Site 1168 is located in middle bathyal water depths (2463 m) on the western Tasmanian margin 70 km from the coast (Fig. F1) and north of the present-day Subtropical Front. Three holes were drilled to a total depth of 883.5 mbsf: Hole 1168A (APC/XCB), Hole 1168B (APC), and Hole 1168C (APC/XCB). Biotic and magnetostratigraphic datums from Hole 1168A only indicate a (upper middle?) upper Eocene to upper Quaternary sequence (Table T1; Figs. F2, F3, F4). The sequence is divided into five lithostratigraphic units (Shipboard Scientific Party, 2001b). Unit V, 121.5 m of organic-rich siltstones and claystones, is overlain by 13.4 m (Unit IV) of uppermost Eocene–lowermost Oligocene glauconitic siltstones and organic-rich claystones with varying carbonate content. Above this is Unit III, 88.6 m of siliciclastic sediments of early Oligocene age. Above Unit III lies 400 m of lower Oligocene–middle Miocene nannofossil chalks and claystones of varying silt content (Unit II). The stratigraphically highest unit (Unit I) comprises 260 m of foraminiferal and nannofossil oozes and chalks of middle Miocene to late Quaternary age. See Shipboard Scientific Party (2001b) for detailed lithologic descriptions. Microfossil and magnetostratigraphic data of age significance for Site 1168 are listed in Table T1 and depicted in Figures F2, F3, and F4.
The age model for the Paleogene intervals of Site 1168 is based on several dinocyst, foraminiferal, and nannofossil events from Hole 1168A correlated only to the magnetostratigraphy (Table T1). The base of Hole 1168A (base Core 189-1168A-95X; 883.5 mbsf) is not dated but a level close to the bottom of the hole (base Core 189-1168A-94X; 880.3 mbsf) is assigned an age of middle to late Eocene (~35–36 Ma) based on the occurrence of several dinocyst marker events (see also Brinkhuis, Munstermann et al., this volume), the LO of the nannofossil Reticulofenestra reticulata (35.9 Ma), and magnetostratigraphic evidence (Table T1). However, the FO of the planktonic foraminifer Globigerapsis index indicates an age at least as old as middle Eocene near the bottom of Hole 1168A (42.9 Ma; ~843 mbsf). Further work will help resolve this dispute, but we currently favor the dinocyst-nannofossil evidence on the majority of data points allowing good age control for these intervals and problems with foraminiferal data higher in the hole. Additionally, the middle/upper Eocene (Bartonian/Priabonian) boundary is difficult to place following such foraminiferal evidence. The preservation of >130 m of sediments of exclusively late Eocene age, therefore, indicates rapid deposition at this time. Some of the absolute ages of the dinocyst datums in the bottom of the hole may need slight revision; we indicate all the data in the primary age model, however, to highlight the stratigraphic position of these datums.
The stratigraphic position of the E/O (Priabonian/Rupelian) boundary (sensu GSSP; 33.7 Ma) is difficult to place due to lack of calcareous markers. However, we approximate its position at just below ~740 mbsf by the onset of Chron C13n (33.535 Ma) (Table T1). The Oligocene interval at Site 1168 is greatly expanded compared to the other Leg 189 sites. Here, a relatively complete ~320-m-thick sequence is well dated by dinocyst, nannofossil, planktonic foraminiferal, and magnetostratigraphic datums. The planktonic foraminiferal datums FO of Chiloguembelina cubensis (41.2 Ma; 738 mbsf), FO of Guembelitria triseriata (32.5 Ma; ~697 mbsf), and LO of Globigerina labiacrassata (27.1 Ma; ~475 mbsf) occur too high in the sequence (or are assigned too old an age) for reasonable resolution with the rest of the data set, however. Revision of the ranges of these species at this site is necessary. A short (~1 m.y.) mid–early Oligocene hiatus is suggested at ~733 mbsf by the dinocyst datum LO of Enneadocysta partridgei (32.5 Ma) and the nannofossil datums LO of Isthmolithus recurvus (32.3 Ma) and LO of Reticulofenestra umbilcus (31.3 Ma). Early Oligocene hiatuses are also recognized at the other Leg 189 sites (see below, and Stickley et al., submitted [N2]), but those at Site 1172 (for example) are much longer in duration (and more frequent) than that at Site 1168. The lower/upper Oligocene (Rupelian/Chattian) boundary (28.5 Ma) is approximated by the onset of Subchron C10n.2n (28.7 Ma) at ~592 mbsf, indicating ~150 m of sediment of late Oligocene age above this level. The resulting age model gives an average sedimentation rate of ~6 cm/k.y. for the late Eocene, falling to ~3 cm/k.y. in the early and late Oligocene.
Age determination for the Neogene intervals of Site 1168 is primarily based on integrated nannofossil and planktonic foraminiferal events with a few diatom and radiolarian datums (Table T1). Marine isotope stages are recognized in the benthic oxygen isotope signal back to MIS 24 (920 ka), which we incorporate into the Quaternary biostratigraphy. Unfortunately, the paleomagnetic signal is too weak to determine a robust magnetostratigraphy in the Neogene and Quaternary intervals (although we present these data in Table T1 as an alternative). For further discussion of the paleomagnetic record of Site 1168 see Touchard and Fuller (in press).
The Oligocene/Miocene (O/M; Chattian/Aquitanian) boundary (23.8 Ma) is approximated at 440 mbsf by the LO of nannofossil Reticulofenestra bisecta bisecta (23.9 Ma) and magnetostratigraphy (Table T1). We retain the Berggren et al. (1995a, 1995b) absolute age for the boundary (23.8 Ma) for reasons discussed above. The O/M boundary itself appears to be relatively expanded compared to other sites of Leg 189, regardless of which age is used.
The chronology of the ~355 m of sediment above the O/M boundary in Hole 1168A is somewhat problematic. There is no dispute that this interval (~84–440 mbsf) is entirely Miocene in age, yet biodatums disagree on the subdivision of its chronology (Table T1); further work should help resolve these disagreements, but currently we favor the nannofossil data because of their smaller depth error. The FO of the planktonic foraminifer Praeorbulina curva (16.3 Ma) approximates the lower/middle Miocene (Burdigalian/Langhian) boundary (16.4 Ma) at ~265 mbsf. The biodatums agree relatively well for the middle Miocene interval (~198–265 mbsf), except three planktonic foraminiferal events that are either stratigraphically too shallow in the sequence (longer range?) or assigned too old an age for this site. The middle/upper Miocene (Serravallian/Tortonian) boundary (11.2 Ma) is approximated at ~198 mbsf by the LO of the nannofossil Cyclicargolithus floridanus (11.9 Ma). A late Miocene age is assigned to the interval ~84–198 mbsf at Site 1168, the Miocene/Pliocene (Messinian/Zanclean) boundary (5.3 Ma), being approximated by the nannofossil datum LO of Triquetrorhabdulus rugosus (5.23 Ma) and the dinocyst datum LO of Reticulatosphaera actinocoronata (5.2 Ma) at ~84 mbsf; however, dispute exists on the sub-chronology of this interval (see Table T1). The nannofossil data are favored because of their smaller depth error.
The interval ~15–84 mbsf is assigned a Pliocene age based on dinocyst, foraminiferal, and nannofossil evidence and appears to be relatively complete at Site 1168. The lower/upper Pliocene (Zanclean/Piacenzian) boundary (3.58 Ma) is placed at ~42.7 mbsf at the onset of Subchron C2An.3n (Table T1; Figs. F2, F4). The nannofossil datum FO of Gephyrocapsa caribbeanica (1.72 Ma) approximates the Pliocene/Pleistocene boundary (1.77 Ma) at ~15 mbsf. The chronology above this level is resolved at high resolution by a robust benthic oxygen isotope stratigraphy and several nannofossil datums. The nannofossil data and the oxygen isotope stratigraphy are in generally good agreement at this site (Table T1). A short hiatus (~300 k.y.) commencing at ~1.6 Ma is suggested by nannofossil data at ~10.8 mbsf. The isotope stratigraphy suggests that just the top 5 cm of Hole 1168A is Holocene in age. The resulting age model gives an average linear sedimentation rate through the early Miocene of ~2 cm/k.y., decreasing to a ~1.6 cm/k.y. throughout from the middle Miocene onward.
Site 1170 is located in deep water (2704 m) on the flat western part of the South Tasman Rise (STR), 400 km south of Tasmania (Fig. F1). The site lies within present-day northern subantarctic surface waters, ~150 km south of the Subtropical Front and well north of the Subantarctic Front. Four holes were drilled to a total depth of 780 mbsf: Hole 1170A (APC/XCB), Holes 1170B and 1170C (APC), and Hole 1170D (rotary core barrel [RCB]). Biotic and magnetostratigraphic datums from Holes 1170A, 1170B, and 1170D indicate a middle Eocene to upper Quaternary sequence at Site 1170 (Table T2; Figs. F5, F6, F7). The sequence is divided into five lithostratigraphic units (Shipboard Scientific Party, 2001d), the oldest of which (Unit V) comprises silty claystones of middle and late Eocene age, overlain by 25 m of glauconite-rich clayey siltstone deposited during the latest Eocene to earliest Oligocene (Unit IV). Unit IV is overlain by 472 m of deepwater pelagic nannofossil chalk and ooze of early Oligocene through Quaternary age (Units III–I) containing abundant siliceous microfossils. See Shipboard Scientific Party (2001d) for detailed lithologic descriptions. Microfossil and magnetostratigraphic data of age significance for Site 1170 are listed in Table T2 and depicted in Figures F5, F6, and F7.
The age model for the Paleogene intervals of Site 1170 is based on several dinocyst (Eocene), diatom (Oligocene), and nannofossil (Eocene and Oligocene) events correlated to the magnetostratigraphy (Table T2). The base of Hole 1170D (base Core 189-1170D-38R; ~780 mbsf) is dated at ~48.5 Ma (earliest middle Eocene) based on the first abundant occurrence (FAO) of the dinocyst E. partridgei, which is tied to Subchron C21r at Site 1172 (Brinkhuis, Sengers, et al., this volume). A greater number of dinocyst events than nannofossil events are recorded in the Eocene (despite better sampling resolution for nannofossils), allowing relatively good age constraint for these intervals.
In general, there are some disagreements between the dinocyst stratigraphy and magnetostratigraphy vs. the nannofossil stratigraphy in the middle Eocene. For example, a questionable hiatus at ~527 mbsf (Subunit VA; Hole 1170D) may be indicated by the co-occurrence of two nannofossil datums—the LO of Chiasmolithus solitus (38.2 Ma) and the FO of Reticulofenestra reticulata (41.2 Ma)—as well as dinocyst datum FO of Hemiplacophora semilunifera (41.4 Ma). Such a hiatus, however, appears to be in conflict with the magnetostratigraphy. Further work is needed to clarify this problem; however, we follow the magnetostratigraphic data in this age model (i.e., no middle Eocene hiatus) but also retain the position of the LO of C. solitus datum (only), based on the position of magnetochrons. The positions of the Eocene stage boundaries are impossible to determine from the present data, however.
The dinocyst and nannofossil data appear to be in good agreement in the upper Eocene at the current resolution, and a relatively expanded upper Eocene section (compared to Site 1172, for example) is recognized. The E/O boundary (sensu GSSP; the Priabonian/Rupelian boundary at 33.7 Ma) is difficult to determine on the given information because several important high-latitude E/O boundary markers are missing at this site (e.g., the LO of Reticulofenestra oamaruensis and the LO of Subbotina brevis). However, we approximate its position at ~472 mbsf by using combined dinocyst and diatom datums in Hole 1170D (cf. Sluijs et al., this volume). A series of short hiatuses over the E–O transition and early Oligocene are possibly recognized, but these are difficult to isolate on the relatively low resolution data available. Further details on the dinocyst and diatom stratigraphy at the E–O transition are presented in Sluijs et al. (this volume) and Stickley et al. (submitted [N2]).
Age control for the Oligocene interval is based largely on diatom events, magnetostratigraphy, and a nannofossil event, which are all in excellent agreement. The combined data suggest that most of the lower Oligocene is missing, whereas the upper Oligocene is relatively complete. The diatom datum FO of Coscinodiscus lewisianus var. levis (28.5 Ma) marks the lower/upper Oligocene (Rupelian/Chattian) boundary at ~432 mbsf (Hole 1170D). The stratigraphic positions of planktonic foraminiferal datums LO of Subbotina angiporoides (30 Ma) and FO of Chiloguembelina cubensis (28.5 Ma) are in disagreement with the nannofossil and diatom stratigraphy for the Oligocene. Taken in isolation they suggest, in contrast to the current interpretation, that more of the lower Oligocene is preserved and that much of the upper Oligocene is missing. The LO of C. cubensis would suggest the Rupelian/Chattian boundary to occur 40 m higher at ~392 mbsf (Hole 1170A). However, these foraminiferal data are based on poor-resolution shipboard core catcher samples. Thus as ongoing foraminiferal studies are being undertaken to resolve this issue, the diatom-nannofossil-magnetostratigraphic interpretation is favored based on postcruise analysis at better resolution (~30–80 cm depth error). In particular, the tightly constrained stratigraphic positions of robust nannofossil datum LO of Chiasmolithus altus (26.1 Ma; ~397 mbsf in Hole 1170A) and diatom datums FO of Rocella vigilans var. B sensu Harwood and Maruyama (1992) (28.1 Ma; ~418 mbsf in Hole 1170A), FO of Rocella gelida (25.8 Ma; ~396.7 mbsf in Hole 1170A), and LO of Rocella vigilans var. B (25.5 Ma; ~395.6 mbsf in Hole 1170A) are difficult to refute. A distinct stratigraphic gap exists between the ranges of R. vigilans var. A sensu Harwood and Maruyama (1992) and R. vigilans var. B over the Rupelian/Chattian boundary (Table T2). This phenomenon has also been reported on the Kerguelen Plateau (Harwood and Maruyama, 1992, Roberts et al., 2003). At Site 1170, this gap is ~20 m.
The resulting age model gives an average sedimentation rate through the middle Eocene of ~2.4 cm/k.y. In the late Eocene sedimentation rates fall to 1.1 cm/k.y. on average, falling still further to ~75 mm/k.y. in the early Oligocene, returning to ~1.1 cm/k.y. in the late Oligocene.
Age determination for the Neogene and Pleistocene intervals of Site 1170 are based on integrated diatom, nannofossil, planktonic foraminifer, and a few radiolarian events tied to the magnetostratigraphy. Marine isotope stages are recognized in the benthic oxygen isotope signal back to MIS 18.2 (722 ka), which we incorporate into the biostratigraphic age model. Although the age model for the Neogene intervals is resolved at a higher resolution than for the Paleogene, generally the chronology for this time period remains problematic because of a high amount of core disturbance, particularly around the (presumed position of the) Miocene/Pliocene (Messinian/Zanclean) boundary (5.3 Ma). We present the most likely age model based on the strategy outlined in "Materials and Methods".
The Oligocene/Miocene (Chattian/Aquitanian) boundary (23.8 Ma) is marked by a hiatus (or series of hiatuses/condensed sections) of ~1 m.y. centered around 380–383 mbsf (Hole 1170A) based on seven biomagnetostratigraphic events including the (apparent) onset and termination of subchron C6Cn.2n (23.8 and 23.6 Ma, respectively) and the LO of Reticulofenestra bisecta s. str. (23.9 Ma), all occurring within an interval of 90 cm (382.0–382.9 mbsf; Hole 1170A). The recognition of the Mi-1 event from the oxygen isotope record of Hole 1170A (see Pfuhl and McCave, this volume; Pfuhl et al., in press) may dispute this short hiatus or condensed section, however. Evidence would suggest that much of the lower and middle Miocene is relatively complete at Site 1170 with no major hiatuses recorded, although higher-resolution work may confirm a possible ~1-m.y. hiatus around the upper lower Miocene to lower/middle Miocene (Burdigalian/Langhian) boundary (16.4 Ma) approximated by the close stratigraphic placement of the FO of Calcidiscus premacintyrei (17.4 Ma) and the onset of Subchron C5Cn.1n (16.3 Ma) at ~310.5 mbsf (Hole 1170A). This nannofossil datum is tightly constrained by a ~10-cm error (partly forced by the position of the chron). An expanded section is suggested for the interval around the middle/upper Miocene (Serravallian/Tortonian) boundary (11.2 Ma), indicated by nannofossil, diatom, and magnetostratigraphic data: the nannofossil datum LO of C. floridanus (11.9 Ma) is placed at ~249 mbsf (Hole 1170A) with an error of 75 cm, the onset of Subchron C5n.2n (10.9 Ma) is recognized 40 m higher at 210 mbsf (Hole 1170B), and the diatom datum LO of Denticulopsis dimorpha (10.7 Ma) is seen at ~196 mbsf (Hole 1170A). Based on this information, the average linear sedimentation rate across this boundary is ~4.5 cm/k.y.
Nannofossil and radiolarian evidence supports a hiatus at ~158 mbsf (Hole 1170A) spanning 7.4–6.1 Ma. This hiatus is based on the concurrent FOs of Amaurolithus primus (7.4 Ma) and Amaurolithus delicatus (7.3 Ma), the first two amauroliths in a well-documented evolutionary lineage (Raffi et al., 1998). The top of the Reticulofenestra pseudoumbilica paracme event (7.1 Ma) (Backman and Raffi, 1997) is also tentatively placed at the same depth. At Site 1168 these three events are separated by ~10 m. However, because of core disturbance problems, an error of 5.1 m is associated with these events at Site 1170. On account of the disturbed nature of the cores in the late Miocene, nannofossil samples within disturbed core intervals (based on examination of core photos) were not included in the final determination of events. The radiolarian datum LO of Amphymenium challengerae (6.1 Ma) marks the termination of the hiatus. It is possible the hiatus may have started 600 k.y. earlier (at 8 Ma) if the planktonic foraminiferal datum LO of Paragloborotalia continuosa (8 Ma) (~165 mbsf, Hole 1170A) is taken into consideration with the above datums. If this is accepted, then the hiatus is placed at ~163 mbsf (Hole 1170A) to incorporate the six biodatums above it (Table T2).
Amauroliths are robust, dissolution-resistant nannofossils that are consistently present, though rare to few, at all Leg 189 sites. The R. pseudoumbilica paracme is well documented and appears isochronous (e.g., Backman and Raffi, 1997). The onset and termination of this paracme event were determined semiquantitatively. The classic zero appearance of this species, as noted by Backman and Raffi (1997), was not observed at the Leg 189 sites (cool-temperate in nature). However, a clear decrease in R. pseudoumbilica and its cooler-water form R. gelida (not shown in Table T2) is quite marked and concomitant (see McGonigal and Wei, this volume; McGonigal, in press).
The Miocene/Pliocene boundary (5.3 Ma) is constrained by nannofossil evidence at ~130 mbsf (Hole 1170A) based on the LO of T. rugosus (5.23 Ma), indicating >250 m of sediment of Miocene age at Site 1170. The Pliocene and Quaternary intervals are dated confidently on several robust and supportive nannofossil and diatom datums (Table T2). These intervals have the most potential for a high-resolution, integrated nannofossil-diatom Southern Ocean stratigraphy for the Pliocene–Pleistocene. In addition, one foraminiferal datum, one radiolarian datum, and three magnetostratigraphic datums complete the age model for these younger intervals. Of particular note is the position of the base of the Olduvai Chron (C2n; 1.95 Ma), which is undisputed at 39.7 mbsf (Hole 1170A). The chronology above this level is resolved at high resolution by a robust benthic oxygen isotope stratigraphy, several nannofossil datums, and one diatom datum. The nannofossil data, diatom data, and the oxygen isotope stratigraphy are in generally good agreement at this site (Table T2). The acme of the nannofossil E. huxleyi has age significance and suggests that the top ~80 cm of Hole 1170A is younger than 85 ka, whereas the isotope stratigraphy suggests that the top 20 cm of Hole 1170A is Holocene in age.
The resulting age model gives an average linear sedimentation rate through the early Miocene of ~1 cm/k.y., increasing to, on average, ~1.4 cm/k.y. in the middle and late Miocene. Pliocene–Pleistocene sedimentation rates are ~2.5 cm/k.y. on average.
Site 1171 is located in lower bathyal water depths of ~2150 m on a gentle southwesterly slope on the southernmost STR, ~550 km south of Tasmania and 270 km southeast of Site 1170. At 48°S, Site 1171 lies in subantarctic waters between the Subtropical Convergence to the north and the Subantarctic Front to the south. Four holes were drilled to a total depth of 959 mbsf: Holes 1171A and 1171B (APC), Hole 1171C (APC/XCB), and Hole 1171D (RCB). Biotic and magnetostratigraphic datums from Holes 1171A–1171D indicate a lower Eocene to upper Quaternary sequence at Site 1171 (Table T3; Figs. F8, F9, F10). There is a 3.6 m offset in mbsf between Holes 1171C and 1171D. This offset is large with regard to the resolution of our data. Therefore, in this report we correct for the offset in order to successfully correlate the age data between overlapping parts of these holes by increasing the mbsf level (archived in the ODP database) by 3.6 m for Hole 1171D. This offset is incorrectly reported in Shipboard Scientific Party (2001e) as occurring the other way around (i.e., Hole 1171D offset too deeply). The error is recognized here from postcruise diatom data (occurring in both Holes 1171C and 1171D) and lithologic descriptions (Shipboard Scientific Party, 2001e). Sluijs et al. (this volume) demonstrate the offset further by comparison of magnetic susceptibility records from Holes 1171C and 1171D.
The sequence was divided into six lithostratigraphic units and a number of subunits Shipboard Scientific Party (2001e). The older sequence consists broadly of ~616 m of silty claystone of earliest Eocene to late Eocene age (lithostratigraphic Units VI and V) overlain by 67 m of diatom-bearing claystone of late Eocene age (lithostratigraphic Unit IV) and 6 m of glauconitic siltstone deposited during the latest Eocene (Unit III). Unit III is overlain by 67 m of deepwater nannofossil chalk and ooze of early Oligocene to early Miocene age (Unit II); limestone and siliceous limestone beds are in the base of the Oligocene section. Unit I consists of 234 m of deepwater foraminiferal-bearing nannofossil ooze and chalk of early Miocene to Holocene age. See Shipboard Scientific Party (2001e) for detailed lithologic descriptions. Microfossil and magnetostratigraphic data of age significance for Site 1171 are listed in Table T3 and depicted in Figures F8, F9, and F10.
The age model for the Paleogene interval of Site 1171 is based on several dinocyst (Eocene and earliest Oligocene), diatom (Oligocene), and nannofossil (Eocene and Oligocene) events correlated to the magnetostratigraphy (from Site 1172) (Table T3). A greater number of dinocyst events than nannofossil events are recorded in the Eocene, allowing relatively good age constraint for these intervals. The base of Hole 1171D (base of Core 189-1171D-75R; ~959 mbsf corrected depth) is tentatively dated at <54 Ma (i.e. Subchron C24r or younger) (earliest Eocene) based on the dinocysts (cf. Röhl et al., in press a).
The lower/middle Eocene (Ypresian/Lutetian) boundary (~49 Ma) is placed at the termination of Chron C22n at ~634 mbsf (Hole 1171D corrected depth). As for Site 1170, nannofossil data suggest a hiatus spanning the interval 41.2–38.2 Ma (at ~302 mbsf; Unit IV, Hole 1171D corrected depth), which is in disagreement with dinocyst and magnetostratigraphic data. We are unable to speculate any further on this given the available information but we dismiss such a middle Eocene hiatus (1) on the basis of similar problems at Site 1170 but, more importantly, (2) on the given (tightly constrained) placement of nannofossil datum FO of R. umbilicus (42 Ma) at ~416 mbsf (depth error 1.5 m) (Hole 1171D corrected depth), which would create a doubtfully high sedimentation rate (of >14 cm/k.y.) should the hiatus exist. Further work is being undertaken to clarify this issue. As for Site 1170, the upper Eocene is relatively expanded at Site 1171 (compared to Site 1172). The middle/upper Eocene (Bartonian/Priabonian) boundary (37 Ma) is difficult to position on the current information although the termination of Subchron C17n.1n (36.6 Ma) at ~302 mbsf (Hole 1171D corrected depth) approximates it.
The E/O boundary (Priabonian/Rupelian; 33.7 Ma) appears to be tightly constrained by the nannofossil datum LO of R. oamaruensis (33.7 Ma) at ~279 mbsf (Hole 1171D corrected depth; 70-cm depth error). A series of short hiatuses (cf. Sites 1170 and 1172) over the entire lower Oligocene interval and possibly some of the upper Oligocene are suggested by complementary data from diatom, dinocyst (Sluijs et al., this volume), and nannofossil datums. These datums are tightly constrained stratigraphically (e.g., the LO of C. altus [26.1 Ma] at ~273 mbsf [Hole 1171D corrected depth] with an error of just 9 cm). The age model indicates that ~25 m of Oligocene-age sediment is preserved at Site 1171 compared to almost 90 m at Site 1170. The relatively thin Oligocene section means many important datums are either not observed at this sampling resolution or are missing altogether. For example, the stratigraphic gap between the distinct diatom datums LO of R. vigilans var. A and FO of R. vigilans var. B, which at Site 1170 was clearly observed (see above), is difficult to resolve at Site 1171. Unfortunately, the paleomagnetic record in the critical (carbonate) Oligocene intervals is very poor and cannot be used to help constrain this age information, yet integrated dinocyst and diatom datums provide a reasonable age assessment (Sluijs et al., this volume).
The Paleogene age model gives an average sedimentation rate of ~4.5 cm/k.y. for the early Eocene, falling to ~2–2.6 cm/k.y. in the middle Eocene, and rising to ~3.4–7 cm/k.y. (depending on the position of the middle/late Eocene [Bartonian/Priabonian] boundary). The high amount of nondeposition through the Oligocene gives rise to a very low sedimentation rate of ~2 mm/k.y. for this Epoch.
Age determinations for the Neogene and Pleistocene intervals of Site 1171 are based on integrated diatom, nannofossil, planktonic foraminiferal, and a few radiolarian events tied to the magnetostratigraphy. The Neogene intervals are resolved at a higher resolution than for the Paleogene intervals, and unlike Site 1170, the stratigraphy is relatively straightforward. The resultant age model for the Miocene and younger sections shows relatively a good integration of siliceous and calcareous microfossil groups.
As for Site 1170, the Oligocene/Miocene (Chattian/Aquitanian) boundary (23.8 Ma) at Site 1171 is marked by a hiatus of ~1 m.y. at ~253 mbsf (Hole 1171C) based on nannofossil, foraminiferal, and radiolarian evidence. Of particular note is the placement of the LO of the R. bisecta s. str. (23.9 Ma) datum at this horizon within a depth error of just 30 cm. The age model suggests >200 m of relatively complete Miocene section at Site 1171 except for a condensed interval over the lower/middle Miocene (Burdigalian/Langhian) boundary (16.4 Ma) at ~197–198 mbsf (Hole 1171C) and a hiatus at ~65 mbsf (Hole 1171A) spanning the interval 7.8–6.3 Ma based on nannofossil data (Table T3). The middle Miocene appears to be relatively complete at Site 1171 with the middle/upper Miocene (Serravallian/Tortonian) boundary (11.2 Ma) placed within the interval 113–123 mbsf (Hole 1171C) on diatom and magnetostratigraphic data. This boundary interval appears to be expanded but not as greatly as that at Site 1170.
The Pliocene and Pleistocene intervals are well dated on several robust and supportive nannofossil and diatom datums (Table T3). As for Site 1170, there is a lot of potential for a high-resolution, integrated nannofossil-diatom Southern Ocean stratigraphy in these intervals. The resulting biostratigraphy appears to be corroborated by a detailed magnetostratigraphy and by a single foraminiferal and radiolarian datum. The Miocene/Pliocene (Messinian/Zanclean) (5.3 Ma) boundary is approximated at ~55 mbsf (Hole 117A) on the position of the nannofossil datum LO of T. rugosus (5.23 Ma). Also of note is the recognition of the lower/upper Pliocene (Zanclean/Piacenzian) boundary at the onset of the Gauss Chron (C2An.3n; 3.58 Ma) at 40.4 mbsf (Hole 1171C) and the Pliocene/Pleistocene (Gelasian/Calabrian) boundary at the termination of the Olduvai Chron (1.77 Ma) at 24 mbsf (Hole 1171C). The age model above this level is resolved at high resolution by a chronology derived from correlation of the Hole 1171A L* record with those from Holes 1170A and 1172A (see "Materials and Methods") and several diatom and nannofossil datums. The nannofossil data, diatom data, and L* stratigraphy are in excellent agreement at this site (Table T3). The acme of nannofossil E. huxleyi suggests that the top ~50 cm of Hole 1171A is younger than 85 ka, whereas the L* stratigraphy suggests that the top 25 cm of Hole 1171A is Holocene in age.
The resulting age model gives an average linear sedimentation rate through the early Miocene of ~0.9 cm/k.y., increasing to ~1.4 cm/k.y. (average) in the middle Miocene, and ~2.5 cm/k.y. (average) in the late Miocene. Pliocene–Pleistocene sedimentation rates are a little over ~1 cm/k.y. on average (0.9 cm/k.y. in the Pliocene rising to ~1.4 cm/k.y. in the Pleistocene).
Site 1172 is located in a water depth of ~2620 m on the flat western side of the East Tasman Plateau (Fig. F1) in cool subtropical water just north of the present-day Subtropical Front. Four holes were drilled to a total depth of 766.5 mbsf: Hole 1172A (APC/XCB), Holes 1172B and 1172C (APC), and Hole 1172D (RCB). Biotic and magnetostratigraphic datums from Holes 1172A and 1172D indicate a lower Maastrichtian (Upper Cretaceous) to upper Quaternary sequence at Site 1172 (Table T4; Figs. F11, F12, F13). The sequence is divided into four lithostratigraphic units (Shipboard Scientific Party, 2001f), the oldest of which (Unit IV) comprises ~263 m of silty organic-rich claystones of Maastrichtian to early Eocene age. Overlying this is ~142 m of middle–upper Eocene diatomaceous organic-rich claystones (Unit III). Unit II is thin (~5 m) but is formed of a complex sequence of glauconitic claystones and siltstones of latest Eocene to earliest Oligocene age. The youngest unit (Unit I) is ~356 m of calcareous nannofossil and foraminiferal ooze. See Shipboard Scientific Party (2001f) for detailed lithologic descriptions.
Microfossil and magnetostratigraphic data of age significance for Site 1172 are listed in Table T4 and depicted in Figures F11, F12, and F13. There is a small offset of ~1 m in absolute mbsf between Hole 1172A and 1172D (age data recognized in both holes are ~1 m deeper by mbsf in Hole 1172D). This offset is not adjusted for in Table T4 (i.e., data are presented "by hole"). See Shipboard Scientific Party (2001f) for general information.
Some of the most successful deep drilling of Leg 189 occurred at Site 1172. For example, recovery included an almost complete K/T interval (see also Schellenberg et al., in press), a possible Paleocene/Eocene boundary interval (see also Röhl et al., in press a), and a complete E/O boundary interval (see also Stickley et al., submitted [N2]). The age model for the Maastrichtian interval is based mainly on dinocyst events with two nannofossil events. The Paleocene and lower Eocene intervals of Site 1172 are dated solely by dinocyst datums tied to a robust magnetostratigraphy (Table T4). Dinocyst and magnetostratigraphic data also provide the basis of the age model for the middle upper Eocene intervals with a few nannofossil and radiolarian datums and one planktonic foraminiferal datum. The upper Eocene/lower Oligocene boundary interval is dated entirely by dinocysts and diatoms tied to the magnetostratigraphy. This site provides the best opportunity of all the deep sites of Leg 189 for studying this critical boundary interval. In the Oligocene, diatoms, nannofossils, and planktonic foraminifers provide the age information, tied to the magnetostratigraphy.
The base of Hole 1172D (base of Core 189-1172D-31R; ~766.5 mbsf) is dated at 70 Ma (early Maastrichtian) based on the FAO of the dinocyst genus Manumiella. The K/T boundary (65 Ma) occurs at 695.99 mbsf on lithologic, dinocyst, diatom (pyritized), and magnetostratigraphic evidence. A hiatus of ~800 k.y. marks the boundary itself, with all of Chron C29r and possibly parts of Chrons C29n and C30n missing. Schellenberg et al. (in press) provide details on the age model and paleoenvironmental interpretation of the K/T boundary at Site 1172. Just over 70 m of Maastrichtian-age sediments were recovered at this site.
Geochemical and palynological data from Röhl et al. (in press a) and Brinkhuis, Sengers, et al., (this volume) suggest the Paleocene/Eocene Thermal Maximum (PETM) (~55 Ma) occurs at ~620 mbsf in Hole 1172D. See the discussion in Röhl et al. (in press a) on the Paleocene/Eocene (P/E) transition and PETM at Site 1172. Brinkhuis, Sengers, et al. (this volume) provide further information on the dinocyst successions through the Paleocene and Paleocene–Eocene (P–E) transition. The resulting age model suggests that ~76 m of sediment of Paleocene age is recovered at Site 1172.
The lower/middle Eocene (Ypresian/Lutetian) boundary (~49 Ma) is marked by the termination of Chron C22n at 526.4 mbsf (Hole 1172D), suggesting that nearly 94 m of relatively complete lower Eocene sediments were recovered at Site 1172. In addition, the bottom of Hole 1172A is dated to the early Eocene. The middle/upper Eocene (Bartonian/Priabonian) boundary (37 Ma) is difficult to place in these sediments because of the commencement of notable condensation at this time (Röhl et al., in press b; Stickley et al., submitted [N2]). However, it is approximated at ~368 mbsf (within Core 189-1172A-40X) by dinocyst datums FAO of Spinidinium macmurdoense (36.9 Ma) and FO of Stoveracysta ornata (36.95 Ma), suggesting that >158 m of middle Eocene sediments are preserved at Site 1172.
The upper Eocene and E/O boundary intervals are condensed into ~10 m of sediment; however, the stratigraphy is resolved at high resolution by several dinocyst and diatom datums with a robust magnetostratigraphy. The exact position of the E/O boundary sensu Berggren et al. (1995a, 1995b) (Priabonian/Rupelian; 33.7 Ma) is difficult to place because of the lack of marker calcareous microfossils, yet its position is approximated to ~33.5 Ma (cf. Oi-1a event of, e.g., Zachos et al., 1996) at 358.9 mbsf (Hole 1172A) by several lines of evidence (e.g., the termination of Chron C13n and the diatom datums LO of Distephanosira architecturalis and LO of Hemiaulus caracteristicus). The E/O boundary to lower Oligocene sequence is interrupted by a series of short hiatuses associated with the initiation of deepwater current action in the Tasmanian Gateway. For detailed information on the upper Eocene through lower Oligocene age model and paleoenvironmental interpretation see Stickley et al. (submitted [N2]).
Just a little more than 18 m of sediments of Oligocene age are preserved at Site 1172. Diatoms and magnetostratigraphy (with one nannofossil and one planktonic foraminiferal datum) effectively provide the age control for the lower Oligocene, whereas nannofossils and magnetostratigraphy resolve the upper Oligocene chronology. For such a condensed sequence, age control is resolved at moderate–high resolution. The lower/upper Oligocene (Rupelian/Chattian) boundary (28.5 Ma) is approximated at ~354 mbsf (Hole 1172A) by the diatom datum LO of Rocella vigilans var. A (29 Ma). However, there is some dispute over the position of the Oligocene/Miocene (O/M) (Chattian/Aquitanian) boundary (23.8 Ma), and therefore over the thickness of the upper Oligocene. Nannofossil evidence approximates the O/M boundary to ~340 mbsf (Hole 1172A) by the LO of R. bisecta s. str. (23.9 Ma), giving a thickness of ~14 m for sediments of late Oligocene age, whereas the planktonic foraminiferal datum LO of Turborotalia euapertura (23.8 Ma) would place the boundary at ~330 mbsf (Hole 1172A) within a foraminifer-only based late Oligocene to early Miocene hiatus. The latter scenario would give ~24 m of upper Oligocene sediments. We favor the nannofossil evidence (and therefore uncertainty regarding such a hiatus) for the placement of the O/M boundary on their smaller depth error (Table T4).
The resulting age model gives an average sedimentation rate of 1.4 cm/k.y. for the Maastrichtian, falling to <1 cm/k.y. in the Paleocene. Sedimentation rates steadily fall from 1.6 cm/k.y., through 1.3 cm/k.y., to 3 mm/k.y. for the early, middle, and late Eocene, respectively, and by the Oligocene rates had fallen to just 2 mm/k.y. on average.
Age determination for the Neogene and Quaternary intervals of Site 1172 are based mainly on integrated nannofossil and planktonic foraminiferal datums tied to the magnetostratigraphy, with a few radiolarian and diatom datums (Table T4). A benthic oxygen isotope stratigraphy back to ~600 ka, as reported in Nürnberg et al. (in press), is incorporated into the age model.
Parts of the chronology within the Miocene interval are problematic, with planktonic foraminiferal data giving slightly different age information than the nannofossil data (Table T4). We favor the nannofossil datums in these problematic intervals on account of their robustness at the other sites of Leg 189 and their small depth error compared to the foraminiferal datums. It is out of the scope of this paper to speculate on the causes for these differences, although it appears many of the discrepancies could be resolved by higher-resolution foraminiferal stratigraphic work. The magnetostratigraphy may also need some revision in light of this. However, we present the most likely scenario at this time. Further, oxygen isotope stratigraphy will greatly aid age assessment through these problematic intervals.
We approximate the lower/middle Miocene (Burdigalian/Langhian) boundary (16.4 Ma) at ~308 mbsf (Hole 1172A) with (coincidently) the placement of a hiatuses determined from nannofossil and foraminiferal evidence. This possible hiatus (or condensed interval) lasts ~1.1 m.y. and is defined by the FO of C. premacintyrei (17.4 Ma), the LO of Catapsydrax dissimilis (17.3 Ma), the FO of Globorotalia miozea (16.7 Ma), and the FO of Praeorbulina curva (16.3 Ma). The resulting age model suggests >33 m of sediment of early Miocene age. The middle/upper Miocene (Serravallian/Tortonian) boundary (11.2 Ma) is unresolved. The nannofossil datum LO of C. floridanus (11.9 Ma) approximates this boundary at ~244 mbsf, suggesting nearly 64 m of middle Miocene sediment, whereas magnetostratigraphic data places the boundary 14 m higher in Hole 1172A (Table T4), giving ~50 m of middle Miocene sediment. Resolution of the subchronology of the middle Miocene varies depending which microfossil group is followed; however, for reasons stated above we favor the nannofossil biostratigraphy and magnetostratigraphy through this interval despite a greater number of observed planktonic foraminiferal datums. The Miocene/Pliocene (Messinian/Zanclean) boundary (5.3 Ma) is placed within a short hiatus at ~79 mbsf at the position of nannofossil datums LO of Discoaster quinqueramus (5.53 Ma) and LO of T. rugosus (5.23 Ma), suggesting nearly 165 m of sediment of late Miocene age. As at Site 1170, core disturbance across this interval results in an error of ~6 m in the depth assignment of these events. Foraminiferal evidence places this boundary deeper in Hole 1172A (at ~96 mbsf), but we reject this information for reasons stated above and because several other foraminiferal datums in the upper Miocene interval give inconsistent and puzzling information (see Table T4). We conclude that age assignments for some of the planktonic foraminiferal datums require revision for Site 1172, and perhaps the generation of an entirely new zonation scheme for this part of the Southern Ocean.
Nannofossil datums and magnetostratigraphy provide good age control for the Pliocene interval. The onset of Subchron C2An.3n (Gauss) (3.58 Ma) is recognized at ~46 mbsf (Hole 1172A), allowing the placement of the lower/upper Pliocene (Zanclean/Piacenzian) boundary at this level. In Hole 1172A, the Pliocene/Pleistocene boundary (1.77 Ma) is placed either at the termination of Chron C2n (Olduvai) at ~17 mbsf, or at ~20 mbsf on nannofossil evidence (Table T4). This gives a thickness of ~59–62 m for sediments of Pliocene age at Site 1172. Further work is required to resolve this dispute. The chronology above 17 mbsf is resolved at high resolution by a robust benthic oxygen isotope stratigraphy and several nannofossil datums. The nannofossil data and the oxygen isotope stratigraphy are in excellent agreement at the current resolution (Table T4). A short hiatus spanning ~1.6–1.3 Ma, defined by nannofossils, is recognized at ~19 mbsf (Hole 1172A). The isotope stratigraphy suggests that the top 13 cm of Hole 1172A is Holocene in age.
The resulting age model gives an average sedimentation rate through the early Miocene of ~0.5 cm/k.y., increasing to ~1.2 cm/k.y. in the middle Miocene, and ~2.5 cm/k.y. in the late Miocene. Pliocene–Pleistocene sedimentation rates are ~1.5 cm/k.y. on average.
Areas for improvement, particularly where only shipboard data are available, include revision of the planktonic foraminiferal data for Sites 1168, 1170, and 1171, the radiolarian data for all sites, the diatom data for the Neogene and Quaternary sections of Sites 1170–1172, and the dinocyst data for the Paleogene of Sites 1170 and 1171. The magnetostratigraphic interpretation also needs some revision in parts of each site, particularly in intervals where core was the most disturbed.