Hayward & Smale - Waitemata Basin sediments

New Zealand Journal of Geology and Geophysics, 1992, Vol. 35:223-242 0028-8306/92/3502-0223 $2.50/0 © The Royal Society of New Zealand 1992

223

Heavy minerals and the provenance history of Waitemata Basin sediments (early Miocene, Northland, New Zealand)

BRUCE W. HAYWARD* DAVID SMALE DSIR Geology and Geophysics P.O. Box 30 368 Lower Hutt, New Zealand *Present address: Auckland Institute and Museum, Private Bag, Auckland 1, New Zealand.

sediment, firstly as sporadic submarine debris flows (Pamell Grit), and later as a broad volcaniclastic apron around its lower slopes. Keywords Northland; Auckland; Waitemata Group; Waitakere Group; heavy minerals; provenance; Miocene; factor analysis INTRODUCTION

Abstract Census data from 100 heavy mineral samples from the early Miocene Waitemata Basin (81 samples) and its potential source rocks (19 samples) from Auckland and southern Northland, New Zealand, were analysed by cluster analysis, multidimensional scaling, and factor analysis. These analyses give rise to seven groups, each characterised by a distinctive mineralogy (factor): (1) dominated by clinopyroxene plus magnetite, from a Miocene andesitic provenance; (2) dominated by ilmenite plus zircon and apatite, from a Mesozoic greywacke (Waipapa) and Paleogene sedimentary (Motatau, Mangakahia) provenance; (3) dominated by hornblende, from a Miocene volcanic or Cretaceous igneous (Tangihua) provenance; (4) co-dominated by hornblende, magnetite and ilmenite, from a Tangihua provenance; (5) dominated by semi-opaque debris plus ilmenite, from a Waipapa provenance; (6) co-dominated by biotite and ilmenite, from a mixed Miocene rhyolitic, Tangihua and Motatau provenance; and (7) dominated by orthopyroxene plus clinopyroxene, from a two-pyroxene andesite provenance. Using these provenance interpretations for the heavy mineral groups, in conjunction with their stratigraphic and geographic distributions, we deduced a model for the paleogeographic and provenance history of the Waitemata Basin, and refined traditional models for the basin. Basal shallow marine sediments were derived exclusively from local Waipapa basement. Following rapid basin subsidence, two discrete sediment sources contributed to the older parts of the mid-bathyal, turbidite basin. These sources were a Cretaceous-Paleogene igneous and sedimentary source (Northland Allochthon) west of central Kaipara (for East Coast Bays and Paremoremo fades), and a contemporaneous volcanic source in north Kaipara or located beneath inferred basement nappes of the Whangarei area (for lower Pakiri facies). Younger parts of the central basin (Blockhouse Bay, Cornwallis, Timber Bay, and upper Pakiri facies) had a single Kaipara source area with a mixture of Northland Allochthon igneous and sedimentary rocks and contemporaneous andesitic volcanism. Another large active andesitic volcano, located west of Auckland, provided increasing amounts of

The intra-arc Waitemata Basin Waitemata Group sediments of the early Miocene (late Waitakian - Altonian Stages) intra-arc Waitemata Basin dominate the surface geology of southern Northland and Auckland (Fig. 1). These rocks mostly lack marker horizons, have a complex structure (e.g., Sporli 1989), and accumulated and were deformed during a period when there were few biostratigraphic events (late Waitakian and Otaian). As a result, the internal stratigraphy and correlation of the basin sediments (Fig. 2) is still incompletely resolved. There is a general regional tilt and younging towards the west (Ballance 1974; Hayward 1979). Basement rocks of the Waitemata Basin are Triassic-Jurassic indurated sediments (metagrey wacke and argillite) of the Waipapa Group. These crop out in the east and directly underlie basinal sediments in the eastern half of southern Northland. Further west, offshore seismic profiles show that the Triassic-Jurassic basement (Murihiku Group) is separated from the early Miocene sequence by a 0.5-2 km thick transgressive sequence of Cretaceous-Oligocene sedimentary rocks (R. H. Herzer pers. comm.). Published heavy mineral results relating to the provenance of Waitemata Basin sediments have all formed parts of studies of the sedimentology or structure of small areas of the basin. These have shown that Waitemata Basin turbiditic sediments around the shores of Waitemata Harbour contain common zircon, ilmenite, biotite, apatite, epidote, pyroxene, and hornblende, with rare titanite, garnet, and clinozoisite, inferred to be derived from metagreywacke and argillite with some input from contemporaneous volcanism in the west (Chappell 1963; Ballance 1964; Jones 1967,1969). Several other studies have shown that the sediments around the Kaipara Harbour in the northwest are dominantly volcanic and plutonic derived, with common hornblende, clinopyroxene, and magnetite, with sporadic orthopyroxene high in the sequence (Carter 1971; Jones 1972). Mayer (1969) found that the common primary heavy minerals in the argillite and metagreywacke basement were variable, but generally biotite, hornblende, ilmenite, and magnetite were dominant, with lesser clinopyroxene, zircon, titanite, chlorite, epidote, and clinozoisite. Early results from the present study were tabulated and discussed by Smale (1988a).

G910O9 Received 21 March 1991; accepted 10 December 1991

The lithostratigraphy of the Waitemata Basin has been largely described elsewhere (see references associated with

New Zealand Journal of Geology and Geophysics, 1992, Vol. 35

224 Whangi

',*.***+

Fig. 1 Map of southern Northland and Auckland showing main paleogeographic elements of the early Miocene Waitemata Basin and its setting (modified after Ballance 1974,1976; Brook 1983; Schofield 1989).

Heads/

Kaipara

(*•%*•% volcano

50 km

A, basal shallow marine facies (Kawau Subgroup); B, central basin turbidite fades (Waitemata Group); Bi, eastern volcanic-poor turbidite fades (East Coast Bays facies); Bii, western volcanic-poor turbidite facies (Paremoremo facies); Biii, mixed turbidite facies (Blockhouse Bay facies); Biv, volcanic-rich proximal turbidite facies (Pakiri facies); Bv, thin-bedded slope facies (Timber Bay facies); Bvi, mixed proximal turbidite facies (Cornwallis facies); C, western volcanic facies (Waitakere Group); Ci, Manukau volcanic centre (Manukau Subgroup); Cii, Hukatere volcanic centres (Hukatere Subgroup); D, northwestern landmass and nappes (Northland Allochthon); E, northern basement "thrust" blocks and associated early Miocene sedimentary and volcanic facies (Coromandel Group); Ei, sedimentary facies (Bream Subgroup); Eii, Taurikura volcanic centre (Taurikura Subgroup); Eiii, Brynderwyn volcanic centre (Parahaki Subgroup); F, eastern basement high and volcanic facies (Coromandel Group); Fi, northern Coromandel volcanic centre (Kuaotunu Subgroup)

STAG*

Wha

"9arei

Wai

P"

Kaipara area

northern Coromandel COROMANDEL GROUP

19 -

GROUP Biii Blockhouse Bay Facies

22 -

25 -

WAIPAPA GROUP (Basement)

Ma

Fig. 2 LJthostratigraphic summary of the early Miocene Waitemata Basin sedimentary (Waitemata Group) and volcanic rocks (Waitakere Group). Facies symbols (A, Bi, Bii, etc.) as in Fig. 1.

Hayward & Smale—Waitemata Basin heavy minerals Fig. 1), but is summarised in Fig. 1,2, and 8. In the centre of the basin, a thin (up to 50 m), transgressive, shallow marine sequence (Kawau Group) buried an irregular shoreline of Waipapa basement (Hayward & Brook 1984). Subsidence continued rapidly to 1000 m or more (Ricketts et al. 1989), but with little sediment accumulation (at most a few metres of mudstone). An unknown thickness (probably 1-2 km) of interbedded turbidites and pelagic siltstones (Warkworth Subgroup) accumulated in bathyal submarine fan and basin floor settings during the Otaian Stage (Ballance 1974; Hayward 1979). In the late Otaian and Altonian, the Manukau and Kaipara volcanic centres (Fig. 1) grew into large volcanoes supplying increasing quantities of volcaniclastic sediment eastward into the basin (Ballance 1974; Hayward 1979). In the north and northwest, in the late Waitakian and early Otaian, thrust or gravity glide nappes of deep-water Cretaceous and Paleogene igneous material (Tangihua Complex) and softer sedimentary rocks (Mangakahia and Motatau Complexes) forming the Northland Allochthon were emplaced into the proto-Waitemata Basin (Hayward et al. 1989). During a late phase of this activity, a stack of wedges of Waipapa basement were thrust in from the north or northeast (Hayward 1989). Several subaerial andesitic stratovolcanoes (Taurikura Subgroup) of Otaian and Altonian age (Hayward et al. 1978; Middleton 1983) and smaller dacitic domes (Parahaki Subgroup) of probable Altonian age (Stipp & Thompson 1971) erupted along faults within the area of thrust faults in the early Miocene. Some may have predated thrusting, but others (Parahaki Subgroup) definitely postdate it. Associated with the thrust wedges are early Miocene sediments of the Bream Subgroup (s.l.), but their relations are not clearly understood; they occur below, within, and above the allochthon. To the east, several subaerial andesitic stratovolcanoes (in part the northern Coromandel volcanic centre—Kuaotunu Subgroup of Altonian and younger age—Skinner 1986) were active on what was probably low-lying Waipapa basement (e.g., Ballance 1974; Hayward 1979). METHODS Sample collection and processing A total of 85 early Miocene sedimentary rock samples and 47 potential source rock samples were processed for heavy mineral study. Samples were disaggregated as gently as possible, but by crushing if necessary. The heavy minerals were separated from the 2-4 phi fraction by floating off the light minerals in a heavy liquid of specific gravity 2.9. The heavy fractions were examined microscopically in refractive index oils (generally 1.63), and percentages of the various heavy minerals were determined by counting all grains in different fields of view until 300 had been counted. Individual mineral grains of doubtful microscopic identification were identified using Xray diffraction powder photography or energy-dispersive Xray analysis on a scanning electron microscope (SEMEDAX). Sample selection and standardisation We have found that heavy mineral suites containing high proportions of authigenic pyrite, barite, or siderite tend to

225 contain fewer other heavy mineral phases than samples without the authigenic minerals, and contribute nothing towards provenance interpretation. Possibly the environment that promotes the growth of the authigenic minerals, or weathering of the pyrite and resulting acidic solutions, tends to dissolve some detrital heavy minerals. Where the authigenic minerals are not abundant, we have assumed that modification of the detrital suites has been minor, and the effect of the authigenic minerals has been simple dilution. Heavy mineral suites with more than 50% (an arbitrary figure) of pyrite, barite, or siderite (4 early Miocene samples and 17 source rock samples) were deleted from the study. Percentage counts for pyrite, barite, and siderite were deleted from all samples in the data set prior to computer analysis. A further 11 source rock samples were not included in the final data set because they merely duplicated the results obtained from the other samples. A final data set consisting of 100 samples (81 early Miocene and 19 source rock—Appendix 1, Fig. 3) was used in the computer analysis and resulting provenance interpretations. Computer methods The data consist of percentage counts of 19 heavy mineral species in 100 samples, and preclude easy interpretation of the heavy mineral content on a sample-by-sample or mineral-bymineral basis. Instead, to assist description and interpretation by reducing the bulk of the data, the samples were grouped statistically using several computer classification and ordination techniques based on the similarity of their heavy mineral compositions, the resemblance measure being their Euclidean distance (Sneath & Sokal 1973, p. 119). Initially the data matrix was standardised by converting counts to proportions of sample totals. Cluster analysis and multidimensional scaling programs in the NTSYS-pc statistical package (Rohlf 1988) were then applied to the data. Cluster analysis The Euclidean distance was calculated between all possible sample pairs (including both Miocene sediments and potential source rocks) resulting in a distance matrix of size 100 X 100. Sample groups were generated using unweighted pair-group cluster analysis using arithmetic averages of the Euclidean distance matrix. The results are displayed on a dendrogram, so that samples most dissimilar are on different "branches", and those most similar are separated by the shortest "twigs". Discussions of this commonly used technique are given by Sneath & Sokal (1973) and Pielou (1984). Multidimensional scaling Nonmetric multidimensional scaling (MDS) is an ordination technique which presents a configuration of the n samples in a fc-dimensional space (2 or 3 in the present instance). MDS differs from other ordination techniques, like principal component analysis, in that interpoint distances in the it-space are related monotonically to the original Euclidean distances, instead of requiring die projection in fc-space to explain a maximum percentage of the variation found. The results are displayed on 2- or 3-dimensional plots, whose axes represent abstract statistical concepts. The technique is discussed by Kruskal (1964), and Hayward & Buzas (1979).


226

VJ

;|i.i- I

:i|:*:1:| l :\i:i:;i.-i :i;:«:i n :

e

o

E TJ 0> CO

o

"o

-o is .2 •a

.a

i

n S * .si

Hayward & Smale—Waitemata Basin heavy minerals Northland Allochthon (Motatau) sedimentary rocks, and the majority of early Miocene samples overlie these allochthonous rocks or are associated with sediments having some obvious allochthonous provenance. Thus the heavy minerals in these early Miocene samples are probably of original Waipapa Or kindred basement provenance, most having been recycled through the Paleogene Northland Allochthon sedimentary rocks. The recycling probably served to enhance the more resistant mineral content (e.g., ilmenite, zircon) at the expense of semi-opaque debris and any Waipapa pyroxene or hornblende. The greater amount of garnet in some samples around Waiotira (1, 2, 5) is more likely to result from variations in parent Waipapa populations than to derivation from Miocene garnet andesites (Taurikura Subgroup) at Whangarei Heads, because the andesites would also have provided hornblende and pyroxene. Subgroup 2b includes four Cretaceous allochthonous source samples, and is less impoverished than 2a, indicating less recycling or less intrastratal solution and possibly a mixed provenance for some samples. Eleven of the 15 Paleogene source and early Miocene samples closely overlie an irregular eroding Waipapa surface and were probably directly derived from it. Variations in the abundance of hornblende, pyroxene, magnetite, and chlorite possibly reflect local variations in the Waipapa source, although some minor volcanic input (perhaps airfall tuff) to the early Miocene samples cannot be ruled out. The three early Miocene samples (42, 46, 50) from the volcanic-poor turbidite facies well above Waipapa basement have a high hornblende, epidote, and magnetite content indicating a possible Cretaceous Tangihua or Mangakahia provenance on its own or mixed with a Waipapa or Paleogene allochthonous provenance. Group 3 Sample distribution and provenance Sample 6 occurs as a block within the Northland Allochthon and sample 16 is from the Hukatere Subgroup in sediments of mixed volcanic and Northland Allochthon provenance. The heavy mineral suite could have been derived from a hornblende-rich ash shower, which would be highly unusual for the Hukatere Subgroup, or it could be derived from a hornblende microdiorite Tangihua source, which is known to have existed in the Kaipara area (Ballance & McCarthy 1975). Group 4 Sample distribution Group 4 includes a single potential source rock—a Cretaceous sandstone (Mangakahia Complex). The 13 early Miocene samples all come from the southern half of the Waitemata Basin in the volcanic-poor turbidite East Coast Bays and Paremoremo facies, and the mixed turbidite Blockhouse Bay and Cornwallis facies. Provenance Although thin-section study of the volcanic-poor East Coast Bays facies indicates primarily a Waipapa source from the northwest (Ballance 1964; Jones 1969), the consistently high magnetite and hornblende, in addition to ilmenite, in this group suggest otherwise. This suite is quite different from that in samples that closely overlie Waipapa (groups 2b and 5). Most transport-direction indicators point to a northwestern (Kaipara) source (e.g., Ballance 1974). Conglomerate (Albany Conglomerate), derived from the same area at the time most

233 group 4 early Miocene samples were being deposited, is dominantly composed of weakly metamorphosed basalt and hornblende microdiorite from the allochthonous Cretaceous Tangihua Complex, with small variable amounts of allochthonous sedimentary clasts and greywacke-argillite (?Waipapa or Mangakahia Complex). Indeed, sample 53 comes from the matrix of these Tangihua-derived conglomerates. A Tangihua provenance for the majority of the group 4 suite (especially the magnetite, hornblende, ilmenite, and epidote) is considered most probable. Some input from secondary sources such as allochthonous sedimentary rocks, and maybe Waipapa Group, is possible. There is some evidence (higher clinopyroxene) for input from contemporary volcanic sources in only two samples. One (58) comes from a volcaniclastic mass flow on Motutapu Island, and the other (66) from a mass flow in Auckland City (Orakei Greensand). Both mass flows have incorporated large amounts of contemporaneous seafloor sediments, as indicated by their presence in group 4 and not the volcanic-derived group 1. Group 5 Sample distribution and provenance All three early Miocene samples closely overlie an eroding Waipapa surface which was the sole source of the heavy mineral suite. Miocene weathering or intrastratal solution are not likely to have affected the suite; had they done so, the semi-opaque debris would have been dissolved and the zircon concentrated. Group 6 Sample distribution and provenance Sample 87 is a Cretaceous sandstone from within the Northland Allochthon and appears to have had a granitic or rhyolitic provenance. Sample 55 (early Miocene), from a volcaniclastic massflow deposit within the Blockhouse Bay facies, has a heavy mineral assemblage suggesting a mixed provenance. Most of the biotite was probably derived from contemporaneous biotite rhyolite, whereas the other heavy minerals were probably derived from a combination of Cretaceous sedimentary (Mangakahia) and weakly metamorphosed igneous (Tangihua) sources. An identical mix of provenances has been reported from a conglomerate and sandstone sequence in the Paremoremo facies at Riverhead 20 km to the north, where a western south Kaipara source is suggested by paleocurrent indicators (Davidson 1990). Group 7 Sample distribution and provenance The abundant heavy mineral assemblage (10% of sample) in this volcaniclastic sandstone from the Comwallis facies, south of Helensville, is derived from a contemporaneous, twopyroxene andesite source in the Kaipara area. FACIES SOURCE AREAS AND STRATIGRAPHIC IMPLICATIONS The structural complexities and lack of marker horizons have resulted in several different models for the stratigraphic relationships between the different turbidite facies within the central Waitemata Basin (e.g., Ballance 1974; Hayward 1982;

234


Schofield 1989). The heavy mineral compositions of the different fades (Table 4) do not resolve the problem but do provide some additional constraints. The volcanic-poor East Coast Bays and Paremoremo fades (Bi and Bii; Fig. 1, Table 4) appear to have an identical provenance of Northland Allochthon igneous (Tangihua) and sedimentary (Motatau and Mangakahia) rocks that was probably located in the west central Kaipara area and no longer crops out. The large magnetic and gravity anomaly beneath North Kaipara Head (Woodward & Riley 1972; Hunt & Syms 1977) at the eastern end of the Kaipara volcano (Fig. 1) could represent remnants of just such an allochthonous igneous (Tangihua) source. The proximal volcanic-rich Pakiri facies (Biv) has a Miocene volcanic provenance. If it was contemporaneous with dther of the volcanic-poor facies, as seems likely, then the source must have been located north of central Kaipara. The presence of the basically non volcanic Bream sedimentary facies (Ei) to the north, makes a Taurikura volcanic centre source around Whangarei Heads seem unlikely, unless these rocks were thrust in (Ei) and erupted (Eii) after Pakiri facies accumulated. Sedimentary structures in the apparently contemporaneous, dominantly Miocene volcanic-derived Timber Bay slope facies (Bv), interfingering with and west of Pakiri facies, indicate a northern or northwestern source (Brook 1983). Thus the volcanic source for the Pakiri facies was probably either from the northwest (north Kaipara area) or the north (beneath the northern basement and Bream thrust blocks). The mixed Blockhouse Bay and Cornwallis turbidite facies (Biii and Bvi) also have sedimentary structures indicating a predominant northwest (Kaipara) source area (e.g., Ballance 1974; Hayward 1979). In part these were probably contemporaneous with the upper parts of the Pakiri and Timber Bay facies, which heavy minerals also indicate had a mixed provenance (subgroup lb). Thus the upper parts of the central basin turbidite facies appear to have had a mixed

Table 4

Bi. Bii. Biii. Biv. Bv. Bvi. Bvii. Ci. Cii. Ei.

PROVENANCE HISTORY OF WATTEMATA BASIN SEDIMENTS Early Otaian (Fig. 9A) Basal shallow marine Kawau facies rocks (A) accumulated around an irregular shoreline of Waipapa basement in the east of the area. Heavy minerals are consistent with derivation of these sediments almost exclusively from local Waipapa sources. A switch in heavy mineral provenance occurred during the interval of sediment starvation as these areas subsided to mid-bathyal depths (Ricketts et al. 1989). The overlying volcanic-poor turbidites (East Coast Bays facies) appear to have had a Northland Allochthon igneous and sedimentary source from the northwest. As these eastern areas were subsiding, nappes of Cretaceous and Paleogene igneous and sedimentary rocks (Northland Allochthon—D) were thrust or slid into the northern and northwestern parts of the basin from the north (Hayward et al. 1989). The frontal nappes (Motatau, Mangakahia sedimentary rocks) came to rest in bathyal depths, but later nappes (including Tangihua igneous rocks) appear to have formed land in the west and north Kaipara area. Lower parts of Bream Subgroup (late Waitakian or early Otaian age), which accumulated prior to their apparent thrust emplacement in the northeast, record the initial rapid subsidence that formed the Waitemata Basin in their area of origin. Both the shallow-water basal Bream sediments and the thin overlying deep-water siltstones have a predominant (or exclusive) local Waipapa provenance. Many of these Bream sequences were then overwhelmed by the emplacement of Northland Allochthon nappes, which also ripped up and incorporated some of the Miocene sedimentary sequence.

Provenance of early Miocene Waitemata Basin facies. Samples

A.

provenance derived from the growing Miocene volcano and the remaining Northland Allochthon, both in the Kaipara area.

Basal shallow marine Kawau facies Volcanic-poor turbidite East Coast Bays facies Volcanic-poor turbidite Paremoremo facies Mixed turbidite Blockhouse Bay facies Volcanic-rich proximal turbidite Pakiri facies Thin-bedded Timber Bay slope facies Mixed proximal turbidite Cornwallis facies Volcaniclastic mass-flow deposits in central basin Western volcanic facies, Manukau centre Western volcanic facies, Hukatere centre Northern sedimentary Bream facies

No. of groups

Inferred provenance

6

2b, 5

Waipapa basement only.

8

2a, 2b, 4

5

2a, 2b, 4

2

lb,4b

11

la, lb

7

la, lb

5

la, 4, 7

Northland Allochthon sedimentary and igneous sources only. Northland Allochthon sedimentary and igneous sources only. Mixture of Miocene volcanic and Northland Allochthon sources. Predominantly Miocene volcanic source with minor Northland Allochthon input high in sequence. Predominantly Miocene volcanic source with some Northland Allochthon input. Mixture of Miocene volcanic and Northland Allochthon sources. Predominantly Miocene volcanic sources with some mixing from turbidite facies sediments. Entirely Miocene volcanic source.

16

la, lb, lc, Id, 4a, 6

3

la

4

la, lb, 2a, 3

13

la, 2a, 2b, 3, 5

Mixture of Miocene volcanic and Northland Allochthon sources. Predominantly Waipapa source near base, Northland sedimentary source higher; minor distal Miocene volcanic and/or Northland igneous sources .

235

Hayward & Smale—Waitemata Basin heavy minerals A. early Otalan c.22 Ma

middle Otaian c.21 Ma

Kaipara Volcano

Paremoremo facies Blockhouse Manukau Volcano i":G>0'• fades

C. late Otaian c.20 Ma

thrusting sediment transport

D. early Altonian c.18.5 Ma

volcaniclastlc mass flows

Fig. 9 Maps of the inferred paleogeographic and provenance history of the early Miocene Waitemata Basin. A-D and Ai-Fi refer to the Waitemata Basin facies shown in Fig. 1 and 2. Numbers 1-7 (circled) refer to heavy mineral provenance groups.

Middle Otaian (Fig. 9B) Following the interval of rapid subsidence in the east and emplacement of nappes in the northwest, the Waitemata Basin began to fill with turbiditic sandstones from two different sources: (1) In the northeast, thick, proximal, volcanic-rich Pakiri facies turbidites (Biv) flowed in from a northern or northwestern contemporaneous andesitic volcanic source. (2) Further south, a submarine fan developed, fed by sediment eroded from the Northland Allochthon landmass in the west central Kaipara area. Heavy mineral suites in these fan sediments suggest considerable Tangihua igneous provenance mixed with recycled allochthonous sedimentary sources. In the west and northwest, the proximal parts of the fan (Paremoremo facies, Bii) buried the frontal allochthonous nappes and included thick deposits of canyon, channel, and fan conglomerate (Albany Conglomerate), largely of Tangihua provenance. Turbiditic sandstones but no conglomerate reached the slightly deeper, more distal parts of this fan (East Coast Bays facies, Bi) to the south and east.

The northern, volcanic-rich Pakiri fan turbidites appear to interfinger with the southern volcanic-poor East Coast Bays fan turbidites along their border in the Waiwera area (Fig. 8). In the southwest, the East Coast Bays facies appears to pass upwards and laterally into the mixed turbidite Blockhouse Bay facies (Biii). Heavy mineral suites confirm a mixed provenance for this facies, with sediment input from the Northland Allochthon source in the northwest and from a contemporaneous andesitic volcanic source in the west, presumably the early eruptive phases of the Manukau volcanic centre. Sporadic volcaniclastic submarine mass-flow beds (Parnell Grit, Bvii) occur within the East Coast Bays and Blockhouse Bay facies and mostly appear to have been derived from the early Manukau volcanic centre in the west. Some of these beds further north around Waiwera also contain allochthonous sedimentary clasts suggesting an origin from an early volcanic centre in the Kaipara area. The single volcaniclastic mass-flow bed within the distal turbidite facies (Colville Formation) on the northern tip of Coromandel Peninsula has a heavy mineral suite similar to those further west, and could well have also been derived from the western volcanic centres.

236 Heavy mineral compositions of these volcaniclastic massflow beds indicate variable levels of mixing with the background volcanic-poor sediments as they flowed into the basin. The volcanic sources were dominanfly clinopyroxene andesite, basalt, or dacite with occasional two-pyroxene andesite. A distinctive biotite rhyolite source, possibly in the offshore Kaipara area, is indicated by the heavy minerals of one bed in the Blockhouse Bay facies. Volcaniclastic mass-flow beds are absent from the proximal parts of the volcanic-poor fan (Paremoremo facies), probably because it was built up above the level of the basin floor and debris flows were diverted around it. Late Otaian (Fig. 9C) Thrust and slide emplacement of the Northland Allochthon into the Waitemata Basin probably continued throughout the Otaian. While there is compelling evidence to interpret the Waipapa basement blocks in the north around Whangarei and Waipu, and most of their capping Bream Subgroup, as intraWaitemata Basin thrust blocks or nappes from the north or northeast (Hayward 1989), the exact timing of their emplacement is not yet fully understood. Upper, shallow-water parts of the Bream Subgroup (Ei) were probably deposited after the main phase of emplacement of the Waipu-Whangarei thrust blocks, which occurred about middle Otaian times. Thrust emplacement coincided with an apparent switch in provenance within Bream Subgroup from a mainly Waipapa source to a predominantly Northland Allochthon sedimentary rock source. Further south, a pulse of increased tectonism and deformation occurred around the middle-late Otaian. At this time, a number of allochthonous nappes were thrust southwestwards over Waitemata Basin sediments in the eastern Kaipara area (F. J. Brook pers. comm.) accompanied by considerable regional uplift in the northern part of the basin. At the same time, many square kilometres of the earlierfrontalnappes and their piggyback Miocene Paremoremo facies slid southwards towards the centre of the central Waitemata Basin (Hayward 1982). This slide came to rest as a jumbled mass of folded and disrupted thrust blocks (Silverdale Dome of Schofield 1989) with more distal Paremoremo strata compressed into a series of folds around its toe. Additional nappes of Pakiri facies and minor allochthonous sedimentary rocks slid or were thrust in behind the major Silverdale lobe. Late Otaian turbidite facies (upper Pakiri, Biv; upper Timber Bay, Bv; and Comwallis, Bvi) that unconformably overlie these nappes all have a mixed provenance, reflecting increased Kaipara and Manukau volcanism and the additional areas of allochthonous sedimentary rocks that had been uplifted to form land in the Kaipara area. Mixed Miocene andesitic and allochthonous igneous and sedimentary conglomerate (Matapoura and Helensville Conglomerates) was fed eastwards from the west Kaipara area into a trough bounded to the east by the new nappes, which redirected it southeastwards into the Waitemata Basin. Further submarine volcaniclastic mass-flow beds (Bvii), derived from the Kaipara volcano, occur in the upper Pakiri turbidite facies. Early and middle Altonian (Fig. 9D) All of the northern and central Kaipara area had been uplifted to form land and shallow marine areas by the beginning of the Altonian. Several small submarine volcanoes erupted in these

New Zealand Journal of Geology and Geophysics, 1992, Vol. 35 shallow seas in east central Kaipara in the early Altonian and were a major source of sediment in the surrounding area. Continued erosion of the local Northland Allochthon land areas also provided large amounts of sediment. This mixed provenance is reflected in the heavy mineral composition of the Hukatere Subgroup (Cii) samples. To the south, the Waitemata Basin appears to have remained at mid-bathyal depths till at least well into the middle Altonian (Hayward & Buzas 1979), although no sediments of Altonian age are now preserved on the eastern side of the basin to define its extent. The Manukau volcano continued to grow in size with submarine flows and volcanic breccia and conglomerate on its bathyal submarine slopes, encroaching eastwards into the Waitakere Ranges area. The heavy minerals in sandstones and siltstones (Ci) that accumulated around the lower flanks of the Manukau volcano at this time appear to be entirely of a Miocene basalt or andesite provenance. Sediment derived from mixed Miocene volcanic and Northland Allochthon sources in the Kaipara area no longer reached this far south. The middle Altonian rocks are the youngest marine sediments known in the Waitemata Basin. Any later history has been eroded away. ACKNOWLEDGMENTS We thank Julie Smith for preparation of the samples for heavy mineral examination; Jeff Lyall for drafting the figures; and Peter Ballance, Steve Weaver, Mike Isaac, and two anonymous referees for critically reading the manuscript and for suggesting improvements.

REFERENCES Ballance, P. F. 1964: The sedimentology of the Waitemata Group in the Takapuna section, Auckland. New Zealand journal of geology and geophysics 7: 466-499. 1974: An inter-arc flysch basin in northern New Zealand: Waitemata Group (upper Oligocene to lower Miocene). Journal of geology 82: 439—471. -1976: Stratigraphy and bibliography of the Waitemata Group of Auckland, New Zealand. New Zealand journal of geology and geophysics 19: 897-932. Ballance, P. F.; McCarthy, J. A. 1975: Geology of Okahukura Peninsula, Kaipara Harbour, New Zealand. New Zealand journal of geology and geophysics 18: 721-743. Black, P. M. 1989: Regional metamorphism in basement Waipapa Group, Northland, New Zealand. Royal Society of New Zealand bulletin 26: 15-22. Brook, F. J. 1983: Lower Miocene geology of the northern and central Kaipara Harbour. Unpublished Ph.D. thesis, Department of Geology, University of Auckland. Brothers, R. N.; Delaloye, M. 1982: Obducted ophiolites of North Island, New Zealand: origin, age, emplacement and tectonic implications for Tertiary and Quaternary volcanicity. New Zealandjournal of geology and geophysics 25; 257-274. Carter, L. R. 1971: Stratigraphy and sedimentology of the Waitemata Group, Puketotara Peninsula, Northland. New Zealandjournal of geology and geophysics 14: 169-191. Chappell, J. 1963: The geology of the Musick Point-Bucklands Beach area. Tane 9: 33-40. Davidson, K. J. 1990: Sedimentology, structure and petrology of the Waitemata Group, upper Waitemata Harbour, Auckland. Unpublished M.Sc. thesis, Department of Geology, University of Auckland.

237

Hayward & Smale—Waitemata Basin heavy minerals Full, W. E.; Ehrlich, R.; Bezdek, J. C. 1982: FUZZY QMODEL—a new approach for linear unmixing. Mathematical geology 14 (3): 259-270. Hayward, B. W. 1979: Eruptive history of the early to mid Miocene Waitakere Volcanic Arc, and paleogeography of the Waitemata Basin, northern New Zealand. Journal of the Royal Society ofNew Zealand 9 (3): 297-320. 1982: A lobe of "Onerahi Allochthon" within Otaian Waitematas. Geological Society of New Zealand newsletter 58: 13-19. 1989: Is Northland's autochthon allochthonous? Abstract. Geological Society of New Zealand miscellaneous publication 43: 48. Hayward, B. W.; Brook, F. J. 1984: Lithostratigraphy of the basal Waitemata Group, Kawau Subgroup (new), Auckland, New Zealand. New Zealand journal of geology and geophysics 27:101-123. Hayward, B. W.; Buzas, M. A. 1979: Taxonomy and paleoecology of early Miocene benthic foraminifera of northern New Zealand and the north Tasman Sea. Smithsonian contributions to paleobiology 36: 154 p. Hayward, B. W.; Moore, P. R.; Francis, D. A. 1978: Geology of Hen Island (Taranga), and reclassification of the "Wairakau Andesites". Tone 24: 55-76. Hayward, B. W.; Brook, F. J.; Isaac, M. J. 1989: Cretaceous to middle Tertiary stratigraphy, paleogeography and tectonic history of Northland, New Zealand. Royal Society of New Zealand bulletin 26: 47-64. Hoskins, R. H. ed. 1982: Stages of the New Zealand marine Cenozoic: a synopsis. New Zealand Geological Survey report 107. Hunt, T. M.; Syms, M. C. 1977: Sheet 2—Whangarei. Magnetic map of New Zealand 1:250 000, total force anomalies. Wellington, New Zealand. Department of Scientific and Industrial Research. Jones, B. G. 1967: An outline of the geology of the St Heliers Bay Glendowie area, Auckland, New Zealand. Tane 13: 119— 142. 1969: Sedimentology of the Waitemata Group in the Stanley Point - Devenport area, Auckland, New Zealand. New Zealand journal of geology and geophysics 12: 215-247. 1972: Sedimentology of the Waitemata Group (lower Miocene) at Pakaurangi Point, Kaipara, New Zealand. Journal of the Royal Society ofNew Zealand 2 (2): 187-209. Kruskal, J. B. 1964: Multidimensional scaling by optimising goodness of fit to a nonmetric hypothesis. Psychometrika 29:1-27.

Mayer, W. 1969: Petrology of the Waipapa Group, near Auckland, New Zealand. New Zealand journal of geology and geophysics 12: 412-435. Middleton, L. M. H. 1983: The Whangarei Heads calc-alkaline Tertiary volcanic complex, Northland, New Zealand. Unpublished Ph.D. thesis, Department of Geology, University of Auckland. Pielou, E. C. 1984: The interpretation of ecological data. New York, Wiley. 263 p. Ricketts, B. D.; Ballance, P. F.; Hayward, B. W.; Mayer, W. 1989: Basal Waitemata Group lithofacies: rapid subsidence in an early Miocene interarc basin, New Zealand. Sedimentology 36: 559-580. Rohlf, F. J. 1988: NTSYS-pc, numerical analysis and multivariate analysis system. Exeter Software. Schofield, J. C. 1989: Sheets Q10 and R10—Helensville and Whangaparaoa. Geological map of New Zealand 1:50 000. Wellington, New Zealand. Department of Scientific and Industrial Research. Skinner, D. N. B. 1986: Neogene volcanism of the Hauraki Volcanic Region. Royal Society of New Zealand bulletin 23: 21—47. Smale, D. 1987: Heavy minerals in Cretaceous-Cenozoic sandstones in Canterbury. New Zealand Geological Survey report SL17. 1988a: Heavy minerals in Cretaceous and Tertiary sandstones from Northland. New Zealand Geological Survey report SL18. 1988b: Detrital pumpellyite and epidote group minerals in Cretaceous and Tertiary sandstones in the South Island, New Zealand. Journal of sedimentary petrology 58 (6): 985-991. 1990: Distribution and provenance of heavy minerals in the South Island: a review. New Zealandjournal of geology and geophysics 33: 557-571. Smith, I. E. M.; Ruddock, R. S.; Day, R. A. 1989: Miocene arc-type volcanic/plutonic complexes of the Northland Peninsula, New Zealand. Royal Society of New Zealand bulletin 26: 205-213. Sneath, P. H.; Sokal, R. R. 1973: Numerical taxonomy. San Francisco, W. H. Freeman and Co. 573 p. Sporli, K. B. 1989: Exceptional structural complexity in turbidite deposits of the piggy-back Waitemata Basin, Miocene, Auckland/Northland, New Zealand. Royal Society of New Zealand bulletin 26:183-194. Stipp, J. J.; Thompson, B. N. 1971: K/Ar ages from the volcanics of Northland, New Zealand. New Zealand journal of geology and geophysics 14: 403-413. Woodward, D. J.; Riley, W. 1.1972: Sheet 2—Whangarei. Gravity map of New Zealand 1:250 000, isostatic anomalies. 2nd ed. Wellington, New Zealand. Department of Scientific and Industrial Research.

(Appendices 1 and 2 follow)

238


APPENDIX 1 Location, age, and stratigraphic data of heavy mineral samples.

Gp

NZGS lab no.

NZ metric map grid reference

Age Epoch

Early Miocene Waitemata Basin samples 1 2a Q7/sl7 Q7/221853 Miocene 2 2a Q7/sl4 Q7/181883 Miocene 3 2a Q8/s8 Q8/322744 Miocene 4 2a Q7/sl Q7/269 806 Miocene 5 2a Q7/s3 Q7/302 873 Miocene 6 3 Q7/sll Q7/222 815 Miocene 7 2b R8/sl R8/538 711 Miocene 8 2b R8/s2 R8/522 716 Miocene 9 la Q7/sl2 Q7/344 859 Miocene 10 5 Q7/sl5 Q7/286 929 Miocene 11 2b Q7/sl3 Q7/357 974 Miocene 12 2b Q7/s8 Q7/443 011 Miocene 13 2b Q7/s9 Q7/444 012 Miocene 14 lb Q8/s9 Q8/163 523 Miocene 15 2a Q8/s6 Q8/262 513 Miocene 16 3 Q8/s7 Q8/259 513 Miocene 17 la Q9/slO Q9/252 486 Miocene 18 lb Q9/s8 Q9/261490 Miocene 19 lb Q9/s7 Q9/262 492 Miocene 20 la Q9/sll Q9/268 496 Miocene 21 lb Q9/sl2 Q9/275 499 Miocene 22 lb Q9/s6 Q9/275 499 Miocene 23 lb Q9/s5 Q9/285 496 Miocene 24 la Q9/sl3 Q9/478 298 Miocene 25 la Q9/sl6 Q9/416 289 Miocene 26 lb Q9/sl Q9/407 253 Miocene 27 lb Q9/s2 Q9/432 246 Miocene 28 lb Q9/s3 Q9/432 246 Miocene 29 lb Q9/sl4 Q9/442 376 Miocene 30 la Q9/sl5 Q9/461354 Miocene 31 la Q9/sl7 Q9/461380 Miocene 32 la Q9/sl8 Q9/47O372 Miocene 33 lb R9/s6 R9/591227 Miocene 34 la R9/s3 R9/708 452 Miocene 35 la R9/s5 R9/703 463 Miocene 36 la R9/s4 R9/707 412 Miocene 37 la R9/s2 R9/716 462 Miocene 38 2b R9/sl R9/718 427 Miocene 39 la Q10/s5 Q10/394123 Miocene 40 la Q10/s6 Q10/394 123 Miocene 41 7 QlO/sl Q10/412 953 Miocene 42 2b Q10/s2 Q10/403 052 Miocene 43 lb S9/sl S9/254 223 Miocene 44 la RIO/sl RIO/636 155 Miocene 45 lb R10/s2 R10/636 155 Miocene 46 2b R10/sl5 R10/634142 Miocene 47 lb R10/sl4 RIO/628 139 Miocene 48 4 R10/sl6 R10/622133 Miocene 49 2a R10/s6 RIO/605 966 Miocene RIO/621012 Miocene 50 2b R10/sl7 Q10/s7 Q10/478 093 Miocene 51 4 Q10/s4 Q10/466 069 Miocene 52 4 Q10/s3 Q10/465 068 Miocene 53 4 Rll/s9 Rl 1/510 652 Miocene 54 4 Rll/s7 Rll/629736 Miocene 55 6 56 lb Rll/s5 Rl 1/653 728 Miocene 57 lb R10/s7 R10/682 917 Miocene 58 4 R10/s9 RIO/796 912 Miocene 59 la RIO/slO R10/671 984 Miocene 60 lb RIO/sll R10/681 933 Miocene 61 lb R10/sl2 R10/681 934 Miocene 62 lb R10/sl3 RIO/680 934 Miocene 63 lb R l l / s l l Rll/702820 Miocene 64 lb Rll/s3 Rll/861716 Miocene 65 4 Rll/sl2 Rll/717 811 Miocene 66 4 Rll/sl4 Rll/715 816 Miocene

NZ stage Po Po Po Po Po Po Lw-Po Lw-Po Lw-Po Lw-Po Lw-Po Lw-Po Lw-Po PI PI PI PI Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po PI PI Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po Po

Facies Lithostratigraphic unit and locality Ei Ei Ei Ei Ei Ei Ei Ei Ei Ei Ei Ei Ei Cii Cii Cii Cii Bv Bv Bv Bv Bv Bv Bvii Bvii Biv Biv Biv Biv Biv Bv Biv Biv Biv Biv Biv Biv A Bvi Bvii Bvi Bvi Bvii Bvii Bi Bi Bi Bi Bii Bii Bii Bii Bii Bvi Bvii Bvii Bvii Bvii Bvii Bvii Bvii Bvii Bvii Bvii Bvii Bvii

Bream SG; Waiotira Bream SG; Omana Rd Bream SG; Finlayson Brook Rd Bream SG; Cassidy Rd Bream SG; Ngatoka Trig Bream SG; Waikiekie Quarry Bream SG; Bream Tail Bream SG; Bream Tail Bream SG; Ormiston Rd Bream SG; Monks Rd Bream SG; Mangawhati Pt Bream SG; Parua Bay Bream SG; Parua Bay Hukatere SG; Strawberry Bay Hukatere SG; Pakaurangi Pt Hukatere SG; Pakaurangi Pt Hukatere SG; Puketotara Pen Waihangaru Fmn; Puketotara Pen Waihangaru Fmn; Puketotara Pen tuff bed in Waihangaru Fmn; Puketotara Pen Timber Bay Fmn; Puketotara Pen Timber Bay Fmn; Puketotara Pen Timber Bay Fmn; Puketotara Pen Timber Bay Parnell Grit in Pakiri Fmn s.l.; Woodcocks Parnell Grit in Pakiri Fmn s.l.; Hoteo River Pakiri Fmn s.l.; Mt Auckland Pakiri Fmn s.l.; Mt Auckland Pakiri Fmn s.l.; Mt Auckland Pakiri Fmn s.l.; Mt Harriet Pakiri Fmn s.l.; Hoteo Timber Bay Fmn; Hoteo Pakiri Fmn s.l.; Hoteo Pakiri Fmn; Windy Hill Pakiri Fmn; Pakiri Hill Pakiri Fmn; Goat Island Bay Pakiri Fmn; Ti Pt wharf Pakiri Fmn; Goat Island Bay Kawau SG; Mathesons Bay Cornwallis Fmn s.l.; Jordans Rd Parnell Grit in Cornwallis Fmn s.l.; Jordans Rd Cornwallis Fmn; Kaipara River Cornwallis Fmn; Kaukapakapa Parnell Grit in Colville Fmn; Fletchers Bay Parnell Grit in East Coast Bays Fmn s.l.; Waiwera East Coast Bays Fmn s.l.; Waiwera East Coast Bays Fmn s.l.; Hadfields East Coast Bays Fmn s.l.; Hadfields East Coast Bays Fmn s.l.; Hadfields Paremoremo Fmn; Okura Paremoremo Fmn; Albany Hill Paremoremo Fmn; Rapsons Rd Paremoremo Fmn; Rapsons Rd Albany Cong in Paremoremo Fmn; Rapsons Rd Cornwallis Fmn; Huia Parnell Grit in Blockhouse Bay Fmn; DuckCk Parnell Grit in Blockhouse Bay Fmn; Waikowhai Parnell Grit in East Coast Bays Fmn; Castor Bay Parnell Grit in East Coast Bays Fmn; Motutapu Is Parnell Grit in East Coast Bays Fmn; Torbay Parnell Grit in East Coast Bays Fmn; Campbells Bay Parnell Grit in East Coast Bays Fmn; Campbells Bay Parnell Grit in East Coast Bays Fmn; Campbells Bay Parnell Grit in East Coast Bays Fmn; Parnell Turanga Greensand in East Coast Bays Fmn; Turanga Creek Orakei Greensand in East Coast Bays Fmn; Hobsons Bay Orakei Greensand in East Coast Bays Fmn; Hobsons Bay {continued next page)

239

Hay ward & Smale—Waitemata Basin heavy minerals APPENDIX 1 (continued)

Gp

NZGS lab no.

NZ metric map grid reference

Epoch

la la la 4 4 lb 4 2a 4 2b 2b 4 2b 5 5

Qll/sl R11M5 Qll/s2 RU/slO Rll/s8 Rll/s6 R10/s8 Rll/sl3 Rll/s4 Rll/sl Rll/s2 R12/sl R12/s6 Rll/sl6 R12/s3

Qll/377 840 Rll/551725 Ql 1/493 717 Rll/510 652 Rl 1/534 665 Rl 1/653 728 RIO/682 917 Rl 1/710 863 Rll/861716 Rll/885 723 Rl 1/885 724 R12/864 567 R12/868 570 Rl 1/880 876 R12/869 570

Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene

PI PI PI Po Po Po Po Po Po Po Po Po Po Po Po

Potential source samples 82 2b O4/sl O4/692 706 83 2b O4/s5 O4/628 727 84 2b P4/s2 P4/755 921 85 2a O5/sl O5/618 626 86 2a O5/s6 O5/631 681 87 6 P4/s3 P4/798 837 88 2a P5/sl P5/789 567 89 2a P7/s4 P7/886 058 90 2b P7/s5 P7/858 071

Oligocene Cretaceous Cretaceous Oligocene Oligocene Cretaceous Oligocene Paleocene Recent,

Lwh Mp-Mh C-R Lwh Lwh Mp-Mh Lwh Dt

91

2b

P7/s6

Recent,

92 93 94 95 96 97 98 99 100

2a 2b 4 2a 2b 2a lb 2a lb

Q7/s2 Q7/s4 Q7/slO Q8/sl Q8/s4 R10/s3 R12/s4 R12/s5 R12/s7

67 68 69 70 71 72 73 74 75 76 77 78 79 80 81

P7/857 072 Q7/223 814 Q7/313 837 Q7/444 013 Q8/261 641 Q8/292 775 R10/560 033 R12/871570 R12/869 570 R12/870 568

Age

Oligocene Oligocene Cretaceous Oligocene Eocene Oligocene ?Mesozoic Eocene ?Mesozoic

NZ stage

Facies

Lithostratigraphic unit and locality

Ci Ci Ci Bvi Biii Biii Bi Bi Bi A A Bi A A A

Manukau SG; Maori Bay Manukau SG; Shaw Rd Manukau SG; Nihotupu Stm Cornwallis Fmn; Huia Blockhouse Bay Fmn; Mill Bay Blockhouse Bay Fmn; Waikowhai East Coast Bays Fmn; Castor Bay East Coast Bays Fmn; Narrow Neck East Coast Bays Fmn; Turanga Ck Kawau SG; Claude Stm Kawau SG; Claude Stm East Coast Bays Fmn; Hays Stm Kawau SG; Hays Stm Kawau SG; Waiheke Island Papakura Lst in Kawau SG; Hays Stm

Northland Allochthon, Motatau Complex lst; Mangapa Northland Allochthon, Mangakahia Complex sst; Opurehu R. Northland Allochthon, Tupou Complex greywacke; Pa Island Northland Allochthon, Motatau Complex sst; Omahuta Rd Northland Allochthon, Motatau Complex lst; Opurehu R. Northland Allochthon, Mangakahia Complex sst; Whangaroa Northland Allochthon, Motatau Complex lst; Waihou R. Nthland Allochthon, Mangakahia Complex mst; Tangowahine V. derived from Northland Allochthon, Tangihua Complex; Tangowahine V. derived from Northland Allochthon, Tangihua Complex; Tangowahine V. Ld Northland Allochthon, Motatau Complex lst; Waikiekie Quarry Lwh-Ld Te Kuiti Gp, Whangarei Lst; Waipu Caves Mh-Dt Northland Allochthon, Mangakahia Complex sst; Parua Bay Lwh-Ld Northland Allochthon, Motatau Complex lst; Maungaturoto Ar Te Kuiti Gp, Ruatangata Sst; Taipuha Lwh-Ld Northland Allochthon, Motatau Complex 1st; Redvale ? Waipapa Gp greywacke; Hays Stm Ak-Ar Te Kuiti Gp, Waikato Coal Measures; Hays Stm ? Waipapa Gp greywacke; Hays Stm

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