Astronomical calibration of a southern hemisphere Plio-Pleistocene reference section, Wanganui Basin, New Zealand

Quaternary Science Reviews, Vol. 17, pp. 695—710, 1998 ( 1998 Elsevier Science Ltd. All rights reserved. Printed in Great Britain PII: S0277—3791(97)00075-9 0277—3791/98/$ — See front matter

ASTRONOMICAL CALIBRATION OF A SOUTHERN HEMISPHERE PLIO-PLEISTOCENE REFERENCE SECTION, WANGANUI BASIN, NEW ZEALAND TIM R. NAISH*,1, STEVEN T. ABBOTT-, BRENT V. ALLOWAY‡, ALAN G. BEU°, ROBERT M. CARTER*, ANTHONY R. EDWARDS±, TIMOTHY D. JOURNEAUXE, PETER J. J. KAMP**, BRAD J. PILLANS--, GORDON SAUL* and KEN J. WOOLFE* *School of Earth Sciences, James Cook University, Townsville QLD 4811, Australia (e-mail: [email protected]) -Northern Territory Department of Mines and Energy, G.P.O. Box 2901, Darwin NT 0801, Australia ‡ Department of Geology, University of Auckland, Tamaki Campus, Private Bag 92019, Auckland, New Zealand ° Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand ± Stratigraphic Solutions Ltd., P. O. Box 295, Waikanae, New Zealand E Western Mining Corporation, Agnew Gold, PMB 10, Leinster WA 6437, Australia ** Department of Earth Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand -- Research School of Pacific and Asian Studies, Australian National University, Canberra, ACT 0200, Australia Abstract—Wanganui Basin, New Zealand, contains one of the most complete late Neogene stratigraphic records in the world. The ca. 3 km thick basin-fill for the last 3.6 Ma comprises 58 superposed fifth and sixth-order shallow marine sedimentary cycles which correspond to individual 100 and 41 ka sea-level cycles since oxygen isotope stage MG6. Stages MG6 to 5 are represented by marine cyclothems, whereas stages 17 to 4 are represented by a suite of coeval and younger uplifted marine terrace sequences. Additionally, a predominantly glacial loess stratigraphy exists for isotope stages 12-2. The Milankovitch-frequency, shallow marine, cyclostratigraphy of Wanganui Basin is here correlated with the astronomically-calibrated Plio-Pleistocene timescale of Lourens et al. (1996, Paleoceanography, 11, 391—413). An integrated chronology is presented for Wanganui Basin based on radiometric ages on interbedded rhyolitic tephra, on biostatigraphic data, on paleomagnetic polarity measurements, and on cycle correlations with the oxygen isotope timescale. Numeric ages on the tephra are consistent with the interpreted magnetostratigraphy and cyclostratigraphy, and fit well with the astronomically-calibrated timescale. Our cyclostratigraphic correlations provide age estimates for 116 stratigraphic horizons in Wanganui Basin that are not otherwise able to be dated, and thereby establish an astronomical chronostratigraphy for the New Zealand Plio-Pleistocene. The historic subdivision of the New Zealand marine Plio-Pleistocene is based on the biostratigraphy of shallow marine strata in both Wanganui and East Coast basins, North Island. Based on the new cyclostratigraphic correlations we re-evaluate the age of all New Zealand PlioPleistocene stage and substage boundaries. After making these revisions, the current age estimates for the base of the Opoitian, Waipipian, Mangapanian, Nukumaruan, Castlecliffian, and Haweran Stages are 5.25, 3.60, 3.03, 2.46, 1.07, and 0.34 Ma, respectively, and the ages of the Hautawan-Marahauan (intra-Nukumaruan) and Okehuan-Putikian (intra-Castlecliffian) Substage boundaries are 2.15 and 0.78 Ma, respectively. ( 1998 Elsevier Science Ltd. All rights reserved.

1990, 1995a,b; Hilgen 1991a, b; Tiedemann et al., 1994; Chen et al., 1995; Lourens et al., 1996). In such studies, proxy climatic records are tuned to the astronomical solutions of the variations of the Earth’s orbital parameters: eccentricity, obliquity, and precession (e.g. Berger and Loutre, 1990; Laskar, 1990; Quinn et al., 1991). Tuned timescales have proved to be of higher resolution and accuracy than conventional timescales based on linear interpolation between radiometrically dated calibration points in seafloor magnetic anomaly sequences (Berggren et al., 1985, 1995), and show that these radiometric ages are consistently too young by 5—7%. At present, the alternative astronomically calibrated

INTRODUCTION Astronomical calibration of sedimentary cycles provides a powerful method for assigning absolute ages to the late Neogene timescale (Shackleton and Opdyke, 1973; Hays et al., 1976; Johnson, 1982; Imbrie et al., 1984; Martinson et al., 1987; Ruddiman et al., 1989. Raymo et al., 1989; Joyce et al., 1990; Shackleton et al.,

1 Present address: 41 Bell Road, South Gracefield, PO Box 30368, Lower Hutt, New Zealand.

695

696

Quaternary Science Reviews: Volume 17

FIG. 1. Map showing the location of Wanganui Basin in western North Island, New Zealand, with respect to the Australia-Pacific plate boundary zone, and other localities referred to in the text.

time scale extends back to the late Miocene (Hilgen, 1991b; Shackleton et al., 1995b; Lourens et al., 1996). Wanganui Basin, North Island, New Zealand (Fig. 1) contains one of the most complete late Neogene stratigraphic records in the world. The entire 5-km-thick basin fill is largely undeformed and comprises recurrent, unconformity-bounded, Milankovitch-scale, shallow marine cyclothems (Fleming, 1953a; Beu and Edwards, 1984; Abbott et al., 1989; Kamp and Turner, 1990; Abbott and Carter, 1994; Naish and Kamp, 1995, 1997a). We summarise here a complete climatic cyclostratigraphy for the last 3.6 Ma, based on our analysis of 58 consecutive fifth and sixth-order sedimentary cycles in Wanganui Basin, that can be assigned to individual 100 and 41 ka isotope stage couplets, respectively. Consecutive stages MG6 to 5 are represented by marine cyclothems (Abbott and Carter, 1994; Journeaux et al., 1996; Naish et al., 1996; Saul et al., in press), whereas stages 17 to 4 are represented by a suite of uplifted marine terrace sequences (Pillans, 1983, 1990). Additionally, a predominantly glacial loess stratigraphy exists for isotope stages 12-2 (Milne, 1973a—c; Pillans, 1988, 1990; Wilde and Vucetich, 1988; summarised in Pillans, 1994).

The presence of interbedded tephra and an established paleomagnetic stratigraphy for the Wanganui Basin has allowed the age of the Matuyama/Brunhes boundary, Jaramillo and Cobb Mountain Subchrons, and the upper Olduvai transition to be assessed independently (Turner and Kamp, 1990; Alloway et al., 1993; Pillans et al., 1994; Naish et al., 1996; Alloway, unpublished data). The ages of the transitions in New Zealand are remarkably consistent with ages implied by recently published astronomically tuned timescales. In this study, we correlate the new cyclostratigraphy (proxy climatic record) with the astronomically calibrated timescale to obtain a high resolution, Plio-Pleistocene record for New Zealand. This compilation allows: (i) age estimates to be made for New Zealand stratigraphic horizons not independently dated; (ii) the correlation of the important New Zealand record with global stratotypes for the PlioPleistocene (e.g. Vrica Plio-Pleistocene GSSP, Naish et al., 1996, 1997; middle/lower Pleistocene boundary, Pillans et al., 1994); and (iii) the age of biostratigraphic events, and the Stage and Substage boundaries for the New Zealand Plio-Pleistocene, to be reassessed.

T.R. Naish et al.: Astronomical calibration of the Plio-Pleistocene reference section New Zealand

697

FIG. 2. High-resolution composite cyclostratigraphy for the last 2.5 Ma from Wanganui Basin used to underpin the chronology presented in this paper. Stratigraphic data are from Abbott (1992), Abbott and Carter (1994), Naish and Kamp (1995), Journeaux et al. (1996), and Saul (unpublished data). This composite stratigraphy is based on regional correlations of sections by Carter et al. (1997) and Saul et al. (in press). Tephrochronology and tephrostratigraphy are after Seward (1974a, 1976), Kohn et al. (1992), Alloway et al. (1993), Pillans et al. (1994), Shane (1994), Wilson et al. (1995), Naish et al. (1996), Shane et al. (1996), and Wilson et al. (1995). Isotope curve is a composite record using Shackleton et al. (1990, 1995a). Biostratigraphy is after Fleming (1953a), Edwards (1976, 1987), Beu and Edwards (1984), Beu et al. (1987), and Naish et al. (1996). Cyclothem motifs are after Saul et al. (in press). H"Hawera motif, C"Castlecliff motif, S"Seafield motif, M"Birdgrove motif, R"Rangitikei motif, and T"Turakina motif. Lithostratigraphic nomenclature follows Superior Oil Co. (1943), Fleming (1953a), Pillans (1994), Abbott and Carter (1994), Naish and Kamp (1995), and Journeaux et al. (1996). Timescale is the astronomical calibration reported by Lourens et al. (1996).

698

Quaternary Science Reviews: Volume 17

CYCLOSTRATIGRAPHY Wanganui Basin is a 200]200 km, ovoid sedimentary basin in western North Island, New Zealand, situated in a back-arc position with respect to the modern Pacific-Australia plate boundary zone in North Island (Fig. 1). Plio-Pleistocene subsidence and basin formation is attributed to lithospheric loading in combination with compressional downwarping driven by coupling of the overriding and subducting plates (Stern and Davey, 1989). Sedimentation evidently kept pace with subsidence throughout much of the basin history, resulting in a 5-km thick succession of predominantly shelf and shallow-water sediment. The eastern margin of the basin has undergone gentle upwarping along the plate boundary, resulting in excellent onland exposures through 58 superposed PlioPleistocene cyclothems (Fig. 2) which represent oxygen isotope stages 5 through to MG 6 (Abbott and Carter, 1994; Journeaux et al., 1996; Naish and Kamp, 1997a; Saul et al., in press). Each 41 ka (d18O stages 100—18) and 100 ka (d18O stages MG6-G2; 17-2) glacial/interglacial stage couplet is represented by an individual depositional sequence comprising transgressive (TST), highstand (HST) and, in many cyclothems, regressive systems tracts (RST). In general, major sedimentary facies represented within the basin fill were deposited in a range of coastal plain, shoreface and shelf marine environments during the late rise, highstand and falling part of each glacio-eustatic cycle. The Wanganui stratigraphic record was therefore dominantly deposited during odd-numbered (interglacial) isotope stages. Glacial stages are represented by the surfaces of marine planation and bioerosion which occur at the base of

each cyclothem, and which mark both cyclothem and sequence boundaries (Fig. 2). An overlapping and younger record of interglacial isotope stages 17-3 (0.68—0.04 Ma) is represented by a flight of 13 marine terraces that extend up to 20 km inland and up to 400 m above present sea-level along the Wanganui coast. The matching of these terraces with the oxygen isotope scale was achieved by Pillans (1983, 1990), who used radiocarbon, amino acid racemisation and tephrochronology for dating. The small size of some eustatic sea-level changes precludes their being represented by a full cyclothem in the sections studied. Cyclothems J1—J5, J7—J9, 12, and 36 (Fig. 2), therefore, each correspond to two isotope stage couplets (i.e. to four stages). Cyclothems 1-47 display repetitive, vertically stacked facies successions (Fig. 2). Typically, the following architectural elements occur in ascending stratigraphic order (Fig. 3), as detailed by Abbott and Carter (1994), Naish and Kamp (1995, 1997a), and Saul et al. (in press): 1. A basal sequence boundary consisting of an unconformity which is coincident with the ravinement surface (RS,"transgressive surface of erosion (TSE)). 2. Either (i) a thick (5—30 m) transgressive systems tract with a shallow-water reworked shellbed at the base, overlain by inner-shelf sandstone and by a condensed shellbed, or (ii) a thin transgressive systems tract ((2 m), corresponding mainly to a shallow-water shellbed. 3. A local flooding surface (LFS), across which rapid deepening occurs, in most cyclothems located at the

FIG. 3. The depositional architecture of two Wanganui Basin cyclothem motifs, showing stratigraphic position of (A) systems tracts and (B) shellbeds.

T.R. Naish et al.: Astronomical calibration of the Plio-Pleistocene reference section New Zealand

base of a mid-cycle condensed shellbed with an offshore fauna. 4. A downlap surface (DLS). 5. A highstand systems tract (10—20 m) comprising an aggradational interval of shelf siltstone. 6. Commonly, a regressive systems tract (10—60 m), which commences with a gradational inner shelf to shoreface facies transition, and passes up into strongly progradational shoreline facies. Traditional facies and biofacies analysis is the basis of the interpretation of the depositional paleoenvironments of the cyclothems. Distinctive shellbeds and their associated stratal discontinuities delineate the stratigraphic geometry of the sequences, and allow systems tracts to be differentiated. Abbott and Carter (1994) distinguished type A shellbeds within the transgressive systems tract (reworked shallow water species, often cross-bedded); and type B shellbeds (offshore shelf species, preserved in or near situ), which straddle the junction between the transgressive and highstand systems tracts, leading to the term mid-cycle shellbed. Alternatively, Naish and Kamp (1997a) and Kondo et al. (in press), after Kidwell (1991), have recognised onlap, backlap, downlap, and flooding surface shellbeds. These shellbeds are associated, respectively, with the ravinement surface, the local flooding surface, the downlap surface, and parasequence-bounding marine flooding surfaces. In offshore settings, where the downlap surface converges with the sequence boundary, elements of both onlap and downlap shellbeds may become superposed. For such cases the term compound shellbed is useful. The sequence architecture, therefore can be represented by facies analysis within a chronostratigraphic template provided by distinctive stratal surfaces and shellbeds (Fig. 3). Paleobathymetric analysis of the cyclothems, based on foraminifera and mollusca, reveals cyclical changes in water depth of ca. 50—200 m amplitude with frequencies corresponding to Milankovitch orbital rhythms (Naish and Kamp, 1997b; Journeaux et al., 1996). Power spectrum analysis of this data set is currently being undertaken, but the water depth changes indicated are consistent with a glacio-eustatic origin for the cyclothems. The indicated water depth changes are also consistent with the lithofacies and sequence stratigraphic data. Within the chronologic framework discussed below, this allows precise correlation of the cyclothems with international oxygen isotope stratigraphies. The older, mid-Pliocene strata discussed here belong to the Paparangi and Utiku Groups (Fig. 2), and include 11 major sedimentary cycles (J cycles, Fig. 2) (Journeaux et al., 1996). Seven of these cycles occur within the mud-dominated Paparangi Group (Mangaweka Mudstone), and are only evident from laboratory textural and microfaunal analyses, which document cyclical changes from outer shelf to upper bathyal environments (Journeaux, 1995). These cycles are also considered to have a glacio-eustatic origin even though they predate 2.5 Ma.

699

TEPHROCHRONOLOGY During the late Neogene, silicic arc volcanism in central North Island regularly contributed material to Wanganui and other New Zealand sedimentary basins (e.g. Seward, 1976; Shane, 1990; Wilson et al., 1995; Shane et al., 1996). Volcaniclastic sediments contain rhyolitic pumice, gravel, and sand derived by airfall, or by fluvial transport from large eruptions in the Taupo Volcanic Zone (Fig. 1). Many of the volcaniclastic horizons (tephra) are similar in field appearance, but chemical fingerprinting of the glass shards (Pillans et al., 1994; Shane, 1994; Naish et al., 1996), ferromagnesian mineralogy (Seward, 1976; Shane, 1994; Naish et al., 1996), and careful lithostratigraphic mapping allow most to be distinguished. The lithostratigraphy, stratigraphic positions and correlation of tephra across the basin have been described by Seward (1976), Pillans et al. (1994), and Naish et al. (1996). Discrete horizons and intervals of volcaniclastic sediment occur intermittently throughout the Wanganui Basin succession, but the majority of the silicic tephra occur within Pleistocene strata. Some tephra have correlatives in other parts of the North Island (e.g. Shane and Froggatt, 1991; Wilson et al., 1995) and in deep sea cores (e.g. Ninkovitch, 1968; Watkins and Huang, 1977; Nelson et al., 1985b; Carter et al., 1995). Silicic tephra occur also in Pliocene strata (Naish et al., 1996; Journeaux et al., 1996), but the Pliocene succession is much less tuffaceous than the overlying Pleistocene. Historically, tephra have played a significant role in the establishment of a chronology for the Wanganui Basin. Radiometric ages have provided independent age control for the bioevents used for Plio-Pleistocene correlation (Seward, 1974a; Beu and Edwards, 1984). The tephra also provide mappable isochronous surfaces within the sediments and across the basin. Within the chronstratigraphic framework provided by cyclostratigraphy and magnetostratigraphy, tephrochonology provides a vital contribution towards an integrated Plio-Pleistocene New Zealand chronostratigraphy. Early attempts at fission-track dating of volcanic glass from Wanganui Basin (Seward, 1974a,b, 1976; Boellstorff and Te Punga, 1977) and zircon (Seward, 1979) produced ages that were largely consistent with the early magnetostratigraphic interpretations (Seward et al., 1986). However, more recent magnetostratigraphies (Turner and Kamp, 1990; Pillans et al., 1994), together with new fission-track (Kohn et al., 1992; Alloway et al., 1993; Kamp, unpublished data) and 40Ar/39Ar (Shane, 1994) ages, have necessitated substantial revision of the chronology of the Pleistocene strata in the basin, as summarised by Pillans et al. (1994). Recently, Naish et al. (1996) have presented paleomagnetic data and isothermal fission-track ages on tephra from the underlying Pliocene strata that are consistent with the new Pleistocene ages. The original fission-track ages on glass were not corrected for partial track annealing, and consequently are now

700

Quaternary Science Reviews: Volume 17

TABLE 1. Position and astronomical ages of biostratigraphic, tephrostratigraphic and magnetostratigraphic datums in Wanganui Basin Datum

Cyclothem

Isotope stage

Age (Ma)

Biostratigraphic LAD Acacia FAD Emiliania huxleyi FAD Pecten novaezealandiae LAD Pecten eotea LAD Pecten marwicki LAD Pseudoemiliania lacunosa FAD Pecten kupei LAD Reticulofenestra asanoi FAD Pecten LAD Eumarcia LAD Glycymeris LAD Patro LAD Globorotalia crassiformis (D) FAD Geophyrocapsa sinuosa FAD Globorotalia truncatulinoides LAD Phialopecten triphooki FAD ¹owaipecten mariae LAD Crassostrea igens FAD Zygochlamys delicatula FAD Globorotalia crassula FAD Rotalia wanganuiensis LAD Cibicides molestus FAD Globorotalia crassiformis (D) LAD Mesopeplum crawfordi FAD Phialopecten thompsoni LAD Phialopecten marwicki FAD ¹owaipecten katieae LAD Sphenolithus noeabies

46 45 44 44 44 43 40 39 39 24 24 24 22 18 13 3 3 2 2 2 2 J6 J5 J4 J4 J4 J4 J1

5 8/7 9/8 9/8 9 11 17 19 19 51 51 51 55 63 73 95 95 97 98/97 97 97 G17 G19 G21 G21 G19 G21 MG8

0.12 0.24 0.29 0.29 0.31 0.42 0.70 0.75 0.75 1.53 1.53 1.53 1.60 1.76 1.96 2.42 2.42 2.45 2.45 2.45 2.45 2.90 3.03 3.03 3.03 2.95 3.03 3.52

¹ephrostratigraphic Taupo Kawakawa Fordell Griffins Road Kakariki Rangitawa (0.34$0.03)* Onepuhi Kupe (0.63$0.08)* Kaukatea (0.87$0.05)* Potaka (1.05$0.05)* Rewa (1.29$0.12)* Mangapipi (1.60$0.18)* Pakihikura (1.63$0.15)* ‘‘Mangahou’’ Ototoka Vinegar Hill (1.75$0.15)* Waipuru (1.87$0.13)* Ohingaiti Kowhai Eagle Hill

47 47 44 44 44 44 41 40 37 36 32 26 25 23 22 19 16 9 J7 J7

1 2 9 9 9 10 15 17 25-23 27 35 47 49 53 55 61 67 83 G13 G13

0.0018 0.0225 0.30 0.30 0.30 0.35 0.57 0.65 0.90 0.99 1.19 1.45 1.49 1.53 1.60 1.73 1.85 2.19 2.88 2.88

38/39 36 34 32 32 17/18 13/14 J11 J4 J2 50 m below J1

20/19 27 31 35 35 64/63 72/71 104 K1/G22 MG1/M2 top Gi1

0.780 0.990 1.070 1.190 1.190 1.785 1.942 2.582 3.032 3.330 3.596

Magnetostratigraphic Matuyama/Bruhnes Top Jaramillo Base Jaramillo Top Cobb Mountain Base Cobb Mountain Top Olduvai Base Olduvai Gauss/Matuyama Top Kaena Base Mammoth Gilbert/Gauss

*Numeric (ITPFT) ages for tephra.

regarded as underestimated, or minimum, ages (Alloway et al., 1993). The stratigraphic position and age of Wanganui Basin tephra are summarised in Fig. 4 and Table 1.

From oldest to youngest, the stratigraphically most important tephras are: Waipuru Tephra, Vinegar Hill Tephra, Mangahou Ash, Pakihikura Pumice, Mangapipi Ash, Rewa Pumice, Potaka Tephra, Kaukatea Ash, Kupe Tephra and Rangitawa Tephra. Tephra names follow Seward (1974a, 1976), Pillans et al. (1994), Shane (1994), Wilson et al. (1995), Naish et al. (1996) and Shane et al. (1996). Glass shards from eight of the tephra (Waipuru, Vinegar Hill, Pakihikura, Mangipipi, Potaka, Kaukatea, Kupe and Rangitawa) have been dated by the isothermal plateau fission track (ITPTF) technique (Alloway et al., 1993; Naish et al., 1996; Shane et al., 1996). An 40Ar/39Ar age reported for the Potaka Tephra by Shane (1994) and Wilson et al. (1995) is consistent with the new ITPFT chronology. Additionally, the Mangahou Ash has been dated by Kamp (unpublished data) using conventional zircon FT analysis. Important comments regarding the chronology of individual tephra or groups of tephra include: 1. Early fission-track dating of the Ohingaiti Tephra produced ages of 1.5$0.21 Ma on glass (Seward, 1976) and 1.78$0.44 Ma on zircon (Seward, 1979). The revised chronology for Wanganui Basin Pleistocene strata, and new ITPFT ages for the Waipuru and Vinegar Hill Tephra (Naish et al., 1996), indicate that the earlier ages are too young. Seward et al. (1986) identified a short normal polarity interval just above the Ohingaiti Tephra, and interpreted it as one of the Reunion Subchrons (Fig. 2), indicating an age near 2.0 Ma. The tephra and the superjacent normal polarity interval occurs in sequence 9 and corresponds to oxygen isotope stage 82, giving an estimated age for the Ohingaiti Tephra of ca. 2.17 Ma. It is noteworthy that Zijderveld et al. (1991) identify a Reunion Subchron in a late Pliocene marine marl section near Monte Singa, Southern Italy, and on the basis of the integrated Mediterranean sapropel astrochronology of Hilgen (1991a,b), suggest that this subchron occurs within oxygen isotope stage 81. 2. Ages for Waipuru Tephra have ranged from 1.7 to 1.8 Ma (e.g. Seward et al., 1986). The new ITPFT age of 1.87$0.15 Ma, and magnetic polarity data, confirm the position of the Waipuru Tephra within the Olduvai Subchron. The stratigraphic position of the tephra within the transgressive systems tract of sequence 16 (Naish and Kamp, 1997a) implies correlation with oxygen isotope stage 67 (Fig. 2), and an estimated age of ca. 1.85 Ma. The Vinegar Hill Tephra has an ITPFT age of 1.75$0.13 Ma, and occurs within a reversed polarity interval interpreted as part of the Matuyama Chron above the Olduvai Subchron (below). The top of the Olduvai Subchron is located ca. 35 m below the Vinegar Hill Tephra near the base of sequence 18. Therefore, the Vinegar Hill Tephra is correlated with oxygen isotope stage 61 (1.73 Ma), in close agreement with its ITPFT age.

FIG. 4. High-resolution integrated chronology for the Plio-Pleistocene stratigraphy in Wanganui Basin. Notes: (1) Timescale is after Lourens et al. (1996). (2) Orbital time series of obliquity (41 ka) and eccentricity (100 ka) is from Laskar (1990). (3) Composite benthonic oxygen isotope record is after Shackleton et al. (1995a; stages Gi4 to 63) and Shackleton et al. (1990; stages 63-1). (4) Tephrostratigraphy is after Milne (1973a, 1973b), Seward (1976), Boellstorff and Te Punga (1977), Pillans (1994), Pillans et al. (1994), Naish and Kamp (1995), and Journeaux et al. (1996). Tephrochronology used follows: ¼aipuru ¹ephra—ITPFT age 1.87$0.15 Ma (Naish et al., 1996); »inegar Hill ¹ephra—ITPFT age 1.75$0.13 Ma (Naish et al., 1996); Pakihikura Pumice—ITPFT age 1.63$0.15 (Alloway et al., 1993); Mangapipi Ash—ITPFT age 1.60$0.18 Ma (Shane et al., 1996); Rewa Pumice—ITPFT age 1.29$0.12 Ma (Shane et al., 1996); Potaka ¹ephra—Ar/Ar age 1 Ma$5% (Shane, 1994; Wilson et al., 1995), ITPFT age 1.05$0.05 (Alloway et al., 1993); Kaukatea Ash—ITPFT age 0.87$0.05 Ma (Shane et al., 1996); Kupe ¹ephra—ITPFT age 0.63$0.08 Ma (Shane et al., 1996); Rangitawa ¹ephra—ITPFT age 0.34$0.03 Ma (Alloway et al., 1993); Kawakawa ¹ephra—24 ka (calendar years, Wilson et al., 1988; Shepherd and Price, 1990; Pillans et al., 1993). (5) Composite cyclostratigraphy (sequences 1—47) is after Saul et al. (in press) and Carter et al. (1997). ‘J’ sequences are after Journeaux et al. (1996). ‘N’ sequences are after Naish and Kamp (1995, 1997a). ‘S’ sequences are after Saul (unpublished data). ‘A’ sequences are after Abbott and Carter (1994). ‘W’ sequences are after Woolfe et al. (unpublished data). (6) Wanganui Basin lithostratigraphy is after Fleming (1953a), Naish and Kamp (1995), and Journeaux et al. (1996). (7) Marine terrace stratigraphy and chronology is from Pillans (1983, 1990). (8) Loess stratigraphy is from Milne (1973a, b, c);), Pillans (1988, 1990) and Wilde and Vucetich (1988); summarised in Pillans (1994). (9) River terrace chronology modified from Milne (1973a, b, c). (10) Correlations of glacial and interglacial stages to the oxygen isotope scale is after Suggate (1990) and Pillans (1991). (11) Magnetostratigraphic datums within Wanganui Basin sediments are as follows: Thvera Subchron, Mammoth Subchron, Kaena Subchron, Gilbert/Gauss boundary are after Wilson (1993) and Journeaux et al. (1996); G/M boundary is after Naish et al. (1996); Reunion Subchron is (from Seward et al. 1986); Olduvai Subchron is after Naish et al. (1996) Cobb Mountain Subchron is after Pillans, et al. (1994); Jaramillo Subchron and the Matuyama/Bruhnes boundary are after Turner and Kamp (1990) and Pillans et al. (1994). (12) Biostratigraphic datums from Fleming (1953a); Hornibrook (1981); Scott (1982); Beu and Edwards (1984); Beu et al. (1987); Hornibrook et al. (1989); Beu et al. (1990); Bussell and Mildenhall (1990); Naish and Kamp (1995); Morgans et al. (1996); A. R. Edwards (pers. commun.), A. G. Beu (pers. commun.) IN¹ denote the international position and age of bioevents. NZ denotes the local NZ position and age of bioevents.

T.R. Naish et al.: Astronomical calibration of the Plio-Pleistocene reference section New Zealand

3. Numeric ages of 1.63$0.15 Ma and 1.60$0.18 Ma have been recently reported for the Pakihikura Pumice (Alloway et al., 1993) and the Mangapipi Ash (Shane et al., 1996), respectively. The integrated chronology presented in this paper correlates the Pakihikura Pumice with isotope stage 49 (ca. 1.49 Ma) and the Mangapipi Ash with isotope stage 47 (ca. 1.45 Ma), showing good agreement with their mean ITPFT ages (within one standard deviation). The underlying Mangahou Ash occurs within stage 51 (ca. 1.54 Ma) and has been fission track dated at 1.50 Ma$0.2 Ma (Kamp, unpublished data). Note that ‘Mangahou Ash’ as used here (following Seward, 1976) is a distinct tephra from the one originally recognised in Mangahou Siltstone on the Wanganui coast by Fleming (1953a). 4. A zone of normal polarity near the Rewa Pumice was interpreted by Pillans et al. (1994) to represent the Cobb Mountain Subchron$1.19 Ma (Shackleton et al., 1990), yielding an age of approximately 1.2 Ma for the Rewa Pumice. The recent ITPFT age of 1.29$0.12 for the Rewa Pumice is consistent with the chronology presented here. 5. Potaka Tephra occurs within cyclothem 36 at Rewa Hill, Rangitikei River, Turakina River and Whangaehu River sections. The tephra has a normal polarity, has been independently dated at 1 Ma ($5%) (Shane, 1994; Houghton et al., 1995; Wilson et al., 1995; Shane et al., 1996), and is correlated with oxygen isotope stage 27. The position of this normal polarity tephra within the Jaramillo Subchron is consistent with its numeric ages, with correlations of the enclosing sedimentary cycles with the isotope scale, and with the astronomical timescale. Remobilised Potaka Tephra occurs at the Wanganui coast and the Whangaehu valley within the shallow-marine Kaimatira Pumice Sand which comprises the transgressive systems tract of the overlying cyclothem 37 and is correlated with oxygen isotope stage 25. 6. Rhyolitic tephra are also important markers for correlation and dating of marine terrace cover beds. The Rangitawa Tephra ("Mt Curl Tephra), which occurs widely throughout the basin, has a mean fission track age of 0.35$0.50 Ma (Kohn et al., 1992), ITPFT ages of 0.34$0.03 Ma (Alloway et al., 1993), and is associated with the L10 loess (Fig. 2) on the Aldworth terrace (d18O stage 10). Upper, Middle, and Lower Griffiths Road Tephra all occur within the Brunswick Terrace cover sequence (interglacial isotope stage 9), and have estimated ages of 0.30—0.34 Ma. Berger et al. (1992) reported a TL age of 0.328$0.43 Ma for the loess immediately beneath Upper Griffiths Road Tephra. All these tephra overlie the Rangitawa Tephra, and underlie the Fordell Ash (estimated age of ca. 0.3 Ma; Bussell and Pillans, 1992). Important younger tephra include the Rotoehu Ash, erupted from Okataina Caldera, which occurs as a glass concentration in the base of the L2 loess, and has an age of 64$4 ka

701

(Wilson et al., 1992), and the Kawakawa Tephra (Aokautere Ash member), which occurs widely in the L1 loess (Ohakea Loess), and is dated at 24 ka (calendar years) (Wilson et al., 1988; Shepherd and Price, 1990; Pillans et al., 1993). 7. Correlation of Wanganui Basin cyclothems with the ODP site 846 d18O record (Fig. 4) allows ages to be interpolated for tephra which are not yet dated directly. For instance, the Kowhai and Eagle Hill Tephra at the base of Cycle J7 within the Mangaweka Mudstone fall within isotope stage G14, giving them an estimated age of ca. 2.88 Ma. That the tephra are separated by 8 m of mudstone suggests an age difference of ca. 8 ka (assuming a sedimentation rate of 1 m ka~1).

MAGNETOSTRATIGRAPHY Early magnetostratigraphic interpretations of the Wanganui Basin succession (Seward et al., 1986) relied upon the early glass fission-track ages for tephra (Seward, 1976). Pillans et al. (1994), building on the work of Turner and Kamp (1990), remeasured the magnetic polarity of the mid-Pleistocene Wanganui Basin sediments and produced a magnetostratigraphy that was consistent with the new numeric ages of Alloway et al. (1993). Given the large revisions made to the Pleistocene magnetostratigraphy, Wilson (1993) and Naish et al. (1996) remeasured and reinterpreted the geomangetic polarity zonation of the underlying Pliocene strata. The stratigraphic positions of major magnetic polarity reversals within the Wanganui Basin succession are summarised below and shown in Fig. 4 and Table 1. All ages ascribed to polarity transitions are after the Lourens et al. (1996) and Shackleton et al. (1995b) astronomically tuned timescales; the corresponding oxygen isotope stages are based on the ODP 846 and ODP 677 records of Shackleton et al. (1990, 1995a). 1. Gilbert/Gauss boundary (3.60 Ma; top of d18O stage Gi1): Located by Seward et al. (1986), and confirmed by Wilson (1993), within the upper part of the Taihape Mudstone, ca. 50 m below the base of the Utiku Group. 2. Mammoth Subchron (3.33—3.21 Ma; d18O stages M2-M1): N—R—N polarity sequence first identified by Seward et al. (1986) low in the Utiku Group, and later interpreted by Journeaux et al. (1996) from data from Wilson (1993) as the Mammoth Subchron. The base of the interval occurs close to the base of cyclothem J2 within the Tarere Formation, corresponding to the top of d18O stage MG2. The top of the Subchron, while not identified by Wilson (1993), is inferred, on the basis of the cyclostratigraphy, to occur in the upper half of cyclothem J3 within the Kawhatau Formation, and corresponds to the top of 18O stage M1. 3. Kaena Subchron (3.12—3.03 Ma; d18O stages K2-K1): N—R—N polarity sequence first identified

702

Quaternary Science Reviews: Volume 17

by Seward et al. (1986) in the upper part of the Utiku Group, and later interpreted by Journeaux et al. (1996) from data from Wilson (1993) as the Kaena Subchron. The top of the subchron is not well constrained, but occurs within the upper-half of cyclothem J4. The base of the subchron is inferred on the basis of cyclo-stratigraphy to occur in the conformity separating cycles J3 and J4. 4. Gauss/Matuyama boundary (2.58 Ma; d18O stage 104): Naish et al. (1996) identified a N—R polarity transition ca. 70 m below the top of the Mangaweka Mudstone as the G/M polarity transition. The Mangaweka Mudstone comprises ca. 500 m of relatively featureless blue—grey massive siltstone. Laboratory microfaunal and textural analyses carried out on closely spaced samples from this unit (Journeaux, 1995; Journeaux et al., 1996) indicate that the G/M transition occurs at a level close to the base of Cycle M11. This corresponds to the shallowest water depth in the cycle, and implies that the G/M transition occurs during a glacial stage (see below). An upper Mangaweka Mudstone position for the G/M boundary at Rangitikei is consistent with the magnetostratigraphic interpretation at Turakina of McGuirre (1989), who also identified a N—R transition within the upper part of the Mangaweka Mudstone. 5. Olduvai Subchron (1.94—1.76 Ma; d18O stages 71-63): The R—N—R polarity sequence reported by Naish et al. (1996) near the top of the Rangitikei Group was interpreted by them as the Olduvai Subchron. The top of the Olduvai Subchron is placed at the N—R polarity change across the Waipuru Shellbed at the base of cyclothem 18 (Fig. 2), which is in broad agreement with the results of Seward et al. (1986). The base of the Olduvai was not able to be located precisely by either Seward et al. (1986) or Naish et al. (1996), because of unsuitable lithologies for paleomagnetic analysis. However, the sequence analysis and correlations with the isotope curve presented in Fig. 2 indicate that the base of the Olduvai Subchron occurs near the base of cyclothem 14. This interpretation requires that four cyclothems (14—17), each of 41 ka duration, and corresponding to d18O stages 71-64, correlate with the Olduvai Subchron. The ITPFT ages determined for the Vinegar Hill and Waipuru Tephra (discussed above) are consistent with this stratigraphic position for the top of the Olduvai, given its astronomically calibrated age of 1.76 Ma. 6. Cobb Mountain Subchron (1.19 Ma; d18O stage 35): A zone of normal polarity recorded near the Rewa Pumice was interpreted as the Cobb Mountain Subchron by Pillans et al. (1994). Independent correlations of the Rangitikei River cyclostratigraphy (Saul et al., in press) show that this normal interval occurs within cyclothem 32 and correlates with d18O stage 35, which is the location of the Subchron in deep sea sediment cores (e.g. Shackleton et al., 1990). The long interval of reversed polarity below the Rewa

Pumice includes the Mangapipi Ash, Pakihikura Pumice, Mangahou Ash, and Vinegar Hill Tephra, and is interpreted to represent the middle Matuyama Chron, above the Olduvai Subchron. 7. Jaramillo Subchron (1.07—0.99 Ma; d18O stages 31-27): The position of the upper Jaramillo transition occurs at the top of cyclothem 36 (Fig. 4), between the Potaka Pumice (cyclothem 36) and the Kaukatea Ash (cyclothem 37). The upper Jaramillo polarity transition in the Castlecliff section (Fig. 4) was placed by Turner and Kamp (1990) at the level of the Okehu Shell Grit. This position is based on a single site of reversed polarity above the Okehu Shell Grit, in a part of the section that is strongly overprinted. However, Pillans et al. (1994), who studied a number of inland sections, reported stable normal polarities in the Lower Okehu Siltstone, Okehu Shell Grit and the overlying Upper Okehu Siltstone, spanning cyclothems 35 and 36 (Fig. 4). Moreover, magnetostratigraphic interpretation of the Jaramillo Subchron is supported by the numeric ages reported by Alloway et al. (1993) and Shane (1994) for the Potaka Tephra (ca. 1 Ma$5%), which are also consistent with the age of the Jaramillo Subchron in astronomically tuned timescales (e.g. Lourens et al., 1996). 8. Matuyama/Bruhnes boundary (0.78 Ma; d18O stage 18/19): Turner and Kamp (1990) and Pillans et al. (1994) both interpreted the R—N polarity transition across the Kaikokopu Shellbed as the B/M transition. This transition occurs at the base of cyclothem 39 (Fig. 2), and correlates with the d18O stage 19/20 stage boundary. 9. The R—N—R—N polarity sequence at Rewa Hill was initially interpreted by Seward et al. (1986) to represent the succession Matuyama-JaramilloMatuyama-Brunhes. Subsequent work by Pillans et al. (1994) confirmed the polarity zonation of Seward, but they applied a different interpretation. Based on the later studies, described above, the Rewa Hill polarity sequence is now accepted as representing the Matuyama-Cobb Mountain-Matuyama-Jaramillo Subchron polarity successions. OXYGEN ISOTOPE STAGE CORRELATIONS Correlations of parts of the Wanganui Basin succession with deep-sea oxygen isotope records have been made by Beu and Edwards (1984), Kamp and Turner (1990), Abbott and Carter (1994), Pillans (1991), Pillans et al. (1994), and Naish et al. (1996), and a complete basin cyclostratigraphy for the last 3.6 Ma has been compiled by Carter et al. (1996) and Saul et al. (in press). The calibration of this cyclostratigraphy with the radiometric and palaeomagnetic ages discussed above allows the mid-Pliocene to Pleistocene Wanganui Basin cyclothemic succession to be correlated directly with the oxygen isotope timescale. This permits age estimates to be made for stratigraphic

FIG. 5. Stratigraphic log of the Rangitikei River section, Wanganui Basin showing 41 ka-duration shallow-marine cyclothems between 2.7 and 1.6 Ma and correlations to the Vrica (contains Plio-Pleistocene boundary GSSP) and Monte Singa cyclic marl/sapropel sections, Calabria, southern Italy. Inset shows details of faunal events and water depth changes within Rangitikei cyclothems in the vicinity of the G/M polarity transition. Sequence thicknesses and lithologies are after Naish and Kamp (1995,1997a) for the Rangitikei cyclothems. Paleobathymetry is based on benthic foraminiferal census data outlined in Naish and Kamp (1997b). Biostratigraphic data are after Fleming (1953a), Beu and Edwards (1984) , and Naish and Kamp (1995). The benthic oxygen isotope curve is that of Shackleton et al. (1990, 1995a). Chronology and stratigraphic details of the Vrica and Monte Singa sections are after Lourens et al. (1996).

T.R. Naish et al.: Astronomical calibration of the Plio-Pleistocene reference section New Zealand

703

704

Quaternary Science Reviews: Volume 17

horizons and events not used in establishing the correlations, such as cyclothem boundaries or biostratigraphic stage boundaries (Fig. 4). In general, each cyclothem corresponds to an odd-numbered isotope stage (interglacial), and its erosional basal sequence boundary marks a hiatus equivalent to the immediately preceding even-numbered stage (glacial). With the exception of cyclothems J1—J5, J7—J9, 12 and 36 (discussed above), each cyclothem corresponds in this fashion to a glacial—interglacial couplet. The key paleomagnetic tie-points used for pinning the isotope record to the Wanganui succession are the Gilbert/Gauss boundary (3.6 Ma), the Gauss/ Matuyama boundary (2.58 Ma), the Olduvai Subchron (1.94—1.76 Ma), the Cobb Mountain Subchron (1.19 Ma), the Jaramillo Subchron (1.07—0.99 Ma), and the Matuyama/Brunhes boundary (0.78 Ma). The ODP site 846 oxygen isotope record for the interval 3.5—3.0 Ma shows four major ‘glacial’ stages; G20, KM2, M2, and MG2 (Fig. 4). Journeaux et al. (1996) correlated these stages, together with stage MG6, to the erosional boundaries of four cyclothems in the Utiku Group. MG6 is the most d18O-enriched stage in the lower part of the Gauss Chron, and was correlated with the unconformity at the base of the Utiku Group. Stages MG2, M2, and KM2 also have major glacial peaks, and were correlated with the bases of cyclothems J2, J3, and J4 (Fig. 4). Stage G20 is the next most enriched stage after KM2 and, in the Rangitikei section, corresponds to a sharp break between the Utiku Group and the Mangaweka Mudstone. Journeaux et al. (1996) proposed an increase in the rate of tectonically driven subsidence at that point, with rapid basin deepening which minimised the effect of glacio-eustasy on sediment character. Nevertheless, seven cyclical changes between shelf and upper bathyal environments occur within the monotonous, ca. 400 m-thick Mangaweka Mudstone (cyclothems J5-11, correlated with isotope stages G20-102) (Journeaux, 1995). The G/M boundary occurs in isotope stage 104 in deep-sea cores (Shackleton et al., 1990, 1995b). In the Rangitikei River section it occurs at the base of Cycle J11 within Mangaweka Mudstone (Naish et al., 1996). Isotope stage 102 is expressed as a relatively minor low-amplitude d18O enrichment in high-resolution records, and does not correspond in the Mangaweka Mudstone to a full sequence, but is expressed as a minor increase in sand content within Cycle J11 (Journeaux et al., 1996). A deeply incised sequence boundary with up to ca. 30 m of relief truncates the upper part of Cycle J11. This is the first unconformity following ca. 400 m of outer shelf/upper bathyal mudstone section, and represents significant base level fall, subaerial exposure and erosion. This sequence boundary is correlated with the high amplitude glacial d18O shift of isotope stage 100 (Fig. 5), which is now generally considered to mark the initiation of major Northern Hemisphere continental glaciation (e.g. Raymo, 1994). The base of the Hautawa Shellbed, and a 2 m interval

of sandy-siltstone underlying it, corresponds to the subsequent glaciation associated with isotope stage 98 (Fig. 5). This is the shellbed that has traditionally been taken as the base of the Nukumaruan Stage and the Plio-Pleistocene boundary in New Zealand, and contains the cold water scallop Zygochlamys delicatula. The shellbed overlying the unconformity at the base of cyclothem 3, Tuha Shellbed, is similar to the Hautawa Shellbed and also contains the subantarctic scallop Z. delicatula. The sequence boundary at the base of cyclothem 3 is correlated with isotope stage 96: the last of the three major glaciations associated with onset of Northern Hemisphere ice sheet growth. The base of the Olduvai Subchron occurs near the base of isotope stage 71 in deep-sea cores (Shackleton et al., 1990, 1995a). In the Rangitikei River section this polarity transition is poorly constrained, but is interpreted to lie near the base of sequence 14, which is correlated with isotope stage 71. The top of the Olduvai Subchron is located in deep-sea oxygen isotope records at the base of isotope stage 63 (Shackleton et al., 1990, 1995b). In the Rangitikei River section it occurs in sequence 18 at the base of the Waipuru Shellbed (Fig. 5). The basal Jaramillo transition occurs within stage 31 in deep-sea cores (Shackleton et al., 1990, 1995a), and is located some ca. 60 m below the Potaka Tephra (stage 27) within the highstand systems tract of cyclothem 34 (Carter et al., 1997) in the Rangitikei and Turakina sections. The upper Jaramillo transition appears to lie in cyclothem 36 in Wanganui Basin, above the normally magnetised Potaka Tephra (Fig. 4; Pillans et al., 1994). Thus the Jaramillo Subchron at Wanganui encompasses two 41 ka cyclothems. The Potaka Tephra, and/or the closely spaced Kidnappers Ignimbrite (Wilson et al., 1995), is also recorded within a normal polarity interval corresponding to isotope stage 28/27 at DSDP Site 593 (Nelson et al., 1985a,b). These correlations to the isotope scale are supported by the numeric ages of both the Kidnappers Ignimbrite and the Potaka Tephra (ca. 1 Ma). The Matuyama/Brunhes transition occurs at the base of isotope stage 19 in deep-sea cores (e.g. Shackleton et al., 1990) and is placed at the unconformity beneath the Kaikokopu Shell Grit at Wanganui (Turner and Kamp, 1990), at the base of cyclothem 39 (Fig. 2). Our correlations imply that two cyclothems (37 and 38) occur between the top of the Jaramillo and the M/B boundary that correspond to three 41 ka isotope stage cycles (stages 24-20). Of the interglacial stages represented by this interval, the stage 23 peak is conspicuously lower than the others, and is probably represented cryptically within cyclothem 37, as the Omapu ‘shellbed’ (cf. Abbott and Carter, 1994). Thus cyclothem 37 is correlated with stages 26-23. The interglacial part of cyclothem 43 (Karaka Siltstone), the last full cyclothem in the Castlecliff section, is correlated with stage 11 (cf. Abbott and Carter, 1994), and the superjacent unconformably-based Mosstown Sand represents the transgressive systems tract

T.R. Naish et al.: Astronomical calibration of the Plio-Pleistocene reference section New Zealand

of cyclothem 44 deposited during early interglacial stage 9 and is correlated to the Brunswick terrace tread. Cyclothems 44-46 correspond to a flight of marine terrace cover sequences, Brunswick, Ngarino, and Rapanui, which have been correlated with interglacial stages 9, 7, and 5, respectively (Pillans, 1983). Cyclothem 47 accumulated since the last glacial maximum and is represented by transgressive Holocene coastal deposits and terrestrial sediments including the L1 loess and the Kawakawa Tephra in the cover stratigraphy of the Rapanui and post-Rapanui marine terraces.

NEW ZEALAND PLIO-PLEISTOCENE STAGES New Zealand’s isolated position in the southern latitudes of the southwest Pacific Ocean is accompanied by a high degree of endemism in its marine faunas. Until the 1970s, the definition of stage boundaries, and correlation, was almost exclusively based upon biostratigraphy (Carter, 1974; Hornibrook et al., 1989; Beu et al., 1990). A local stage system arose as an aid to the correlation and subdivision of New Zealand Cenozoic sediments as long ago as Thompson (1916). Stages were initially based upon benthic invertebrates such as molluscs, and brachiopods, but pioneering work by Harold Finlay in the 1930s on microfossils led to a greatly increased accuracy of correlation, and to an ability to date the thick, massive, ‘unfossiliferous’ mudstones and siltstones which characterise many Cenozoic sedimentary basins (Finlay and Marwick, 1940, 1947; Fleming, 1953a). The increasing diversity of molluscan faunas in the younger, Plio-Pleistocene strata and the increasing proportion of shallow-water, near-shore deposits in the stratigraphic record of progressively younger stages in New Zealand has meant that planktonic foraminifera, in particular, decrease sharply in biostratigraphic utility after the early Nukumaruan Stage, and Molluscs and other rapidly evolving groups (largely the calcareous nannofossils) have assumed a greater and greater importance for biostratigraphic subdivision of young marine rocks. The rapidly changing environments of New Zealand basins through plate tectonic activity during the late Neogene, combined with highfrequency sea-level changes and coeval temperature changes of the Plio-Pleistocene, produced a rapid turnover of molluscan fauna. A large number of biostratigraphic events is available at the generic level, as well as the species level. For example, eight molluscan genera became extinct in New Zealand at the end of Miocene (Kapitean) time, including such obviously warm-water taxa as Cucullaea, Conus and Cypraea; seven genera at the end of the Opoitian Stage; 14 genera at the end of the Waipipian Stage; three genera at the end of Mangapanian time; and 17 genera at the end of the Nukumaruan Stage, including such longranging, warm-water, ‘middle Tertiary’ taxa as Glycymeris, Eumarcia, Patro and ¸amprodomina (Beu et al., 1990, Figs. 5—8; Beu, 1990; Beu, 1995, (p. 65)).

705

Nevertheless, the facies control on the distribution of benthic molluscs means they are of little use in deepwater basins. For example, the traditional Plio-Pleistocene boundary indicator, Zygochlamys delicatula, first appears in oxygen isotope stage 98/97 in Wanganui Basin (Fleming, 1953a; Naish et al., 1997), but not until stage 86 in Mangaopari Basin in South Wairarapa (Paul Gammon, pers. comm.), which was uplifted to neritic depths during the Nukumaruan Stage; possibly Z. delicatula will be found to have appeared earlier than stage 98/97 in North Canterbury. The subdivision and correlation of the regional stages of the Plio-Pleistocene within New Zealand will continue to rely on biostratigraphy of the richly diverse, highly endemic local faunas for routine geological applications (Vella, 1975; Hornibrook et al., 1989; Beu et al., 1990; Beu, 1995). That said, the time is approaching when biostratigraphy will be unsuited for use as the sole criterion for correlation of young strata, and it will be necessary to adopt as well other pragmatic means of defining and correlating the local stages. Though we anticipate that local stages (of the Plio-Pleistocene) may ultimately fall into disuse, to be replaced by global application of astronomically tuned climatic cycles (oxygen isotope scales) there remains a need for their use for the time being. Thus, we recalibrate the ages of the established New Zealand Plio-Pleistocene biostratigraphic stages as follows: based on our new chronology the current age estimates for the base of the Opoitian, Waipipian, Mangapanian, Nukumaruan, Castlecliffian, and Haweran Stages are 5.25, 3.60, 3.03, 2.46, 1.07 and 0.34 Ma, respectively, and the ages of the Hautawan-Marahauan (intraNukumaruan) and Okehuan-Putikian (intra-Castlecliffian) Substage boundaries are 2.15 and 0.78 Ma, respectively. Futher discussion as to the future value of local stages, and suggestions for amending their boundaries to coincide with modern correlation criteria are presented by Carter and Naish (in press).

CORRELATION WITH THE PLIO-PLEISTOCENE BOUNDARY STRATOTYPE AT VRICA The Hautawa Shellbed, containing the subantarctic bivalve Zygochlamys delicatula, marks the historical base of the New Zealand Nukumaruan Stage as defined by Fleming (1953a,b) in Wanganui Basin. The incoming of Z. delicatula (commonly in association with the subantarctic crab Jacquinotia edwardsii) to Wanganui and other basins of southern and eastern North Island (Fleming, 1944; Beu et al., 1977) represents the earliest faunal evidence of climatic cooling in New Zealand Plio-Pleistocene marine sequences. Accordingly, for many years the Pliocene-Pleistocene boundary in New Zealand was placed at the base of the Nukumaruan Stage. When Fleming (1944) first drew attention to the paleoclimatic significance of Z. delicatula in early Nukumaruan sediments of the North Island, several

706

Quaternary Science Reviews: Volume 17

hundred kilometres north of its modern range, the Nukumaruan Stage was considered to be Pliocene in age. Subsequently, with the 1948 designation of the international Plio-Pleistocene boundary at the horizon of the first indication of climatic cooling in the Italian Neogene succession (at the base of the Italian Calabrian Stage), the way was clear to correlate the boundary to the base of the Nukumaruan. Although such a correlation is widely attributed to Fleming (1953a), he qualified the correlation by admitting that ‘‘more evidence is desirable before such a step is taken...’’ (Fleming, 1953a; p.127). However, an internal memorandum from Dr L. I. Grange, then Director of the New Zealand Geological Survey, in July 1953 recommended (at the request of C. A. Fleming) that ‘‘geologists draw the Pliocene-Pleistocene boundary between the Waitotaran and Nukumaruan [Stages]’’. This circular had the effect of fixing the correlation of the boundary position for the next 30 y. The first radiometric age estimate for the base of the Nukumaruan Stage in New Zealand was given by Mathews and Curtis (1966), who obtained a K/Ar date of 1.89 Ma$15% [1.94$0.29 Ma recalculated to new K/Ar constants-Dalrymple (1979)] from andesite pebbles in strata about 750 ft above the Hautawa Shellbed in Wanganui Basin. By assuming a constant rate of sedimentation, they estimated an age of about 2.15 Ma [2.21 Ma] for the Hautawa Shellbed, and by inference the Plio-Pleistocene boundary. In the same paper they also noted that Timaru Basalt, which they dated at 2.47 Ma ($15%) [2.54$0.38 Ma] in the South Island, overlay sediments containing pollen evidence of significant climatic cooling at what had been interpreted previously (Harris in Gair, 1961) as the Plio-Pleistocene boundary. Shortly after, Stipp et al. (1967) reported K/Ar ages of 2.4—2.6 Ma for basalts overlying early Nukumaruan sediments (containing cool climate floras) in western North Island, thus supporting the Timaru chronology independently. Kennett et al. (1971) also presented isotopic and faunal evidence of climatic cooling close to the Gauss/Matuyama polarity transition (then dated at 2.43 Ma) from the Mangaopari Stream section in southern North Island, but noted that the internationally accepted Plio-Pleistocene boundary at the base of the Calabrian Stage in Italy probably lay close to the base of the Olduvai (Gilsa) event at about 1.79 Ma. Thus, by the early 1970s, there was already considerable uncertainty about the age and position of the Plio-Pleistocene boundary in New Zealand (e.g. Fleming, 1975), and although the fission-track method provided further age estimates (e.g. Seward, 1974b; Boellstorff and Te Punga, 1977), the uncertainties remained until the early 1980s. This was partly because the international Pliocene-Pleistocene boundary definition itself remained uncertain. With its formal definition in the Vrica section in southern Italy (Backman et al., 1983; Tauxe et al., 1983; Aguirre and Pasini, 1985), the way was open to establish the position of the boundary

in New Zealand. This was accomplished for the first time by Beu and Edwards (1984), and refined by Beu et al. (1987) who showed that the boundary, as defined at Vrica, lay towards the top of the Nukumaruan Stage, well above Hautawa Shellbed. Within Wanganui Basin, the precise location of the Plio-Pleistocene boundary, as defined at Vrica, has recently been established by Naish et al. (1996). The boundary lies 650 m above the Hautawa Shellbed in the Rangitikei section at the downlap surface of sequence 17, 60m below Vinegar Hill Tephra (1.75 Ma) and 40 m above the Waipuru Tephra (1.87 Ma), and is correlated with isotope stage 65. This position is consistent with the chronologies of Hilgen (1991a), Zijderveld et al. (1991), and Lourens et al. (1996), who correlated the Plio-Pleistocene boundary at the Vrica GSSP (sapropel e, Fig. 5) and other Calabrian sections (Southern Italy) with the oxygen isotope stage 65 and insolation cycle 176 (Fig. 5).

CONCLUDING REMARKS This study presents a new timescale for the New Zealand Plio-Pleistocene, based upon the shallow marine cyclostratigraphy of Wanganui Basin, which corresponds to isotope stages MG6-2 (58 cyclothems). Our integrated high-resolution chronology, based on the new magnetostratigraphic and tephrochronologic data presented in Wilson (1993), Alloway et al. (1993), Pillans et al. (1994), Shane (1994), Shane et al. (1996), Naish et al. (1996), Journeaux et al. (1996), and here, allows the Wanganui Plio-Pleistocene cyclostratigraphy to be correlated with the astronomically calibrated oxygen isotope timescale (Shackleton et al., 1990, 1995b), and the astronomically calibrated sapropel/ marl cycles of the Mediterranean region (e.g. Hilgens 1991a,b; Lourens et al., 1996). In terms of New Zealand stratigraphy, the PlioPleistocene boundary has no physical significance: recurrent 41 ka cyclothems occur above and below the boundary. Moreover, because the global oxygen isotope chronology can be correlated to the Rangitikei section, thereby transferring age information for at least 116 time horizons between 3.6 and 0 Ma, the identification of the Plio-Pleistocene boundary in the section transfers no additional age information, and it is not associated with any feature of global significance. Beu et al. (1987) and Naish et al. (1997) have argued that it would be more useful to have an international boundary based upon a feature of global significance, such as the onset of northern hemisphere glaciations or a major paleomagnetic boundary. Historically, the Plio-Pleistocene boundary in New Zealand has been placed at the base of the Hautawa Shellbed because of the first appearance of cold-water taxa within it. The new chronology presented by Naish et al. (1996) and in this paper shows that the base of the Hautawa Shellbed corresponds to Stage 98, yet the first major Northern Hemisphere glaciation occurred

T.R. Naish et al.: Astronomical calibration of the Plio-Pleistocene reference section New Zealand

during Stage 100, which we correlate with the base of cyclothem 1 in the Rangitikei section (Fig. 5). It is possible that faunal evidence of climatic cooling in New Zealand occurred prior to Stage 98; local factors such as paleoceanography, or the rate of sediment accumulation, may have precluded the appearance of cold-water taxa during Stage 100 in Wanganui Basin. Further work may yet demonstrate the first appearance of Z. delicatula in North Island sections during isotope stage 100. Nevertheless, we show in the Rangitikei section stratigraphic proximity between the G/M boundary and sequence stratigraphic and faunal evidence for major climatic and sea-level changes. If the Plio-Pleistocene boundary is formally redefined near the G/M boundary, it will be possible to place the boundary precisely within the Wanganui Basin succession, and within other similar sections world-wide. At the very least Wanganui Basin deserves status as a Southern Hemisphere reference section for PlioPleistocene stratigraphy, regardless of where the PlioPleistocene boundary is ultimately placed.

ACKNOWLEDGEMENTS We acknowledge gratefully the funding provided towards this study by the Australian Research Council (RMC, TRN, GS, KJW), by the New Zealand Foundation for Research Science and Technology (Contract UOW 607; PJJK, TRN, BJP, TJJ), through a University of Auckland Research Grant (BVA), by the FRST Plio-Pleistocene boundary project (ARE, BJP, TRN), and by the N. Z. Institute of Geological and Nuclear Sciences Timscale Project (contribution no. 1248; AGB). Journal reviews by Gary Wilson and Nick Shackleton are gratefully acknowledged. Enlarged A3, A2, or A1 copies of the latest edition of Fig. 4 may be requested by emailing for details to geology@ jcu.edu.au.

REFERENCES Abbott, S.T. (1992) Sedimentology of mid-Pleistocene cyclothems from Wanganui, New Zealand. Ph.D. Thesis, James Cook University, Townsville, unpublished. Abbott, S.T. and Carter, R.M. (1994) The sequence architecture of mid-Pleistocene (ca. 1.1—0.4 Ma) cyclothems from New Zealand: facies development during a period of orbital control on sea level cyclicity. In: P.L. de Boer, and D.G. Smith, (eds), Orbital Forcing and Cyclic Sequences, International Association of Sedimentologists Special Publication, 19, 367—394. Abbott, S.T., Haywick, D.W., Carter, R.M. and Henderson, R.A. (1989) Facies signature of late Neogene eustatic sea-level fluctuations exemplified in Plio-Pleistocene cyclothems, North Island, New Zealand. 28th International Geological Congress, Washington, DC, Abstracts, pp. 1—2. Aguirre, E. and Pasini, G. (1985) The Pliocene-Pleistocene boundary. Episodes, 8, 116—120. Alloway, B.V., Pillans, B., Sandhu, A.S. and Westgate, J.A. (1993) Revision of the marine chronology in Wanganui Basin, New Zealand, based on isothermal plateau fission-track dating of tephra horizons. Sedimentary Geology, 82, 299—310.

707

Backman, J., Shackleton, N.J. and Tauxe, L. (1983) Quantitative nannofossil correlation to open ocean deep-sea sections from Pliocene-Pleistocene boundary at Vrica, Italy. Nature, 304, 156—158. Berger, A. and Loutre, M.F. (1990) Insolation values for the climate of the last 10 m.y. Quaternary Science Reviews, 10, 297—317. Berger, G.W., Pillans, B.J. and Palmer, A.S. (1992) Dating loess up to 800 ka by thermoluminescence. Geology, 20, 403—406. Berggren, W.A., Kent, D.V. and Van Couvering, J.A. (1985) Neogene geochronology and chronostratigraphy. In: N.J. Snelling (ed.) ¹he Chronology of the Geological Record, Geological Society of ¸ondon Memoir, 10, 211—260. Berggren, W.A., Kent, D.V., Swisher, C.C. and Aubry, M.P. (1995) A revised Cenozoic geochronology and chronostratigraphy. In: W.A. Berggren et al. (eds), Geochronology, ¹ime Scales and Global Stratigraphic Correlation, SEPM Special Publication 54, 139—158. Beu, A.G. (1995) Pliocene limestones and their scallops: Lithostratigraphy, pectinid biostratigraphy and paleogeography of eastern North Island Late Neogene limestones. Institute of Geological and Nuclear Sciences Monograph, 10, 244pp. Beu, A.G. (1990) Molluscan generic diversity of New Zealand Neogene stages: Extinction and biostratigraphic events. Palaeogeography, Palaeoclimatology, Palaeoecology, 77, 179—288. Beu, A.G., Maxwell, P.A. and drawings by Brazier, R.C. (1990) Cenozoic Mollusca of New Zealand. New Zealand Geological Survey Paleontological Bulletin, 58, 518pp. Beu, A.G.and Edwards, A.R. (1984) New Zealand Pleistocene and late Pliocene glacio-eustatic cycles. Palaeogeography, Palaeoclimatology, Palaeoecology, 46, 119—142. Beu, A.G., Edwards, A.R. and Pillans, B.J. (1987) A review of New Zealand Pleistocene stratigraphy, with emphasis on the marine rocks. In: M. Itinara and T. Kamei (eds), Proceedings of the 1st International Colloquium on Quaternary Stratigraphy of Asia and the Pacific Area, Osaka, pp. 250—269. Science Council of Japan, Osaka. Beu, A.G., Grant-Taylor, T.L. and Hornibrook, N. de B. (1977) Nukumaruan records of the subantarctic scallop Chlamys delicatula and crab Jacquinotia edwardsii in central Hawke’s Bay. New Zealand Journal of Geology and Geophysics, 20, 217—248. Boellstorff, J.D. and Te Punga, M.T. (1977) Fission-track ages and correlation of Middle and Lower Pleistocene sequences from Nebraska and New Zealand. New Zealand Journal of Geology and Geophysics, 20, 47—58. Bussell, R. and Mildenhall, D.C. (1990) Extinct palynomorphs from middle and late Pleistocene terrestrial sediments, South Wanganui basin, New Zealand. New Zealand Journal of Geology and Geophysics, 33, 439—447. Bussell, R. and Pillans, B. (1992) Vegetational and climatic history during oxygen isotope stage 9, Wanganui district, New Zealand and correlation of the Fordell Ash. Journal of the Royal Society of New Zealand, 22, 41—60. Carter, L., Nelson, C.S., Neil, H.L. and Froggatt, P.C. (1995) Correlation, dispersal and preservation of the Kawakawa Tephra and other late Quaternary tephra layers in southwest Pacific Ocean. New Zealand Journal of Geology and Geophysics, 38, 29—46. Carter, R.M. (1974) A New Zealand case-study of the need for local time-scales. ¸etheia, 7, 181—202. Carter, R.M., Abbott, S.T., Naish, T. and Saul, G. (1996) Basin analysis of the cyclothemic record of oxygen-isotope stages 5-100, Wanganui Basin, western North Island N.Z. (abstract). EOS (American Geophysical Union), 77(46), F328. Carter, R.M., Abbott, S.T., Naish, T. and Saul, G. (1997) A Shallowmarine Glacio-Eustatic Cyclostratigraphy for the last 2.5 Ma, ¼anganui Basin, New Zealand. Poster, Department of Earth Sciences, James Cook University. Carter, R.M. and Naish, T.R. (in press) Have local stages outlived their usefulness for the New Zealand Plio-Pleistocene? New Zealand Journal of Geology and Geophysics. Chen, J.J.W., Farrell, D.W., Murray and Prell, W.L. (1995) Timescale and paleoceanographic implications of a 3.6 m.y. oxygen isotope record from the northeast Indian Ocean (Ocean Drilling Program Site 758). Paleoceanography, 10, 21—47.

708

Quaternary Science Reviews: Volume 17

Dalrymple, G.B. (1979) Critical tables for conversion of K-Ar ages from old to new constants. Geology, 7, 558—560. Edwards, A.R. (1976) Gephyrocapsa and the Pliocene-Pleistocene boundary in the New Zealand region. Geological Society of New Zealand Annual Conference, Miscellaneous Publication 21A. Edwards, A.R. (1987) An integrated biostratigraphy, magnetostratigraphy and oxygen isotope stratigraphy for the late Neogene of New Zealand. New Zealand Geological Survey Record 23. Finlay, H.J. and Marwick, J. (1940) The divisions of the Upper Cretaceous and Tertiary of New Zealand. ¹ransactions of the Royal Society of New Zealand, 70, 77—135 Finlay, H.J. and Marwick, J. (1947) New divisions of the New Zealand Upper Cretaceous and Tertiary. New Zealand Journal of Science and ¹echnology, B28, 288—236. Fleming, C.A. (1944) Molluscan evidence of Pliocene climatic change in New Zealand. ¹ransactions of the Royal Society of New Zealand, 74, 207—220. Fleming, C.A. (1953a) The geology of the Wanganui Subdivision. New Zealand Geological Survey Bulletin, 52, 361pp. Fleming, C.A. (1953b) New evidence for world correlation of marine Pliocene. Australian Journal of Science, 15, 135—136. Fleming, C.A. (1975) The Quaternary record of New Zealand and Australia. Royal Society of New Zealand Bulletin, 13, 1—20. Gair, H.S. (1961) Drillhole evidence of the Pliocene-Pleistocene boundary at Timaru, South Canterbury. New Zealand Journal of Geology and Geophysics, 4, 89—97. Hays, J.D., Imbrie, J. and Shackleton, N.J. (1976) Variations in the Earth’s orbit: pacemaker of the ice ages. Science, 194, 1121-1132. Hilgen, F.J. (1991a) Astronomical calibration of Gauss to Matuyama sapropels in the Mediterranean and implications for the geomagnetic polarity timescale. Earth and Planetary Science ¸etters, 104, 226—234. Hilgen, F.J. (1991b) Extension of the astronomically calibrated (polarity) timescale to the Miocene/Pliocene boundary. Earth and Planetary Science ¸etters, 107, 349—368. Hornibrook, N. de B. (1981) Globorotalia (planktic Foraminiferida) in the Late Pliocene and Early Pleistocene of New Zealand. New Zealand Journal of Geology and Geophysics, 24, 263—293. Hornibrook, N. de B., Brazier, R.C. and Strong, C.P. (1989) Manual of New Zealand Permian to Pleistocene foraminiferal biostratigraphy. New Zealand Geological Survey Paleontological Bulletin, 56. Houghton, B.F., Wilson, C.J.N., McWilliams, M.D., Lanphere, M.A., Weaver, S.D., Briggs, R.M. and Pringle, M.S. (1995) Chronology and dynamics of a large siliciclastic magmatic system. Geology, 23, 13—16. Imbrie, J., Hays, J.D., Martinson, D.G., McIntyre, A., Mix, A.C., Morley, J.J., Pisias, N.G., Prell, W.L. and Shackleton, N.L. (1984) The orbital theory of Pleistocene climates: Support from a revised chronology of the marine 18O record. In: A. Berger, et al. (eds), Milankovitch and Climate, pp. 269—305. Reidel, Norwell, Johnson. Johnson, R.G. (1982) Brunhes-Matuyama magnetic reversal dated at 790,000 yr BP. by marine-astronomical correlations. Quaternary Research, 17, 135—147. Journeaux, T.D. (1995) Lithostratigraphy, foraminiferal paleoecology and sequence stratigraphy of middle Pliocene strata, Wanganui Basin. M.Sc. Thesis, The University of Waikato, Hamilton New Zealand, unpublished. Journeaux, T.D., Kamp, P.J.J. and Naish, T.R. (1996) A lithostratigraphic framework for Middle Pliocene cyclothems, Mangaweka region, Wanganui Basin, New Zealand. New Zealand Journal of Geology and Geophysics, 39, 135—149. Joyce, J.E., Tjalsma, R.C. and Prutzman, J.M. (1990) High-resolution planktic stable isotope record and spectral analysis for the last 5.35 m.y.: Ocean Drilling Program Site 625, northeast Gulf of Mexico. Paleoceanography, 5, 507—529. Kamp, P.J.J. and Turner, G. (1990) Pleistocene unconformity-bounded shelf sequences (Wanganui Basin, New Zealand), correlated with the global isotope record. Sedimentary Geology, 68, 155—161.

Kennett, J.P., Watkins, N.D. and Vella, P. (1971) Paleomagnetic chronology of Pliocene-Early Pleistocene climates and the Pliocene-Pleistocene boundary in New Zealand. Science, 171, 276—279. Kidwell, S.M. (1991) Condensed deposits in siliciclastic sequences: expected and observed features. In: W. Einsele, A. Ricken and A. Seilacher, (eds), Cycles and Events in Stratigraphy, pp. 682—695. Springer, Berlin. Kohn, B.P., Pillans, B. and McGlone, M.S. (1992) Zircon fissiontrack age for middle Pleistocene Rangitawa Tephra, New Zealand: Stratigraphic and paleoclimatic significance. Palaeogeography, Palaeoclimatology, Palaeoecology, 95, 73—94. Kondo, Y., Naish, T.R. and Kamp, P.J.J. (in press) Macrofaunal paleoecology of Pliocene-Pleistocene shelf cyclothems, Wanganui Basin, New Zealand. Paliaos. Laskar, J. (1990) The chaotic motion of the solar system: A numerical estimate of the size of the chaotic zones. Icarus, 88, 266—291. Lourens, L.J., Antonarakou, A., Hilgen, F.J., Van Hoof, A.A.M., Vergnaud-Grazzini, C. and Zachariasse, W.J. (1996) Evaluation of the Plio-Pleistocene astronomical timescale. Paleoceanography, 11, 391—413. Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore, T.C. and Shackleton, N.J. (1987) Age dating and the orbital theory of the ice ages. Quaternary Research, 27, 1—29. Mathews, W.H. and Curtis, G.H. (1966) Date of the Pliocene-Pleistocene boundary in New Zealand. Nature, 212, 979—980. Milne, J.D.G. (1973a) Upper Quaternary Geology of the Rangitikei Drainage Basin, North Island, New Zealand. Ph.D. Thesis, Victoria University of Wellington, unpublished. Milne, J.D.G. (1973b) Mt Curl tephra, a 230,000 year old marker bed in New Zealand and its implications for Quaternary chronology. New Zealand Journal of Geology and Geophysics, 16, 519—532. Milne, J.D.G. (1973c) Map and sections of river terraces in the Rangitikei Basin, North Island, New Zealand. Four Sheets. New Zealand Soil Survey Report 4. McGuirre, D.M. (1989) Paleomagnetic Stratigraphy and Magnetic Properties of Pliocene Strata, Turakina River, North Island, New Zealand. Ph.D. Thesis, Victoria University of Wellington, unpublished. Morgans, H.E.G., Scott, G.H., Beu, A.G., Graham, I.J., Mumme, T.C., St George, W. and Strong, C.P. (1996) New Zealand Cenozoic time scale. Science Report 96/38, New Zealand Institute of Geological and Nuclear Sciences. Naish, T.R. and Kamp, P.J.J. (1995) Late Pliocene marine cyclothems, Wanganui Basin, New Zealand: A lithostratigraphic framework. New Zealand Journal of Geology and Geophysics, 38, 223—243. Naish, T.R. and Kamp, P.J.J. (1997a) High-resolution sequence stratigraphy of 6th order (41 ka) Plio-Pleistocene cyclothems, Wanganui Basin, New Zealand: A case for the regressive systems tract. Geological Society of America Bulletin, 109, 978—999. Naish, T.R. and Kamp, P.J.J. (1997b) High-resolution foraminiferal depth paleoecology of late Pliocene shelf sequences and systems tracts, Wanganui Basin, New Zealand. Sedimentary Geology, 110, 237—255. Naish, T.R., Kamp, P.J.J., Alloway, B.V., Pillans, B.J., Wilson, G.S. and Westgate, J.A (1996) Integrated tephrochronology and magnetostratigraphy for cyclothemic marine strata, Wanganui Basin: Implications for the Pliocene-Pleistocene boundary in New Zealand. Quaternary International, 34/36, 29—48. Naish, T.R., Pillans, B. and Kamp, P.J.J. (1997) Recurring global sea-level changes recorded in shelf deposits near the G/M polarity transition, Wanganui Basin, New Zealand: Implications for redefining the Plio-Pleistocene boundary. Quaternary International, 40, 61—72. Nelson, C.S., Hendy, C.H., Cuthbertson, A.M. and Jarrett, G.R. (1985a) Late Quaternary carbonate and isotope stratigraphy, subantarctic Site 594, southwest Pacific. In: J.P. Kennett and C.C. von der Borch et al., (eds), Initial Reports of the Deep Sea Drilling Project, 90, 1425—1436.

T.R. Naish et al.: Astronomical calibration of the Plio-Pleistocene reference section New Zealand Nelson, C.S., Froggatt, P.C. and Gosson, G.J. (1985b) Nature, chemistry, and origin of late Cenozoic megascopic tephra in Led 90 cores from the southwestern Pacific. In: J.P. Kennett and C.C. von der Borch et al. (eds), Initial Reports of the Deep Sea Drilling Project, 90, 1161—1171. Ninkovitch, D. (1968) Pleistocene volcanic eruptions in New Zealand recorded in deep sea sediments. Earth and Planetary Science ¸etters, 4, 89—102. Pillans, B.J. (1983) Upper Quaternary marine terrace chronology and deformation, South Taranaki, New Zealand. Geology, 11, 292—297. Pillans, B. (1988) Loess chronology in Wanganui Basin, New Zealand. In: D.N. Eden, and R.J. Furkert, (eds), ¸oess, its Distribution, Geology and Soils, pp. 175—191. Balkema, Rotterdam. Pillans, B. (1990) Late Quaternary marine terraces, south TaranakiWanganui (Sheet Q22 and part Sheets Q20, Q21, R21 and R22), 1 : 100000. New Zealand Geological Survey Miscellaneous Series Map 18. Pillans, B.J. (1991) New Zealand Quaternary stratigraphy: an overview. Quaternary Science Reviews, 10, 405—418. Pillans, B.J. (1994) Direct marine-terrestrial correlations, Wanganui Basin, New Zealand: The last 1 million years. Quaternary Science Reviews, 13, 189—200. Pillans, B., McGlone, M., Palmer, A., Mildenhall, D., Alloway, B. and Berger, G. (1993) The last glacial maximum in central and southern North Island, New Zealand: A paleoenvironmental reconstruction using Kawakawa Tephra Formation as the chronostratigraphic marker. Paleogeography, Paleoclimatology, Paleoecology, 101, 283—304. Pillans, B.J., Roberts, A.P., Wilson, G.S., Abbott, S.T. and Alloway, B.V. (1994) Magnetostratigraphic, lithostratigraphic, and tephrostratigraphic constraints on Lower and Middle Pleistocene sea-level changes, Wanganui Basin, New Zealand. Earth and Planetary Science ¸etters, 121, 81—98. Quinn, T.R., Tremaine, S. and Duncan, M. (1991) A three million year integration of the Earth’s orbit. Journal of Astronomy, 101, 2287—2305. Raymo, M.E., Ruddiman, W.F., Backman, J., Clement, B.M. and Martinson, D.G. (1989) Late Pliocene variation in northern hemisphere ice sheets and North Atlantic deep-water circulation. Paleoceanography, 4, 413—446. Raymo, M.E. (1994) Initiation of the Northern Hemisphere glaciation. Annual Reviews Earth and Planetary Science, 22, 353—383. Ruddiman, W.F., Raymo, M.E., Martinson, D.G., Clement, B.M. and Backman, J. (1989) Pliocene evolution: Northern Hemisphere ice sheets and the North Atlantic Ocean. Paleoceanography, 4, 353—412. Scott. G. (1982) Review of Kapitean stratotype and boundary with Opoitian Stage (upper Neogene, New Zealand). New Zealand Journal of Geology and Geophysics, 25, 475—485. Seward, D. (1974a) Some aspects of the sedimentology of Wanganui Basin, North Island, New Zealand. PhD thesis, Victoria University of Wellington, Wellington, unpublished. Seward, D. (1974b) Age of New Zealand Pleistocene substages by fission-track dating of glass shards from tephra horizons. Earth and Planetary Science ¸etters, 24, 242—248. Seward, D. (1976) Tephrostratigraphy of marine sediments in Wanganui Basin, New Zealand. New Zealand Journal of Geology and Geophysics, 19, 9—20. Seward, D. (1979) Comparison of zircon and glass fission-track ages from tephra horizons. Geology, 7, 479—482. Seward, D., Christoffel, D.A. and Lienert, B. (1986) Magnetic polarity stratigraphy of a Pliocene-Pleistocene marine sequence of North Island, New Zealand. Earth and Planetary Science ¸etters, 80, 353—360. Saul, G., Naish, T.R., Abbott, S.T. and Carter, R.M. (in press) Sedimentary cyclicity in the marine Plio-Pleistocene of Wanganui Basin (N.Z.): sequence stratigraphic motifs of the last 2.5 Ma. Bulletin of the Geological Society of America. Shackleton, N.J. and Opdyke, N.D. (1973) Oxygen isotope and palaeomagnetic stratigraphy of equatorial Pacific core V28-238:

709

oxygen isotope temperatures and ice volumes on a 105 and 106 year scale. Quaternary Research, 3, 39—59. Shackleton, N.J., Berger, A. and Peltier, W.R. (1990) An alternative astronomical calibration of the Lower Pleistocene timescale based on ODP Site 677. ¹ransactions of the Royal Society of Edinburgh, 81, 251—261. Shackleton, N.J., Hall, M.A. and Pate, D. (1995a) Pliocene stable isotope stratigraphy of ODP site 846. In: N. Pisias, L. Mayer, T. Janacek et al. (eds), Proceedings of Ocean Drilling Program Scientific Results, 138, 337—353. Shackleton, N.J., Crowhurst, S., Hagelberg, T. Pisias, N. and Schneider, D.A. (1995b) A new late Neogene timescale: Application to leg 138 sites, In: N. Pisias, L. Mayer, T. Janacek, et al. (eds), Proceedings of Ocean Drilling Program Scientific Results, 138, 73—101. Shepherd, M.J. and Price, D.M. (1990) Thermoluminescence dating of late Quaternary dune sand, Manawatu/Horowhenua area, New Zealand: A comparison with 14C age determinations. New Zealand Journal of Geology and Geophysics, 33, 535—539. Shane, P.A.R. (1990) Correlation of some Pliocene tuffs in southern Wairarapa, New Zealand, and the comparison with biostratigraphic and magnetostratigraphic data. New Zealand Journal of Geology and Geophysics, 33, 349—355. Shane, P.A.R. (1994) A widespread early Pleistocene tephra (Potaka tephra, 1 Ma) in New Zealand: character, distribution, and implications. New Zealand Journal of Geology and Geophysics, 37, 25—36. Shane, P.A.R. and Froggatt, P.C. (1991) Glass chemistry, paleomagnetism, and correlation of middle Pleistocene tuffs in southern North Island, New Zealand, and western Pacific. New Zealand Journal of Geology and Geophysics, 34, 203—211. Shane, P.A.R., Black, T.M., Alloway, B.V. and Westgate, J.A. (1996) Early to middle Pleistocene tephrochronology of North Island, New Zealand: implications for volcanism, tectonism, and paleoenvironments. Geological Society of America Bulletin, 108, 915—925. Stern, T.A. and Davey, F.J. (1989) Crustal structure and origin of basins formed behind the Hikurangi subduction zone, New Zealand. In: R.A. Price, (ed.), Origin and Evolution of Sedimentary Basins and their Energy and Mineral Resources. International ºnion of Geodesy and Geophysics and American Geophysical ºnion, Geophysical Monograph, 48, 73-85. Stipp, J.J., Chappell, J.M.A. and McDougall, I. (1967) K/Ar age estimate of the Pliocene-Pleistocene boundary in New Zealand. American Journal of Science, 265, 462—474. Suggate, R.P. (1990) Late Pliocene and Quaternary glaciations of New Zealand. Quaternary Science Reviews, 9, 175—195. Superior Oil Co. (1943) Geology of the Palmerston-Wanganui Basin, ‘‘West Side’’, North Island, New Zealand, by A.E. Feldmeyer, B. Jones, C.W. Firth and Knight, J. (Typescript and maps filed with the Institute of Geological and Nuclear Sciences Ltd, Lower Hutt.) Tauxe, L., Opdyke, N.D., Pasini, G. and Elmi, C. (1983) Age of the Pliocene-Pleistocene boundary in the Vrica section, southern Italy. Nature, 304, 125—129. Thompson, F.A. (1916) On the names applicable to the division of the Tertiary in New Zealand. ¹ransactions of the New Zealand Institute, 48, 28—40. Tiedemann, R., Sarnthein, M. and Shackleton, N.J. (1994) Astronomical timescale for the Pliocene Atlantic d18O and dust flux records of Ocean Drilling Program site 659. Paleoceanography, 9, 619—638. Turner, G.M. and Kamp, P.J.J. (1990) Paleomagnetic location of the Jaramillo Subchron and the Matuyama-Brunhes transition in the Castlecliff stratotype section, Wanganui Basin, New Zealand. Earth and Planetary Science ¸etters, 100, 42—50. Vella, P. (1975) The boundaries of the Pliocene in New Zealand. In: T. Saito, and L.H. Burkle, (eds), ¸ate Neogene Epoch Boundaries, pp. 85—93. Special Publication 1, Micropalaeontology Press, New York.

710

Quaternary Science Reviews: Volume 17

Watkins, N.D. and Huang, T.C. (1977) Tephra in abyssal sediments east of New Zealand: chronology, paleowind velocity, and paleoexplosivity. New Zealand Journal of Geology and Geophysics, 20, 179—198. Wilde, R.H. and Vucetich, C.G. (1988) Aeolian cover beds of marine terraces in the western Wanganui district, North Island, New Zealand. In: D.N. Eden, and R.J. Furkert, (eds.), ¸oess, its Distribution, Geology and Soils, pp. 215—232. Balkema, Rotterdam. Wilson, G.S. (1993) Ice induced sea-level changes in the Late Neogene. PhD Thesis, Victoria University of Wellington, Wellington, unpublished. Wilson, C.J.N., Houghton, B.F., Kamp, P.J.J. and McWilliams, M.A. (1995) An exceptionally widespread ignimbrite with implications for pyroclastic flow emplacement. Nature, 378, 605—607.

Wilson, C.J.N., Houghton, B.F., Lanphere, M.A. and Weaver, S.D. (1992) A new radiometric age estimate for the Rotoehu Ash from Mayor Island volcanoe, New Zealand. New Zealand Journal of Geology and Geophysics, 35, 371—374. Wilson, C.J.N., Switsur, V.R. and Ward, A.P. (1988) A new 14C age for the Oruanui (Wairakei) eruption, New Zealand. Geological Magazine, 125, 297—300. Zijderveld, J.D.A., Hilgen, F.J., Langereis, C.G., Verhallen, P.J.J.M. and Zachariasse, W.J. (1991) Integrated magnetostratigraphy and biostratigraphy of the upper Pliocene-lower Pleistocene from Monte Singa and Crotone areas in Calabria, Italy. Earth and Planetary Science ¸etters, 107, 697—714.