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Pre-Miocene lithostratigraphy ofTaranaki Basin, New ZealandJulie Palmer aa Petroleum Corporation of New Zealand (Exploration) Ltd ,P.O. Box 5082, Wellington , New ZealandPublished online: 28 May 2012.

To cite this article: Julie Palmer (1985) Pre-Miocene lithostratigraphy of Taranaki Basin,New Zealand, New Zealand Journal of Geology and Geophysics, 28:2, 197-216, DOI:10.1080/00288306.1985.10422220

To link to this article: http://dx.doi.org/10.1080/00288306.1985.10422220

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New Zealand Journal of Geology and Geophysics, 1985, Vo!. 28: 197-2160028-8306/85/2802-0197$2.50/0 © Crown copyright 1985

Pre-Miocene lithostratigraphy of Taranaki Basin, New Zealand

197

JULIE PALMERPetroleum Corporation of New Zealand (Explora­tion) LtdP.O. Box 5082Wellington, New Zealand

Abstract The stratigraphy and sedimentologyof the Paleocene-Oligocene sedimentary sequenceof Taranaki Basin is reviewed using data obtainedfrom exploration wells. Sixteen of these wells aresited in the Taranaki Graben, an infilled, down­faulted block extending westwards from the Tar­anaki Fault to the Cape Egmont Fault Zone. Afurther seven wells are sited on the Western Plat­form, which extends westwards from the CapeEgmont Fault Zone seaward to beyond the edge ofthe continental shelf.

In the past, the lithostratigraphic nomenclatureapplied to the sequences encountered in the wellswas adopted from adjoining onshore areas. Whereexisting names were inadequate, new names werecreated, but never formally defined.

The term "Kapuni Formation" is an informalname for the Paleocene-Oligocene sandstone-coalmeasure sequence which was first encountered inthe Kapuni-1 well. It is proposed that the thicksequence currently known as the Kapuni Forma­tion be formally named the Kapuni Group. KapuniGroup is subdivided into four formations. Fromoldest to youngest they are Kaimiro Formation,Ornata Formation, Mangahewa Formation, andMcKee Formation. A lateral, fully marine equiva­lent of the Kapuni Group is described.

A further three formations are defined. TheWhaingaroan marine mudstone (Kaiata Formationof Shell BP and Todd Oil Services Ltd) is herenamed the Turi Formation; the Whaingaroan-Wai­takian calcareous siltstone sequence informallyknown as the lower Mahoenui Group is named theOtaraoa Formation; and the Waitakian limestoneimmediately underlying the Mahoenui Formationproper is here named the Tikorangi Formation.

The stratigraphy of Taranaki Basin is comparedwith that of adjoining onshore areas to the northand south. Similarities are apparent and possiblenorthern and southern correlatives are proposed.

Received 22 July 1983. accepted 28 August 1984

Sig. I·

The environments of deposition of the variousunits range from bathyal to outer shelf throughinner shelf to lagoonal and terrestrial. Based onthese interpretations, a paleogeographic recon­struction of Taranaki Basin shows a major pre­Miocene transgression. It progressed across thebasin in a generally southeasterly direction. Theproximity of sediment source combined with atransgressive shoreline accounts for the diachron­ous nature of the lithostratigraphic boundaries.

Keywords Kapuni Group; Kaimiro Formation;Ornata Formation; Mangahewa Formation; McKeeFormation; Tikorangi Formation; Otaraoa For­mation; Turi Formation; Matapo Sandstone Mem­ber;: new stratigraphic names; Taranaki Basin;paleoenvironment

INTRODUCTION

Taranaki Basin, which lies along the western sideof the North Island of New Zealand, is one of thecountry's largest sedimentary basins. It extendswestward from the Taranaki Fault Zone (Fig. I)and underlies the Taranaki peninsula and much ofthe adjacent continental shelf and slope (McBeath1976). The basin extends northwards from thenorthwest of the South Island to about the latitudeof Auckland (Pilaar & Wakefield 1978; Fig. 1).

Taranaki Basin contains a thick sequence of LateCretaceous-Recent sediments that overlie Paleo­zoic and early Mesozoic basement rocks. Isolatedoccurrences of pre-Miocene sediments crop out inthe basin, but most information on the oldest partof the sequence comes from wells drilled for hydro­carbon exploration and production. The first sig­nificant well was Kapuni-I, drilled in 1959 by ShellBP and Todd Oil ServicesLimited (SBPT). It drilledthe Kapuni Structure and discovered New Zealand'sfirst commercial gas-condensate field. Since 1959,a further 25 wildcat wells have penetrated the pre­Miocene sedimentary sequence. Of these, Maui-Idiscovered the offshore Maui gas-condensate fieldin 1969, and McKee-2 discovered the onshoreMcKee oil field in 1980. The three fields producefrom Paleocene-Oligocene sandstones of theKapuni "Formation". Other wells that penetratedthe Kapuni Formation contained some hydrocar­bons. The most significant are.the onshore wellsMangahewa-1, Urenui-1, and McKee-I; and theoffshore well Maui-4 (Fig. 1).

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198 New Zealand Journal of Geology and Geophysics, 1985, Vol. 28

10 0 10 20 30 40 50 60 70 80 90 100 kmI , " , I I ! I I I I I I I ,

~

I

* After Knox 1961

NOTE All depths metres subsea-- unless otherwise stated

ji7S·00'E

~

~

WESTERNPLATFORM

173·00'E

FRESNE-1

SCALE

TANE-1GRANITE4444m

~

-¢-COOK-1

40·00'S

39"oo'S

Fig. 1 Major structural elements of Taranaki Basin, New Zealand, showing the location of exploration wells drilledsince 1959 and the distribution, type, and depth of basement in wells drilled in the basin and on the adjacent Patea­Tongaporutu High,

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Palmer-Pre-Miocene lithostratigraphy, Taranaki Basin 199

Many of the lithostratigraphic names applied tothe sequences encountered in Taranaki Basin wellswere adopted from adjoining onshore areas. In thepast, where existing names were inadequate, newnames were created, but never formally defined,and boundaries therefore were often vague. Theresulting stratigraphic nomenclature containeduncertainties and was often used inconsistently.This paper provides a lithostratigraphic nomencla­ture for the Late Cretaceous-Oligocene sediments,based on data gathered from exploration and pro­duction wells. Several new names are introduced.Hedberg (1976) has been followed in constructingthe nomenclature. The depository for material usedin this study (i.e. ditch cutting samples, cores andwell logs (Table 1)) is the New Zealand GeologicalSurvey, Lower Hutt. Unless stated otherwise, thedatum for all well depths is below kelly bushing(BKB).

STRUCTURE

Taranaki Basin is composed of two major struc­tural blocks (Fig. 1), the Western Platform and theTaranaki Graben (Pilaar & Wakefield 1978; Knox1982). The Western Platform, over 100 km wide,is the western, wholly offshore part of the basin. Itis characterised by broad, simple structure and2000-5000 m of Late Cretaceous-Recent sedi­ments. It was affected by Late Cretaceous-Eocenenormal block faulting, which created local fault­angle depressions or half grabens (Pilaar & Wake­field 1978), but has been relatively stable through­out the remainder ofthe Tertiary. The north-southto northeast-southwest trending Cape Egmont FaultZone (Fig. 1) consists of a series of steep, subpar­allel, normal to reverse faults (McBeath 1977);maximum throw is 2100 m.

The north-south trending Taranaki Fault Zone(Fig. 1) consists of a narrow zone of steep reversefaults that become nearly vertical and normal withdepth (Pilaar & Wakefield 1978). The zone wasdownthrown on the western side, resulting in theaccumulation of a thick sedimentary sequence inthe adjacent graben. Several aligned, shallow thrustfaults are associated with the Taranaki Fault. Theycomprise the Tarata Thrust Fault Zone (Haskell1981) (Fig. 1). Vertical throw along the TaranakiFault Zone is estimated to be 7000 m (McBeath1976), and the top of the Kapuni Formation adja­cent to the fault is at least 5000 m below sea level.East of the Taranaki Fault lies the Patea-Tonga­porutu High, an upthrust basement block whichseparates Taranaki Basin from the late CenozoicWanganui Basin to the east (Fig. 1).

The overall structure of the Taranaki Graben iscontrolled by movement along basement and Late

Cretaceous-Eocene faults. From Late Eocene to atleast Late Miocene time, folding in the grabenoccurred contemporaneously with deposition. Sev­eral generally north-south trending anticlines occur.Their extended growth is evidenced by thinning ofthe sedimentary sequence at the crest of each.Examples include the Kapuni, Maui, Inglewood,Kaimiro, Mangahewa, and Kupe Structures.

BASEMENT

Basement rocks crop out in northwest Nelson andeast of the Taranaki Basin in Waitomo County.Basement has only been encountered in wellsdrilledoffshore. The nature of basement varies from wellto well (Fig. 1). Two wells in the northern part ofthe basin, Mangaa-l and Tangaroa-I, encounteredandesitic and basaltic lavas. Although these rocksmay not be true basement, they obscured theunderlying rocks and, at the time of drilling, wereconsidered economic basement. In Moa-l B, schis­tose basement was encountered. Further south,basement is a granite-diorite suite of rocks. Theproven depth to basement ranges from 4444 mbelow sea level in Tane-l, in the northwest Tar­anaki Basin, to 1521 m below sea level in Tasman­1, in the South Taranaki Basin. There is a generalsouthward shallowing of basement and, onshore innorthwest Nelson, granite and schist crop out atthe surface.

Basement rocks have not yet been drilled in theonshore Taranaki Graben. Seismic data indicatethat, in the deepest parts of the graben, the sedi­mentary cover may be as thick as 7000 m.

STRATIGRAPHY

The surface geology of the Taranaki peninsula isdominated by Recent volcanics (Hay 1967; Neall1979), which mask the Upper Cretaceous-Recentsedimentary sequence. Hay (1967)and Neall (1979),and Bishop (1971), map the stratigraphy of the out­cropping basin sequence for onshore Taranaki andnorthwest Nelson, respectively. However, theextent, nature, and age of the underlying sedimentswas unknown before wells were drilled. Severalauthors refer to, and briefly describe, the subsur­face stratigraphy (Short 1962;McBeath 1976, 1977;Pilaar & Wakefield 1978; Hill & Collen 1978;Hogan 1979). Of these, Short (1962) gives the mostcomplete presentation.

This paper presents the results of a detailed studyof the pre-Miocene stratigraphy of Taranaki Basinand revises the stratigraphic units. New names areproposed for the Oligocene, Eocene, and Paleocene

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Tab

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erty

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der

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onal

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nic;

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mpl

esev

ery

Gam

ma

ray-

neut

ron;

Nor

ris

1966

;m

udst

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(Ger

lings

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64).

cove

rage

);19

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ion

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ris

1966

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one

and

mud

ston

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mpl

esev

ery

elec

tric

al;

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war

det

al.

(Ger

lings

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eous

1982

)A

beel

e19

64).

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lings

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Palmer-Pre-Miocene lithostratigraphy, Taranaki Basin 201

LITHOLOGIC

LEGEND

1=;= =;=1 SHALE

r:TlINTERBEDDED~ SEQUENCE

§COAL

D CARBONACEOUS

g LIMESTONE

1 = ICALCAREOUS

G GLAUCONITIC

EJMICA

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[~ul UNCONFORMITYo DISCONFORMITY

1~:~::ii~/21 SANDSTONE

I~':: JSANDY LITHOLOGY

I~:: :::: ~I SILTSTONE

n JSILTY LITHOLOGY

[-_- -j ARGILLACEOUS- - LITHOLOGY

interbeddedsandstonesi Itstcne ,mudstoneand coal

lnterbeddad sandstone , occasionally~~~~.lomerQtic, siltstone, mudstone and

Silty mudstone with occasionalcalcareous streaks.

LITHOLOGY

Predorninuntly lirnestone with abQ5Q.1 sandstone.

Int.rb.dd.dsi I tstone,si l tysandstoneandsiltymudstone.

Calcareous siltstone DAd mudstone with °1 Dbasal glauconihc sandstone.IMatuposst. rnbr.l -s- MUDSTONE

Nonca(cQreous carbonaceous mudstone

Calcareous mudstone, siltstoneand sandston.

Silty mudstone with minor conqlcrnerute.

Sandstone. ercnsionnllv crniltnceeus

Interbedded siltstone and mudstone.

Volcanics and clastic sediments.

Silty mudstone

Sandy, silty mudstones interbedded with

l\quartz ose conglomerates, with occasionalthin lignit. beds.

o,::::>a0::'-"

FORMATIONI Z::::>c,«~

KAIMIROFORMATION

MCKEEFORMATION/

TURI FORMATION

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FORMATIONnCOl"'lC'ITC'

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Fig.2 Summary of the stratigraphy of the Cretaceous-Recent sedimentary sequence deposited in Taranaki Basin,New Zealand.

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Palmer-Pre-Miocene lithostratigraphy, Taranaki Basin 203

rocks (Fig. 2). The units are defined by lithologicalchanges determined from well data and theirrespective log responses. Some of the lithostrati­graphic units are diachronous (Fig. 3) and relategeographically to environments of deposition. Inparticular, I propose to elevate Kapuni Formationto Kapuni Group, consisting of four formations.Application of the name Mahoenui Group asdefined by Glennie (1956) and Kear & Schofield(1959) necessitates erection of three additional stra­tigraphic units, the Tikorangi, Otaraoa, and TuriFormations, which were erroneously included inMahoenui Group. A fully marine, lateral equiva­lent of the Kapuni Group is described for rockspenetrated in offshore wells in the north and north­west part of the basin (Fig. 3).

PAKAWAU GROUP (Bishop 1971)

The oldest sedimentary rocks known in TaranakiBasin belong to the Pakawau Group. This Creta­ceous-Paleocene conglomerate, sandstone, and coalmeasure sequence, which crops out in the north­west of the South Island, was encountered in off­shore wells Cook-I, Fresne-l, North Tasman-I,Maui Field, Maui-4, and Tane-l (Fig. 3).

Field and seismic evidence indicate that depo­sition of Late Cretaceous and early Tertiary rockswas largely structurally controlled. The thickestsequences of these rocks occur in fault-angledepressions formed by tilted basement blocks. Somewells have drilled more than 2000 m of PakawauGroup rocks without reaching the base of thesequence.

The Pakawau Group rests on an erosion surfacewhich truncates igneous and metamorphic base­ment rocks (Pilaar & Wakefield 1978). It also cropsout in the northwest of the South Island, and theunit is widely distributed over the Western Plat­form and southern Taranaki Graben, but has notyet been encountered in the central or northern partof the graben.

In the south, both onshore and in the Fresne-land Cook-l offshore wells, Pakawau Group con­sists of a basal conglomeratic coarse sandstoneoverlain by alternating sandstone, mudstone, andcoal. Northwards the sequence is more uniform,consisting of fine- to coarse-grained sandstones withthin beds of mudstone and coal.

KAPUNI GROUP (new name)

Kapuni Formation is a convenient name which hasbeen applied to coal measures of Paleocene-EarlyOligocene age encountered in wells drilled in Tar­anaki Basin. These rocks were first encountered inKapuni-l and were correlated (van der Klugt et al.

1959) with an outcrop of similar strata in NorthTaranaki (the Mangaotaki Formation of Glennie(1956)). The Mangaotaki Formation consists ofOligocene sandstone (including glauconitic and cal­careous sandstone), siltstone, coal, mudstone, andconglomerate found in the predominantly calcar­eous sandstone facies in North Taranaki. In com­paring the Eocene-Paleocene Kapuni coal measureswith the type section of the Mangaotaki Forma­tion, Short (1962) noted a difference in lithology,thickness, and age. He, therefore, proposed thename Kapuni Coal Measure Formation, morecommonly referred to as the Kapuni Formation.In a study of the stratigraphy and sedimentology,Hogan (1979) divided the Kapuni Formation intofour members, the boundaries of which weredefined from the Kapuni-l well, but which provedto be impractical for correlation elsewhere in Tar­anaki Basin.

Different correlatable subdivisions within theKapuni Formation subsequently were recognisedover much of the Taranaki Basin, and this paperproposes that the Kapuni Formation be elevatedto group status. In descending order, the upper partof the Kapuni Group consists of the McKee andMangahewa Formations (defined below) and thelower part consists of the Omata and Kaimiro For­mations (defined below). Type sections for theseformations are located in the eastern and centralTaranaki Graben, where the greatest density of welldata is available. The units are correlated westwardon the available well data.

The top of the Kapuni Group is marked by amajor sedimentation change at the top of theMcKee Formation boundary where the lithologychanges from a sandstone to a massive silty mud­stone. The McKee Formation, consisting predom­inantly of sandstone beds, has been encountered inwells located in the eastern and central TaranakiGraben. Immediately underlying this unit is a coalmeasure sequence, here formally named the Man­gahewa Formation.

The distribution and lateral changes within thelower part of the Kapuni Group are not as wellknown as those of the upper part of the KapuniGroup. A sequence of marine siltstone and mud­stone encountered onshore (in Inglewood-l andKaimiro-l wells and probably in the Kapuni-2 andNew Plymouth-2 wells) is here formally named theOmata Formation, and an older sandstone-mud­stone sequence, the lowermost known unit of theKapuni Group, is here formally named the Kai­miro Formation.

Kapuni Group rocks occur across the TaranakiBasin. The majority of onshore wells drilled theupper part of the Kapuni Group, and several wellsdrilled the lower part of the group, but none of

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204 New Zealand Journal of Geology and Geophysics, 1985, Vol. 28

HORIZONTAL SCALE

10 3919m17)' 00' E

I

Fig. 4 Stratigraphiccolumns showing thethickness and distribu­tion of pre-Miocenesequence in TaranakiBasin. Total depthsare shown in metresbelow kelly bushing(m BKB).

39'oO'S

1:::·:.;.:·::::3 ABEL HEAD

0· KAPUNI GROUP.. EOUIVA l ENT

CD PAKAWAU

IJ!nJ] BASEMEN

f fAULlU UNCONf ORM ITY

Ul v -.

0' L;?,; TO 397Lm

,"~K~~e~ 1- . . -

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,~B

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174 00' E

New Plymouth -2

Formotlon ~g~

17400' E

I.: :..: JMAHO~N UI

~ TlKORAN(j1

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F:=:j TURI

~ KA PUN I GROUP

T 0 35L6 ..

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KapUni r.r .,up Equivotent

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Palmer-Pre-Miocene lithostratigraphy, Taranaki Basin

AMoa-1B

205

ATuri-1

OTAIAN pn MahoenuiLATE WAITAKIAN LLwEARLY WAITAKIAN e LwDUNTROONIAN Ld Tikorangi

WHAINGAROAN LwhRUNANGAN Ar

~Turi

KAIATAN AkBORTON IAN AbPORANGAN - HERETAUNGAN Do- DhMANGAORAPAN - WAIPAWAN Om-Dw Kapuni Group Equivalent

TEURIAN DIHAUMURIAN Mh ? ?

Rn~pinpn .

BTane-l

B'New Plymouth-Z Mangahewa-l

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c

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KAPUNIGROUP

PakawauBusernent

oMaui-4

Kaimiro

Otaraoa Tikorangi

0'Kupe-l

Fig. 5 (above, and bottom opposite page) West-east andnorth-south cross sections of pre-Miocene sequence inTaranaki Basin. The horizontal scale is shown in Fig. 4.

Abel Head

No Deposition.~

Pakawau

Basement

Oloraoa

KAPUNIGROUP--

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206 New Zealand Journal of Geology and Geophysics, 1985, Vol. 28

these wells have penetrated the base of the group.On some seismic records in the graben, acousticbasement reflectors occur at about 4 s two-way-time(TWT) which represents some 7000 m of sedi­mentary section. Several offshore wells have drilledthrough the Kapuni Group into the underlyingsequence, which is correlated with the PakawauGroup of northwest Nelson.

Jonkers et al. (1969) recognised Kapuni Grouprocks in the Maui-I well. Later, several correlatablehorizons were identified in the Maui Field and thesewere given informal names (Jonkers et al. 1970;McBeath 1977): the CI to C3 sands and C2 andC3 shales correlate with the upper part of theKapuni Group; the 01 shale correlates with theOrnata Formation.

Distribution of Kapuni Group rocks (Fig. 3) ismore regular than that of the older Pakawau Group.Their deposition was predominantly structurallycontrolled. The sequence is thickest in the centralTaranaki Graben and becomes thinner southwardsand westwards (Fig. 4, 5). The thickness, lateralcontinuity, and nature of the sediments comprisingthe Kapuni Group suggest that during Paleoceneand Eocene times large areas ofthe basin were sub­siding contemporaneously with deposition.

KAIMIRO FORMAnON (new)

Kaimiro Formation, named after the North Tar­anaki township of Kaimiro, is the lowermostrecognised formation of the Kapuni Group. It con­.sists predominantly of sandstone with interbeddedsiltstone and mudstone.

The interval from 4633 m to 5061 m BKB (totaldepth) in Inglewood-1 is designated the type sec­tion (Fig. 6). Here the formation consists of 428 mof light grey to grey, fine- to occasionally coarse­or very coarse-grained, poorly to moderately sorted,generally hard, in part argillaceous, in part calcar­eous sandstone with interbeds of dark blackishbrown, silty, sandy, micaceous, in part carbona­ceous mudstone (Gerlings & van der Abeele 1964).The sequence is unfossiliferous. However, agesestablished for the overlying Ornata Formation(defined below) indicate a Heretaungan or older agefor the Kaimiro Formation (Mcintyre & Norris1966; Hayward et al. 1982).

The upper contact of the formation is conform­able with the overlying Ornata Formation. OnshoreInglewood-I, Kaimiro-I, and possibly Kapuni-2reach the Kaimiro Formation, but they terminatein it, and the nature of the basal contact and of theunderlying sequence therefore is unknown. Off­shore, the lower part of the Kapuni Group has beenpenetrated (e.g., in Maui-4) and it conformablyoverlies the Pakawau Group. In the Maui Field,

the oldest producing sequence is sandstones withinthe Kaimiro Formation in the lower part of theKapuni Group. To date, this is the only locationwhere hydrocarbons are being produced from thelower part of the Kapuni Group.

OMAT A FORMAnON (new)

Ornata Formation, named after the North Taran­aki township, consists of mudstone and siltstone,considered to be marine, and overlies the KaimiroFormation.

The interval from 4616 m to 4633 m BKB inInglewood-1 is designated type section (Fig. 6). Itconsists of 17 m of dark brown, sandy, slightly cal­careous, slightly carbonaceous, in part glauconitic,silty, sandy, fossiliferous mudstone (Gerlings & vander Abeele 1964). Foraminifera, palynoflora, andmicroplankton from 4633 m indicate a Mangaor­apan-Heretaungan age (Mcintyre & Norris 1966;Hayward et al. 1982).

The lower boundary of Ornata Formation is con­formable with the Kaimiro Formation. The upperboundary is conformable with the MangahewaFormation. Few wells have drilled the Ornata For­mation and its distribution is therefore poorlyknown (Fig. 4, 5). The Heretaungan-Bortonianmudstone penetrated in the Maui Field (informallycalled the D1 shale) (Jonkers et al. 1969) is similarin age and lithology and is here correlated with theOrnata Formation. This mudstone is the cap rockof the lower part of the Kapuni Group reservoir inthe Maui Field. In Kapuni-2, the mudstone from3932 m to 3941 m is tentatively identified as OrnataFormation, and the New Plymouth-2 well termi­nated in the Ornata Formation. These correlationsare based on faunal and lithological comparisons.

MANGAHEWA FORMAnON (new)

Mangahewa Formation, named after the Manga­hewa-1 well, consists of a thick sequence ofinterbedded sandstone, siltstone, mudstone, andcoal. This, the lowermost formation. of the upperpart of the Kapuni Group, occurs wiffely across thebasin and is one of the primary exploration targetsin the basin.

The interval from 3742 m to 4616 m BKB inInglewood-1 is designated the type section (Fig. 6).Here, Mangahewa Formation consists of 874 m ofinterbedded fine- to occasionally coarse-grained,white to light brown to light grey to grey, poorlyto moderately well sorted, angular to subrounded,quartzose, in part calcareous, in part friable, occa­sionally glauconitic sandstone with fine argilla­ceous and carbonaceous laminae; occasional darkbrown, sandy, micaceous siltstone; light bluish grey

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Palmer-Pre-Miocene lithostratigraphy, Taranaki Basin 207

Fig.6 Type section of KaimiroFormation, thc interval from 4633m to 5061 m BKB in Inglewood­I ; Ornata Formation, the intervalbetween 4616 m and 4633 m BKBin Inglewood-I : and MangahcwaFormation, the interval between3742 m and 4616 m BKB inInglewood-L

CO-ORDINATES' N.I NATIONAL YARD GRID LOCATION M~373264 YOS N N." Plymout ~

INGLEWOOD -1 176 S31 YOS E.

HEV. Gl 310 m A.S L. R K.B. 316 m A5L . 1NGC:'

TOTAL DEPTH 506 1 m SPUD DATE 14·1· 63 1 0 . REACHEO 3 3·63

DEPTHAG ~ FORMATION LITHOLOGY

Im lr--

/\ "3700 ~ . :w v.;.

/314 1- 4616", MANGAHEWA FORMATIONH<KEE

3800H:KC:' ~

A seq ve oce of CQrbol'\Qe~u~ mud~tOf'lt·5

ol'\d cool eees ln tt"rcolott"d ..... Ith slig htlycc reereeus siltst ones a nd sand ston es .

3900 I I Cool beds Off up to 'Om th ick Of\dconsis t of high Yolat ile bituminou, ( 0'11.

4000 Ak-Ar ~ I ,

4100::;:;::::1 .1~MANGAHEWA 46 16 - ~ 6 33 m OMAlA fORMATION

420l>- . Ir I Dar k brown mudstone that is In part

I .: ..1.si lt y or sondy . mirac lP ous , sli ghtly

4300 calcar eous Qnd CQrbonouous : contai ns

- J__ 'J globular glaucon ite Qnd foraminife ra4400

4500 Ab-Ak:::.- ~. ~ .: .:" :-::-:r:"'"'' ,,,,,,ro,

4600 1~

.:';::. -:::".:::::::.:'; li ght gre y fa qrey . 'In e to eeer segra ined, poorl) sor red sandsron e wi rh

4700

IIm~:"" 7~I nter beds of dark blac kISh bro wn,silty mudst one

L800KAIMIRO It(~ -

4900 Ow-Oh

H? ~SOOO I :\?i~:{)

Toio l O.pth 5061",5100

to brownish grey to dark brown carbonaceousmudstone that is often silty or sandy and occa­sionally calcareous; and black, bituminous coalseams from a few centimetres to 10 m thick (Ger­lings & van der Abeele 1964).

Two palynofloral samples, taken in the intervalfrom 4368 m to 4538 m in Inglewood-l , have beenanalysed (Mcintyre & Norris 1966; Hayward et al.1982). The species present and their relative abun­dances suggest a Bortonian-Kaiatan (Middle-LateEocene) age (Mcintyre & Norris 1966).

At its type section, Mangahewa Formation con­formably overlies Ornata Formation , with the lowerboundary being the top of the marine mudstone.The formation is conformably overlain by theMcKee Formation, the upper boundary being thetop of the uppermost coal measure cyclothemencountered.

Mangahewa Formation has been penetrated byexploration and production wells in Taranaki Basin.It is thickest in the eastern part of the graben andthins to the south and west (Fig. 4, 5). The sedi­ments deposited in the eastern part of the basin aretypically coal measure with siltstone and mudstoneand minor sandstone. Less coal was deposited inthe west, and some sandstone beds are well

developed to the west. Good reservoir sandstonesare present in the Maui Field. However, rapid facieschanges make it unlikely that the good reservoirproperties present at Maui will be continuous overlarge distances. In onshore Taranaki, individualsandstone units within the coal measures cannot besatisfactorily correlated more than severalkilometres .

McKEE FORMATION (new)

McKee Formation, named after the McKee-I well,is the uppermost formation of the Kapuni Group.The interval from 2130 m to 2220 m along hole(AH) in McKee-3A is designated the type' section(Fig. 7). Here, McKee Formation consists of 90 mof white to very light grey to medium light grey,fine- to coarse-grained, moderately well sorted, firmto friable, quartzose sandstone with occasionalclasts of dark brown, fissile mudstone (especiallyin the upper 20 m), fragments of black, brittle coalwith subconchoidal fracture, and interbeds of milky­white, calcareous cemented sandstone (Palmer &Beardman 1983). No satisfactory age determina­tions have been obtained for the unit because ofits sandy nature. However, a Runangan-early

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208 New Zealand Journal of Geology and Geophysics, 1985, Vol. 28

LATITUDELONGITUDEMcKEE-3A

TOTAL DEPTH 2250 m

COORDINATES:

ELEV GL. 150m A.SL.SPUD DATE 18 - 11- 81

39 0 05' 45" S174 0 19' 59" E

R.K B. 160m A.SL.TO. REACH ED 14-12 -81

New Plymout h

LOCATION MAP

NEUTRON DENSIT Y %30 LIMESTONE MATRIX 0

DEPTH1- - - - - - - T - - - - - - -

': .' ."".,.. . . ..

DE SCR IP TIO N

"; " ." . ". '- ..

p'l 2123 - 2130m TURI FORMATION

. . . . I}I-2130 - 2120 m McKEE FORMATIONWhite ro ver y light gr ey to medium tig ht gr ey .f ine t o coarse grained . f r ia ble to f i rm ,moder a te ly 'W elt so r ted . qua r tzo se sa nd s to nr .Conta in s scatte r ed coal f r agmen ts and da rlc.brown mudstone cla sts .OccQsiona l Inter beds of mi lky . Wh i te calcar eouss c n d s t e ne , m ed ium to dar k bro w n . c ar b e nec ee u s .

f iss il e muds t one . a nd bla ck br it t le coal wit hsun - conchoidal f raou t e .

.... .-_-: -:-~

~' :' : :~ , :. :• • • • ' , ;:Z;: .

~

.;.:": ~ :.:

. .- '

py..,. "'!i '

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I ~;:~ ·; ::

BULK DENSITY g/ cm '

2 '45 2' 10

. ~:~

2 20

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2100

2150

2200

1125

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1175

50 100

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20

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TURI

:Mat;p-;-I Ss t mbr .1-

OTARAOA

MANGAHEWA

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Lw h

Fig. 7 Type section of McKee Formation, the interval from 2130 m to 2220 m along hole BKB in McKee-3A.McKee-3A was a directionally drilled deviated well, hence the along hole depths.

Whaingaroan age is inferred from its stratigraphicposition (Hayward & Mildenhall 1980; Hayward1982).

At the type section, the lower boundary is thebase of the sandstone unit which conformablyoverlies the uppermost coal measure cyclothem ofthe Mangahewa Formation. The upper boundary

is conformable with the overlying massive mud­stones of the Turi Formation.

McKee Formation, distinguished by its predom­inantly sandy lithology, is widely distributed overTaranaki Basin (Fig. 4, 5) and comprises the res­ervoir beds of the McKee Field. McKee Formationis an inner shelf-coastal sediment.

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Palmer-Pre-Miocene lithostratigraphy, Taranaki Basin 209

Marine equivalent of the Kapuni GroupSeveral offshore wells have encountered a sequenceof marine siltstone and mudstone that is a laterallyequivalent facies to the Kapuni Group. Beddoes &Watson (1969) described the Eocene-Paleocenemarine siltstone and mudstone sequence in Moa­IB. Subsequent wells have encountered a similarsequence and these beds were called the KapuniFormation Equivalent (Hematite and Shell BP andTodd Oil Services Ltd 1975; Shell BP and ToddOil Services Ltd 1977). In Tane-I, this interval wasdivided into three distinct units. In descendingorder they are Tane Siltstone Member, Kaiata For­mation, and Island Sandstone (Shell BP and ToddOil Services Ltd 1977). The subdivision was infor­mal and does not correlate directly with other off­shore wells. Island Sandstone is a brown, calcareoussandstone from the Greymouth region of the West­land Basin (Nathan 1974). Island Sandstone doesnot occur beyond the Greymouth area of the SouthIsland (Nathan 1974); it is impractical to apply thename to a localised occurrence of a similar unit atTane-l, some 400 km NNE of Greymouth.

Few wells have encountered the marine rocks(Fig. 2, 3) laterally equivalent to the Kapuni Group.The real extent of these is poorly known, but indi­cations are that they are thickest and most wide­spread in the north and northwest of the basin (Fig.4, 5). The division into three units (by Shell BPand Todd Oil Services Ltd) has not been adoptedhere. Further information is needed before subdi­vision should be attempted. Hence the nameKapuni Group Equivalent is used.

TURI FORMAnON (new)

Turi Formation is a marine mudstone named afterthe Turi-l well drilled offshore in North Taranaki.

Jonkers et al. (1969) described a distinctive, darkbrown, massive mudstone in the Maui-l well. Thisunit was given the informal name Cl shale by ShellBP and Todd Oil Services Ltd and later becameknown as the Kaiata Formation (Pilaar & Wake­field 1978). The term Kaiata Formation or KaiataMudstone is widely used in the Westland and Bullerareas of the South Island (Nathan 1974). KaiataFormation is the name applied to all dark brown,micaceous, muddy sediments between the under­lying Island Sandstone or Brunner Coal Measures(where the Island Sandstone is missing) and theoverlying Cobden Limestone or its correlatives (Fig.8) (Nathan 1974). Kaiata Formation is not foundin the Nelson area or the northwest of the SouthIsland, making it impractical to apply the name toa possible correlative in Taranaki Basin, some 300­400 km to the northwest of its type area, Westland.The marine mudstone encountered in Taranaki

Basin that has become known as the Kaiata For­mation is defined here as the Turi Formation.

The interval from 3472 m to 3479 m in Man­gahewa-l (Fig. 9) is designated the type section.Here, Turi Formation consists of 7 m of massive,brown grey to medium dark grey, slightly to noncalcareous, in part carbonaceous, micaceous mud­stone (van Rijen & van der Abeele 1963). Logsexhibit a low resistivity response (Fig. 9) and a highgamma ray response (Fig. 7) across the Turi For­mation in central and eastern Taranaki in particu­lar. The high gamma ray response is due tocarbonaceous material and mica concentrated inthe fine-grained sediment. In offshore wells, thegamma ray response is not as high, probablybecause organic material and mica were not depos­ited in such concentrations in the deeper waterenvironment. A core recovered from the Turi For­mation at Mangahewa-l contains Whaingaroanforaminifera, and fragments of bryozoans and gas­tropods are present at 3472 m (Hogan 1979).

In the Mangahewa-l well, the lower boundary ofTuri Formation is conformable with sandstone ofthe McKee Formation. The top of the unit is con­formable with the Matapo Sandstone Member ofthe overlying Otaraoa Formation.

Turi Formation, an inner-middle shelf mud­stone in onshore wells and a middle-outer shelfdeposit in offshore wells, is present over much ofthe Taranaki Graben and on the Western Platform(Fig. 4, 5). It is a lateral time equivalent of theWhaingaroa Siltstone of Waitomo County to thenortheast. The two units are, however, lithologi­cally different and geographically isolated.

OT ARAOA FORMATION (new)

Otaraoa Formation, named after Otaraoa Road innortheast Taranaki, consists of a sequence of cal­careous siltstone and mudstone first described byvan Rijen & van der Abeele (1963) in Mangahewa­1. The sequence was encountered in later wells andwas named the Lower Mahoenui Formation byAdams et al. (1980). The Mahoenui Group wasdefined from outcrop as "all those calcareous mud­stones, sandstones, siltstones and limestones ...above the Te Kuiti Limestone or its lateral equiv­alent and older than the unconformity or discon­formity found at the base of the Mokau Formation"(Glennie 1956; Kear & Schofield 1959). This paperrecognises that Tikorangi Formation, defined here,is a correlative ofTe Kuiti Limestone and is there­fore overlain by Mahoenui Group. It is further pro­posed that a new name, Otaraoa Formation, begiven to the sediments named Lower MahoenuiFormation by Adams et al. (1980).

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Palmer-Pre-Miocene lithostratigraphy, Taranaki Basin 211

DESCRIPTION

3213-3250m T1KORANGI FORMATIONBlue- grey sandy Limestone. calcareoussandstone and white crystallinelimestone interbedded with culcureousmudstone

3250- 3472m OTARAOA FORMATIONGrey, very calcareous, silty mudstone.f.- =­

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The interval from 3250 m to 3472 m BKB inMangahewa-I is designated the type section for theOtaraoa Formation (Fig. 9). It consists of 214 mof grey, very calcareous, silty mudstone (van Rijen& van der Abeele 1963). It is conformably under­lain by 8 m of very glauconitic sandstone. At itstop, the formation is conformably overlain bylimestone of the Tikorangi Formation. Microfaunafrom cuttings in Mangahewa-I give a Waitakian­late Whaingaroan age for the formation (Cope1963).

One subdivision, the Matapo Sandstone Mem­ber, is recognised at the base of the Otaraoa For­mation. Its type section is Mangahewa-I well,between 3464 m and 3472 m, where it consists oflight greenish grey, medium- to coarse-grained, very

glauconitic, in part calcareous, quartzose sandstone(van Rijen & van der Abeele 1963). The base isconformable with the underlying Turi Formation.

Otaraoa Formation is restricted to the TaranakiGraben (Fig. 4, 5). In the north, it overlies the TuriFormation. To the west, on the Western Platform,Turi Formation is its time equivalent. It is lithol­ogically similar to, and the time equivalent of, theAbel Head Formation of the South Taranaki Gra­ben and its onshore extension in the northwest ofthe South Island (Pilaar & Wakefield 1978). Thetwo units are, however, geographically isolated.

Matapo Sandstone Member is known only fromwells drilled onshore and is thickest in central andnortheast onshore Taranaki. This member is avaluable marker horizon. It is a lateral equivalent

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214 New Zealand Journal of Geology and Geophysics, 1985, Vol. 28

of, but lithologically different and geographicallyisolated from, the Aotea Sandstone of WaitomoCounty to the northeast (Nelson 1978).

The Turi and Otaraoa Formations mark thebeginning of a major marine transgression in cen­tral Taranaki Basin. Marine conditions existed inthe north and west of Taranaki Basin during LateCretaceous-Paleocene times and reached centralTaranaki by the Late Eocene-Oligocene.

TIKORANGI FORMATION (new)

Tikorangi Formation is a deep-water, bioclasticlimestone named after the North Taranaki town­ship of Tikorangi. It was first encountered in theMangahewa-l well. Van Rijen & van der Abeele(1963) described a limestone within the Mahoenui"Formation" in Mangahewa-l. A similar sequencehas been encountered in subsequent wells in thearea. The names Tikorangi Member (van Rijen &van der Abeele 1963) and Tikorangi Limestone(Pilaar & Wakefield 1978)have been applied infor­mally to the limestone. Van Rijen & van der Abeele(1963) recognised the correlation between Tiko­rangi Limestone and Te Kuiti Limestone but con­sidered the Tikorangi Limestone was a member ofthe Mahoenui "Formation". Later, the informalsubdivision of Upper Mahoenui Formation, for thebeds overlying the limestone, and Lower MahoenuiFormation, for those beneath, was adopted (Adamset al. 1980). This paper proposes the name Tiko­rangi Formation for the limestone, with MahoenuiGroup restricted to the sequence overlying (asdefined by Glennie (1956) and Kear & Schofield(1959», and Otaraoa Formation applied to the siltymudstone immediately underlying, the TikorangiFormation.

The interval from 3213 m to 3250 m BKB inMangahewa-l is designated the type section (Fig.9). Here, Tikorangi Formation consists of 37 m ofblue-grey, sandy limestone, calcareous sandstone,and white crystalline limestone interbedded withcalcareous mudstone (van Rijen & van der Abeele1963). The microfauna in cuttings samples fromMangahewa-l indicate a Waitakian age (McIntyre1962; Cope 1963).

At the type section, Tikorangi Formation is con­formable on the calcareous siltstone and mudstoneof the underlying Otaraoa Formation. The upperboundary is conformable with the calcareous mud­stone of the overlying Mahoenui Group.

Tikorangi Formation is a bioclastic, deep-waterdeposit that is widespread on the Western Platformand in the north and east of the Taranaki Graben(Fig. 4, 5). A lateral equivalent, the Takaka Lime­stone, is present in the South Taranaki Basin andnorthwest of the South Island. The Takaka Lime-

stone is an inner-middle shelf deposit (Leask 1980).Further north, the Takaka Limestone grades to adeep-water calcareous mudstone which geograph­ically isolates it from the Tikorangi Formation (Fig.8).

PALEOGEOGRAPHY FROM CRETACEOUSTO EARLY MIOCENE

During the Late Cretaceous and Paleocene, largeareas of Taranaki Basin lay above or very near sealevel (Fig. 10). The sediments deposited were pre­dominantly coal measures and coastal plain depos­its. The oldest sediments, the Cretaceous PakawauGroup coal measures, are sporadically distributedacross the basin (Fig. 3). The predominantly ter­restrial sediments were deposited in fault-angledepressions formed by normal faulting of base­ment (Pilaar & Wakefield 1978).These and the LateCretaceous-Early Oligocenecoal measure sequencesare the primary exploration objectives in the Tar­anaki Basin.

The Kapuni Group is a Paleocene-Oligocenesequence comprised of a lower sandstone-mud­stone sequence, the Kaimiro Formation (Dh orolder); overlain by a marine mudstone, the OmataFormation (Dm-Dh). The coal measure sequence,the Mangahewa Formation (Dp-Ak), is overlain byan estuarine to shallow marine sandstone sequence,the McKee Formation (Ar-Lwh). In the easternTaranaki Basin, the sediments are lagoonal-flood­plain-coastal deposits, whereas westwards, thesediments exhibit more marine influences. TheOligocene Turi (Lwh) and Otaraoa (Lwh-Lw) For­mations and the Late Oligocene-Early MioceneTikorangi (Lw-Po) Formation were deposited in amarine environment.

Paleoenvironmental reconstruction of TaranakiBasin (Fig. 10) shows a major pre-Miocene marinetransgression. This transgression commenced inLate Cretaceous-Paleocene times and progressedthrough to the Miocene. Drilling and regionalseismic data indicate that, during the Late Creta­ceous and Paleocene, the Taranaki Basin was anarea oflow relief with a gentle, generally westward,slope. At the beginning of the Eocene, the sea beganto encroach southeastward onto this landmass (Fig.10). Shallow marine sediments were deposited inclose association with terrestrial sediments. The seacontinued to transgress during the Eocene and Oli­gocene, and by Early Miocene time, the basin laybeneath a sea of bathyal depth (Fig. 1'0).

The stratigraphic correlation of the sequencesalong the west coast of New Zealand (Fig. 8) showsclose similarities between the sequence of the Tar­anaki Basin, the Waitomo County to the northeast(Nelson 1978),and the Westland Basin to the south

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Palmer-Pre-Miocene lithostratigraphy, Taranaki Basin 215

(Nathan 1974). During Late Cretaceous-Miocenetimes, similar conditions prevailed along the lengthof the western margin of New Zealand.

The Cretaceous-Early Miocene stratigraphicsequence described for Taranaki Basin (Fig. 2, 3)is a regressive-transgressive sequence.

The environments of deposition of the strati­graphic units range from bathyal to outer shelf,through shallow marine, to lagoonal or terrestrial.Interfingering marine and non- to marginal marinesediments indicate a fluctuating but generallytransgressive shoreline that progressed from thenorthwest to the southeast.

Local variations in the sequence were controlledby the paleorelief, relative tectonic movementsbetween the source and depositional areas, prox­imity to the coast and the source rocks, and thenature of the source rocks. Because of all thesefactors, rapid facies changes occur both locally andregionally, and different formations are laterallyequivalent.

ACKNOWLEDGMENTS

The author thanks Dr T. Haskell and fellow staff ofPetro­corp (Exploration), Mr D. Haw of BP Exploration, andMr G. Pearce of Shell BP and Todd Oil Services Ltd fortheir useful comments. Special thanks also to Mr D. Pim­blott and the drafting section of Petrocorp (Exploration)for their assistance in preparing the diagrams.

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