134A, the coexistence of G. trilobus and G. praescitula indicates part of SAN4 is missing. The hiatus is subsumed in the gap between Zones SAN2 and SAN8 in Hole 1132C, in the gap between Zones P22 and SAN17 in Hole 1130A, and in the debrite at Site 1128. Its duration is estimated to be ~0.5 m.y.
5. Hiatus 5, between Zone SAN6 and SAN7, is equivalent to Bur5/Lan1 at the lower/middle Miocene boundary at 16.4 Ma. The absence of at least part of these two zones from Holes 1126B, 1132C, and 1134A best exemplifies this hiatus. It is subsumed in the gap between Zones P22 and SAN17 in Hole 1130A and in the debrite at Site 1128. The estimated duration is ~0.5 m.y.
6. Hiatus 6, between Zones SAN8 and SAN9, is equivalent to middle Miocene boundary Lan2/Ser1 at 14.8 Ma. It is documented in Holes 1126B, 1132C, and 1134A, where much of SAN8 is missing and SAN9 is highly condensed. It is subsumed in the gap between Zones P22 and SAN17 in Hole 1130A and in the debrite at Site 1128. The estimated duration is at least 0.5 m.y.
7. Hiatus 7, within Zone SAN11, is proximal to middle Miocene boundary Ser2 at 13.5 Ma. It is marked by F. peripheroronda with (in Hole 1134A) or without (in Hole 1126B) P. mayeri. The estimated duration is >0.5 m.y.
8. Hiatus 8, between Zones SAN12 and SAN13, is proximal to middle Miocene boundary Ser4/Tor1 at 11.7 Ma, the second-order TB2/TB3 boundary. It is represented in Holes 1126B, 1132C, and 1134A with Zones SAN13 or SAN14 overlying Zone SAN10, indicating that the hiatus may also incorporate middle Miocene sequence boundary Ser3 with >1 m.y. duration.
9. Hiatus 9, between Zones SAN15 and SAN16, is equivalent to upper Miocene boundary Tor2 at 9.3 Ma. Zone SAN17 sediments unconformably overlie, respectively, Zones SAN14 in Hole 1134A, Zone SAN10 in Hole 1132C, and Zone P22 in Hole 1130A. Contemporary sediment sections are highly condensed in Hole 1126B (Fig. F12), and a major reduction in warm-water species including Menardella spp. and Globigerinoides spp. in Zone SAN16 between 95 and 100 mbsf probably coincides with this event (Fig. F4). The hiatus is subsumed in the debrite at Site 1128. The estimated duration is ~2 m.y.
10. Hiatus 10, between Zones SAN17 and SAN18, is proximal to upper Miocene boundary Tor3/Me1 at ~7.0 Ma. It is represented by a slump in Holes 1126B and 1126C and by a highly condensed interval with these two zones in Holes 1134A and 1134B and 1128B and 1128C (upper part of the debrite). In Hole 1132C, undifferentiated Zones SAN16-SAN17 unconformably underlie Pleistocene sediments. The estimated duration is at least 0.5 m.y.
11. Hiatus 11, between Subzones SAN19a and SAN19b, is proximal to the uppermost Miocene boundary Me2 at 5.7 Ma. It is subsumed in the gaps between Subzone SAN19b and Zone SAN18 in Holes 1126B and 1126C (coeval with a slump) and between Zone SAN17 and the Pleistocene in Hole 1132C. However, it cannot be recognized at Sites 1130 and 1134. Its duration is estimated to be <0.5 m.y.
12. Hiatus 12, between Zones SAN20 and SAN21, is equivalent to lower Pliocene boundary Za1 close to 4.5 Ma. In Holes 1130A and 1130B, Zone SAN22 overlies a condensed SAN21 sediment, with SAN20 likely missing. In Holes 1134A and 1134B, Zone SAN21 is not only similarly condensed but is also deluged by slumps. The entire Zone SAN20 appears to be missing from all sites, including the deepest Site 1128 (Fig. F11). Its estimated duration is ~0.5 m.y.
13. Hiatus 13, between Zones SAN22 and SAN23, is proximal to the lower/upper Pliocene boundary at ~3.5 Ma. In Holes 1126B and 1126C, Zone SAN23 unconformably overlies Subzone SAN19b, whereas at Sites 1128, 1130, and 1134, Zone SAN24 overlies Zone SAN22. Slumps are also observed in Holes 1126B, 1126C, 1130A, and 1130B. The hiatus is subsumed in the gap between upper Miocene Zones SAN17 and the lower Pleistocene in Hole 1132C. Its duration is estimated to be ~0.5 m.y.
14. Hiatus 14, lower Zone SAN24, is equivalent to upper Pliocene boundaries Ge1 and Pia2 between 2.5 and 2.8 Ma. A slump at ~51 mbsf in Holes 1126B and 1126C and another one between 50 and 56 mbsf in Holes 1134A and 1134B coincide with this event. The hiatus is subsumed in the gaps between Zones SAN22 and SAN24 at Sites 1128, 1130, and 1134 and between upper Miocene Zones N16-N17 and the lower Pleistocene in Hole 1132C. Its duration is estimated to be ~0.5 m.y.
15. Hiatus 15, within the lower Pleistocene, is probably equivalent to boundaries Cala1 and Cala2 between 1.56 and 1.40 Ma. This judgment is based on the condensed sections between the onset of the Jaramillo (1.07 Ma) and termination of the Olduvai (1.77 Ma) in Holes 1130B (respectively, at 212 and 215 mbsf) and Hole 1132B (respectively, at 193 and 222 mbsf), as well as in holes from the eastern transect (Feary, Hine, Malone, et al., 2000). Soon after its FO at ~2 Ma, G. truncatulinoides disappeared from all sites and reappeared just prior to or during the Jaramillo (0.99-1.07 Ma). The duration of hiatus 15 is estimated to be at least 0.5 Ma.

Although the unconformable Oligocene/Miocene contact cannot be positively decided, the absence or rarity of such markers as P. kugleri and T. euapertura indicate there is a possibility. The basal Miocene from the Gambier Basin (western Otway Basin) (Fig. F1), a more temperate locality from the east of the Great Australian Bight, contains many specimens of P. kugleri, indicating warm-water influence after glaciation Mi-1 of Miller et al. (1991, 1998) (see Li et al., 2000). The subsequent occurrence of G. dehiscens and G. woodi signifies the biotic response to an early stage of the Miocene climatic oscillations (McGowran, 1979; McGowran and Li, 1994). McGowran and Li (1996, 1997) quantified changes in Miocene planktonic and benthic foraminiferal assemblages through the Lakes Entrance section from the Gippsland Basin, finding parallel trends with sea level and isotope climatic curves at both the 10⁷ (second-order) and 10⁶ (third-order) years scales. Regional transgressions, each defining a regional stage, reflect major third-order changes in global sea level, although the uplift of the southern Australian margin in the later Miocene obscured part of the record (McGowran et al., 1997b). This neritic record is confirmed and strengthened by the results of Leg 182, as summarized in Fig. F13.

Clifton Transgression (Upper Janjukian Regional Stage)

Deposited during the Clifton Transgression are the Clifton Formation and upper Gambier Limestone (both Otway Basin), upper Abrakurrie Limestone (Eucla Basin), upper Port Willunga Formation (St. Vincent Basin), lower Mannum Formation (Murray Basin), and Puebla Clay (Torquay Basin). The planktonic foraminiferal assemblage is characterized by G. dehiscens, G. woodi, and G. connecta.

Longford Transgression (Longfordian Stage)

The presence of the larger benthic foraminifers Operculina and Amphistegina is the most distinctive biofacies feature of this transgression in many neritic localities along the southern Australian margin. Planktonic species include G. trilobus, G. praescitula, and G. zealandica.

Batesford and Balcombe Transgressions (Batesfordian and Balcombian Stages)

Although distinguishable with or without the larger benthic Lepidocyclina howchini and the Balcombe also by the planktonic O. suturalis, the foraminiferal assemblage in these two transgressions comprises a similarly high diversity with many keeled globorotaliid forms. The larger benthic species found in these and previous transgressions are inferred to have immigrated from the tropics probably by way of the Leeuwin Current (McGowran et al., 1997a). Shallow-water limestones of these transgressions reach their maximum inland limit in several basins, including the Eucla Basin to the north of the Great Australian Bight (Lowry, 1970). They accumulated in a warm and oligotrophic environment at the zenith of the Miocene climatic maximum (McGowran, 1986; McGowran and Li, 1994; McGowran et al., 1997b).

Later Middle Miocene to Late Miocene Transgressions (Bairnsdalian and Mitchellian Stages)

Although the two local stages, Bairnsdalian and Mitchellian, characterize these regional events, only in the Otway and Gippsland Basin can any onshore upper middle to upper Miocene sediments be observed. Records of other basins were eroded because of a structural uplift of the southern Australian margin in the late Miocene (McGowran et al., 1997b; Dickinson et al., 2001). In the Gippsland Basin, planktonic foraminiferal assemblages shifted from dominance by Globigerinoides and Globorotalia to dominance by Neogloboquadrina and Globigerina (Li and McGowran, 2000). The later middle Miocene instability surely also reflects major growth of the East Antarctic ice sheet and associated Antarctic cooling and a major drop in global sea level (Flower and Kennett, 1994).

Pliocene Transgressions

Packages of calcareous sandstones formed in several basins during Pliocene transgressions contain shallow-water foraminiferal assemblages with few age-diagnostic species. Planktonic foraminifers are represented mainly by G. woodi. The Jemmys Point Formation from the eastern Gippsland Basin and Hallet Cove Sandstone in the St. Vincent Basin, respectively, signify these regional events in the early to mid-Pliocene. The unconformable contacts between the Pliocene and the underlying Miocene (mostly middle Miocene) and overlying Quaternary have been well documented (Ludbrook, 1961; Lowry, 1970; McGowran et al., 1997b; Li et al., 2000). Together with those found in the later middle to late Miocene, they indicate periods of regional uplift and erosion probably resulting from collision to the north between Australia and Indonesia (Veevers, 2000).