petroleum geochemistry of NZ

ABSTRACT

From a basin-wide evaluation of organic geo-chemical data, it has been possible to characterizeand differentiate various source rock units and toestablish the genetic relationships of oils. Most ofthe oils are primarily terrestrially sourced, and it ispossible to recognize varying contributions fromsource rocks within the Paleogene Kapuni Groupand late Cretaceous Pakawau Group. This distinc-tion is attributable to the rise to dominance ofangiosperms over gymnosperms in coastal plainswamp communities by the Eocene. Apart from theMaui family (i.e., Maui field, Maui-4, and Moki-1)oils, the inferred relative contributions from themain source rock types generally correlate with therelative proportions of suitably thick and matureunits near reservoirs, given that most Cretaceous-sourced oil appears to have escaped prior to trapdevelopment. Maui family oils do appear to be pri-marily sourced by Rakopi Formation (late Creta-ceous) coals. In the northern part of the TaranakiPeninsula, where heat flows are highest, Mangahe-wa/Kaimiro Formation (Eocene) coals are the chiefsources of oils. Farther south, in the Kapuni andKupe South fields, Farewell Formation (Paleocene)coals appear to be the main oil source rocks.Biomarkers suggest that the onset of oil expulsionfrom coals occurs at a maturity level correspondingto a vitrinite reflectance of ca. 0.8% Ro, and may beaided by the evolution of large volumes of carbondioxide. The terrestrial inf luence on Paleogenesource rocks diminishes to the north-northwest ofthe basin and increasing marine contributions tooils are observed. A late Paleocene marine blackshale is the source of oil in the Kora volcanic struc-

ture. It is possible that shales interbedded withcoals, ref lecting periodic marine incursions ofcoastal flood plains, also contribute to oil genera-tion throughout much of the basin.

INTRODUCTION

The Taranaki Basin, which can be divided intothe Western Stable platform and the Eastern Mobilebelt, covers an area of some 100,000 km2 lying offthe west coast of the North Island of New Zealandand extending under the post-Pliocene volcanicdeposits of the Taranaki Peninsula (Figure 1). It isthe primary petroleum-producing basin of NewZealand, with an estimated 1678 × 106 bbl of recov-erable petroleum (1213 × 106 bbl equivalent of gas,210 × 106 bbl of condensate, 255 × 106 bbl of oil) inthe main fields (Figure 1 and Table 1). Oil accumu-lations are commonly accompanied by large vol-umes of gas and condensate, and all petroleum dis-coveries to date have been associated withstructural traps developed during the Neogene.Reservoirs include Eocene coastal/shore sand-stones, Oligocene to early Miocene fractured lime-stones, Miocene volcaniclastics, and Miocene-Pliocene turbiditic/fan sandstones (Bennett et al.,1992). Potential reservoir capabilities are alsodemonstrated by Late Cretaceous sandstones.

On the basis of organic content, hydrogen rich-ness, and maturity constraints, the coals of the Paleo-gene Kapuni Group, and in particular the Late Creta-ceous Pakawau Group, have been considered themost likely petroleum source rocks (e.g., Cook,1987; Johnston et al., 1990; Thrasher, 1992). Atten-tion has been paid, therefore, to the organic geo-chemistry of these coaly sediments in order to corre-late oils and their source rocks (for which biomarkeranalysis is a powerful tool) and to determine matura-tion history and petroleum-expulsion characteristics.Previous biomarker studies have mostly centered onthe ubiquitous hopanes and steranes, and only limit-ed source information has been gained, mainly fromthe relative abundance of the angiosperm-derivedcompound 18α(H)-oleanane (e.g., Cook, 1987;Cook, 1988; Czochanska et al., 1988; Johnston et al.,

1560 AAPG Bulletin, V. 78, No. 10 (October 1994), P. 1560–1585.

©Copyright 1994. The American Association of Petroleum Geologists. Allrights reserved.

1Manuscript received July 27, 1993; revised manuscript received May 4,1994; final acceptance May 27, 1994.

2Institute of Geological and Nuclear Sciences, P.O. Box 30368, LowerHutt, New Zealand.

3Industrial Research Ltd., Gracefield Research Centre, P.O. Box 31310,Lower Hutt, New Zealand.

We wish to thank colleagues at IGNS, particularly Rick Allis and RobFunnell, and also Phil Armstrong, University of Utah, and Vanessa Killops forhelp in the preparation of this article.

A Geochemical Appraisal of Oil Generation in theTaranaki Basin, New Zealand1

S. D. Killops,2 A. D. Woolhouse,3 R. J. Weston,3 and R. A. Cook2

1991). More recently, the source-specific potential ofgymnosperm-derived diterpanes (Weston et al.,1989) and various angiosperm-derived triterpanes(Woolhouse et al., 1992) has been recognized andpartially applied in subsequent correlation studies(Johnston et al., 1990; Collier and Johnston, 1991;Johnston, 1992), but precise oil-to-source-rock corre-lation has still proven elusive. The study reported inthe following sections attempts to use source indica-tors to determine genetically related families of oilsand to identify their most likely source rocks. Basin-wide oil generation and expulsion is then consid-ered in the light of the distribution and maturity ofpotential source rock units.

The geology of the Taranaki Basin is complex(e.g., King, 1990; Palmer and Bulte, 1991; King

and Thrasher, 1992), and the following summa-rizes the depositional environment of potentialsource rocks and their spatial and temporal rela-tionships with traps. Extension of the Paleozoic tomiddle Cretaceous basement began ca. 80 m.y.a.and led to the development of north-northeast–trending subbasins (up to 100 km long by 30 kmwide), in which up to ca. 3000 m of Late Creta-ceous sediments accumulated. These are the ter-restrial sediments of the Pakawau Group, whichare thicker to the west of the basin and include thecoals of the Rakopi Formation (Figure 2). Towardthe end of the Cretaceous, a rapid, southeast–trending, marine transgression resulted in deposi-tion of the mudstones and sandstones of the NorthCape Formation (Figure 2).

Killops et al. 1561

Figure 1—The Taranaki Basin and its major petroleum fields, structural features, well locations, and heat-flow pat-terns. (A) Petroleum fields and main fault systems. (B) Well locations and heat-flow patterns. (Heat flow after Allis,personal communication. Location of cross sections in Figures 10 and 11 also shown. Ari = Ariki-1, Awk = Awakino-1, Fre = Fresne-1, Kai = Kaimiro-1 and 2, KDp = Kapuni Deep-1, Kpe = Kupe-1, KS4 = Kupe South-4, McK = McKee-1and 3A, NP2 = New Plymouth-2, Tne = Tane-1, Tng = Tangaroa-1, Wai = Waihapa-1 and 2, Wit = Witiora-1; see Table 2for other well abbreviations. Republic New Plymouth wells 1 and 4 lie close to New Plymouth-2.)

(A) (B)

Tectonic activity waned during the Paleocene,resulting in continued marine incursion. Exten-sional faulting ceased by the end of the Paleocene,subsequent passive-margin cooling and subsidenceled to a southwest-directed marine transgressionover coastal plains, and sediment supply dimin-ished. During the tectonic quiescence of the Paleo-gene, the terrestrial sediments of the KapuniGroup were deposited, dominated by sandstonesand lower f lood plain coal measures with someshales. Four regressive cycles have been recog-nized in which coastal/marginal marine sand-stones pass upward into coal-bearing intervals(e.g., Johnston et al., 1990). The Kapuni Group isextensive in the southeast of the basin (Farewell,Kaimiro, Mangahewa, and McKee formations, Fig-ure 2), whereas to the north and northwest amarine equivalent can be recognized in the dark-brown to gray, partly carbonaceous and mica-ceous, marine siltstones and mudstones of the TuriFormation (Figure 2). In the northwest, theEocene/Oligocene Tangaroa Formation representsa sandy submarine-fan complex. The transgressionreached a maximum in the early Oligocene, cover-ing the entire basin and marking the culminationof passive-margin subsidence. The terrigenous sup-ply of sediment became limited. However, rapidsubsidence recommenced in the mid-Oligocene.Oligocene sedimentation is characterized by lime-

stones of the Tikorangi Formation and mudstones,siltstones, and sandstones of the Otaraoa Forma-tion (Figure 2).

In the early Miocene, uplift of the hinterland andoverthrusting along the eastern margin led toincreased sediment supply and a regressive sedi-mentation pattern, which has persisted to the pres-ent. The Manganui Formation represents mud-stones deposited off the shelf edge, whereas theMoki Formation comprises slope-fan sandstones(Figure 2). The Mohakatino Formation in the north-ern part of the basin consists mainly of stratifiedvolcaniclastic deposits of the middle to lateMiocene, derived from andesitic volcanoes associ-ated with subduction of the Pacific plate. Along thenortheast margin of the basin, turbiditic sandstonesof the Mount Messenger Formation were deposit-ed, overlain by finer slope sediments of the UrenuiFormation (Figure 2). At this time, compression inthe south of the basin initiated the inversion ofexisting structures. Renewed uplift of the easternhinterland increased the sediment supply duringthe Pliocene–Pleistocene, with the accumulation ofshelf conglomerates, sandstones, and mudstones ofthe Matemateaonga Formation in the east and theGiant Foresets Formation (prograding shelf mud-stones and minor sandstones) farther west, the lat-ter representing most of the sediment on the West-ern Stable platform (Figure 2).

1562 Oil Generation in the Taranaki Basin

Table 1. Proven, Recoverable, Petroleum Reserves in the Taranaki Basin*

GasField Reservoir Oil Condensate (106 bblor Well Formation (106 bbl) (106 bbl) oil equivalent)

Kora Mohakatino 1 – –Mangahewa Mangahewa – – 2Moturoa Matemateaonga <1 – –Kaimiro Mt. Messenger na na na

McKee – 1 6Ngatoro Mt. Messenger 1 – <1Stratford McKee/Mangahewa – 1 4Urenui-1 McKee – – 6McKee McKee 38 – 20Tariki Otaraoa – 2 10Ahuroa Otaraoa – 1 5Waihapa Tikorangi 21 – 4

Kaimiro – <1 3Ngaere Tikorangi 6 – 1Kapuni Mangahewa – 55 196Toru Farewell 7 – 20Kupe South Farewell 128 – 144Maui Mangahewa/Kaimiro – 151 792

Farewell 10 – –Moki Moki 36 – –Maui-4 Mangahewa 7 – –

*1 bbl oil equivalent = 150 m3 gas. See Figure 1 for field locations. na = data not available.

MATERIALS AND METHODS

The locations of wells from which oils/conden-sates and organic-rich sediment samples weretaken are shown in Figure 1. Wells and formationsfrom which oil/condensate (DST or production)samples were taken are listed in Table 2. Samplesfrom Kapuni-2, Maui-3, Toru-1, Urenui-1, and Wai-hapa-1A are classified as condensates, whereas sam-ples from Okoki-1, Pukearuhe-1, and Tangaroa-1 areoil shows. Additional biomarker analyses were car-ried out on condensates and oils from Kupe Southwells 2–5; a condensate from Maui-1; oils fromMcKee wells 1, 2A, and 4; and oil from Toetoe-2. Allthese samples were found to be chemically almostidentical to other samples from the fields con-cerned and so are not considered further here.

Cuttings were selected from the following for-mations: Farewell (Kapuni Deep-1, Kupe-1, KupeSouth-1, Kupe South-4, and Maui-4); Kaimiro(Kaimiro-1, Kapuni Deep-1, Maui-4, and Waihapa-1); Mangahewa (Kaimiro-1, Kapuni Deep-1, McKee-1, Maui-4, Urenui-1, and Waihapa-1); North Cape(Kupe South-4, Maui-4, and Tane-1); Rakopi (Fresne-1, Maui-4, and Tane-1); and Turi (Ariki-1, Awakino-1, Kaimiro-1, and Witiora-1). For some samples, acoal fraction was separated from shale by a rapid

flotation method using a carbon tetrachloride/hex-ane mixture with a density of 140 kg⋅m–3. Afterbeing milled to a fine powder, sediment sampleswere solvent-extracted using either Soxhlet extrac-tion or ultrasound. Saturate fractions were isolatedfrom oils and sediment extracts by TLC on silica gelwith hexane eluant. Where necessary, n-alkaneswere removed from saturate fractions by 5Å molec-ular sieve or urea adduction prior to gas chro-matography–mass spectrometry (GCMS) analysis ofbiomarkers using columns coated with 5% phenyl-methylsilicone stationary phase and monitoring ofselected ions. Relative biomarker abundance wascalculated from peak heights in m/z 123 (sesquiter-panes and diterpanes), m/z 191 (triterpanes,including hopanes), and m/z 217 (steranes) masschromatograms. From these data, the followingindices and ratios were obtained (see Figure 4 leg-end for key to compound abbreviations).

Angiosperm/gymnosperm index:

Killops et al. 1563

Figure 2—Generalized stratigraphy ofthe Taranaki Basin (after Bennett et al.,1992), showing main oil/condensateaccumulations. (KS = Kupe South fieldoils; MK = oils from McKee-3A, Pouri-1A, Pukemai-2A, Stratford-1, Toetoe-1and Urenui-1; Mu = oils from Maui-1and Maui-3; NP = oils from Moturoa-2,Republic New Plymouth-1, RepublicNew Plymouth-4 and Taranaki-5; seeTable 2 and Figure 1 legend for otherwell abbreviations.)

AGI = m/z191 (O + dO + dL + dU)

m/z123 ( L + R + NT + B +18NIP +19NIP + IP + P

m/z123 (IP)m/z191 (IP)

∑∑

×

β β

1564 Oil Generation in the Taranaki BasinT

able

2.

Geo

chem

ical

Ch

arac

teri

stic

s o

f W

ho

le-O

ils*

AP

ISa

ts.

δ13 C

δ13 C

δ13 C

δ34 S

Wel

lR

eser

voir

grav

ity

SH

C(%

of

Sats

.A

rom

s.T

ota

lT

ota

lV

Pr

Ab

br.

Fiel

dFo

rmat

ion

(°

)(%

)(%

)H

C)

(‰)

(‰)

(‰)

(‰)

V +

Ni

Ph

CP

I

Ko

ra-1

Ko

rK

ora

Mo

hak

atin

o35

0.27

9469

–23.

6–2

2.0

–22.

9–8

.0–

2.5

1.0

Tan

garo

a-1

Tn

gT

uri

––

––

––

–23.

7–

–2.

71.

1P

uke

aru

he-

1P

khB

asem

ent*

*30

0.18

9576

28.2

––2

7.5

+6.

00.

985.

71.

2O

koki

-1O

koM

anga

hew

a–

–75

40–

–26.

3–

––

5.5

1.1

New

Ply

mo

uth

-1N

P1

Mo

turo

aM

atem

atea

on

ga34

0.09

9375

(–28

.2)

(–26

.5)

(–27

.2)

+3.

01.

007.

01.

1N

ew P

lym

ou

th-4

NP

4M

otu

roa

Mat

emat

eao

nga

320.

0890

82(–

28.2

)(–

26.4

)(–

27.5

)+

6.4

–7.

21.

2T

aran

aki-5

Trn

Mo

turo

aM

atem

atea

on

ga31

0.07

9275

–28.

8–2

6.8

–28.

1+

12.7

–5.

91.

1M

otu

roa-

2M

ot

Mo

turo

aM

atem

atea

on

ga37

0.08

9176

–28.

8–2

6.6

–28.

0+

4.7

–7.

01.

2

Man

gah

ewa-

1M

anM

anga

hew

aM

anga

hew

a41

0.07

9583

–28.

2–2

5.9

–27.

5–

–6.

01.

1K

aim

iro

-1K

m1

Kai

mir

oM

cKee

420.

1085

76–2

8.3

–26.

1–2

7.6

+14

.1–

6.6

1.1

Kai

mir

o-2

Km

2K

aim

iro

Mt.

Mes

sen

ger

–0.

05–

––

––2

7.4

+11

.4–

6.5

–N

gato

ro-1

Nga

Nga

toro

Mt.

Mes

sen

ger

–0.

06–

––

––2

7.4

+11

.8–

4.5

–St

ratf

ord

-1St

rSt

ratf

ord

McK

ee–

0.10

9386

–28.

8–2

6.4

–28.

3+

8.6

–9.

2–

Ure

nu

i-1U

reU

ren

ui

McK

ee o

vert

hru

st48

–92

86–2

8.4

–26.

2–2

8.0

––

9.0

1.1

Tu

hu

a-1

Tu

hM

cKee

McK

ee o

vert

hru

st38

0.16

9387

–28.

7–2

6.3

–28.

0+

9.4

–8.

21.

1P

ou

ri-1

AP

ou

McK

eeM

cKee

ove

rth

rust

370.

1094

86–2

8.7

–26.

5–2

8.3

+13

.3–

7.4

1.2

Pu

kem

ai-2

AP

kmM

cKee

McK

ee o

vert

hru

st–

0.13

9382

–28.

6–2

6.4

–28.

0+

10.6

–7.

21.

2M

cKee

-3A

MK

3M

cKee

McK

ee o

vert

hru

st39

0.08

9687

–28.

8–2

6.4

–28.

2+

13.3

–7.

51.

1T

oet

oe-

1AT

oe

McK

eeM

cKee

ove

rth

rust

–0.

2489

85–2

8.8

–26.

6–2

8.4

+12

.41.

008.

31.

2

Tar

iki-1

AT

ikT

arik

iO

tara

oa

–0.

15–

––

––

+8.

11.

007.

61.

2A

hu

roa-

1A

hu

Ah

uro

aO

tara

oa

–0.

10–

––2

8.8

–26.

3–2

8.1

+13

.8–

7.4

1.2

Wai

hap

a-1A

Wp

1W

aih

apa

Kai

mir

o47

0.03

7776

–28.

5–2

6.0

–27.

7+

11.3

–7.

91.

1W

aih

apa-

2W

p2

Wai

hap

aT

iko

ran

gi–

0.08

––

––

–28.

0+

15.1

–8.

0–

Kap

un

i-2K

apK

apu

ni

Man

gah

ewa

480.

0694

81–2

8.4

–26.

4–2

7.9

+15

.6–

8.2

1.1

To

ru-1

To

uT

oru

Fare

wel

l0.

0295

87–

––

––

7.2

1.1

Ku

pe

Sou

th-1

KS1

Ku

pe

Sou

thFa

rew

ell

230.

1284

92–2

8.4

–26.

4–2

7.5

+16

.3–

6.3

1.1

Mau

i-3M

u3

Mau

iM

anga

hew

a48

0.08

8779

(–27

.1)

(–26

.2)

(–26

.5)

––

9.0

0.9

Mau

i-1M

u1

Mau

iM

anga

hew

a44

0.06

9493

–27.

8–2

6.2

–27.

3+

13.2

1.00

6.1

1.3

Mo

ki-1

Mki

Mo

kiM

oki

370.

1181

77–2

7.9

–26.

1–2

7.3

+9.

6–

8.3

1.2

Mau

i-4M

u4

Mau

i-4M

anga

hew

a44

0.30

8984

–28.

1–2

6.2

–27.

4+

13.7

0.99

8.3

1.2

*Dat

a fo

r T

anga

roa-

1 af

ter

Gib

bons

et

al.,

1981

; fo

r O

koki

-1 a

fter

Ana

labs

, 19

89;

and

for

Tor

u-1

afte

r A

nala

bs,

1991

. O

ther

car

bon

isot

opic

dat

a (r

elat

ive

to P

DB

) m

ainl

y af

ter

Wes

ton

et a

l., 1

988b

.A

ccur

acy

of 1

3 Cda

ta in

par

enth

eses

(af

ter

Hirn

er a

nd L

yon,

198

9) is

dou

btfu

l, pr

obab

ly r

elat

ed t

o in

com

plet

e so

lven

t re

mov

al f

rom

sat

urat

e fr

actio

ns.

Sul

fur

isot

opic

dat

a (r

elat

ive

to C

DT

) af

ter

Hirn

er a

ndR

obin

son,

198

9, a

nd R

obin

son,

per

sona

l com

mun

icat

ion;

and

tra

ce-m

etal

dat

a af

ter

Fra

nken

berg

er e

t al

., 19

94.

Pr/

Ph

= p

rista

ne:p

hyta

ne;

CP

I =

car

bon

pref

eren

ce in

dex

(Kill

ops

and

Kill

ops,

199

3);

Sat

s. =

satu

rate

s; A

rom

s. =

aro

mat

ics;

das

hes

= d

ata

not a

vaila

ble.

The

two

New

Ply

mou

th o

ils a

re fr

om w

ells

dril

led

by th

e R

epub

lic O

il C

o.

**In

Puk

earu

he-1

, Pal

eoge

ne a

nd C

reta

ceou

s st

rata

are

abs

ent a

nd o

il sh

ow w

as in

frac

ture

zon

e as

soci

ated

with

intr

abas

emen

t thr

ust i

n la

te T

riass

ic to

ear

ly J

uras

sic

sedi

men

ts.

(The m/z 123/1 91 response factor for isopimaraneis used to obtain an equivalent m/z 191 responsefor all the diterpanes, most of which do not yieldappreciable m/z 191 responses, for comparisonwith the m/z 191 responses of the triterpanes.)

Terrestrial/marine index:

Hopane:sterane ratio:

[where m/z 217 response includes C27, C29, and C305α(H)-steranes and 13β(H),17α(H)-diasteranes]

Tricylic:tetracyclic terpane ratio:

Most of the biomarker data were obtained fromtwo sample sets analyzed on different GCMS sys-tems (see Table 3). To facilitate comparison ofthese two data sets, some oils were analyzed onboth systems to permit compensation for variationsin the relative responses of components betweenGCMS systems.

OIL-GEOCHEMISTRY INFERENCES FORSOURCE AND DEPOSITIONAL ENVIRONMENT

The bulk geochemical and biomarker character-istics of the oils/condensates (hereafter collectivelyreferred to as oils) analyzed are listed in Tables 2and 3, well locations are shown in Figure 1, and theformations associated with reservoirs/shows areshown in Figure 2. Relative terrestrial and marinecontributions to the source rocks of the oils can beevaluated from a plot of δ13C for aromatic vs. satu-rated hydrocarbon fractions, as shown in Figure 3.Oils tend to plot on or near the terrestrial or marinelines in Figure 3, depending on the origins of theirsource kerogens (Sofer, 1984). Most Taranaki Basinoils appear to be predominantly terrestrial in ori-gin, with limited variation in carbon isotopic com-position (Table 2). This is consistent with the waxynature of these oils, high hopane:sterane ratios, andhigh relative proportions of C29 steranes (Table 3).C29 sterols are the dominant phytosterols in terres-trial higher plants but are generally less abundant inplankton, and so dominant C29 steranes usually

indicate significant contributions from terrestrialhigher plants, although care is required in applyingthis ratio in the absence of information on stereo-chemistry at C-24 (Killops and Killops, 1993, andreferences therein). This relationship for TaranakiBasin oils can be expressed by the ratio of C29 toC27 and C30 regular steranes, the terrestrial/marineindex (TMI), because the relative abundance of C28steranes is reasonably constant (Table 3). Thehopane:sterane ratio (H/S, Table 3) provides a mea-sure of bacterial activity, particularly that associatedwith the degradation of the lignified tissues of high-er plants resulting in the concentration of lipid-richstructures, such as leaf cuticles and waxes and bac-terial membranes. It is not unexpected, then, thatthe highest hopane:sterane ratios are recorded forthe most waxy oils, from Kupe South-1, McKee-3A,Pouri-1A, and Stratford-1, and that a reasonable pos-itive correlation is found between H/S and TMI(correlation coefficient, r = 0.71).

A slight odd-over-even predominance (OEP) ispresent among n-alkanes in the C23–C33 range forthe terrestrial oils (CPI ca. 1.1, Table 2), characteris-tic of a higher plant epicuticular wax contribution(Baker, 1982). Typical biomarker distributions areshown in Figure 4. Angiosperm contributions areindicated by the presence of oleanane (O) and theC24 ring-A degraded counterparts of oleanane (dO),lupane (dL), and ursane (dU) in the m/z 191 masschromatogram (which probably derive from micro-bial alteration of the pentacyclic analogues; Wool-house et al., 1992, and references therein). The fiveC30 pentacyclic triterpenoids marked by asterisks(Woolhouse et al., 1992) are thought to beangiosperm-derived because their abundances inthe oils vary in a manner broadly similar to that foroleanane. All oils contain 18α(H)-30-norneohopane(29N) and 17α(H)-15α-methyl-27-norhopane (ordiahopane, 30D), which have also been observedin various terrestrial oils from around the world,usually accompanied by 18α(H)-oleanane (Killopsand Howell, 1991, and references therein). Thepeak immediately to the left of 27α in the m/z 191mass chromatogram in Figure 4 is an unidentifiedtriterpane that co-elutes with trans,trans,trans-bicadinane (BC), a compound believed to derivefrom cadinene polymers in angiosperms of thedipterocarp family (van Aarssen et al., 1992).Because of the co-elution, the relative abundanceof bicadinane cannot be ascertained from m/z 191mass chromatograms alone, but traces of this com-pound do appear to be present in most oils fromcharacteristic m/z 369 and 412 responses.

The angiosperm-derived sesquiterpenoids eudes-mane and bisabolane (E and BA, respectively, m/z123 mass chromatogram, Figure 4) are present inlow levels in all the oils analyzed (ca. 5% relative todrimane, D). The ratio of 8ß(H)-homodrimane

TTR =m/z191 (23T)m/z191 (dH)

H/S =m/z191 (dH + 30 + 30 )

m/z217 (27 + 29 + 30)αβ βα∑

∑

TMI =m/z217 (29D S + 29D R)

m/z217 (27D S + 27D R + 30D S + 30D R)βα βα

βα βα βα βα∑

∑

Killops et al. 1565

(HD) to 8β(H)-drimane (D) is similar for most oils[HD/(HD + D), Table 3], a possible exception beingStratford-1. It is probable, therefore, that D and HDare primarily derived from hopanoidal precursorsrather than there being a significant contribution todrimane from higher-plant-derived drimenol.

All of the labeled diterpanes in the m/z 123 masschromatogram in Figure 4 except HB (which isprobably of bacterial origin) are believed to bederived from gymnosperms (especially podocarpsand araucarians; Noble et al., 1986; Weston et al.,1989). Distributions of diterpanes other than isopi-

marane (IP) and the C21 bicyclane (HB) are quiteuniform and so only relative abundances of IP andHB are given in Table 3. Abietane (A) is never morethan a very minor diterpenoid in Taranaki oils (≤1%relative to total diterpanes).

The δ13C plot in Figure 3 indicates that there isonly one primarily marine oil, that from Kora-1.The marine signature in this oil is characterized bya low TMI value (Table 3) and unusually abundantC30 regular steranes (Figure 5, m/z 217 mass chro-matogram), believed to be derived from chryso-phyte algae (Moldowan et al., 1990). However,


Table 3. Aliphatic Biomarker Ratios of Oils (All Values as Percentages)*

Sesqui-/Diterpanes SteranesHD RD1+RD2 IP HB 29D S ββ TMI

HD+D RD1+RD2+D ΣDT ΣDT 27:28:29:30 Σ29 S+R ββ+αα (%)

Kora-1 70 69 8 24 30:10:19:41 31 53 58 36Tangaroa-1 – – – – 34:13:21:32 34 59 57 32Pukearuhe-1 66 64 28 18 28:20:34:18 57 58 48 74Okoki-1 73 76 24 26 35:26:39:0 42 45 49 111

New Plymouth-1 – – – – 21:25:54:0 53 53 48 257New Plymouth-4 63 53 24 – 25:21:54:0 61 61 44 216Taranaki-5 71 64 16 – 23:22:55:0 51 61 46 239Moturoa-2 72 69 15 33 34:24:42:0 64 55 48 124

Mangahewa-1 63 64 61 8 42:24:34:0 71 60 51 81Kaimiro-1 66 57 28 21 33:22:45:0 63 59 51 136Kaimiro-2 75 58 35 13 26:23:51:0 57 62 47 196Ngatoro-1 77 56 46 9 23:20:57:0 48 59 46 252Stratford-1 82 45 27 13 23:22:55:0 47 49 44 239

Urenui-1 66 60 31 12 14:21:65:0 62 52 45 464Tuhua-1 71 59 15 – 11:15:74:0 54 53 41 672Pouri-1A 73 58 34 12 11:17:72:0 46 55 43 655Pukemai-2A 66 64 21 13 14:18:68:0 46 50 40 486McKee-3A 77 55 17 10 12:18:70:0 39 46 44 583Toetoe-1A 71 56 9 19 18:19:63:0 59 49 49 350

Tariki-1A 71 64 22 22 12:19:69:0 53 44 44 575Ahuroa-1 62 50 26 21 18:19:63:0 62 53 47 350Waihapa-1A 56 74 54 6 24:26:50:0 45 47 46 208Waihapa-2 73 44 36 14 12:16:72:0 44 60 45 615

Kapuni-2 64 43 51 12 12:23:65:0 56 53 47 542Toru-1 52 44 50 12 12:20:68:0 37 46 49 567Kupe South-1 65 44 46 9 10:22:68:0 47 46 43 680

Maui-3 69 66 62 3 15:19:59:7 51 51 48 268Maui-1 57 65 55 2 21:21:54:4 61 53 50 216Moki-1 60 58 60 4 23:21:52:4 66 55 53 193Maui-4 61 61 62 3 19:20:57:4 55 50 49 248

*Sesqui-/diterpanes: ΣDT = sum of diterpanes labeled in Figure 4. Steranes: 29D/Σ29 = ratio of 13ß(H),17α(H),20S/R-diasteranes to sum of C29 5α(H)-steranes and 13ß(H),17α(H)-diasteranes; S/(S + R) = ratio of 20S to 20R for 5α(H),14α(H),17α(H)-24-ethylcholestanes; ßß/(ßß + αα) = ratio of5α(H),14ß(H),17ß(H)- to 5α(H),14α(H),17α(H)-24-ethylcholestane (20S + 20R); TMI, see Materials and Methods section. Triterpanes: αß/(αß + ßα) = ratio of17α(H)-hopane to 17ß(H)-moretane; S/(S + R) = ratio of 22S to 22R for 17α(H)-homohopane; AGI and H/S, see Materials and Methods section. Foridentification of all other components, see Figure 4 legend. Data for Tangaroa-1 after Gibbons et al., 1981; for Okoki-1 after Analabs, 1989; and for Toru-1after Analabs, 1991. nd = 28B not detected.

Kora-1 is not entirely marine sourced, because itcontains oleanoid biomarkers of angiosperm ori-gin. Similar biomarker characteristics are alsoexhibited by the oil show in late Paleocene strata inTangaroa-1 (Table 3), suggesting a common sourcewith Kora-1 oil. Carbon isotopic data (Figure 3),TMI value, and C30 sterane content (Table 3) sug-gest that there is a smaller contribution from amarine, Kora-type source to the oil show fromPukearuhe-1. Traces of C30 regular steranes werealso observed in Maui-1 and Maui-4 oils (frommolecular ion and m/z 217 responses), and possi-bly also in Maui-3 and Moki-1 (from m/z 217responses only), suggesting a minor marine contri-bution, which is also supported by carbon isotopicdata (Figure 3) and intermediate TMI and low H/Svalues (Table 3). In all the oils exhibiting identifi-

able marine contributions, the level of tricyclic ter-panes relative to hopanoidal terpanes is higher(23T/dH, Table 3), which is consistent with the tri-cylics being derived from bacteria dwelling insaline environments (De Grande et al., 1993). Asmight be expected, therefore, TMI and 23T/dH val-ues exhibit a negative correlation coefficient (r =–0.61). On the basis of TMI, 23T/dH, and H/S val-ues, there appears to be a marine contribution tothe source rocks of the oils from Kaimiro-1, Motur-oa-2, and Okoki-1, although C30 regular steraneswere not detected. A marine influence in the oilsalso appears to correlate with lower (29αß +31αß)/30αß hopane ratios (Table 3), which is con-sistent with the greater importance of the C31 andC29 components in lignites (e.g., Brassell et al.,1986; Lu and Kaplan, 1992). C30 4-methylsteranes

Killops et al. 1567

Table 3. Continued.

Triterpanesαβ S 27N dL 28B 30D 29αβ+31αβ AGI 23T H

αβ+βα S+R 27N+27α dL+dO 30αβ 30αβ 30αβ (%) dH S

89 55 54 18 1 13 104 61 100 3189 59 49 – 2 6 96 – 100 4590 58 42 13 2 27 129 22 79 5888 60 44 14 9 15 129 80 74 94

90 60 52 9 8 30 108 – – –90 60 42 15 2 26 114 52 16 27892 59 58 4 1 31 87 66 15 15591 60 53 12 2 27 132 39 21 154

90 61 35 21 1 19 162 22 26 9089 60 21 29 2 9 180 46 33 16487 61 20 30 2 11 145 51 15 29886 61 16 41 1 9 162 41 14 33287 60 10 65 1 6 192 55 15 287

88 62 24 52 nd 14 187 75 25 11789 59 18 41 nd 15 156 188 8 19690 60 18 43 nd 12 148 112 6 35488 59 21 28 nd 12 165 30 14 24788 59 18 40 nd 12 188 388 14 34390 58 23 46 1 14 175 68 13 157

89 59 14 52 2 8 172 148 20 16091 60 23 38 1 15 141 74 15 14682 60 28 6 nd 33 222 13 21 16290 60 16 48 <1 6 134 35 5 509

88 60 19 38 2 13 167 19 11 20185 61 19 6 14 156 14 13 14287 58 17 38 1 11 167 19 12 335

87 60 29 15 2 13 139 3 32 16190 58 48 16 6 19 131 2 31 6788 60 35 34 5 27 164 10 38 11388 54 37 43 6 23 154 5 21 105


Figure 3—Plot of δ13C values foraromatic vs. saturated hydrocar-bon fractions from TaranakiBasin oils. (Data after Weston etal., 1988b, and Reed, 1992; terres-trial and marine classificationafter Sofer, 1984. See Table 2 forwell abbreviations.)

have been detected in all oils for which suitableGCMS data (m/z 231 responses) are available (Kora-1, Kupe South-1, Maui-1, Maui-4, Okoki-1, andPukearuhe-1). For most of these oils, a marinedinoflagellate origin for the 4-methylsteranes is like-ly (Summons et al., 1987, and references therein).

All oils have low sulfur contents (≤0.3%; Table 2)and low levels of nickel and vanadium (<2 ppb and<650 ppb, respectively; Frankenberger et al.,1994), probably ref lecting low levels of asphal-tenes/resins (mostly <20%), with which most sulfurand trace metals are usually associated. Oils forwhich nickel and vanadium concentrations areavailable (Frankenberger et al., 1994) exhibit V/(V+ Ni) ratios approaching unity, which, togetherwith sulfur contents of 0.3% or less (Table 2), sug-gest limited sulfate-reducing bacterial activity(Lewan, 1984). The δ34S values for most oils (Table2) fall within the range previously attributed torestricted marine or high-rate sedimentation envi-ronments, in which sulfate supply and hence sul-fate-reducer activity are limited by the rate at whichbacterial sulfide oxidation occurs (Hirner andRobinson, 1989). Such indications can be recon-ciled with predominantly terrestrial depositionalenvironments undergoing minor marine incur-sions. Because sulfur levels are low in terrestrialand freshwater plants, only a small marine sulfatecontribution is required to yield the observed lowsulfur levels that exhibit an isotopic signature clos-er to ambient marine (+19 < δ34S < +21) than fresh-water (+1 < δ34S < +7) sulfate (Hirner and Robin-son, 1989). Periodic marine innundations of coastalflood plains permit sulfate to percolate down intopreviously deposited freshwater peats (Suggate,1959), resulting in stimulation of sulfate-reducer

activity and subsequent diagenetic incorporation ofsulfide into the organic matrix of peat. Because lit-tle microbial isotopic fractionation would beexpected from such a limited sulfate supply, thismechanism explains the high positive δ34S signa-ture (approaching that of ambient seawater) ofcoals from Taranaki wells (Table 4). Shales interbed-ded with the coals exhibit the greater isotopic frac-tionation (i.e., negative shift in δ34S values, Table 4)and sulfur levels expected for a less restricted sul-fate supply. If source rock coals and shales through-out the Taranaki Basin exhibit these sulfur isotopicpatterns, it would seem that coals are the mainsource of most of the oils for which sulfur isotopicdata are available (Table 2), but that there is a signif-icant marine shale contribution to Moturoa-familyoils and the oil show in Pukearuhe-1. The sulfur iso-topic signature for Kora-1 oil is consistent with anopen-marine depositional environment.

Although pristane:phytane ratios (Pr/Ph, Table 2)can be significantly source-dependent, it appearsthat redox conditions are reflected in the valuesreported for Taranaki oils (Killops and Killops, 1993,and references therein). Values for the predominant-ly terrestrially-sourced oils lie in the range ca. 7–9,suggesting that associated depositional environ-ments were not entirely anoxic. The chiefly marine-sourced oils from Kora-1 and Tangaroa-1 exhibitlower Pr/Ph values (<3), which probably reflect lessoxygenated conditions. In peat swamp environ-ments, it can be envisaged that the sheer quantity ofhigher plant organic detritus overwhelms the capaci-ty of the decomposer community to degrade it fully,allowing preservation of organic-rich sedimentsunder relatively oxidizing conditions and the con-centration of more resistant, hydrogen-rich compo-

nents. In fully marine environments, preservation ofsufficient phytoplankton-derived sedimentary organ-ic matter to generate petroleum is generally associat-ed with high primary productivity and dysaerobia oranoxia, resulting either from the impingement of anopen-ocean, oxygen-minimum layer on the shelf/slope or from oxygen depletion during degradationof large amounts of phytoplankton detritus in anarea with restricted inflow of fresh, oxygenated bot-

tom water. Most Taranaki oils seem to contain smallamounts of 17α(H),18α(H),21β(H)-28,30-bisnor-hopane (28B/30αβ, Table 3). This compoundappears to be characteristic of oxygen-deficient,restricted marine, depositional environments (Melloet al., 1988; Burwood et al., 1992), and again sug-gests that there is a small marine contribution to thesource rocks of even those oils exhibiting the mostterrestrial characteristics.

Killops et al. 1569

Figure 4—Typical distributions of terpanes and steranes in terrestrially sourced oils of the Taranaki Basin. [Insesquiterpanes: D = 8β(H)-drimane; HD = 8β(H)-homodrimane; RD1 and RD2 = rearranged drimanes; E = 4β(H)-eudesmane; BA = bisabolane. In diterpanes: βL = 8β(H)-labdane; 18NIP and 19NIP = 4α(H)-18- and 4β(H)-19-norisopi-marane; R = rimuane; NT = 17-nortetracyclane (C19); B = ent-beyerane; IP = isopimarane; HB = homobicyclane (C21);βP = 16β(H)-phyllocladane; βK = ent-16β(H)-kaurane; A = abietane. In triterpanes: numbers correspond to carbonnumbers; T = tricyclic terpane; dO, dL, and dU = 10β(H)-des-A-oleanane, -lupane, -ursane; dH = 18β(H)-des-E-hopane; 27N = 18α(H)-22,29,30-trisnorneohopane; +BC = unidentified triterpane + trans,trans,trans-bicadinane;27α = 17α(H)-22,29,30-trisnorhopane; 28B = 17α(H),18α(H)-28,30-bisnorhopane; C29-C31 hopanes are labeledaccording to stereochemistry at C-17 and C-21, and also at C-22 for 31αβ; 29N = 18α(H)-30-norneohopane; 30D =17α(H)-15α-methyl-27-norhopane; O = 18α(H)-oleanane; * = C30 pentacyclic triterpanes. In steranes: numbers corre-spond to carbon numbers; regular (4-desmethyl) sterane stereochemistry at C-14, C-17, and C-20 is given, all com-ponents have 5α(H) configuration; diasteranes are indicated by D and stereochemistry at C-13, C-17, and C-20.]

A final observation about depositional environ-ment can be made regarding the high levels of rear-ranged relative to regular steranes in the terrestrialoils compared with those in the predominantlymarine-sourced oils (29D/Σ29, Table 3). Rearrange-ment of steroids occurs during diagenesis followingdehydration of sterols to sterenes, and is catalyzedby clays (Killops and Killops, 1993, and referencestherein). However, the extent to which clay-cataly-sis contributes to steroid rearrangement in low-ashNew Zealand coals is not certain. Dominance ofdiasteranes over regular steranes may primarilyresult from the greater resistance of diasteranestoward biodegradation during diagenesis. The gen-erally low levels of steroids probably reflects bacte-rial degradation of mesophyll, with which most ofthe higher-plant phytosterols are associated. Thereappears to be some correlation between the rela-tive abundances of C24 tetracyclanes (dO, dL, dU,and dH) and diasteranes, which could be related tomicrobial activity.

A clay source has been suggested for severaltrace elements, such as aluminum, in Taranaki oils(Frankenberger et al., 1994). Although it is possiblethat trace elements in clay minerals are incorporat-ed into the organic macromolecular structure ofthe source rock during diagenesis and are liberatedas an integral part of the asphaltenes fraction dur-ing catagenesis, it would seem unlikely that col-loidal clay particles would undergo migration fromthe source rock with the liquid hydrocarbon phase(Frankenberger et al., 1994) on the basis of sizerestrictions on migration. It is more likely that clayminerals from reservoir formations (e.g., Hill andCollen, 1978) may become dispersed in the oils.Whatever the origin of the clay minerals, it is notdirectly linked to the sources of the organic materi-al from which the oils are generated, and so theproposition that all Taranaki oils apart from Maui-1belong to the same genetic family, based on trace-metal content (Frankenberger et al., 1994), is notnecessarily valid. Indeed, various plots of source-related biomarker parameters suggest that fourmain families of oils can be recognized: Kapuni(Kapuni-2, Kupe South-1, and Toru-1); McKee


Figure 5—Mass chromatograms showing triterpane andsterane distributions in Kora-1 oil and bitumen fromWaipawa Black Shale equivalent in Ariki-1 well. [Triter-panes: 27β = 17β(H)-21,29,30-trisnorhopane, 29βα =17β(H)-30-normoretane, 31βα = 17β(H)-31-homomore-tane. Steranes: 21 = diginane, 22 = 20-methyldiginane,30DβαS/R = 20S/R epimers of 13β(H),17α(H)-24-n-propy-ldiacholestane, 30ααR = 20R-5α(H),14α(H),17α(H)-24-n-propylcholestane, 30ββ = 5α(H),14β(H),17β(H)-24-n-propylcholestane. See Figure 4 legend for othercomponent identifications.]

(McKee-3A, Pouri-1A, Pukemai-2A, Toetoe-1A,Tuhua-1, and Urenui-1); Maui (Maui-1, Maui-3, Maui-4, and Moki-1) and Moturoa (Moturoa-2, New Ply-mouth-1, New Plymouth-4, and Taranaki-5). In addi-tion, oils from Kaimiro, Ngatoro, and Stratfordfields share some similarities, and oils from Ahuroa-1 and Tariki-1A exhibit some affinities with theMcKee family. These associations can be seen inthree plots based on terpane distributions fromm/z 123 and 191 mass chromatograms in Figure 6.The enhanced levels of tricyclic terpanes in themost strongly marine-influenced oils from Kora-1,Okoki-1, Pukearuhe-1, and Tangaroa-1 can be seenin the plot of 27N/(27N + 27α) vs. 23T/(23T + dH)(Figure 6). The ratio 27N/(27N + 27α) is often usedas a maturity indicator, but it is also significantlyaffected by variations in sources of organic matter.Whether the genetic characteristics are sufficientlydistinct for specific source rock intervals to beidentified is considered in the following section.

OIL-TO-SOURCE ROCK CORRELATION

The selection of potential source rock samplesfor correlation studies was based on measurementsof genetic potential and estimates of horizons likelyto have entered the oil window. Maturity considera-tions suggest that Pakawau and Kapuni Group coalsand shales are the most probable source rocks.Genetic potential is summarized in Table 5 forsome formations that have previously been system-atically screened by TOC and Rock-Eval analysis(Analabs, 1984).

Paleogene and Late Cretaceous coals appear to bereasonable candidates for the source rocks of themore terrestrial oils, and can be seen to possessmixed oil and gas potential (Table 5). The RakopiFormation (Figure 2) is widespread and containsabundant coal, on the basis of seismic reflectioncharacteristics (Thrasher, 1992). However, the distri-bution of coal-rich units in Paleogene strata reflectsthe general extent of marine transgressional cycles,with progressively terrestrial-dominated sedimentsbeing deposited toward the east-southeast. TheEocene Mangahewa Formation (Figure 2) is particu-larly coal-rich and is found throughout the onshorepart of the basin and in the Maui-4 area. It is signifi-cantly thickened within the northern part of theTarata thrust zone (Figure 1). The Kaimiro Formationis coal-rich within the Tarata thrust zone, but west-ward around New Plymouth (Figure 1) it is apprecia-bly marine influenced and appears to have poor oilpotential. The Paleocene Farewell Formation gener-ally contains less coaly material and exhibits varyingmarine influence. In the Maui-4 area, it is predomi-nantly terrestrial with oil potential, but in the KupeField, only the lower half of the unit contains car-bonaceous and coaly material in significant quantity(Puponga Member), whereas the upper half is organ-ic poor and marine influenced. The marine, Paleo-gene, Turi Formation predominates to the west andnorth, and it is generally not particularly carbona-ceous. Within the Turi Formation in the northwestregion of the basin there is an organic-rich shaleequivalent to the late Paleocene Waipawa BlackShale, which is found in several other New Zealandbasins, such as the East Coast (Weston et al., 1988a),

Killops et al. 1571

Table 4. Sulfur Stable Isotopic Compositions for Selected Coal and Shale Samples*

Depth Kerogen Approx.Well (m) Formation Sediment %S δ34S‰ TMI

McKee-1 3662–3672 Mangahewa Shale 5.5 +10.0 –3662–3672 Mangahewa Coal 2.1 +19.4 –

Maui-1 3103–3106 Kaimiro Shale 3.4 +5.7 –3106–3109 Kaimiro Coal 0.1 +3.3 –3362–3365 Farewell Coal 2.8 +3.5 –3365–3367 Farewell Shale 6.1 –7.0 –

Maui-4 2091–2118 Mangahewa Coal 0.3 +11.9 4.33246–3252 Rakopi Coal 0.6 +19.5 4.33822–3828 Rakopi Coal 0.7 +12.0 4.63828–3837 Rakopi Shale 8.0 +9.1 3.4

Fresne-1 2486–2501 Rakopi Shale 5.4 +2.7 2.42486–2501 Rakopi Coal 0.9 +16.4 8.4

Castlepoint** Outcrop Turi (Waipawa) Shale 2.1 –6.1 0.4

*After Hirner and Robinson, 1989.**Castlepoint sample of Waipawa Black Shale is from East Coast Basin.

Canterbury (Gibbons and Fry, 1986), and GreatSouth (Raine et al., 1993). This shale is present in theAriki-1 well, and representative TOC and Rock-Evaldata from other locations are presented in Table 5 inthe absence of data from Ariki-1.

Although there are no perfect matches betweenany particular source rock sample and any oil, there

are some broad similarities in biomarker distribu-tions. For example, 10ß(H)-des-A-lupane is relative-ly abundant in McKee-family oils (Table 3) and inMangahewa Formation samples. The lack of perfectmatches is not surprising in view of the rapidchanges in flood plain swamp environments andassociated flora on a geological time scale. Suchchanges are reflected in the pronounced variationsobserved in diterpane fingerprints over depth inter-vals on the order of 100 m or less in Rakopi coalsfrom Tane-1. Hence, generated oils can be expect-ed to reflect a mixture of these biomarker varia-tions, given the vertical extent of source rock unitslikely to be in the oil window at a given time.

Correlation of oils with their potential sourcerocks is most readily achieved by following higher-plant evolution. Although angiosperms firstappeared in the Cretaceous and rapidly rose todominance on a global basis, in New Zealand thepollen record shows that gymnosperms, particular-ly podocarps and araucarians, dominated the high-er-plant communities of coastal flood plains duringthe Late Cretaceous and were still major membersthroughout the Paleocene, but had become subor-dinate to angiosperms by the Eocene (Mildenhall,1980). Biomarker distributions ref lect thesechanges in the flora. Coals and interbedded shalesfrom the Late Cretaceous Rakopi Formation exhibitvery high levels of gymnosperm-derived diter-panes, often dominated by isopimarane, andextremely low levels of 18α(H)-oleanane [≤2% rela-tive to 17α(H)-hopane from m/z 191 response]. Incontrast, Eocene Mangahewa and Kaimiro forma-tion coals exhibit relatively high levels ofangiosperm-derived triterpenoids, particularlyoleanoids, ursanoids, and lupeoids, and much-reduced levels of diterpanes. Paleocene coals inKapuni Deep-1 (i.e., belonging to Kapuni Groupcycle A) appear to exhibit biomarker source char-acteristics more like those of Late Cretaceous coals(Johnston et al., 1990).

The biomarker characteristics discussed above canbe represented by an angiosperm/gymnosperm index(AGI), which is calculated from the relative amountsof selected diterpanes and triterpanes in m/z 123 and191 mass chromatograms, respectively. A plot of logAGI vs. log TMI for various sediment samples, labeledaccording to formation, and oils is presented in Figure7 (see Materials and Methods section for evaluation ofindices). As expected, coals and shales of the Manga-hewa and Kaimiro formations generally plot at highAGI, whereas those of the Rakopi Formation plot atlow AGI. The lowest AGI values (<0.5) for Eocene sed-iments were recorded for samples from the Kaimiroand deepest Mangahewa formations in Waihapa-1,and are consistent with the expected slightly lowerangiosperm contribution in the early Eocene com-pared with the mid-to-late Eocene.


Figure 6—Differentiation of main oil families frombiomarker parameters derived from m/z 191 mass chro-matograms (see Table 3 for description of parameters).

For Rakopi and Mangahewa/Kaimiro formationsediments, TMI values are generally greater than 2.Within predominantly terrestrial sediments, howev-er, varying marine influences are suggested by thepresence of marine organisms (e.g., dinoflagellates)and general stratigraphy (Flores et al., 1993), andare reflected in biomarker distributions. For exam-ple, a bulk upper Rakopi sample from Fresne-1exhibits a TMI of 2.4, whereas coal isolated fromthis sample has a TMI of 8.4. It appears that theshales interbedded with coals in such sedimentsrepresent relatively brief marine incursions duringa phase that is basically regressive but in which theinput of terrestrial organic detritus is still domi-nant. Rakopi samples from Maui-4 have lower TMIvalues (<6) than those from Tane-1, suggesting agreater marine inf luence in the Maui-4 region.These inferences of marine influence in Maui-4 areconsistent with the sulfur isotopic distributions dis-cussed in the previous section (Table 4).

AGI values for Turi Formation samples rangefrom intermediate to high (ca. >0.1), as expectedfor Paleogene samples, whereas TMI values are low(ca. <2), which is consistent with significantmarine contributions. Farewell Formation samplesexhibit intermediate to low AGI values, again asexpected; the lowest value, similar to those of theyoungest Rakopi Formation coals, is recorded for asample from near the base of the main Farewellcoal unit in Kapuni Deep-1 (within the D cycle,4693 m). The deepest Farewell samples in KapuniDeep-1 (5308 and 5520 m) show an increasinglymarine character, with TMI values of 1.0 or less andhigh 23T/dH values (>3.5).

A strong correlation is apparent between oils ofthe northern part of the Tarata thrust zone (McKee-3A, Pouri-1A, Toetoe-1, and Urenui-1, Figure 7) andEocene coals. There also appears to be a majorEocene contribution to oils from Ahuroa, Moturoa,Kaimiro, Ngatoro, Stratford, and Tariki fields and oilfrom the Tikorangi reservoir in the Waihapa field(Ahuroa-1, Kaimiro-1, Moturoa-2, Stratford-1, Tariki-1A, and Waihapa-2, Figure 7). However, fairly lowTMI values for the oils from Moturoa, Kaimiro, Nga-toro, and Stratford fields (Table 3) suggest a greatermarine inf luence than for the other Eocene-sourced oils. The oils from Mangahewa-1 and theKaimiro reservoir in Waihapa-1A appear to have agreater Paleocene contribution than other oils fromjust west of the Tarata thrust zone (Figure 7). Mauioils correlate well with Rakopi coals, whereas theoil from Moki-1 may contain Late Cretaceous andPaleocene contributions (Figure 7). Oils of theKapuni and Kupe South fields plot at intermediateAGI, suggesting Paleocene or mixed Eocene/LateCretaceous sources, predominantly coals from thehigh TMI values (Figure 7).

Levels of trans,trans,trans-bicadinane relative tohopane were assessed from m/z 369 and 412responses for some representative oils (Table 6),and are consistent with AGI values. Oils with signif-icant contributions from Eocene coals (e.g., inMcKee and Kaimiro fields) exhibit the highest rela-tive levels, whereas those of predominantly Pale-ocene origin (e.g., Kupe South field) containmarkedly lower levels and Cretaceous-sourced oils(e.g., Maui field) contain the lowest amounts (atthe limit of detection). Bicadinane levels do not

Killops et al. 1573

Table 5. Mean Total Organic Carbon and Rock-Eval Data for Formations in Various Regions of theTaranaki Basin*

TOC S2 HIField/Region Formation (%) (‰) (‰)

Kaimiro Mangahewa 13.9 42.3 239Turi + Kaimiro 1.6 2.3 120

Kapuni Mangahewa 13.0 27.5 137Kupe Farewell 1.7 1.5 85McKee Mangahewa (upper) 9.7 29.8 230Maui-4 Mangahewa + Kaimiro 10.4 21.8 194

Farewell 9.4 16.1 174North Cape 0.9 0.8 75Rakopi 8.9 23.4 243

Tane-1 Turi 0.6 0.1 16North Cape 0.4 0.1 25Rakopi 4.9 4.9 118

Witiora-1 Turi 1.9 3.2 138Angora Stream Turi (Waipawa) 3.2 7.5 236Galleon-1 Turi (Waipawa) 6.1 19.9 323

*Waipawa Black Shale samples are from the East Coast Basin (Angora Stream), after Leckie, personal communication; and Canterbury Basin (Galleon-1well), after Gibbons and Fry, 1986; other data after Analabs, 1984.

parallel those of oleanane exactly: for example, theBC:O ratio for Maui-4 oil is very low compared withthat for McKee-3A (Table 6). Similarly, althougholeanane is present in a mature Rakopi coal samplefrom Fresne-1 (4% relative to 30αβ from m/z 191response), no bicadinane was detected, suggestingno more than minor occurrence of dipterocarp-type flora in the Late Cretaceous in New Zealand.

Kora-1 and Tangaroa-1 oils exhibit good biomark-er correlation with a late Paleocene shale (WaipawaBlack Shale equivalent) at 4120–4130 m in Ariki-1(Figure 5), although the shale is less mature thanthe oils. The marine biomarker signature is aug-mented by varying levels of angiosperm-derivedbiomarkers [e.g., wax n-alkanes and 18α(H)-oleanane]. Sulfur isotopic ratios for Kora-1 oil(Table 2) and the shale in the East Coast Basin

(Castlepoint; Table 4) are similar and consistentwith a depositional environment near the shelfbreak or on the slope, probably under a highly pro-ductive photic zone. The development of anoxicityin surface sediments is indicated by an intense γ-logsignal for the shale in both Ariki-1 and Galleon-1(Canterbury Basin). Although the shale is onlysome 10 m thick in Ariki-1 and 7 m thick inGalleon-1, it has a high petroleum genetic potential(Table 5). A contribution from an equivalent of thisshale is also apparent in the oil show fromPukearuhe-1. It should be noted that none of thesediment samples analyzed in this study exhibits anexclusively marine signature, owing to the input ofvarying quantities of terrestrial detritus to shelfenvironments.

OIL GENERATION AND EXPULSION FROMNEW ZEALAND COALS

The Taranaki and Gippsland (southwest Aus-tralia) basins were relatively close together at theend of the Cretaceous and so, not surprisingly, theirterrestrial oils have compositional affinities, reflect-ing general similarities in depositional environ-ments associated with lower coastal plain swampecosystems (Thomas, 1982). These include thepresence of oleanane (O), C29 neohopane (29N),diahopane (30D), and gymnosperm-derived diter-panes; abundant diasteranes; limited amounts of tri-cyclic terpanes; high hopane:sterane ratios, waxcontents, and pristane:phytane ratios (≥4); and lowsulfur contents (Philp and Gilbert, 1986; Alexanderet al., 1987). Low sulfur levels are consistent withdeposition in freshwater to low-salinity environ-ments—typical conditions for the source rocks ofhigh-wax oils, most of which appear to have beendeposited in the Cretaceous and Tertiary (Hedberg,1968; Gould, 1980). It is now recognized that oil-prone coals were deposited under conditions inwhich microbial degradation of woody tissue couldoccur, resulting in concentration of the more resis-tant, hydrogen-rich components such as cuticlesand resin bodies (Kirkland et al., 1987; Powell,1988; Powell et al., 1991). Such conditions appearto be mostly associated with temperate rather thantropical climates (Thomas, 1982), as during sourcerock deposition in the Taranaki Basin (Mildenhall,1980).

The oil potential of the hydrogen-rich, MiddleJurassic Walloon and Tertiary Latrobe group coalsof Australia is attributed to high exinite content, inthe form of suberinite, cutinite, and, in particular,resinite (Thomas, 1982; Khorasani, 1987). Howev-er, New Zealand coals are vitrinite-rich and containlittle exinite (Newman and Newman, 1982). Thevitrinite is mainly in the form of the amorphous,


Figure 7—Logarithmic plot of angiosperm/gymnospermvs. terrestrial/marine indices for oils and sedimentextracts (labeled by formation: F = Farewell, K =Kaimiro, M = Mangahewa, N = North Cape, R = Rakopi, T= Turi). Circled areas represent relative bacterial contri-butions to oils (hopane:sterane ratio). (See Table 2 forwell abbreviations.)

hydrogen-rich, submaceral desmocollinite, which isprobably primarily derived from lipid-rich, leaf-cuticular membranes (comprising epicuticular waxand the cuticle proper; Holloway, 1982) and bacte-rial cell walls and membranes. These componentsare known to be resistant to bacterial degradationduring diagenesis (e.g., Nip et al., 1986; Tegelaar etal., 1989; Le Berre et al., 1991), and can be majorcomponents in lignites [e.g., Yallourn lignite(Noble et al., 1985) and some Northland lignites(Mildenhall, 1988)]. It is the epidermal cell wallarchitecture that confers the characteristic shape ofcutinite, but once the cell wall has been degradedit is possible for the cuticular material to adoptwhatever shape is dictated by external pressuresand become unrecognizable (i.e., amorphous). Asimilar fate may also be possible for suberinite, andbacterial cell walls and membranes (containinglarge amounts of hopanoids) would also be expect-ed to yield amorphous material. Hence, not all oil-prone coals contain large amounts of suberiniteand cutinite (Powell et al., 1991), and hydrocarbonpotential, when not associated with high liptinitecontent, correlates with hydrogen-rich vitriniteabundance (Bertrand, 1989). The presence of leaf-cuticular membrane material would account forthe waxy nature of Taranaki oils and their abundanthigher plant diterpanes and triterpanes (Aplin etal., 1963; Cambie and Weston, 1968; Killops andFrewin, 1994). In addition, the highly resistantcuticular component cutan is probably responsiblefor the significant polymethylene signal observedin 13C NMR studies of Late Cretaceous and TertiaryNew Zealand coals (Collen et al., 1988).

It has been proposed that, although oil can begenerated by New Zealand coals at a rank of ca.0.7% Ro, it is not expelled until significantly highermaturity levels of ca. 1.0% Ro are reached at burialdepths in excess of 5 km, because of the

chemisorption and molecular sieve properties ofcoals (Cook, 1987; Cook, 1988; Johnston et al.,1991). Because exploration wells have not pene-trated source rock horizons exhibiting biomarkermaturity levels as high as those recorded for oils, ithas not proven possible to establish exact genera-tion and expulsion maturity thresholds. The mostuseful molecular maturity parameter from the satu-rated hydrocarbons over the maturity range inquestion, the relative amount of 5α(H),14β(H),17β(H)-24-ethylcholestanes compared with 5α(H),14α(H),17α(H)-24-ethylcholestanes, can vary invalue at the end of diagenesis as a result of source-related effects (Peakman et al., 1989), and so it isnot possible to obtain absolute maturity estimatesof the expulsion threshold from this ratio in oilsalone. However, such estimates are possible whenpotential source rock data are available, permittingdiscrimination between source- and maturity-relat-ed effects. Given that McKee field and related oilsare largely sourced by Eocene coals, that Kapuni/Kupe oils are Paleocene-sourced, and that Maui oilsare predominantly sourced by Late Cretaceouscoals, an approximation of expulsion thresholdscan be obtained.

In Figure 8, the extent of isomerism at C-14 andC-17 in 5α(H)-24-ethylcholestanes [ββ/(ββ + αα)] isplotted against depth for Mangahewa Formationsediments from McKee-1 and the maturity trend isextrapolated to the mean value exhibited by oilsfrom the area, which is an approximation of theexpulsion threshold. The corresponding vitrinitereflectance and rank (S) values for the source rockat oil expulsion are obtained by reference to theplots for McKee-1 coals, based on established depthtrends (Lowery, 1988; Sykes et al., 1992). Theexpulsion threshold is ca. 0.8 ± 0.1% Ro, or ca. 13.2± 0.5 R(S), at a depth of just over 4000 m in McKee-1 [allowing for uncertainties in vitrinite reflectanceand rank (S) trends].

A similar biomarker maturity approach forKapuni/Kupe oils and Farewell Formation sedi-ments in Kapuni Deep-1 yields expulsion-thresholdvalues of 0.85 ± 0.1% Ro and 14.6 ± 1.0 R(S) at ca.5500 m depth (Figure 8). For Maui oils, as will beseen, the exact source area is unknown, but expul-sion characteristics can be examined for RakopiFormation sediments in Maui-4 and Tane-1 if it isassumed that Rakopi coals throughout the basinhave similar chemical characteristics. The oil-expul-sion threshold appears to be ca. 0.9 ± 0.1% Ro or13.8 ± 0.5 R(S) in Tane-1 and 0.9 ± 0.1% Ro or 13.3± 0.5 R(S) in Maui–4 (Figure 8). These values areself-consistent and do not appear to be affected bydiffering thermal regimes for the two regions andthe loss of ca. 1300 m of sediment in the Maui-4area during late Miocene uplift and erosion.Although the Maui oils appear slightly more mature

Killops et al. 1575

Table 6. Distribution of trans,trans,trans-Bicadinane (BC) in Some Taranaki Oils Relative to17α(H)-Hopane (30αβ) and 18α(H)-OleananeBased on m/z 369 Responses

BC BCOil 30αβ O

Moturoa-2 2.99 7.84Kaimiro-1 2.28 5.18Kaimiro-2 1.36 3.55McKee-3A 1.07 1.64Waihapa-1A nd* ndWaihapa-2 0.75 2.26Kupe South-1 0.29 0.92Maui-1 nd ndMaui-4 0.13 0.29

*nd = BC not detected.

than the northern Tarata thrust zone oils on thebasis of implied vitrinite reflectance values for theirsource rocks during expulsion, rank (S) values aresimilar. Rank (S) (also known as Suggate rank) moreaccurately represents absolute maturity (e.g., vary-ing heating rates) and does not exhibit the source-related effects of Ro measurements (e.g., Suggateand Boudou, 1993).

It appears that the oil-expulsion threshold forNew Zealand coals occurs at ca. 12.5–14 R(S),although it must be remembered that this valuerepresents an average rank for all the source rock

strata that have contributed to the pooled oil andso is likely, if anything, to overestimate the maturityat which expulsion commences. However, it is con-sistent with peak hydrogen index (HI) for NewZealand coals being reached around 13 R(S) andthereafter decreasing, as a consequence of theexpulsion of generated hydrocarbons (Bertrand,1989; Sykes et al., 1992). There is no evidence thatbiodegradation has occurred in oil accumulationsto a degree that would affect the ββ/(ββ + αα) ster-ane ratio (which would, in any event, tend to causean overestimation of the expulsion threshold;


Figure 8—Depth correlations of the extent of isomerism at C-14 and C-17 in 5α(H)-24-ethylsteranes with vitrinitereflectance (Ro) and rank (S) [R(S)] for Mangahewa Formation sediments from McKee-1 (and Urenui-1), FarewellFormation sediments from Kapuni Deep-1, Rakopi Formation sediments from Tane-1, and Rakopi Formation sedi-ments from Maui-4. [Ro and R(S) depth calibration after Sykes et al., 1992; Ro data after Lowery, 1988.]

McKirdy et al., 1983). The bulk chemical constitu-tion and petroleum potential of Pakawau andKapuni group coals are similar and fall within thematurity trend of the New Zealand coal band onvan Krevelen-type diagrams (Figure 9), and so simi-lar petroleum generation and expulsion characteris-tics are to be expected. Typically, the hydrogenindex (HI) of New Zealand coals rises to ca. 300 atrank (S) 12.5–14 (vitrinite ref lectance of ca.0.7–0.9% Ro), and the Rock-Eval S2 parameter is ca.200‰ (Suggate and Boudou, 1993).

It is possible to model fluid evolution from a typ-ical New Zealand coal with increasing rank (S), asshown in Figure 9, based on an established kineticmodel for type III kerogen (Burnham and Sweeney,1989; Sweeney, 1990; Sweeney and Burnham,1990). Oil expulsion appears to occur when ca.30% of the genetic potential has been realized,which occupies ca. 10% of the source rock volumeat typical subsurface conditions. Applying this 30%threshold to more sophisticated thermal historyand kinetic modeling (Armstrong et al., 1994)yields expulsion-threshold depths very close tothose obtained above from the biomarker maturityapproach.

The potential for early generation of oil fromhydrogen-rich coals, such as those of the TaranakiBasin, and the limited extent of absorption and

adsorption processes that might hinder expulsion,have recently been recognized (e.g., Noble et al.,1991; Sandvik et al., 1992). Clearly, primary migra-tion may occur at significantly shallower depthsthan has been generally thought possible in theTaranaki Basin. This conclusion applies to the aver-age coal on the New Zealand coal band, and therewill be some variation in oil generation and expul-sion characteristics depending on the plant and tis-sue types preserved in a given peat, which are relat-ed to depositional environment, as found for thecoals of the Talang Akar Formation of Java (Nobleet al., 1991).

Large quantities of carbon dioxide are associatedwith gas/condensate accumulations within theupper part of the Mangahewa Formation inonshore wells where this formation has not yetentered the oil window. For example, ca. 40% ofthe gas is CO2 in the Kapuni field (McBeath, 1977).Compositional and isotopic studies suggest that theCO2 originates from carboxyl group eliminationfrom coals during the lignite to early high-volatilebituminous coal stages (Boudou et al., 1984;Giggenbach et al., 1993). Various removal process-es and dilution with methane from more deeplyburied coals probably lead to a quite rapid declinein CO2 concentrations once CO2 generation ceases,but large amounts are still being evolved by the

Killops et al. 1577

Figure 9—van Krevelen-type diagram for the New Zealand coal band showing Suggate isorank contours (elementalcompositions expressed on nitrogen-free, sulfur-free, and dry-mineral-matter-free basis; after Suggate, 1959; Sug-gate, personal communication) and generalized representation of fluid generation from a typical New Zealand coalwith increasing rank (S) per tonne of carbon in lignite of initial R(S) ca. 4. [Fluid volumes based on typical Mangahe-wa reservoir densities in Kapuni field of 0.6 g⋅cm–3 for CO2 and 0.8 g⋅cm–3 for oil, represented by (CH2)n.]

onset of significant oil generation (Figure 9). Undertypical subsurface temperature and pressureregimes for accumulations in the Taranaki Basin,CO2 (and mixtures with CH4) is a supercriticalfluid, possessing considerable solvating potentialfor hydrocarbons, which aids the primary migra-tion of oil (see also McKirdy and Chivas, 1992). Thelarge volume of CO2 evolved prior to oil generationwould also be anticipated to aid primary migrationindirectly, by effecting microfracturing of thesource rock. It may also be responsible for remobi-lizing oils, generated at greater depth, that have

become trapped beneath the upper Mangahewacoal unit. The f luid is less dense than oil and,together with methane evolved from deeperRakopi coals, may displace oil past reservoir spillpoints, causing what may be termed tertiary migra-tion into shallower traps. This process may accountfor the dominance of gas (under surface condi-tions) in upper Mangahewa reservoirs of theKapuni and Kaimiro fields, and the accumulation ofoils/condensates in late Miocene Mount MessengerFormation sandstones in the Kaimiro and Ngatorofields (Table 1 and Figure 2).


Figure 10—Cross sections of onshore and near-shore areas of the Taranaki Basin (after King et al., 1991), showingthe main petroleum source rock formations (F = Farewell, K = Kaimiro, M = Mangahewa, N = North Cape, R =Rakopi, T = Turi) and their spatial relationships to oil accumulations (black lenses). (See Figure 1 for location ofcross sections. Medium tone = organic-rich units, partial tone = reduced organic richness, dark tone = units thathave entered oil-expulsion window. Random ticks indicate seismic basement.)

BASIN-WIDE OIL GENERATION ANDEXPULSION CHARACTERISTICS

The cross sections in Figures 10 and 11 show themain source rock units in various regions of thebasin and horizons likely to have entered the oilwindow at some time (i.e., generation and expul-sion), based on biomarker maturity parameters thatare in agreement with preliminary kinetic models(Armstrong et al., 1994). The composition of oilaccumulations generally reflects the largest volumeof source rock in the vicinity that has entered theoil window within the last 10 Ma (cf. Armstrong etal., 1994). It appears that oils of distinctly Rakopi

origin, with the exception of those from the Mauifield, Maui-4, and possibly Moki-1, have largelyescaped from the system, being mostly expelledmore than 20 Ma, prior to the development oftraps. The expulsion window occurs at a present-day depth of 5.0–5.5 km in the low-heat-flow areain the southeast region of the basin (includingKapuni and Kupe South fields; cross sections AA′and BB′, Figure 10), at ca. 4 km in the higher-heat-f low area of the northern Taranaki Peninsula(encompassing Moturoa, Kaimiro, and McKeefields; cross section CC′, Figure 10) and at interme-diate depths over much of offshore Taranaki Basin(depending on heat flow, Figure 1).

Killops et al. 1579

Figure 11—Cross sections of offshore regions of the Taranaki Basin. (See Figure 1 for locations of cross sections andFigure 10 legend for key to symbols. Dots immediately above seismic basement in Tangaroa-1 represent oil show.)

Eocene coals have not reached sufficient maturi-ty to contribute to the oils of the Kapuni and KupeSouth fields (cross section AA′, Figure 10), and so amixed Eocene/Late Cretaceous origin seems far lesslikely than a predominantly Paleocene (i.e., FarewellFm.) coal source for the Kapuni and Kupe Southoils. Rakopi coals probably make a significant con-tribution to hydrocarbon gas accumulations in theKapuni field (cf. Armstrong et al., 1994), whereasimmature Mangahewa coals have generated theexisting CO2. The Farewell Formation becomesquite organic poor to the south of the Kapuni field,other than the coals of the Puponga Member, whichspans the base of the Farewell Formation and thetop of the North Cape Formation (cross section BB′,Figure 10). It would appear that the Kupe Southfield oils are sourced mainly by the Farewell Forma-tion in the Kapuni field region. However, theKapuni/Kupe oils exhibit a lower marine contribu-tion than the sediments analyzed from depthsgreater than 5000 m in Kapuni Deep-1, which sug-gests that if this interval has sourced the oils, coalbands are present in the drainage area and have asignificantly greater oil potential than the marine-influenced horizons sampled. The Rakopi Forma-tion must lie within the oil window in the region ofToru-1 (cross section BB′, Figure 10), but there is noindication that expelled oil has been trapped. Here,as elsewhere in the basin where exploration wellshave not penetrated the Rakopi Formation, the pres-ence of coals can be inferred only from seismicreflection characteristics.

In the Waihapa field there are clearly composi-tional differences between the oils of the Kaimiroand Tikorangi formation reservoirs. The KaimiroFormation oil appears to be predominantly Pale-ocene sourced, like the Kapuni/Kupe oils. Howev-er, biomarker maturity parameters suggest that theoil-expulsion threshold is a little shallower (at ca.5000 m) than in the Kapuni field, which is consis-tent with a slightly higher heat flow (Figure 1), andthat Mangahewa Formation coals near the base-ment-wall thrust have entered the expulsion win-dow (cross section AA′, Figure 10). Mangahewa-sourced oil could not accumulate in the KaimiroFormation reservoir, but would be anticipated tocontribute to the Tikorangi reservoir, accountingfor the observed compositional differencesbetween oils from the two reservoirs.

The oils of the northern Tarata thrust zone, suchas those from the McKee field, appear to besourced mainly from Mangahewa coals at the baseof the overthrust, the oils having migrated up-struc-ture to reservoirs in the McKee Formation sand-stones (cross section CC′, Figure 10). There is noreason to suspect that oleanane and otherangiosperm-derived biomarkers have beenentrained by oil generated from deeper sources

during its vertical migration through Eocene coals(Philp and Gilbert, 1986; Johnston et al., 1991),because diterpane levels relative to hopanes are toolow for a Rakopi source and kinetic modeling indi-cates that Rakopi coals expelled oil in the Pale-ocene and are now gas prone (Armstrong et al.,1994).

To the west of the Tarata thrust zone, a gradualchange in oil composition can be observed on mov-ing northwest through Stratford, Ngatoro, Kaimiro,and Moturoa fields. An increasing marine contribu-tion is observed, which is expected from theincreasingly marine character of Paleogene (TuriFm.) units (cross section CC′, Figure 10). Althoughnot particularly organic-rich, these units are quitethick. However, the dominant inf luence on oilcomposition is from adjacent, mature, Eocene coals(mainly Mangahewa, because the Kaimiro Forma-tion is relatively organic lean in this region),although it is probable that mature, terrestrial, Pale-ocene (Farewell Fm.) strata immediately to thewest of the Tarata thrust zone also contribute. BothMangahewa and Mount Messenger formation reser-voirs in the Kaimiro field lie above the source rockstrata (cross section CC′, Figure 10), and so source-related compositional differences of the typedescribed above for the two Waihapa field reser-voirs would not be expected. The oils from the twoKaimiro field reservoirs are compositionally alikeand so could have a common source. Gas, particu-larly CO2 released from Mangahewa Formationcoals, may be responsible for displacing oil fromthe Mangahewa reservoir into the shallower MountMessenger reservoir in the Kaimiro field.

Only thin and immature Rakopi sediments areencountered in the Maui wells and Moki-1 (crosssection AA′, Figure 10). Preliminary thermal model-ing indicates that, in areas where Late Cretaceoussediments are thickest, the Rakopi Formation firstentered the oil window in the Paleocene and isnow gas prone (Armstrong et al., 1994), and soexpelled oil probably escaped. The source area forthe Maui oils is most likely to be found where theRakopi Formation has entered the oil windowwithin the last 10 Ma. Two possible sourceregions that satisfy this criterion have previouslybeen proposed, one lying to the east, across theCape Egmont fault (Thrasher, 1990), and the otherlying to the northeast in the vicinity of New Ply-mouth (Haskell, 1991, 1992). It is not possible toeliminate either of these on the basis of datapresently available. Anomalously high 3He/4Heratios recorded in gases from both Maui and NewPlymouth areas do not necessarily establish a link(Giggenbach et al., 1993). This mantle-gas signa-ture could be the result of crustal fractures in theQuaternary rift zone identified under the CentralGraben and the southern part of the North


Graben (King and Thrasher, 1992), and so may bea feature of the entire rift zone (Allis, personalcommunication).

Rakopi coals below a depth of 4 km may haveentered the oil window in the vicinity of Maui-4(cross section DD′, Figure 11), but were removedfrom it again by ca. 1300 m of post-Miocene uplift.Deeper into the Southern Inversion Zone, whereup to 3 km of uplift and erosion has occurred in theQuaternary (Allis et al., personal communication;Kamp and Green, 1990), source rocks that werepreviously in the oil window had their maturationreactions suspended by the uplift (e.g., Rakopicoals in Fresne-1; cross section EE′, Figure 11). Incontrast, on the Western Stable platform it appearsthat base-Rakopi coals may only just be approach-ing the expulsion window (e.g., Tane-1; cross sec-tion FF′, Figure 11).

The probable source of the Kora-1 oil, theWaipawa Black Shale equivalent, probably entersthe oil window at 5.0–5.5 km burial depth to theeast of Kora-1 well (cross section GG′, Figure 11),and migration up into the Kora volcanic structureappears straightforward (cross section HH′, Figure11). From north-south and east-west stratigraphiccross sections for the region (King et al., 1991), thelikely drainage area for the Kora oil is ca. 500 km2.Assuming that the shale is consistently 10 m thick,a gas:oil ratio of 0.3 as for the shale from Galleon-1(Gibbons and Fry, 1986), a porosity of 10% and wetdensity of 250 kg⋅m–3 (typical for the burial depth),and using the Rock-Eval data in Table 5, the oilpotential of this source rock unit is ca. 155 Mt orca. 170 × 106 m3 under surface conditions (ca. 200× 106 m3 under reservoir conditions of density ca.740 kg⋅m–3 at 17.8 MPa and 68°C). The volume ofoil in the Kora-1 reservoir is estimated at 5 × 106 bbl(McManamon, 1993), or just under 106 m3. Thisrepresents no more than ca. 1% of the geneticpotential of the assumed drainage area, and so theshale is a reasonable source for the Kora oil onquantitative grounds. It appears that the WaipawaBlack Shale equivalent extends northward into theNorthland Basin and is a potential oil source rockthere (Isaac and Herzer, 1994).

CONCLUSIONS

It is possible to determine the relative terrestrialand marine contributions to source rocks in theTaranaki Basin from the carbon number distribu-tions of steranes (terrestrial/marine index). In addi-tion, the trend in increasing importance ofangiosperms in coastal flood plain plant communi-ties from the Late Cretaceous to the Eocene can befollowed by monitoring the relative proportions ofangiosperm-derived triterpanes and gymnosperm-

derived diterpanes (angiosperm/gymnospermindex), yielding age-related source rock informa-tion. The use of a plot of angiosperm/gymnospermindex vs. terrestrial/marine index permits thesources of Taranaki Basin oils to be determinedwith reasonable accuracy, especially when com-bined with maturity considerations based on heat-flow data and derived kinetic models of petroleumgeneration. Coals of the Pakawau and Kapunigroups are the main oil-source units, but marine-inf luenced shales also contribute to varyingextents.

Oil composition ref lects the distribution ofmature source rocks near reservoirs, given thatmost Rakopi-sourced oil may have escaped prior toNeogene trap formation. Distinctly Rakopi-sourcedoil is represented only by the Maui accumulationsand contributions to the Moki field oil. There is thepossibility, however, that some could be trapped indeeper reservoirs where secondary porosity hasdeveloped. Kapuni and Kupe South oils seem to bepredominantly sourced by Paleocene (FarewellFm.) sediments. There is also a Paleocene contribu-tion to oils in the Waihapa field, at the south end ofthe Tarata thrust zone, although the Neogene reser-voir in this field has also received a contributionfrom Eocene coals. In the north of the TaranakiPeninsula there is a high-heat-flow area centered onNew Plymouth, and mature source rock units lienearer the surface.

Oils of the northern part of the Tarata thrustzone originate mainly from Eocene coals of theMangahewa Formation and, to a lesser extent, theKaimiro Formation. Toward New Plymouth, coal-rich strata within the Kaimiro and Farewell forma-tions grade into relatively organic-lean, marineshales of the Turi Formation, which appear to con-tribute to the oils of the area (e.g., Kaimiro andMoturoa fields). Mangahewa coals are still presentbut are mostly early mature and so their contribu-tions are relatively limited compared with those ofthe northern Tarata thrust zone. There is probablyalso a significant contribution from matureFarewell coals lying immediately to the east of theNew Plymouth/Kaimiro region. In the northwest ofthe basin an equivalent of the late PaleoceneWaipawa Black Shale is present and has beenburied sufficiently deeply to source some oil, suchas that in the Kora volcanic structure.

Hydrogen-rich, Late Cretaceous and TertiaryNew Zealand coals are capable of generating andexpelling oil by rank (S) 12.5–14.0 throughout theTaranaki Basin, based on biomarker maturity stud-ies and the implications of compositional changesoccurring through the New Zealand coal band. Thecorresponding vitrinite ref lectance range is ca.0.7–0.9% Ro, over a depth range of 4.0–5.5 km,depending on thermal regime. The oil potential of

Killops et al. 1581

New Zealand coals (and associated shales) isattributable to the submaceral desmocollinite. Thisamorphous material appears to be composed main-ly of leaf-cuticular membranes (accounting for highsaturates and wax content and the presence ofabundant higher-plant diterpanes and triterpanes)and bacterial remains (also aliphatic-rich and con-tributing the hopane content). Such material ischaracteristically deposited under relatively oxidiz-ing conditions in temperate swamp environmentsin which microbial degradation of the bulk of ligni-fied, cellulosic tissue occurs, concentrating themore resistant, aliphatic-rich components. Primarymigration of oil from coal appears to be aided bythe generation of large volumes of supercritical car-bon dioxide from coals, creating expulsion path-ways by microfracturing source units and trans-porting the first phase of generated oil in solution.

REFERENCES CITEDAlexander, R., R. A. Noble, and R. I. Kagi, 1987, Fossil resin

biomarkers and their application in oil to source-rock correla-tion, Gippsland Basin, Australia: APEA Journal, v. 27, p. 63–72.

Analabs, 1984, Petroleum geochemistry of the Taranaki Basin:IGNS Petroleum Report 1013, Institute of Geological andNuclear Sciences, Lower Hutt.

Analabs, 1989, Petroleum Geochemistry: Okoki-1: IGNS PetroleumReport 1495, Institute of Geological and Nuclear Sciences,Lower Hutt.

Analabs, 1991, Petroleum Geochemistry: Toru-1: IGNS PetroleumReport 1668, Institute of Geological and Nuclear Sciences,Lower Hutt.

Aplin, R. T., R. C. Cambie, and P. S. Rutledge, 1963, The taxonom-ic distribution of some diterpene hydrocarbons: Phytochem-istry, v. 2, p. 205–214.

Armstrong, P. A., D. S. Chapman, R. H. Funnell, R. G. Allis, and P. J.J. Kamp, 1994, Thermal state, thermal modelling and hydrocar-bon generation in the Taranaki Basin: Proceedings of NewZealand Petroleum Conference 1994, Ministry of Commerce,Wellington, p. 289-307.

Baker E. A., 1982, Chemistry and morphology of plant cuticularwaxes, in D. F. Cutler, K. L. Allen, and C. E. Price, eds., Theplant cuticle: Linnean Society, London, Academic Press,p. 139–165.

Bennett, C., R. Gregg, and P. King, 1992, Petroleum geology of theTaranaki Basin, with emphasis on the north-eastern quadrant:Petroleum Exploration New Zealand News, May, p. 14–25.

Bertrand, P. R., 1989, Microfacies and petroleum properties ofcoals as revealed by a study of North Sea Jurassic coals: Interna-tional Journal of Coal Geology, v. 13, p. 575–595.

Boudou, J.-P., B. Durand, and J.-L. Oudin, 1984, Diagenetic trendsof a Tertiary low-rank coal series: Geochemica et Cosmochimi-ca Acta, v. 48, p. 2005–2010.

Brassell, S. C., G. Eglinton, and F. Jiamo, 1986, Biological markercompounds as indicators of the depositional history of theMaoming oil shale: Organic Geochemistry, v. 10, p. 927–941.

Burnham, A. K., and J. J. Sweeney, 1989, A chemical kinetic modelof vitrinite maturation and reflectance: Geochimica et Cos-mochimicaActa, v. 53, p. 2649–2657.

Burwood, R., P. Leplat, B. Mycke, and J. Paulet, 1992, Rifted mar-gin source rock deposition: a carbon isotope and biomarkerstudy of a West African Lower Cretaceous “lacustrine” section:Organic Geochemistry, v. 19, p. 41–52.

Cambie, R. C., and R. J. Weston, 1968, Chemotaxonomy of the

New Zealand Podocarpaceae: Journal of New Zealand Instituteof Chemistry, v. 32, p. 105–121.

Collen, J. D., J. H. Johnston, P. J. Dunn, and R. H. Newman, 1988,13C NMR spectra from Upper Cretaceous and lower Tertiarycoal measures, Taranaki Basin, New Zealand: Geology Board ofStudies Publication, no. 2, Victoria University, Wellington.

Collier R. J., and J. H. Johnston, 1991, The identification of possi-ble source rocks, using biomarker geochemistry, in the Tarana-ki Basin, New Zealand: Journal of Southeast Asian Earth Sci-ences, v. 5, p. 231–239.

Cook, R. A., 1987, The geology and geochemistry of crude oils andsource rocks of western New Zealand: New Zealand GeologicalSurvey Petroleum Report 1250, Institute of Geological andNuclear Sciences, Lower Hutt.

Cook, R. A., 1988, Interpretation of the geochemistry of oils ofTaranaki and west coast region, western New Zealand: EnergyExploration and Exploitation, v. 6, p. 201–212.

Czochanska Z., T. D. Gilbert, R. P. Philp, C. M. Sheppard, R. J.Weston, T. A. Wood, and A. D. Woolhouse, 1988, Geochemicalapplication of sterane and triterpane biomarkers to a descrip-tion of oils from the Taranaki Basin in New Zealand: OrganicGeochemistry, v. 12, p. 123–135.

De Grande, S. M. B., F. R. Aquino Neto, and M. R. Mello, 1993,Extended tricyclic terpanes in sediments and petroleums:Organic Geochemistry, v. 20, p. 1039–1047.

Flores, R. M., J. M. Beggs, and P. R. King, 1993, Sedimentology oftide-dominated reservoir sandstones in the Eocene KapuniGroup, Taranaki Basin, New Zealand (abs.): AAPG 1993 AnnualConvention, p. 102.

Frankenberger A., R. R. Brooks, H. Varela-Alvarez, J. D. Collen, R. H. Filby, and S. L. Fitzgerald, 1994, Classification of someNew Zealand crude oils and condensates by means of theirtrace element contents: Applied Geochemistry, v. 9, p. 65–71.

Gibbons M. J., and S. Fry, 1986, A geochemical study of theGalleon-1 well, Canterbury Basin, offshore New Zealand: IGNSPetroleum Report 1146, Institute of Geological and Nuclear Sci-ences, Lower Hutt.

Gibbons M. J., H. A. Bockmeulen, and S. O’Reilly, 1981, Petroleumgeochemistry of the Shell BP Todd well: Tangaroa-1, offshoreTaranaki, New Zealand: IGNS Petroleum Report 793, Instituteof Geological and Nuclear Sciences, Lower Hutt.

Giggenbach, W. F., Y. Sano, and H. Wakita, 1993, Isotopic compo-sition of He, and CO2 and CH4 contents in gases producedalong the New Zealand part of a convergent plate boundary:Geochimica et Cosmochimica Acta, v. 57, p. 3427–3455.

Gould, R., 1980, The coal-forming flora of the Walloon coal mea-sures: Coal Geology, v. 1, p. 83–105.

Haskell, T., 1991, An analysis of Taranaki Basin hydrocarbonmigration paths; some questions answered: Petroleum Explo-ration New Zealand News, Jan., p. 19–25.

Haskell, T., 1992, An analysis of Taranaki Basin hydrocarbon migra-tion systems. Proceedings of 1991 New Zealand Oil ExplorationConference, Ministry of Commerce, Wellington, p. 146.

Hedberg, H. D., 1968, Significance of high wax oils with respect togenesis of petroleum: AAPG Bulletin, v. 52, p. 736–750.

Hill, P. J., and J. D. Collen, 1978, The Kapuni sandstones fromInglewood-1 well, Taranaki—petrology and the effect of diage-nesis on reservoir characteristics: New Zealand Journal of Geol-ogy and Geophysics, v. 21, p. 215–228.

Hirner, A. V., and G. L. Lyon, 1989, Stable isotope geochemistry ofcrude oils and of possible source rocks from New Zealand—1:carbon: Applied Geochemistry, v. 4, p. 109–120.

Hirner, A. V., and B. W. Robinson, 1989, Stable isotope geochem-istry of crude oils and of possible source rocks from NewZealand—2: sulphur: Applied Geochemistry, v. 4, p. 121–130.

Holloway, P. J., 1982, Structure and histochemistry of plant cuticu-lar membranes: an overview, in D. F. Cutler, K. L. Allen, and C. E. Price, eds., The plant cuticle: Linnean Society, London,Academic Press, p. 1–32.

Isaac, M. J., and R. H. Herzer, 1994, Beyond Taranaki—is the nextMaui field west of Northland?: Proceedings of the New Zealand


Petroleum Conference 1994, Ministry of Commerce, Welling-ton, p. 129.

Johnston, J. H., 1992, The characterisation of potential hydrocarbon-generative source rocks in the North Taranaki Basin by geochemi-cal biomarkers: Proceedings of New Zealand Oil Exploration Con-ference 1991, Ministry of Commerce, Wellington, p. 357–363.

Johnston, J. H., R. J. Collier, and J. D. Collen, 1990, What is thesource of Taranaki oils? Geochemical biomarkers suggest it isthe very deep coals and shales: Proceedings of New ZealandOil Exploration Conference 1989, Ministry of Commerce,Wellington, p. 288–295.

Johnston, J. H., R. J. Collier, and A. I. Maidment, 1991, Coal assource rocks for hydrocarbon generation in the Taranaki Basin,New Zealand: a geochemical biomarker study: Journal ofSoutheast Asian Sciences, v. 5, p. 283–289.

Kamp, P. J. J., and P. F. Green, 1990, Thermal and tectonic historyof selected Taranaki Basin (New Zealand) wells assessed byapatite fission track history: AAPG Bulletin, v. 74, p. 1401–1419.

Khorasani, G. K., 1987, Oil-prone coals of the Walloon coal mea-sures, Surat Basin, Australia, in A. C. Scott, ed., Coal and coal-bearing strata: recent advances: Geological Society Special Pub-lication, no. 32, Blackwell Scientific, Oxford, p. 303–310.

Killops, S. D., and N. L. Frewin, in press, Triterpenoid diagenesisand cuticular preservation: Organic Geochemistry.

Killops, S. D., and V. J. Howell, 1991, Complex series of penta-cyclic triterpanes in a lacustrine sourced oil from Korea BayBasin: Chemical Geology, v. 91, p. 65–79.

Killops, S. D., and V. J. Killops, 1993, An introduction to organicgeochemistry: Longman, Harlow.

King, P. R., 1990, Polyphase evolution of the Taranaki Basin, NewZealand: changes in sedimentary and structural style: Proceed-ings of New Zealand Oil Exploration Conference 1989, Min-istry of Commerce, Wellington, p. 134–150.

King, P. R., and G. P. Thrasher, 1992, Post-Eocene development ofthe Taranaki Basin, New Zealand: convergent overprint of apassive margin, in J. S. Watkins, F. Zhiqiang and K. J. Miller,eds., Geology and geophysics of continental margins: AAPGMemoir 53, p. 93–118.

King, P. R., T. R. Naish, and G. P. Thrasher, 1991, Structural crosssections and selected palinspastic reconstructions of theTaranaki Basin, New Zealand: New Zealand Geological SurveyReport G-150, Institute of Geological and Nuclear Sciences,Lower Hutt.

Kirkland, D. W., T.-F. Tsui, and M. L. Stockton, 1987, Generationof oil from coals and carbonaceous shales: AAPG Bulletin, v. 71, p. 577.

Le Berre, F., S. Derenne, C. Largeau, J. Connan, and C. Berkaloff,1991, Occurrence of non-hydrolysable, macromolecular, wallconstituents in bacteria, in D. A. C. Manning, ed., Organic geo-chemistry. Advances and applications in energy and the naturalenvironment: University Press, Manchester, p. 428–431.

Lewan, M. D., 1984, Factors controlling the proportionality ofvanadium to nickel in crude oils: Geochimica et CosmochimicaActa, v. 48, p. 2231–2238.

Lowery, J. H., 1988, Catalogue of vitrinite reflectance measure-ments and coal analyses from oil prospecting wells in TaranakiBasin, New Zealand: Report M168, Institute of Geological andNuclear Sciences, Lower Hutt.

Lu, S.-T., and I. R. Kaplan, 1992, Diterpanes, triterpanes, steranesand aromatic hydrocarbons in natural bitumens andpyrolysates from different humic coals: Geochimica et Cos-mochimica Acta, v. 56, p. 2761–2788.

McBeath D. M., 1977, Gas-condensate fields of the Taranaki Basin,New Zealand: New Zealand Journal of Geological Geophysics,v. 20, p. 99–127.

McKirdy D. M., and A. R. Chivas, 1992, Nonbiodegraded aromaticcondensate associated with volcanic supercritical carbon diox-ide, Otway Basin: implications for primary migration from terres-trial organic matter: Organic Geochemistry, v. 18, p. 611–627.

McKirdy, D. M., A. K. Aldridge, and P. J. M. Ypma, 1983, A geo-chemical comparison of some crude oils from pre-Ordovician

carbonate rocks, in M. Bjorøy et al., eds., Advances in organicgeochemistry 1981: Wiley, Chichester, p. 99–107.

McManamon, D., 1993, Kora exploration and drilling results:Petroleum Exploration New Zealand News, July, p. 18–27.

Mello, M. R., N. Telnaes, P. C. Gaglianone, M. I. Chicarelli, S. C.Brassell, and J. R. Maxwell, 1988, Organic geochemical charac-terisation of depositional palaeoenvironments of source rocksand oils in Brazilian marginal basins: Organic Geochemistry,v. 13, p. 31–45.

Mildenhall, D. C., 1980, New Zealand Late Cretaceous and Ceno-zoic plant biogeography: a contribution: PalaeogeographyPalaeoclimatology Palaeoecology, v. 31, p. 197–233.

Mildenhall, D. C., 1988, Kaihu Group at Chases Gorge, in D. T.Pocknall and R. Tremain, eds., New Zealand palynology andpalaeobotany—a field guide to palynological and palaeobotani-cal localities: Institute of Geological and Nuclear Sciences,Lower Hutt, p. 12–15.

Moldowan, J. M., F. J. Fago, C. Y. Lee, S. R. Jacobson, D. S. Watt,N.-E. Slougui, A. Jeganathan, and D. C. Young, 1990, Sedimen-tary 24-n-propylcholestanes, molecular fossils diagnostic ofmarine algae: Science, v. 247, p. 309–312.

Newman, J., and N. A. Newman, 1982, Reflectance anomalies inPike River coals: evidence of variability in vitrinite type, withimplications for maturation studies and “Suggate rank”: NewZealand Journal of Geological Geophysics, v. 25, p. 233–243.

Nip, M., E. W. Tegelaar, H. Brinkhuis, J. W. de Leeuw, P. A.Schenck, and P. J. Holloway, 1986, Analysis of modern and fos-sil plant cuticles by Curie point Py-GC and Curie point Py-GC-MS: Recognition of a new, highly aliphatic and resistantbiopolymer: Organic Geochemistry, v. 10, p. 769–778.

Noble, R. A., R. Alexander, R. I. Kagi, and J. Knox, 1985, Tetra-cyclic diterpenoid hydrocarbons in some Australian coals, sedi-ments and crude oils: Geochimica et Cosmochimica Acta,v. 49, p. 2141–2147.

Noble, R. A., R. Alexander, R. I. Kagi, and J. Knox, 1986, Identifica-tion of some diterpenoid hydrocarbons in petroleum: OrganicGeochemistry, v. 49, p. 825–829.

Noble, R. A., C. H. Wu, and C. D. Atkinson, 1991, Petroleum gener-ation and migration from Talang Akar coals and shales offshoreN.W. Java, Indonesia: Organic Geochemistry, v. 17, p. 363–374.

Palmer, J., and G. Bulte, 1991, Taranaki Basin, New Zealand, in K. T.Biddle, ed., Active margin basins: AAPG Memoir 52, p. 261–282.

Peakman, T. M., H. L. ten Haven, J. R. Rechka, J. W. de Leeuw, andJ. R. Maxwell, 1989, Occurrence of (20R)- and (20S)-∆8(14) and∆14 5α(H)-sterenes and the origin of 5α(H),14ß(H),17ß(H)-ster-anes in an immature sediment: Geochimica et CosmochimicaActa, v. 53, p. 2001–2009.

Philp, R. P., and T. D. Gilbert, 1986, Biomarker distributions inAustralian oils predominantly derived from terrigenous sourcematerial: Organic Geochemistry, v. 10, p. 73–84.

Powell, T. G., 1988, Developments in concepts of hydrocarbongeneration from terrestrial organic matter, in H. C. Wagner, L. C. Wagner, F. F. H. Wang, and F. L. Wong, eds., Petroleumresources of China and related subjects: Earth Science Series, v. 10, Circum-Pacific Council for Energy & Mineral Resources,Houston, p. 807–824.

Powell, T. G., C. J. Boreham, M. Smyth, N. Russell, and A. C. Cook,1991, Petroleum source rock assessment in non-marinesequences: pyrolysis and petrographic analysis of Australiancoals and carbonaceous shales: Organic Geochemistry, v. 17, p. 375–394.

Raine, J. I., C. P. Strong, and G. J. Wilson, 1993, Biostratigraphicreview of petroleum exploration wells, Great South Basin, NewZealand: IGNS Sci. Rep. 93/32, Institute of Geological andNuclear Sciences, Lower Hutt.

Reed, J. D., 1992, Exploration geochemistry of the Taranaki Basinwith emphasis on Kora: Proceedings of the New ZealandExploration Conference 1991, Ministry of Commerce, Welling-ton, p. 364–372.

Sandvik, E. I., W. A. Young, and D. J. Curry, 1992, Expulsion fromhydrocarbon sources: the role of organic absorption: Organic

Killops et al. 1583

Geochemistry, v. 19, p. 77–87.Sofer, Z, 1984, Stable carbon isotope compositions of crude oils:

application to source depositional environments andpetroleum alterations: AAPG Bulletin, v. 68, p. 31–49.

Suggate, R. P., 1959, New Zealand coals: their geological settingand its influence on their properties: Bulletin 134, Institute ofGeological and Nuclear Sciences, Lower Hutt.

Suggate, R. P., and J. P. Boudou, 1993, Coal rank and type variationin Rock-Eval assessment of New Zealand coals: Journal ofPetroleum Geology, v. 16, p. 73–88.

Summons, R. E., J. K. Volkman, and C. J. Boreham, 1987, Dinoster-ane and other steroidal hydrocarbons of dinoflagellate origin insediments and petroleum: Geochimica et Cosmochimica Acta,v. 51, p. 3075–3082.

Sweeney, J. J., 1990, BASINMAT—FORTRAN program calculates oil andgas generation using a distribution of discrete activation ener-gies: Geobyte, v. 5, p. 37–43.

Sweeney, J. J., and A. K. Burnham, 1990, Evaluation of a simplemodel of vitrinite reflectance based on chemical kinetics:AAPG Bulletin, v. 74, p. 1559–1570.

Sykes, R., R. P. Suggate, and P. R. King, 1992, Timing and depth ofmaturation in Southern Taranaki Basin from reflectance andrank(S): Proceedings of the New Zealand Oil Exploration Con-ference 1991, Ministry of Commerce, Wellington, p. 373–389.

Tegelaar, E. W., J. W. de Leeuw, S. Derenne, and C. Largeau, 1989,A reappraisal of kerogen formation: Geochimica et Cos-mochimica Acta, v. 53, p. 3103–3106.

Thomas, B. M., 1982, Land-plant source rocks for oil and their sig-nificance in Australian basins: APEA Journal, v. 22, p. 164–178.

Thrasher, G. P., 1990, The Maui field and the exploration potentialof Southern Taranaki; a few unanswered questions: PetroleumExploration New Zealand News, July, p. 26–30.

Thrasher, G. P., 1992, Late Cretaceous source rocks of TaranakiBasin: Proc. NZ Oil Explor. Conf. 1991, Ministry of Commerce,Wellington, p. 147–154.

van Aarssen, B. G. K., J. K. C. Hessels, O. A. Abbink, and J. W. deLeeuw, 1992, The occurrence of polycyclic sesqui-, tri-, andoligoterpenoids derived from a resinous polymeric cadinene incrude oils from Southeast Asia: Geochimica et CosmochimicaActa, v. 56, p. 1231–1246.

Weston R. J., Z. Czochanska, C. M. Sheppard, A. D. Woolhouse,and R. A. Cook, 1988a, Organic geochemistry of the sedimenta-ry basins of New Zealand. Part III. A biomarker correlation ofthree petroleum seeps and some rock bitumens from the EastCoast of the North Island: Journal of Royal Society of NewZealand, v. 18, p. 225–243.

Weston, R. J., M. H. Engel, R. P. Philp, and A. D. Woolhouse,1988b, The stable carbon isotopic composition of oil from theTaranaki Basin of New Zealand: Organic Geochemistry, v. 12,p. 487–493.

Weston, R. J., R. P. Philp, C. M. Sheppard, and A. D. Wool-house,1989, Sesquiterpanes, diterpanes and other higher ter-panes in oils from the Taranaki Basin of New Zealand: OrganicGeochemistry, v. 14, p. 405–421.

Woolhouse, A.D., J.-N. Oung, R. P. Philp, and R. J. Weston, 1992,Triterpanes and ring-A degraded triterpanes as biomarkerscharacteristic of Tertiary oils derived from predominantly high-er plant sources: Organic Geochemistry, v. 18, p. 23–31.


ABOUT THE AUTHORS

Steve Killops

Steve Killops is an organic geo-chemist in the Hydrocarbon Re-sources and Basin Studies Group atthe Institute of Geological & Nucle-ar Sciences (IGNS). He has beeninvolved in petroleum geochem-istry since obtaining a B.Sc. degreeand a Ph.D. at Bristol University.Following a postdoctoral researchfellowship, Steve worked in thecommercial sector on biomarkerstudies for the exploration industry and, prior to joiningIGNS at the end of 1992, he spent five years as lecturerin organic geochemistry at Royal Holloway and BedfordNew College, University of London. He is the author ofAn Introduction to Organic Geochemistry (Longman,1993).

Tony Woolhouse

Tony Woolhouse is an organicchemist with Industrial ResearchLtd. (IRL). He graduated in 1973from the Victoria University ofWellington (B.Sc. and Ph.D.) and,following postdoctoral work(1974–1975) at the University ofLiverpool, he joined the OrganicChemistry Group of the ChemistryDivision of the then Department ofScientific and Industrial Research(now part of IRL). During 1984–1989, Tony set up aresearch group to evaluate the genetic relationships ofoils and sediments in New Zealand from biomarker dis-tributions, and also worked for a time with Paul Philp atthe University of Oklahoma.

Rod Weston

Rod Weston is a graduate of theUniversities of Auckland (M.Sc.),Oxford (D.Phil.), and London(DIC). He joined the ChemistryDivision of the Department of Sci-entific and Industrial Research(now Industrial Research Ltd.) in1965 as an undergraduate and hasbeen with them ever since. He isan organic chemist with interestsin the chemistry of natural prod-ucts, especially essential oils, terpenoids, and steroids,and has worked with Sir Derek W. R. Barton in Londonand R. Paul Philp in Oklahoma.

Richard Cook

Richard Cook received his Ph.D.(Petroleum Geochemistry ofTaranaki Basin) from Victoria Uni-versity of Wellington in 1987. Hehas been part of the Basin StudiesGroup of IGNS since joining whatwas then the New Zealand Geologi-cal Survey (NZGS) in 1978. Richardhas published numerous papers onbasin studies, oil seeps, petroleumgeochemistry, and resource evalua-tion. He has also been business manager and group com-mercial coordinator in both DSIR and IGNS. Prior tojoining the NZGS, he worked for Texaco for four yearsin exploration in the North Sea, Portugal, south Texas,and international new ventures.

Killops et al. 1585

petroleum geochemistry of NZ

Documents

source of oil

bbl of oil

main oil source rocks

cretaceoussourced oil

oil generation

likely petroleum source

ofthe oils

late cretaceous sandstones