using Modern Analogue Technique, and the subsidence history of the early Miocene

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1 New Zealand Journal of Geology and Geophysics ISSN: (Print) (Online) Journal homepage: Foraminifera based estimates of paleobathymetry using Modern Analogue Technique, and the subsidence history of the early Miocene Waitemata Basin Bruce W. Hayward To cite this article: Bruce W. Hayward (200) Foraminifera based estimates of paleobathymetry using Modern Analogue Technique, and the subsidence history of the early Miocene Waitemata Basin, New Zealand Journal of Geology and Geophysics, 7:, , DOI: / To link to this article: Published online: 21 Sep Submit your article to this journal Article views: 1520 Citing articles: 19 View citing articles Full Terms & Conditions of access and use can be found at

2 New Zealand Journal of Geology & Geophysics, 200, Vol. 7: /0/ The Royal Society of New Zealand Foraminifera-based estimates of paleobathymetry using Modern Analogue Technique, and the subsidence history of the early Miocene Waitemata Basin BRUCE W. HAYWARD Geomarine Research 9 Swainston Rd St Johns, Auckland, New Zealand b.hayward@geomarine.org.nz Abstract Cluster and Canonical Correspondence Analyses were used to group 52 early Miocene (Waitemata Group) benthic foraminiferal faunas into eight associations and relate them to proxies for paleobathymetry and bottomwater energy. Modern Analogue Technique (MAT) was used to estimate the paleodepth of each fossil fauna by comparing their generic composition with 71 modern New Zealand faunas. MAT estimates are mostly consistent with, but no more precise than, those inferred by conventional subjective means. MAT estimates could be improved by broadening the modern database. The less precise paleodepth estimates for outer shelf and bathyal faunas were improved using the known upper depth limits of several key bathyal taxa. The combined use of MAT and conventional methods is advocated to provide the most robust paleoenvironmental interpretations. The paleobathymetry estimates are consistent with previously inferred regional subsidence during formation of the Waitemata Basin. The faunas document the submergence of a land with up to 100 m of rolling relief, with initial creation of both sheltered bays (Elphidium and Melonis associations) and exposed coasts (Amphistegina and Cribrorotalia, Gaudryina, Cibicides associations). Dysoxic faunas (Nonionella dominated) provide evidence for the accumulation of fine sediment on the quiet floor of several sheltered, deeper water inlets (20-0 m). As subsidence continued, the former ridge crests became islands and finally disappeared, coincident with cessation of coarse terrigenous sediment supply. Paleobathymetry estimates imply that several coarse, shallow-water gravel or shell hash units slid down the submarine slopes of these small islands to be interbedded with mid-outer shelf sediment (with Bolivina and Cibicides dominated faunas). Aperiod of sediment starvation (hiatus or thin mudstone) ensued: in the south, it spanned an interval during which the basin subsided from c. 150 m down to > m; in the north, it lasted until the basin floor reached lower bathyal depths (c. >1700 m, Oridorsalis- Nodosaria association), before sand turbidites flowed in from the northwest. G0065; Online publication date 1 December 200 Received 25 July 200; accepted 22 November 200 Keywords benthic foraminifera; New Zealand; Waitemata Basin; Canonical Correspondence Analysis; Modern Analogue Technique; early Miocene INTRODUCTION This paper investigates the use of two methods to provide paleobathymetry estimates that document the subsidence history of the early Miocene Waitemata Basin in northern New Zealand. Both methods are based on the same quantitative census counts of fossil and Recent benthic foraminiferal faunas. Foraminifera are one of the most commonly used fossil groups for estimating the depth of deposition of marine Cenozoic sedimentary rocks one of the essential prerequisites for successful sedimentary basin analysis and paleogeographic reconstruction. Conventional techniques usually estimate paleobathymetry from fossil foraminiferal faunas utilising a combination of the planktic foraminiferal percentage, benthic species diversity, and the taxonomic composition of the dominant benthic taxa (e.g., Murray 197, 1991; Hayward & Buzas 1979; Hayward 196). Approximate water depth may be inferred using the trends of increasing planktic percentage and benthic species diversity, from marginal marine across the shelf to bathyal depths (e.g., Buzas & Gibson 1969; Gibson 199; Hayward et al. 1999). Associations of dominant species or genera of benthic foraminifera may be determined qualitatively by perusal of the fauna (e.g., Kennett 1962; Vella 1962; Hayward 1990a), or quantitatively by detailed census counts in conjunction withmultivariate analysis techniques (e.g., Scott 1970,1971; Hayward & Buzas 1979; King et al. 199; Hayward & Brook 199; Naish & Kamp 1997). These associations of dominant taxa are used to subjectively estimate the paleobathymetry at which they may have lived, based mostly on the ecological distribution patterns of their modern counterparts. The ecological distribution of shallow-water (<50 m) benthic foraminifera is strongly influenced by varying combinations of factors linked to tidal exposure or water depth, salinity, wave and current energy, and bottom water oxygen concentration (e.g., Hayward et al. 1999). The ecological distribution of deep-sea benthic foraminifera is determined by the complex interplay of a number of physical and biological factors, especially nutrient flux and bottom water oxygen concentration (e.g., Murray 1995; van der Zwaan et al. 1999). The resulting benthic foraminiferal distribution usually exhibits a zonation that is roughly coincident with increasing water depth, but absolute depths and taxonomic composition of these zonations vary from region to region (e.g., Culver 19; Murray 1991). This paper investigates the use of an alternative method- Modern Analogue Technique (MAT) to provide quantitative paleobathymetry estimates for benthic foraminiferal assemblages, based on their census counts. This technique,

3 750 New Zealand Journal of Geology and Geophysics, 200, Vol. 7 together with Transfer Function methods, has become increasingly popular in the last two decades for providing estimates of paleosea-surface water temperatures, based on the census counts of planktic foraminiferal faunas (e.g., Imbrie & Kipp 1971; Weaver et al. 199; Barrows et al. 2000; Sabaa et al. 200a). In the last decade, Transfer Functions and MAT have been introduced as methods for quantitatively estimating the paleotidal elevation for paleoseismic displacement and sea-level change studies, based on the census counts of Holocene benthic foraminiferal faunas from salt marshes (e.g., Horton et al. 1999; Gehrels 2000; Hayward et al. 200a). MAT requires a sizeable database of census counts of contemporary faunal assemblages from a wide range of environments, with related measurements on the environmental factor being estimated. The previous lack of such a database on normal salinity benthic foraminiferal faunas from a wide range of depths in any one region explains why this method has not been utilised for paleobathymetry estimates, until now. The northwestern Gulf of Mexico is a region with an equally large dataset to that of New Zealand of modern benthic foraminiferal census data extending from the coast down to abyssal depths (Culver & Buzas 191). Culver (19) used cluster analysis to recognise 1 depth-related benthic foraminiferal zones at the generic level. He then used discriminant analysis to classify modern and Neogene test samples in terms of the established depth zones. WAITEMATA B ASIN The early Miocene Waitemata sedimentary basin in northern New Zealand was a relatively short lived (c Ma) marine depression that accumulated m thickness (Raza et al. 1999) of turbiditic sand and interbedded mud (Waitemata Group; Ballance 197,1976), prior to its eversion in the latter part of the early Miocene (Hayward 1979,199). Subsequent uplift, regional westward tilting, and erosion have resulted in extensive exposures of Waitemata Group rocks throughout the Auckland region. Greater uplift has exposed the oldest Waitemata Basin sediments (Kawau Subgroup; Hayward & Brook 19) in the east and south of the region and these record the initial subsidence history of the basin, which is the target of this study. Tectonic setting In the early Miocene, northern New Zealand lay to the west of the Australian-Pacific plate boundary above a southwestplunging subduction zone (Brothers 197; Ballance et al. 192). Two belts of calc-alkaline, arc-related volcanoes erupted along either side of the Northland Peninsula during the early Miocene (Ballance 197). During the period of subsidence and later turbidite accumulation in the Waitemata Basin, two large andesitic stratovolcanoes were active to the west and northwest of the basin, but volcanism did not start in the east until after the basin's eversion (Hayward et al. 2001a). The regional subsidence and later eversion of the Waitemata Basin was presumably related to oblique compression across the plate boundary. It lagged 2- m.y. behind a similar cycle of subsidence and eversion in northern Northland, during which giant nappes of Cretaceous-Paleogene rocks (Northland Allochthon) were emplaced from the northeast (Ballance & Spörli 1979; Hayward et al. 199; Hayward 199), burying older in situ Miocene sedimentary rocks. Kawau Subgroup (basal Waitemata Group) This subgroup contains the thin (up to 60 m), highly variable sequence of shallow-water sediments that accumulated during the initial subsidence and formation of the marine Waitemata Basin. They outcrop along the east coast of southern Northland and Auckland, in the northern Hunua Ranges, at the tip of Coromandel Peninsula, and on the west coast of northern Waikato, and have been intersected at depth by drillholes at Orewa and Awhitu (Fig. 1). Kawau Subgroup strata lap onto and partly bury an irregular paleoshoreline of Waipapa Terrane greywacke basement in the central and northern part of the basin, and unconformably overlie Oligocene Te Kuiti Group in the south (Hayward & Brook 19; Ricketts et al. 199). Kawau Subgroup contains a transgressive sequence of paralic and shallow marine boulder, cobble, and pebble breccia and conglomerate ( Formation), shelly calcareous sandstone ( Sandstone), and coarse bioclastic limestone (Papakura Limestone), described in detail by Hayward & Brook (19) and Ricketts et al. (199). Rock fragments and heavy minerals indicate derivation exclusively from the local underlying Waipapa Terrane greywacke or Te Kuiti Group (Hayward & Smale 1992). These coarse, shallow-water Kawau Subgroup sedimentary rocks are overlain abruptly by a deep-water turbiditic sequence (Warkworth Subgroup), or separated from it by a few metres of massive or weakly laminated mudstone (Ricketts et al. 199). Foraminiferal and molluscan fossils give an early Miocene (Otaian, Ma) age for the Kawau Subgroup and overlying Warkworth Subgroup turbiditic sequence (Hayward & Brook 199; Eagle et al. 1995). Previous studies on Kawau Subgroup fossil foraminifera, molluscs, corals, barnacles, echinoderms, and other groups indicate intertidal through to uppermost bathyal paleodepths of accumulation, with the majority at inner and middle shelf sites (e.g., Hornibrook & Schofield 196; Eagle et al. 199, 1995, 1999; Hayward & Brook 199; Ricketts et al. 199). METHODS Laboratory Fifty-two Miocene samples were selected for this study (Appendix 1) from a pool of over 200 washed foraminiferal samples from the Kawau Subgroup and basal Warkworth Subgroup, on the basis of providing maximum stratigraphic and geographic coverage of rich, well-preserved foraminiferal faunas (Fig. 1). Sedimentary rock samples were pre-treated by coarsely crushing, drying, and then soaking overnight in water, hydrogen peroxide, or kerosene (depending on the degree of induration). Miocene (and recent seafloor) sediment were next washed over a 6 µm sieve to remove mud. The sand residue was dried and microsplit down to an amount containing c. 200 benthic specimens. All benthic foraminifera (>6 µm) were picked from the split, mounted on faunal slides, identified, and counted. The percentage of the foraminiferal fauna composed of planktic forms was counted during picking (Appendix 1). Taxonomic references for all species mentioned in this paper are provided in Appendix 2 and the more common species are illustrated in Fig. 2. Data repositories Unpicked washed residue, faunal slides, and figured specimens (catalogue numbers prefixed by BWH) are housed

4 Hay ward Waitemata Basin subsidence 751 Mudstone Shelly sandy mudstone Limestone Pebbly conglomerate Sandstone Fig. 1 Oblique map of the Auckland region viewed from the west, showing location of early Miocene samples on representative stratigraphic columns through the Kawau Subgroup at key localities spread throughout the basal Waitemata Basin outcrop. The base of every column is an unconformable contact on Mesozoic greywacke (north of Stream) or Oligocene limestone (four southern columns). More detailed columns for most localities are given in Hayward & Brook (19). in the collections of the Institute of Geological & Nuclear Sciences, Lower Hutt, New Zealand. Copies of the dataset can be obtained from the author. Cluster and Canonical Correspondence Analyses Cluster analysis of the Miocene foraminiferal faunas was undertaken using the "MVSP" statistical package (Kovach 199). The fossil data matrix (census counts of 2 foraminiferal species in 52 samples) was standardised by converting counts to proportions of sample totals. Unweighted pair group Q-mode cluster analysis using arithmetic averages of a Bray-Curtis distance matrix was used to produce a dendrogram classification from which sample associations were selected (Fig. 2). Detrended Correspondence Analysis (DCA; Kovach 199) was used to summarise and help interpret the Miocene benthic foraminiferal faunal data. An ordination of the samples and abundant species was plotted on the first two axes, on which the sample associations produced by cluster analysis were overlaid. Canonical Correspondence Analysis (CCA; Ter Braak 195) was used to relate several environmental and faunal proxy datasets to the ordination. CCA produces vectors that show the axis and direction of increasing values of each proxy. The length of each vector arrow is ameasure of the correlation between that factor and the faunal pattern the longer the arrow, the stronger the correlation. Ranking of species or samples with respect to each variable may be determined by projecting their plotted position perpendicularly onto the appropriate proxy arrow. Modern Analogue Technique, MAT The paleodepth at which each Miocene fossil foraminiferal fauna accumulated, was estimated using MAT, similar to the technique described for estimating tidal elevation by Hayward et al. (200a), based on the benthic foraminiferal census counts. Squared chord distances were used as a measure of dissimilarity (Prell 195) between fossil and modern analogue assemblages. Algorithms were implemented in Microsoft EXCEL macro language. The modern assemblage census data are contained in a dataset from inner-shelf to upper abyssal depths from around New Zealand. This dataset of 71 census counts of modern benthic foraminiferal faunas (>6 µm) has been assembled from a number of previous studies in New Zealand normal marine salinity environments from intertidal down to the carbonate compensation depth (CCD) at c. 600 m (Table 1). Many of the samples were collected by small dredge from the upper 5-10 cm of seafloor sediment. The dataset counts are on total or dead assemblages only and avoid most of the seasonal variability and clumped population problems of using live census counts. To assist faunal comparisons between modern and fossil Neogene faunas (with many extinct species), all species identifications were lumped together into 7 generic or higher taxonomic groups (Table 2). This modern dataset was taphonomically adjusted by deleting all records of weakly agglutinated taxa that usually disaggregate soon after depth, and recalculating the relative abundance of remaining counts (as in Hayward et al. 2001b).

5 752 New Zealand Journal of Geology and Geophysics, 200, Vol. 7 Fig. 2 Dendrogram classification of the 52 Miocene benthic foraminiferal samples produced by cluster analysis using Bray-Curtis distance. The eight associations and two sub-associations were selected by the author. Benthic foraminifera that characterise these associations are illustrated. Unless otherwise specified all scale bars = 100 µm. A, B Elphidium crispum (Linnaeus). FP5, R11/f2; C Elphidium kanoum Hayward. FP0, R1 1/f751; D Haynesina depressula (Walker & Jacob). USNM2, Q0/f955; E Amphistegina aucklandica (Karrer). BWH/15, R10/f9001 A; F, G Cribrorotalia ornatissima (Karrer). BWH7/16,1 R1 1/f751; H Gaudryina convexa (Karrer). BWH 5/9, R11/f7555; I, J Nonionella novozealandica Cushman. BWH52/1,12 R10/f951; K, L Notorotaliapowelli Finlay. BWH7/11,15 R11/f751; M Quinqueloculina seminula (Linnaeus). BWH7/2, R11/f7555; N Melonis simplex (Karrer). BWH52/22, R12/f75; O Haeuslerella hectori Finlay. BWH5/2, R11/f7555; P Bolivina finlayi Hornibrook. BWH/21, R11/f107; Q Bolivina mantaensis Cushman. USNM229, Q11/f7002d; R, S Cibicides mediocris Finlay. BWH52/26,27, Q10/f951; T Cibicides temperatus Vella. BWH52/, Q11/f; U Cibicides temperatus Vella. BWH52/7, G/f19; V Bolivina reticulata Hantken. FP0, R11/f107; W Oridorsalis umbonatus (Reuss). BWH52/0, Q10/f; X Nodosaria longiscata d'orbigny. BWH7/7, Q10/f.

6 Hay ward Waitemata Basin subsidence 75 Table 1 Source of census data used as modern analogue set for estimating New Zealand Neogene normal marine salinity paleodepths. Copies of the data can be obtained from the author. Locality No. of samples Depth range (m) Source Cavalli Islands Bay of Islands Taiwawe Bay Tutukaka Harbour Chicken Islands Great Barrier Island Little Barrier Island Waitemata Harbour Cuvier Island Whale Island Taranaki offshore Wanganui Bight Pauatahanui Inlet Marlborough Sounds Purakanui Inlet South Island offshore east Stewart Island Chatham Island Hay ward 192a Haywardetal. 191 Reid & Hay ward 1997 Brook etal. 191 Haywardetal. 19 Hay ward & Grenfell 199 Hay ward 192b Haywardetal Hayward & Grace 191 Hay ward 1990b Hayward et al. 200 Haywardetal Hayward & Triggs 199 Haywardetal Haywardetal Haywardetal. 2001b Haywardetal. 199 Hayward & Grenfell 1999 Total Table 2 Generic or higher taxonomic groups used for Modern Analogue Technique comparisons between early Miocene and Recent census database. Abditodentrix Alabaminella Ammonia Amphicoryna Amphistegina Anomalinoides/Anomalina Astrononion Bolivina/Sigmavirgulina Bolivinita Bulimina Buliminella/Buliminoides/Elongobula Cassidella Cassidulina Chilostomella Cibicides/Cibicidoides/Dyocibicides Cribrostomoides Cyclammina Discorbinella/Hanzawaia Eggerella Ehrenbergina Eilohedra Elphidium Epistominella Evolvocassidulina Fursenkoina Gaudryina Gavelinopsis Glabratellidae Globobulimina Globocassidulina Guttulina/Globulina/Sigmomorphina Gyroidinoides Haynesina Heronallenia Hoeglundina Ioanella Karreriella Laticarinina Lenticulina Martinotiella Melonis/Nonion Miliolinella miscellaneous agglutinated miscellaneous miliolids Neoconorbina Neouvigerina Nonionella/Nonionellina Notorotalia Oridorsalis Osangularia Patellinella Porogavellinella Pullenia Pyrgo Quinqueloculina Reophax/Cuneata/Schlerochorella Rosalina Saidovina Sigmoidella Sigmoilopsis/Siphonaperta Siphonina tubulosa Siphotextularia Sphaeroidina Spiroloculina/Inaequalina Textularia/Spiroplectinella/Spirotextularia Trifarina Triloculina/Triloculinella Trochammina/Portotrochammina/Paratrochammina Trochulina unilocular uniserial elongate Uvigerina costate Virgulopsis Zeaflorilus

7 75 New Zealand Journal of Geology and Geophysics, 200, Vol. 7 Using the chord dissimilarity coefficient results, three estimates of the water depth were computed for each fossil fauna: (1) the mean elevation and range of the five most similar modern faunas; (2) the mean elevation of the 10 most similar modern faunas; and () the mean of all faunas with chord dissimilarity values <70. Results of all three methods are relatively similar, and thus estimate (1) has been adopted for use throughout this study (Appendix 1), except where otherwise stated. The reliability of these elevation estimates depends on a number of factors, such as the breadth of environmental coverage represented by the modern dataset, differences in nutrient flux between the early Miocene and present day, and evolutionary and paleobiogeographic changes in faunal composition. Species diversity Three measures of species diversity have been calculated for each Miocene foraminiferal fauna (using the statistical package MVSP; Kovach 199) and are presented in Appendix 1: (1) number of species, S in each pick of 200 specimens; (2) Shannon-Wiener Information Function, H (MacArthur & MacArthur 1961); () evenness, J (Pielou 1966; Hayek & Buzas 1997). Bathymetric terminology Bathymetric terminology in this paper follows van Morkhoven et al. (196): inner shelf = 0-50 m, mid shelf = m, outer shelf = m, upper bathyal = m, mid bathyal= m, lower bathyal = m, abyssal = m. SAMPLE ASSOCIATIONS AND MAT PALEOBATHYMETRY ESTIMATES The following sample associations and 2 sub-associations (7 A, ) were selected by inspection from the Q mode cluster analysis of the 52 Miocene samples (Fig. 2). The mean relative abundance of the common species in each association is shown in Fig.. The three MAT estimates of paleobathymetry for each Miocene sample are presented graphically in Fig., together with an indication of the similarity between the Miocene fauna and the five nearest modern analogues (mean chord dissimilarity distance). Association 1: Elphidium This association is strongly dominated by Elphidium crispum and E. kanoum, and contains the highest relative abundance of Haynesina depressula. Planktic percent (mean 10%), species diversity (mean S = ), and evenness (J = 0.7) are low. This association is most similar to the modern Elphidium charlottense and H. depressula-e. charlottense associations that occur around New Zealand today at shallow, inner-shelf depths (0-17 m), in fine sand and sandy gravel in relatively sheltered bays and inlets (Hayward et al. 1999). This is identical to the MAT depth estimates of m, with the most similar analogues (Cavalli Islands) to samples 20 and 21 indicating a low tidal beach environment. Association 2: Amphistegina Large, robust Amphistegina aucklandica comprise over 0% of the two benthic foraminiferal faunas in this association. This warm-water genus no longer lives around New Zealand today and therefore the MAT chord dissimilarity values are large (Fig. ) and the paleobathymetry estimates (2.5,25 m) based on comparison with modern New Zealand faunas are unreliable. Faunas dominated by large, thick-walled Amphistegina are today characteristic of coarse sediment in higher energy and light environments on the shallow (0-0 m), exposed, outer reef slope of tropical islands (e.g. Cushman et al. 195; Todd 1976; Hallock & Hansen 1979; Hallock et al. 196). This is consistent with the low planktic percentage (mean 2%), low species diversity (S=9,H=0.), and evenness (J= 0.6), and the occurrence of both samples in pebbly, granule conglomerate. The fauna is closely similar to thanatotope A of Hayward & Buzas (1979), which occurred in coarse sedimentary rocks in younger parts of the Waitemata Basin. Association : diverse This association of seven faunas has moderate diversity (S = 2, H = 2.5), high evenness (J = 0.), and is codominated (mean relative abundance -16%) by six species: Amphistegina aucklandica, Cribrorotalia ornatissima, Elphidium crispum, Gaudryina convexa, Cibicides mediocris, and C. temperatus. The first two genera no longer live around New Zealand, whereas the latter three co-occur in similar relative abundances to this in current-swept, oxic, relatively coarse substrates at inner-shelf depths of c. 5-0 m (Hayward et al. 1999). MAT depth estimates for six of the seven faunas in this association (11-26 m) are consistent with the above interpretation, as is the low planktic percentage (0-10%) for the same six faunas. The seventh sample (16) has 5% planktics and a MAT depth estimate of m. Its composition could be a result of downslope transport and mixing. Association : Nonionella This association is dominated by Nonionella novozealandica (mean relative abundance %) with sub-dominant (each 6- %) Bolivinafinlayi, Notorotaliapowelli, and Quinqueloculina seminula. It has similar generic composition to the modern Nonionellina flemingi and Notorotalia finlayi associations, that occur around New Zealand today in dysoxic mud or fine sand at deep, inner-shelf depths (12-0 m) on the floors of sheltered, often silled, deep-water inlets (Hayward et al. 1999). This environmental interpretation is consistent with the MAT depth estimates of 27-2 m for seven of the eight faunas in this association (Fig. ). The variable and somewhat high planktic percentage in this association (0-65%) is also found in these modern deep-water inlets (Hayward & Grenfell 199; Hayward et al. 199). The eighth fauna (1) lacks the sub-dominant species, which are replaced by Cassidulina and Globocassidulina, which gives it a much greater MAT depth estimate and range (217 m; 0-50 m). Association 5: Melonis Melonis simplex dominates the two faunas in this association (relative abundance 2%), with sub-dominant (each 6-9%) Cibicides mediocris, Haeuslerella hectori, Notorotalia powelli, and Quinqueloculina seminula. Haeuslerella is extinct and Melonis does not live at shelf depths (0-200 m) around New Zealand today. The three remaining subdominant genera are prominent members of the inner-shelf associations and above, and similar paleodepths are indicated for this association by the mean planktic percentage of 10%. MAT paleodepth estimates concur, with narrow ranges around mean values of 19 and 27 m. The similarity

8 Hay ward Waitemata Basin subsidence 755 Fig. Mean relative abundance of the common benthic species in each of the eight sample associations and two sub-associations (selected from the cluster analysis dendrogram in Fig. 2). standard deviation 0 % 20 mean relative abundance T Associations T. T. T T x i 1 ] T T + ^ _ 6 7 of this association with an Arenodosaria-Melonis assemblage from New Zealand Oligocene sediments (Hayward 195) suggests that it lived in a relatively sheltered, fine sediment environment. Association 6: Bolivina This association is co-dominated (-11 % each) by two species of Bolivina: B. finlayi and B. mantaensis. The faunas have high diversity (S= 2; H =.1) and evenness (J= 0.), and a relatively high planktic abundance (mean 65%). No similar modern associations have been recorded so far from around New Zealand. Faunas strongly dominated by Bolivina are often characteristic of low-oxygen, muddy environments (e.g., Verhallen 1991; Bernhard & Sen Gupta 1999), but their relative abundance is not so high in this association. Around New Zealand today, the highest relative abundances

9 756 New Zealand Journal of Geology and Geophysics, 200, Vol. 7 Mean of all analogues <70 dissimilarity coefficient Mean of nearest 5 analogues D Mean of nearest 10 analogues Range of nearest 5 analogues MAT paleodepth estimates P a ft co a. P u "CM * IO O) <O lo 00 CM Chord dissimilarity Fig. Plot of three Modern Analogue Technique estimates of paleobathymetry of each Miocene fossil foraminiferal sample (grouped together in cluster analysis associations from Fig. 2). The plot of the mean chord dissimilarity coefficient between each Miocene fauna and the five most similar modern analogues provides an indication of the degree of possible accuracy of the depth estimates (higher values indicate less similar faunas). of this genus (15-25%) occur in more sheltered, quiet water and deeper parts (5-0 m) of harbours and bays, and at bathyal and abyssal depths (Hayward et al. 1999, 2001b). MAT water-depth estimates for this association reflect this broad modern range, with mean values of m (range 2-50 m) for three of the four faunas in this association. The fourth fauna (7) gives a consistently shallower depth estimate (mean 7 m). Association 7: Cibicides This large association of 2 faunas is characterised by the co-dominance of Cibicides mediocris and C. temperatus, with sub-dominant Bolivina reticulata. The cluster analysis dendrogram groups these faunas into two sub-associations, with two faunas (, 52) ungrouped. There are no recorded faunas living around New Zealand today that have close generic composition to association 7, but it is essentially the same as early Miocene thanatotope B of Hayward & Buzas (1979), which accumulated in younger mudstone and sandstone on the northwestern flanks of the Waitemata Basin, at inferred mid-outer-shelf paleodepths ( m). Two sub-associations are recognised: Sub-association : Cibicides-Amphistegina This sub-association is co-dominated by C. mediocris (mean 0%) and C. temperatus (mean 1%), with sub-dominant, thin-walled specimens of the subtropical and tropical Amphistegina aucklandica (mean %). The greatest abundance of Cibicides s.l. in modern oceans is in midouter-shelf depths ( m; Boltovskoy & Wright 1976). These paleodepths are supported by the 0% mean planktic percentage and by the abundance of relatively fragile

10 Hay ward Waitemata Basin subsidence 757 Amphistegina, which Todd (1976) noted was typical of deeper water situations down to depths of c. 00 m. Other studies (e.g., Hallock & Hansen 1979) suggest that because Amphistegina has symbiotic photosynthesising algae, its depth range is limited to the euphotic zone (shallower than c. 100 m). Deeper occurrences of shells are probably due to post-mortem downslope transport. MAT estimates for the 11 faunas in 7 A also indicate mid-outer shelf depths (mean of 5 closest analogues, 0-10 m). Sub-association : Cibicides-Bolivina This sub-association differs from by its lack of Amphistegina, its much greater relative abundance of Bolivina reticulata (mean relative abundance 12%), and its higher species diversity (S = 1, cf. 0 in ). The lack of Amphistegina and abundance of Bolivina suggest that lived in lower oxygenated, more sheltered, finer grained sediment. The higher mean relative abundance of planktic foraminifera (72%) in this sub-association suggests that accumulated farther offshore, possibly in deeper water than. MAT estimates for the 10 faunas in have a similar wide mid-outer shelf range (0-200 m) to 7 A, and do not support the greater depth inferred from planktic percentages. Association : Oridorsalis-Nodosaria The three faunas in association are co-dominated (17-20% each) by Oridorsalis umbonatus and Nodosaria longiscata, and have moderately high species diversity (mean S = 27, H = 2.7) and planktic abundance (mean 70%). There are no recorded modern faunas with similar compositions, as Nodosaria longiscata is now extremely rare in the world's oceans, following near extinction during the mid-pleistocene Climate Transition (Hayward 2002). Oridorsalis umbonatus is still relatively common and occurs with relative abundances of 5-20% at lower bathyal and abyssal depths ( m) around New Zealand today (Hayward et al. 2001b, 200). Faunas co-dominated by O. umbonatus and Globocassidulina subglobosa are common at abyssal depths (>2000 m) throughout the Neogene and are typical of relatively high oxygen, carbonate corrosive bottom environments (e.g., Murray 19; Mackensen et al. 1995; Hayward et al. 200b). MAT estimates give lower bathyal depths of m, slightly shallower than inferred above. DISCUSSION Chord dissimilarity coefficient distances The chord dissimilarity distances are generally high (Fig. ), reflecting poor matches between these early Miocene faunas and the modern analogues, even at generic level. The most similar faunas (mean distance 9-56) are in association 1 (because of the strong dominance of Elphidium). The most dissimilar faunas (mean distance ) are in association 2 (because of the strong dominance of Amphistegina, which is absent from modern New Zealand faunas). The lack of any close modern analogues for sample 1, when it is clearly from a high energy, inner-shelf environment, explains the anomalously deep MAT estimate of 25 m for this fauna. The remaining associations have moderately poor chord distances (mean of five modern analogues) in the range 55-95, but surprisingly many give relatively good paleodepth estimates. There are several possible reasons that combine to explain the large chord dissimilarity distances between most of these Miocene and modern foraminiferal faunas. 1. Global climate changes have resulted in a cooling of mid-latitude surface waters since the middle Miocene, resulting in the disappearance from New Zealand waters of tropical genera and assemblages. Particularly significant in this study is the equatorial contraction of the range of Amphistegina and Elphidium crispum. In addition, some of the common early Miocene genera and families are now extinct (e.g., Haeuslerella, Cribrorotalia, Stilostomellidae, Pleurostomellidae; Hornibrook et al. 199; Hayward 2002). 2. The generic compositions of modern bathyal and abyssal faunas around New Zealand are markedly different from those in the early Miocene, even in the same ODP and DSDP cores (e.g., Kurihara & Kennett 19, 1992; Hayward et al. 200b). These changes have been ascribed to the growth of the polar ice sheets, the consequent impact on the character of deep sea water, and an overall increase in the flux of food supply, especially since the onset of the ice ages in the last few million years (Hayward et al. 200b). Deep-sea benthic foraminiferal changes, especially in the µm fraction, include: major increases in the relative abundance of Epistominella, Alabaminella, Bulimina, Cassidulina, and Abditodentrix; and major decreases in the relative abundance of Oridorsalis, Globocassidulina, and elongate, uniserial nodosariids.. The dataset of 71 modern analogue faunas (Table 1) is strongly representative of inner-shelf (0-50 m) environments, and with a weaker sampling (c. 100) of faunas from outer-shelf and greater depths (>100 m). As a result, shallow-water paleodepth estimates are likely to be more accurate than those from bathyal or upper abyssal depths. Reliability and accuracy of MAT estimates The majority of the MAT estimates of paleobathymetry (mean of 5 or 10 nearest modern analogues; Fig. ) give results closely consistent with those inferred by conventional means of comparison with documented modern faunas. Perhaps this is not so surprising as both methods are strongly based on comparisons at the generic level with the same modern dataset, albeit one method intuitively and the other by computer methods. The resolution of MAT depth estimates is somewhat degraded by the use of generic categories (e.g., Cibicides, Notorotalia, Quinqueloculina, Ammobaculites etc.), which ignore differences in depth ranges at a species level. Use of generic-level groupings cannot be avoided, as >50% of the early Miocene species in this study are now extinct. Studies on modern faunas clearly show that associations characteristic of marginal marine environments live in the narrowest depth ranges, followed progressively by those at inner-shelf depths, and mid-outer shelf depths, with bathyal and abyssal associations having extremely large depth ranges, most strongly influenced by food supply and bottom oxygen levels (e.g., Culver 19; Hayward et al. 1999,2002). Thus, it is not surprising that the paleobathymetry range of the five nearest modern analogue faunas is narrowest for the marginal marine association (1) and inner-shelf associations (,5, most

11 75 New Zealand Journal of Geology and Geophysics, 200, Vol. 7 of ). The depth range for the inner-mid-shelf faunas (most of associations 6 and 7) is broad ( m), and even broader for the bathyal association () with ranges of m (Fig. ). Two faunas (16, 1) within the mostly inner-shelf associations and have mid-outer-shelf MAT depth estimates and correspondingly broad confidence ranges. Both these samples, from Motuihe and Stream, occur stratigraphically between or above mid-outer-shelf association 7 and 6 faunas, and their greater depth estimates are probably correct, but they also have mixed in allochthonous inner-shelf associations. Three faunas (7,,) within the dominantly mid-outershelf associations 6 and 7, have inner-shelf MAT depth estimates and narrow inner-shelf confidence ranges (Fig. ). In two instances (,7), these shallower depth estimates are possible, as they are stratigraphically transitional between inner and mid-outer-shelf associations (Fig. 1). There is no easy way of assessing the potential validity of the single sample from Awhitu (), although its planktic abundance (55%) favours a deeper locus. With only one or two exceptions, the MAT estimates do not appear to improve on the resolution of my conventional intuitive interpretations of paleodepth, although they introduce more apparent objectivity. Refining bathyal paleobathymetry estimates A method has been developed for improving the resolution of bathyal paleodepth estimates using the upper water depth limits of a number of less common deep-water benthic taxa (Hayward 196, 1990a; King et al. 199; Crundwell et al. 199). These limits have been derived from three sources: (1) the documented water depth range of taxa living around New Zealand today (e.g., Hayward et al. 2001b, 200); (2) the upper paleodepth limits of some extinct bathyal taxa in drillholes through a thick, regressive Neogene sequence of giant foreset beds calibrated to the depth of the adjacent, prograding continental slope (Hayward 1990a); and () the upper paleodepth limits of these key taxa in Neogene sections in DSDP and ODP sites on stable crust in the surrounding southwest Pacific (e.g. Hayward et al. 200b). Six of these rarer taxa are present in eight of the early Miocene faunas in this study (Table ) and can be used to check and refine their MAT paleodepth estimates. The three taxa with the greatest depth limits only occur in the three faunas (, 6, 7) that belong to association, and have the deepest MAT estimates. The presence of Laticarinina pauperata in and 7 suggests paleodepths >c ± 00 m for these faunas, consistent with the mean MAT estimate of 210 m for, and within the range ( m) of the five closest modern analogues for 7. The presence of Cibicides kullenbergi in faunal sample 6 suggests a paleodepth >100 ± 00 m, which is consistent with the MAT estimate of 100 m. The other five faunas (1, 15, 5,, 52) belong to associations 6 and 7 with mid-outer-shelf MAT paleodepth estimates between 55 and 210 m. Each contains one or more of the genera Osangularia, Pleurostomella, or Siphonodosaria, whose upper depth limits imply somewhat deeper paleoenvironments >50-00 m. This is within the broad depth range of the five closest modern analogues (Fig. ) of 1, 5, and, but not the remaining two. A mid-upper bathyal paleodepth is stratigraphically acceptable for all these five samples, indeed more plausible at least for the Motutapu faunas (1, 15), which co-occur with bathyalrestricted barnacle fossils (Ricketts et al. 199). Factors influencing the Miocene faunal distribution Most of the faunal associations plot separately on the first two axes of the Correspondence Analysis ordination (Fig. 5), with association separated from and 5 on the third axis. The CCA vectors show a fairly strong left to right trend of increased species diversity (S, H), evenness (J), and planktic foraminiferal percentage. In modern seafloor sediment, there is usually a general trend of increasing relative abundance of planktic foraminifera moving away from land into the more open ocean (e.g., Gibson 199; Hayward et al. 2001b). This trend usually coincides with increasing water depth and therefore is a useful, but not always reliable, indicator of paleobathymetry. Thus, a deepening trend from left to right is indicated, from associations 1 through to. Low species diversity and evenness are characteristic of shallow, marginalmarine, foraminiferal faunas. These diversity measures increase rapidly with increasing inner-shelf depth, and then rise more slowly to a maximum at bathyal depths (Buzas & Gibson 1969; Murray 1991; Hayward et al. 1999). Thus, a left to right deepening trend is supported by the diversity and evenness vectors. The shorter vector for increasing grain size displays a weaker correlation with the faunal pattern, with the coarsest sediment in the upper left (association 2), and finest sediment in the deepest association, suggestive of higher bottom water energy conditions (waves, currents) in the top left (associations 2 and ) and low energy towards the bottom right (associations 6,, and ). The left to right trend in increasing depth is supported by the plot of MAT estimates for paleobathymetry (mean of five nearest modern analogues) for each sample on the ordination (Fig. 5). Table Upper paleodepth limits of some deep-water taxa (from Hayward 1990a; Crundwell et al. 199; Hayward et al. 1999, 2001b, 200, 200b) present in some early Miocene Kawau Subgroup faunas. Taxon Osangularia spp. Pleurostomella spp. Siphonodosaria spp. Eggerella spp. Cibicides kullenbergi Laticarinina pauperata Upper water depth limit (m) 00 ± ± ± ± ± ± 00 Miocene samples 7,15,5,52 6,15,,7,1,5 7,6,7,7

12 Hay ward Waitemata Basin subsidence 759 Fig. 5 Two-dimensional configuration of early Miocene benthic foraminiferal samples ( ) and common species, produced by Detrended Correspondence Analysis. Sample associations (1-) are from the cluster analysis (Fig. 2). Vectors (arrows) produced by Canonical Correspondence Analysis show the correlation of the faunal distribution pattern with species diversity (S, H), evenness (J), planktic foraminiferal percentage (plank), and grain size. Four-letter species abbreviations are given in Appendix 2. Faunal sample plot Am pa Haeh Pulb Amob Axisi outer shelf marginal marine inner shelf mid-outer shelf B bathyal MAT paleodepth estimates (in metres) (mean of 5 nearest modem analogues) Because the Correspondence Analysis ordination is strongly influenced by depth-related trends, it also can be used to infer the paleodepth preferences of plotted species (Fig. 5). Thus, characteristic Miocene bathyal taxa include Bolivinopsis cubensis, Nodosaria longiscata, Oridorsalis umbonatus, Pullenia bulloides, and Siphonodosariapomuligera. Common mid-outer-shelf taxa include Bulimina pupula, Cassidulina laevigata, Cibicides mediocris, Cibicides temperatus, Cibicides vortex, Discorbinella bertheloti, Ehrenbergina marwicki, Haeuslerella hectori, and Sphaeroidina bulloides. Distinctively inner-shelf species include Ammobaculites, Amphistegina aucklandica, Cribrorotalia ornatissima, Elphidium spp., Gaudryina convexa, Haynesina depressula, Pileolina zelandica, Quinqueloculina, and Triloculina trigonula. PALEOGEOGRAPHIC AND SUBSIDENCE HISTORY OF THE KAWAU SUBGROUP In all but 2 of the 1 stratigraphic sections through the Kawau Subgroup, the planktic foraminiferal percentage increases upwards (Fig. 6). This is consistent with the inferred regional subsidence as the Waitemata Basin was being formed, with increasingly more oceanic water spreading across the Auckland region. In a similar way, the association numbers increase upwards through the majority of stratigraphic columns (Fig. 7), consistent with inferred increasing depth. The columns containing exceptions to these trends are Motuihe, Claude, and Streams. In the first two sections, an association fauna occurs in shelly limestone within a finer grained sequence (Fig. 7). These shelly limestone units have lower planktic percentages than the enclosing beds (Fig. 6), and have previously been interpreted as downslope mass flow deposits derived from shallower water (e.g., Ricketts et al. 199), and this explanation is consistent with the foraminiferal record in this study. Although association 6 lies beneath association in the Stream section (Fig. 7), the MAT paleodepth estimates indicate a probable upwards increase in depth. Tracing the unconformable contact between the Kawau Subgroup and underlying basement rocks shows considerable paleorelief, reflecting the rolling landscape prior to the start of regional subsidence. The maximum paleodepth estimates for terrigenous Kawau Subgroup sand or gravel of c. 100 m (sample 2), provides a reasonable approximation for the maximum elevation of the pre-subsidence topography, as once the land was completely submerged the supply of terrigenous gravel and sand would have ceased. As the region slowly subsided, first the valleys and lower areas of land were drowned by the sea, forming bays and inlets partly surrounded by the crests of the former ridges. In the early stages of subsidence, continued erosion of the ridges and coastal cliffs still above sea level, provided sediment that

13 760 New Zealand Journal of Geology and Geophysics, 200, Vol. 7 C. Rodney Kawau Orewa Core Waiheke PLANKTIC FORAMINIFERAL PERCENT 50 km Fig. 6 Planktic percentage of foraminiferal faunas plotted on stratigraphic columns through the early Miocene Kawau Subgroup. Kawau Orewa 50 km Mudstone Limestone Shelly sandy mudstone Sandstone too, Pebbly conglomerate Boulder conglomerate Fig. 7 Miocene foraminiferal associations (from Fig. 2) plotted on stratigraphic columns through the early Miocene Kawau Subgroup.

14 Hay ward Waitemata Basin subsidence 761 Kawau Orewa Waiheke Adjusted MAT paleodepths C. Rodney Fig. Modern Analogue Technique (MAT) paleobathymetry estimates (mean of five nearest modern analogues), which document the subsidence of the Waitemata Basin, plotted on the Kawau Subgroup stratigraphic columns. The depth estimates of five faunas have been adjusted from outer shelf to upper bathyal on the basis of the presence of several key deep-sea taxa (Table, Appendix 1). Additional paleoenvironmental interpretations are included. began filling the bays and other subtidal areas. The thickest sequences accumulated in the former valleys (e.g., Waiheke), and the foraminiferal faunas record the transgression (Fig. ). Accumulating at this stage around the fringes of sheltered bays were intertidal to shallow subtidal beach gravel (samples 20, 21) and shelly mud (6). In the quiet, dysoxic centre of these sheltered bays, mud containing association and 6 faunas accumulated (Waiheke, 22-29;, 0, 1; Waiwiri, 7). Boulder, cobble, and pebble gravel, containing lenses of coarse sand, accumulated along more exposed coasts during these early phases of subsidence, with high energy beach or shallow subtidal faunas (association 2) preserved at (2) and Cape Colville (1). Association accumulated in the higher energy, current-swept, inner-shelf sand and gravel along the exposed coasts and is preserved at Kawau (,5), Motuketekete (9), Hays Creek (2), and Hunua (). Finer grained, oxic, sandy mud accumulated in slightly deeper and less current-swept environments offshore and was home to association 5 and shallow association 7 faunas, such as those in the lower parts of Orewa and Awhitu drillholes (12,1,). As subsidence continued, more and more of the original land was submerged. Eventually only the highest peaks remained above sea level as islands, with greatly reduced erosion and supply of sediment to the surrounding sea. At this stage the region was clearly separated from any other land areas that might supply sediment. Banks of shell and shell hash, swept clean of mud and broken-up by bottom currents, slowly accumulated in the shallows. With burial and time these shell deposits were transformed into limestone. In some places, shell and/or gravel bank material that accumulated in the shallows around the fringes of the upstanding islands, slid downslope into deeper water (submerged former valleys) and is interbedded with in situ sand and mud (Fig. ), containing association foraminiferal faunas indicative of lower oxygen conditions at mid-outer-shelf depths (samples 17,, 7, 2, ). The in situ and displaced limestone and conglomerate units contain association and foraminiferal faunas (Fig. 7), indicative of current-swept, oxic sediment with estimates of inner, mid, and outer shelf paleodepths. The innershelf faunas presumably inhabited the shell and gravel banks where they initially accumulated and are either in situ or have been displaced downslope in the slumped sediment (samples 16, 1, 5). Limestone or conglomerate faunas with mid or outer shelf ( m) paleodepth estimates may have: (1) been incorporated into the sediment during slump displacement; (2) colonised the sediment after its displacement (e.g., Motuihe, 16; Claude Stream, 6; Bloomfield Stream, 0); or () colonised the sediment after it had tectonically subsided to these greater depths, but was still forming the seafloor (e.g., Motuketekete,,10,11 ;Opuatia Stream, 5; Kaawa, 9,50).

15 762 New Zealand Journal of Geology and Geophysics, 200, Vol. 7 Finally, continued subsidence resulted in the complete submergence of the whole Auckland region to below wave base. There followed a period of sediment starvation. In some places (e.g.,, Kawau, Motutapu), this period is represented by c m of massive to weakly laminated mudstone, and elsewhere by a hiatus (Fig. ). Foraminiferal faunas in this mudstone (samples, 6, 7, 1, 15) cluster in associations 6,7, and (Fig. 7) and have adjusted paleodepth estimates of 10 to >1700 m. In the south (Waiwiri, Kaawa), the starvation interval is represented by a m thick, nodular phosphatic bed (sample, association ) with adjusted paleodepth estimate of >500 m. Throughout the central and northern parts of the region, substantial terrigenous sedimentation did not recommence until the basin had subsided to sufficient depths to create a submarine slope down which turbidity currents could flow from their source area km to the northwest (Ballance 197; Hayward & Smale 1992; Hayward 199). In the north, paleodepth estimates for foraminiferal association faunas in the starvation interval mudstone (samples, 6, 7) imply that the basin had subsided to at least lower bathyal and probably greater depths (>1700 m) before the arrival of the first turbidite sand. A basinal depth of 2000 m would provide an average seafloor slope of 2 over 60 km, clearly sufficient for maintenance of a turbidity current flow. In the south, association 7 faunas that accumulated in the starvation interval (samples 5,, 52) have adjusted paleodepth estimates of > m. Here the source of the overlying Waikawau Formation sand has not been determined, but the indicated depth would have been insufficient for the sand to have flowed in from the northwest; a more proximal southern provenance is probable. SUMMARY Cluster analysis has been used to identify eight associations of benthic foraminiferal faunas from the early Miocene Kawau Subgroup (Fig. 2), and Canonical Correspondence Analysis has produced an approximation of their paleoenvironmental distribution and relationship to proxies for paleobathymetry and bottom-water energy (Fig. 5). Comparison of the faunal composition of the associations with Recent faunas from around New Zealand provides a means for inferring the paleoenvironments in which they accumulated. Shallow-water faunal associations that lived in sheltered environments inside bays or inlets (associations 1,, 5) are clearly identified as separate from those that accumulated off the more exposed coasts of the submerging land (associations 2,). These support inferences from modern outcrop patterns that the subsiding land had considerable paleotopography, sufficient to create sheltered bays, inlets, and islands as it was progressively flooded. The depth of submergence at which terrigeneous gravel and sand supply ceased provides a proxy estimate of c. 100 m for the maximum elevation of ridges and hills prior to the initiation of basin subsidence. This study shows good agreement between paleobathymetry estimates made by conventional subjective methods, and the more objective, Modern Analogue Technique. This is not surprising as both are based on current knowledge of the depth distribution of modern foraminiferal faunas around New Zealand. In the few instances where results differ substantially, they are readily explained by high dissimilarity distances through lack of good modern analogue faunas. Estimates by both methods are consistent with the general trend of increasing paleobathymetry upwards through all stratigraphic sections, as inferred previously from the fining-upwards sequences, and macrofossil paleoecology, and independently in this study from increasing planktic foraminiferal percentage. The range of depths of the five closest modern analogue faunas, suggests that MAT paleobathymetry estimates become progressively less precise with increasing water depth, just as they do with the subjective methods. In this study, the precision of some of the broad-ranging outer shelf and bathyal estimates has been improved using the known upper water depth limits of a number of key deeper water genera. These adjusted, deeper water estimates suggest that the southern part of the Waitemata Basin was sediment starved as the basin subsided from c. 150 m down to > m. In contrast, the northern and central parts of the basin (-Hunua) appear to have been sediment starved for longer as the basin subsided to >1700 m before turbidite sediment input began. This implies a minimum average slope of 2 on the northern flanks of the Waitemata Basin along the path of the turbidity currents. CONCLUSION This study shows that MAT, based on generic categories of benthic foraminifera, can provide more objective estimates of paleobathymetry that are consistent, but at the present time no more precise, than those obtained by conventional intuitive methods. MAT estimates need to be checked to ensure consistency with other evidence and not always accepted at face value. The addition of more faunal census data, especially from deeper water and from tropical shallow water, to the modern analogue dataset should result in closer matches with fossil Neogene faunas, and hopefully more accurate and precise estimates. The upper depth limits of rarer bathyal taxa can be employed to improve the precision of deeper water estimates. At present, the modern database only provides for MAT estimates of water depth. MAT should be used in conjunction with subjective interpretations of the faunal composition, as these provide additional paleoenvironmental information on factors such as food supply, bottom oxygen conditions, strength of bottom currents or waves, and possible post-mortem mixing or winnowing effects. ACKNOWLEDGMENTS The fieldwork, sample processing, and foraminiferal identifications which are the basis of this study were undertaken in the 190s, while I was employed at the New Zealand Geological Survey (now the Institute of Geological & Nuclear Sciences). I thank Fred Brook for assistance in the field and the late Adrian Trask for assistance in the laboratory. The scanning electron microscope photographs are the work of Barry Burt, Sue Bishop, and Hugh Grenfell. The Excel macro programming used to generate MAT results was kindly provided by George Scott. The manuscript has benefited from the critical reading of Hugh Grenfell, George Scott, Hugh Morgans, Ewan Fordyce, and George Chaproniere. REFERENCES Ballance, P. F. 197: An inter-arc flysch basin in northern New Zealand: Waitemata Group (upper Oligocene to lower Miocene). Journal of Geology 2: 9-71.

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17 76 New Zealand Journal of Geology and Geophysics, 200, Vol. 7 Hayward, B. W.; Brook, F. J.; Isaac, M. J. 199: Cretaceous to middle Tertiary stratigraphy, paleogeography and tectonic history of Northland, New Zealand. Royal Society of New Zealand Bulletin 26: 7-6. Hayward, B. W.; Hollis, C. J.; Grenfell, H. R. 199: Foraminiferal associations in Port Pegasus, Stewart Island, New Zealand. New Zealand Journal of Marine and Freshwater Research 2: Hayward, B. W.; Grenfell, H. R.; Cairns, G. A.; Smith, A. 1996: Environmental controls on benthic foraminiferal and thecamoebian associations in a New Zealand tidal inlet. Journal of Foraminiferal Research 26: Hayward, B. W.; Grenfell, H. R.; Reid, C. 1997: Foraminiferal associations in Wanganui Bight and Queen Charlotte Sound, New Zealand. New Zealand Journal of Marine and Freshwater Research 1: Hayward, B. W.; Grenfell, H. R.; Reid, C. M.; Hayward, K. A. 1999: Recent New Zealand shallow-water benthic foraminifera: taxonomy, ecologic distribution, biogeography, and use in paleoenvironmental assessment. Institute of Geological & Nuclear Sciences Monograph p. Hayward, B. W.; Black, P. M.; Smith, I. E. M.; Ballance, P. F.; Itaya, T.; Doi, M.; Takagi, M.; Bergman, S.; Adams, G. J.; Herzer, R. H.; Robertson, D. J. 2001a: K-Ar ages of early Miocene arc-type volcanoes in northern New Zealand. New Zealand Journal of Geology and Geophysics : Hayward, B. W.; Carter, R.; Grenfell, H. R.; Hayward, J. J. 2001b: Depth distribution of Recent deep-sea benthic foraminifera east of New Zealand, and their potential for improving paleobathymetric assessments of Neogene microfaunas. New Zealand Journal of Geology and Geophysics : Hayward, B. W.; Neil, H.; Carter, R.; Grenfell, H. R.; Hayward, J. J. 2002: Factors influencing the distribution patterns of Recent deep-sea benthic foraminifera, east of New Zealand, southwest Pacific Ocean. 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18 Hay ward Waitemata Basin subsidence 765 Scott, G. H. 1971: Miocene foraminiferal environments: Tarakohe Mudstone, western Nelson. New Zealand Journal of Geology and Geophysics 1: Ter Braak, C. J. F. 195: Canoco a fortran programme for canonical correspondence analysis and detrended correspondence analysis: IWIS-TNO. The Netherlands, Wageningen. Todd, R. 1976: Some observations about Amphistegina (Foraminifera). In: Takayanagi, Y.; Saito, T. ed. Progress in micropaleontology: Selected papers in honour of Professor Kiyoshi Asano. New York, Micropaleontology Press. Pp van der Zwaan, G. J.; Duijnstee, I. A. P.; den Dulk, M.; Ernst, S. R.; Jannink, N. T.; Kowenhoven, T. J. 1999: Benthic foraminifers: proxies or problems? A review of paleoecological concepts. Earth-Science Reviews 6: van Morkhoven, F. P. C. M.; Berggren, W. A.; Edwards, A. S. 196: Cenozoic cosmopolitan deep-water benthic foraminifera. Bulletin des centres de recherches exploration-production Elf-Aquitaine Memoir p. Vella, P. 1962: Determining depths of New Zealand Tertiary Seas. Tuatara 10: Verhallen, P. J. J. M. 1991: Late Pliocene to early Pleistocene Mediterranean mud-dwelling foraminifera; influence of a changing environment on community structure and evolution. Utrecht Micropaleontological Bulletin p. Weaver, P. P. E.; Carter, L.; Neil, H. L. 199: Response of surface water masses and circulation to late Quaternary climate change east of New Zealand. Paleoceanography 1: 70-. (Appendicies 1 and 2 follow)

19 766 New Zealand Journal of Geology and Geophysics, 200, Vol. 7 Appendix 1 Miocene fossil sample data, foraminiferal association (Ass.), planktic foraminiferal percentage, and diversity (H, J, S) measures. FRF no. = New Zealand Fossil Record File catalogue number. MAT=mean water depth of the five most similar modern analogue samples. APD = adjusted paleobathymetry estimate based on upper depth limits of rarer bathyal-restricted taxa. Ass. Sample FRF no. Locality Formation %Planktics H / S MAT (m) APD (m) R11/f2 R11/f R1/f57 S09/f R09/f5 R09/f79 R09/f7 R09/f72 R11/f5 R11/f2 S12/f20 R12/f R11/f1 R11/f11 R11/f12 R11/f15 R10/f10 R10/f12 R10/f S12/f1 R10/f1,27-9 m R10/f1,25-7 m R10/f2 R11/F27 S12/f16 R1/f59 R09/f75 R09/f R09/f7 R11/f6 R11/f6 R11/f5 R11/f7 R11/f9 S11/f20 R1/f66 R1/f1 R10/f29 R11/f61 R11/f7 R11/f75 R11/f1 R11/f R12/f7627 R1/f5 R1/f651 R1/f65 R12/f62,70-1 m R1/f21 R09/f R09/f76 R09/f6 Waiheke, Te Rere Waiheke, Fossil Bay Waiwiri Bch. Cape Colville PakiriR. Kawau I. Kawau I. Motuketekete I. Motuihe I. Claude Stm Cossey Stm Hays Stm Waiheke, Fossil Bay Waiheke, Fossil Bay Waiheke, Fossil Bay Waiheke, Fossil Bay Waiheke, W Bay Waiheke, W Bay Waiheke, W Bay Stm Orewa drillhole Orewa drillhole Motutapu I. Waiheke, Oneroa Stm Waiwiri Beach Motuketekete I. Motuketekete I. Motuketekete I. Motuihe I. Motuihe I. Bloomfields Stm Bloomfields Stm Claude Stm Taitaia Stm Kaawa Gibson Beach Motutapu I. Motuihe I. S Bloomfields Stm S Bloomfields Stm Claude Stm Claude Stm Hays Stm Opuatia Stm Waiwiri Beach Kaawa Awhitu drillhole Gibson Beach Kawau I. Kawau I. Warkworth Subgp Warkworth Subgp Warkworth Subgp Warkworth Subgp Warkworth Subgp Warkworth Subgp Waikawau Cast Bed Warkworth Subgp Warkworth Subgp Warkworth Subgp >500 >500 >500 >500 >00 >1700 >100 >1700

20 Hay ward Waitemata Basin subsidence 767 Appendix 2 Taxonomic reference list for early Miocene benthic foraminiferal species. All taxa cited in the paper are included, together with citations of figured specimens that reflect the taxonomic concept followed here. Generic classification largely follows Loeblich & Tappan (197). The original descriptions of these species can be found in the Ellis & Messina world catalogue of foraminiferal species on (References to specimens in Fig. 2 in this paper are cited in bold). Amob Ammobaculites sp. Ampa Amphistegina aucklandica Karrer. Hayward & Buzas, pl., fig. 9. Fig. 2E Bofi Bolivina finlayi Hornibrook. Hayward & Buzas 1979, pl. 6, fig. 67. Fig. 2P Boma Bolivina mantaensis Cushman. Hayward & Buzas 1979, pl. 6, fig. 69, 70. Fig. 2Q Bore Bolivina reticulata Hantken. Hayward & Buzas 1979, pl. 6, fig. 72. Fig. 2V Bolc Bolivinopsis cubensis (Cushman & Bermudez). Hornibrook et al. 199, fig. 15:5. Bulp Bulimina pupula Stache. Hayward & Buzas 1979, pl. 7, fig.. Casl Cassidulina laevigata d'orbigny. Hayward & Buzas 1979, pl. 7, fig. 90. Ckul Cibicides kullenbergi (Parker). Hayward & Buzas 1979, pl. 10, fig. 12. Cmed Cibicides mediocris Finlay. Hayward & Buzas 1979, pl. 10, fig Fig. 2R,S Cnot Cibicides notocenicus Dorreen. Hayward & Buzas 1979, pl. 10, fig Ctem Cibicides temperatus (Vella). Hayward & Buzas 1979, pl. 11, fig Fig. 2T,U Cvor Cibicides vortex Dorreen. Hayward & Buzas 1979, pl. 11, fig Crio Cribrorotalia ornatissimum (Karrer). Hayward & Brook 199, fig., Fig. 2F,G Disb Discorbinella bertheloti (d'orbigny). Hayward & Buzas 1979, pl., fig Egg Eggerella sp. Ehrm Ehrenbergina marwicki Finlay. Hayward & Buzas 1979, pl. 12, fig Elpc Elphidium crispum (Linnaeus). Hayward et al. 1999, pl. 17, fig Fig. 2 A,B Elpk Elphidium kanoum Hayward. Hayward & Brook 199, fig., 16. Fig. 2C Gauc Gaudryina convexa (Karrer). Hayward et al. 1999, pl. 2, fig Fig. 2H Gcsu Globocassidulina subglobosa (Brady). Hayward & Buzas 1979, pl. 17, fig Haeh Haeuslerella hectori Finlay. Hornibrook et al. 199, fig. :. Fig. 2O Hayd Haynesina depressula (Walker & Jacob). Hayward et al. 1999, pl. 15, fig Fig. 2D Latp Laticarinina pauperata (Parker & Jones). Hornibrook 196, fig. 9. Mels Melonis simplex (Karrer). Hayward & Buzas 1979, pl. 20, fig. 25, 257. Fig. 2N Nodl Nodosaria longiscata d'orbigny. Hayward & Buzas 1979, pl. 21, fig Fig. 2X Nonz Nonionella novozealandica Cushman. Hayward & Buzas 1979, pl. 21, fig Fig. 2I,J Notp Notorotalia powelli Finlay. Hayward & Brook 199, fig., Fig. 2K,L Orid Oridorsalis umbonatus (Reuss). Hayward & Buzas 1979, pl. 2, fig. 295, 296. Fig. 2W Osac Osangularia culter (Parker & Jones). Hayward & Buzas 1979, pl. 22, fig Pilz Pileolina zealandica Vella. Hayward et al. 1999, pl. 12, fig Plet Pleurostomella tenuis Hantken. Hayward & Buzas 1979, pl. 25, fig Pulb Pullenia bulloides (d'orbigny). Hayward & Buzas 1979, pl. 2, fig. 0, 0. Qsem Quinqueloculina seminula (Linnaeus). Hayward & Buzas 1979, pl., fig.. Fig. 2M Snop Siphonodosaria pomuligera (Stache). Hayward & Buzas 1979, pl. 2, fig. 1, 2. Sphb Sphaeroidina bulloides d'orbigny. Hayward & Buzas 1979, pl. 27, fig. 55. Trit Triloculina trigonula (Lamarck). Hayward & Buzas 1979, pl., fig. 9.