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Upper Cretaceous and Tertiary geologyof the upper Waitahaia River, RaukumaraPeninsula, New ZealandC. J. Phillips a ba Forest Research Institute , P.O. Box 31 01l, Christchurch , NewZealandb University College of Agriculture, Lincoln College , Canterbury ,New ZealandPublished online: 20 Jan 2012.

To cite this article: C. J. Phillips (1985) Upper Cretaceous and Tertiary geology of the upperWaitahaia River, Raukumara Peninsula, New Zealand, New Zealand Journal of Geology andGeophysics, 28:4, 595-607, DOI: 10.1080/00288306.1985.10422535

To link to this article: http://dx.doi.org/10.1080/00288306.1985.10422535

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New Zealand Journal of Geology and Geophysics, 1985, Vol. 28: 595-607 595 0028-8306/85/2804-0595$2.50/0 © Crown copyright 1985

Upper Cretaceous and Tertiary geology of the upper Waitahaia River, Raukumara Peninsula, New Zealand

C. J. PHILLIPS Forest Research Institute P.O. Box 31 011 Christchurch, New Zealand*

Abstract In the upper Waitahaia River valley of Raukumara Peninsula, a sequence of allo­chthonous Early Cretaceous - Early Miocene sedi­ments is faulted against a sequence of autochthonous Early Cretaceous - Early Paleocene sediments. The Waitahaia Thrust Zone separates the structurally simple autochthonous sequence from the more complex allochthonous sequence.

Four autochthonous units are present: Waita­haia Formation (new) (Motuan-Ngaterian), con­sisting of folded, indurated, poorly fossiliferous alternating sandstone and siltstone; Karekare For­mation (Ngaterian-Teratan), consisting of siltstone and occasional sandstone beds; Owhena Formation (new) (lower Haumurian-Haumurian), consisting of alternating sandstone and siltstone, and sandy mudstone; and Whangai Formation (Haumurian­Teurian), consisting of siliceous to calcareous mud­stone and siltstone and occasional greensand. An unconformity separates Waitahaia Formation from Karekare Formation and Karekare Formation from Owhena Formation.

The allochthonous sequence comprises a series of sheets separated by southeast dipping, low-angle thrust faults. The sheets are composed of a variety of rock types which range in age from Motuan to Altonian.

Emplacement of older thrust sheets is considered to have occurred between Late Oligocene and Early Miocene (Waitakian-Otaian) time. Emplacement of the younger thrust sheet (lhungia Allochthon) is considered to have occurred early in the Late Pliocene.

Keywords stratigraphy; autochthons; allo­chthons; thrust faults; Cretaceous; Waitahaia River; Raukumara Peninsula; Waitahaia Formation; Owhena Formation; new stratigraphic names; Wai­tahaia Thrust Zone

*Present address: University College of Agriculture, Lin­coln College, Canterbury, New Zealand.

Received 23 July 1984, accepted 5 June 1985

INTRODUCTION

An 80 km2 area in the upper reaches of Waitahaia River, the largest tributary ofMata River, has been geologically mapped as part of Forest Research Institute studies of the relationships between slope stability and geology in the east coast region of the North Island, New Zealand. The mapped area lies approximately 80 km due north of Gisborne and 35 km west of Tokomaru Bay (Fig. 1). This paper describes the stratigraphy of the mapped area and outlines its geologic structure and history.

The area examined falls within metric NZMS 260 (1:50 000) map sheets Yl5 and Yl6. Fossil local­ities (e.g., Yl6/f165), are recorded in the metri­cated New Zealand Fossil Record File held by the New Zealand Geological Survey, Lower Hutt.

PREVIOUS WORK

The earliest detailed work in the area was carried out by Ongley & MacPherson (1928). Successive work by a number of oil companies included parts of the study area (e.g., Pick 1962). Kingma (1965) synthesised all previous work in a 1:250 000 scale map. Reconnaissance mapping of 30 km2 of Toko­maru State Forest within the study area was carried out in 1979 by R. D. Black. Parts of this unpub­lished work are incorporated in the present study and are hereby acknowledged.

PHYSIOGRAPHY

The Waitahaia River flows eastwards from the steep bush-clad hills of Raukumara Forest Park. The western and northern parts of the area are steep and dissected, with dendritic drainage and numer­ous small gorges and waterfalls reflecting the influ­ence of the harder indurated rocks. In contrast, the central and eastern parts of the study area are less dissected and show a predominance of mass move­ment landforms (Phillips & Pearce 1985). Here, less competent, uppermost Cretaceous and lowermost Tertiary rocks are sheared and tectonised within the major southwest-northeast trending Waitahaia Thrust Zone (amended from the Waitahaia Fault Zone of Pick 1962). This fault zone separates a structurally simple autochthonous sequence to the west from a structurally complex allochthonous sequence to the east (Fig. 1).

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

0 ..,. g: 0

Y15

Elevation {m)

Y15 40

Y16

42 43

X <E(---AAutochthon~ 1000

Fig. 1 Simplified geological map of upper Waitahaia River valley and cross-section A-B.

STRATIGRAPHY

Autochthonous sequence

WAITAHAIA FORMATION (Moore et al. in press)

The name is taken from Waitahaia River, the dom­inant physical feature of the study area. A descrip­tion of the formation is to be published in a forthcoming New Zealand Geological Survey report (Moore et al. in press: "A revised Cretaceous- Early Tertiary stratigraphic nomenclature for eastern North Island, New Zealand," NZGS report Gl04),

and a formal definition including its type section is expected thereafter. For this paper, a reference section is located within the Waitahaia River gorge 1 km upstream of the unconformable contact with the overlying Karekare Formation at grid ref. Y16/453363.

The sandstone-dominated sediments forming the lowest part of MacKay's (1887) Awanui Series were included in the Raukumara Series by Ongley & MacPherson (1928). Kingma (1965) mapped both Ngaterian and undifferentiated Clarence Series rocks in the area. Similar rocks have been named

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Phillips-D. Cret. geology, Waitahaia R. 597

LEGEND

+ N

I

Motu an

sequence Older

allochthonous sequence within Waitahaia Thrust

Zone

Younger allochthonous

sequence

0 20 '-----' km

<!#' -' Thrust fault

"' u_..r( Fault ,

~ 40 Dip and strike- facing known

X 40 Bedding overturned

--'27 Dip and strike- facing not known ~ ~ , , ' Lithologic contact

U ~Unconformity

Fig. 1 (continued)

"Hikurangi Beds" (MacKay 1887) by many geol­ogists. However, the name "Hikurangi Formation" has never been defined formally (Kenny 1980).

For the purposes of this study, Waitahaia For­mation refers to alternating beds of sandstone and siltstone of Ngaterian age or immediately older. The formation is lithologically similar to "Hikurangi Formation" (Kenny 1980) and Raukumara For­mation (I. G. Speden pers. comm.), but may not be the same age as these formations.

Well-bedded, indurated, flysch-like alternating sandstone and siltstone is the dominant rock type (Fig. 2). In upper parts of the sequence, massive sandstone beds predominate. Sandstone:siltstone ratios and bedding thicknesses vary, but typical sections are sandstone dominated, with ratios of sand to silt of 2: 1 or greater. Sandstone beds vary from 5 em to 1 m thick whereas siltstone beds rarely exceed 30 em. Sedimentary structures are abun­dant. Incomplete Bouma sequences A-B and A-C are common. Parallel lamination is common within sandstone units, and cross lamination and convo­lute lamination occur sparsely. Laminae are gener­ally carbonaceous. Sandstone beds are in places graded and show a variety of sole marks - flute

casts, load casts, and feeding traces or burrows. Tabular or lensoidal calcareous concretions up to 1 m long occur sporadically throughout. Tuff beds, although rare, are generally about 5 em thick. Sandstones are fine-medium grained, quartzo­lithic, blue-grey when fresh, and weather grey to yellow-brown. Siltstones are dark blue-grey to black, weathering pale yellow to brown, and tend to fritter out.

A poorly bedded, thick (5 m beds), blue-grey but weathering brown, medium grained, lithic sand­stone (massive sandstone unit) is the only variant of the flysch sequence. Siltstone interbeds are rare or absent. The massive sandstone is a ridge-form­ing unit restricted to the southwest of the study area, ¥16/423342-423348 (Ohinepaka Trig. XXIII), where a minimum thickness of 20 m has been recorded. Similar rocks to the northeast have been included in the Rangikohua lithofacies described by Kenny (1984).

Waitahaia Formation crops out in the western and northern parts of the study area (Fig. 1), cover­ing approximately one-third of the mapped area. This formation is generally better exposed in streambeds than the younger formations.

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598 New Zealand J oumal of Geology and Geophysics, 1985, Vol. 28

LEGEND for figures 2-4

F + + + Thrust fault

Allochthonous ~~

I:.::··.: .··I Sandstone

I::..~= I Siltstone Uf\IVVVV\IVV\I\U U nco n form ity

~Alternating

E:::1 sandstone/siltstone

~~Conglomerate 0 metres

100

~· ~Breccia 200

~Limestone 300

I [3J Concretions 400

500

Autochthonous seguence

~~~~~~~~~~~-r---F f68(Dt)

f167(Dt)

Whangai Formation

f196(Lwh- Ld) p~;::r::::=rJ

.•.. 0. • .•• •

lhungia Formation

Landon Series lithotypes

Melange

Whangai Formation

Tikihore Formation

--1~. i.i. ~. ~-~-~iiru~n=di:erentiated

l~~~~i~~ Karekare f171(Ra) Formation

.......

. •· ....... '• ... ·.

Fig. 2 Stratigraphic column for upper Waitahaia River valley.

~~~~~~ ----------~

.... ·.·. Clarence Series rocks

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Phillips-D. Cret. geology, Waitahaia R.

The folded and faulted nature of Waitahaia For. mation makes estimates of thickness imprecise, but a minimum thickness of 300 m is suggested. Total thickness of the flysch further north and west is unlikely to exceed 1 000 m (Speden in Stevens & Speden 1978).

In situ macrofaunas are scarce. Thin-shelled Ino­ceramus spp. are seen in broken shellbeds and as fragments within siltstones or at the base of fine sandstone units. Inoceramus sp. ex. gr. ipuanus­kapuus Wellman (Urutawan-Motuan) was found at one locality in the Mangawhero Stream (Y 16/f63). Fragments of shell thought to belong to Inoceramus sp. ex. gr. hakarius-fyfei Wellman (Ngaterian) were found in several localities. Wai­tahaia Formation is therefore considered to be of Urutawan-Ngaterian age.

KAREKARE FORMATION (Moore 1978)

The lower part of the formation is exposed in the Waitahaia River, from the unconformable contact with the underlying Waitahaia Formation {¥16/453363) (Fig. 2, 3) downstream for 900 m to the unconformable contact with the overlying Owhena Formation {¥16/459365). The upper part is less well exposed in Waingata Stream, strati­graphically upward from the unconformable con­tact with the underlying Waitahaia Formation {¥16/496398-507393).

The formation consists of a moderately thick sequence of siltstone with thin sandstone beds. The predominant rock type is moderately indurated, medium, blue-grey siltstone which is weakly lam­inated. Local Inoceramus shells, fragments, and prisms are common. Thin beds of fine-medium sandstone occur throughout the formation but are more common in basal sections. Calcareous con­cretions, both lensoidal and nodular, are sca!tered throughout but are generally more abundant m the upper parts. The upper part of the formation is marked by a 2 m thick, whitish concretionary hori­zon. The concretions vary in shape and size from 10-20 em to 2m long tabular concretions or bands. The concretions are well cemented and lithified and form a useful marker horizon. In a few places (e.g., Y16/458364), siltstones grade locally into greenish sandy siltstones or muddy sandstones, massive in appearance, and often poorly consolidated. Red and green siltstone beds in various parts of the study area (e.g., Y16/463394) are similar to what Ongley & MacPherson (1928) called the "Mangaotane mudstone". Crystals of pyrite, up to 1 em, and nodular blocks of pyrite are common in the upper parts of the sequence.

Karekare Formation extends from a ridge on the Waitahaia-Takapau road near Ruatahunga Station

599

{¥16/445349) northeastward in a narrow band towards Waingata Stream (Fig. 1). It forms long dip slopes in the catchments of Hikutamomimomi and Chaffeys' Streams* and is prone to earthflow and slide erosion in these areas (Phillips & Pearce 1985). In the Waitahaia River section, the forma­tion is 250 m thick, but to the north the formation thins to 1 00 m.

Pick (1962) considered the Waitahaia River sec­tion from Waitahaia Formation through Karekare Formation up into Owhena Formation to represent a complete age sequence from Mangaotanean (middle Raukumara Series) through to Haumurian (upper Mata Series). Ages were assigned on the basis of a sequence of Inoceramus species {Wellman 1959). I have been unable to find any index fossils of the upper Raukumara Series in the Waitahaia River section. All fossils within the middle to lower parts of Karekare Formation in this section were identified as the Ngaterian index fossil Inoceramus sp. ex. gr. hakarius-fyfei (Y16/fl89) (1. G. Speden pers. comm.). Several specimens of the Arowhanan index fossil/. rangatira Wellman (Y16/fl71) were found near the top of the formation, generally in association with the sandier phases. Microfossils from Karekare Formation in the Waitahaia River section gave wide age ranges (e.g., Y16/fl63, Korangan-Haumurian; Y16/f214, Arowhanan­Piripauan). C. P. Strong and G. J. Wilson (pers. comm.) consider that the age range in this section is latest Ngaterian to Arowhanan.

Inoceramus opetius Wellman and I. bicorrugatus Marwick have been found in Waingata Stream (P. R. Moore & J. Kenny pers. comm.), suggesting an age of Mangaotanean-Teratan.

The lack of Mangaotanean and Teratan rocks in the Waitahaia River section can be explained as the result of erosion of these sediments before dep­osition of the Owhena Formation sandstones. This major unconformity is of regional extent {Isaac 1971; Moore 1978) and occurs generally near the base of the Haumurian strata.

From the cumulative fossil evidence, Karekare Formation is considered to range in age from Nga­terian to Teratan.

OWHENA FORMATION (new)

The formation is named after Owhena Station. The type section is located in Waitahaia River and is defined as a 100 m section downstream from the unconformable contact with the underlying Kare-

*Informal name used by the author, taken from New Zealand Forest Service road which crosses the upper stream catchment.

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600

vertical scale

Karekare Formation

-u-----

Waitahaia Formation

~

I

.tlo

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

Parallel laminaled-massive, medium-dark blue-grey siHstone. Some in1erbedded greener beds higher in sequence. Inoceramus hakarius fragments.

Obscured and slumped.

Massive silts\:Jne; some minor sandstone beds (1 0 em~ Silts\:Jne fr~rs out 40 em sparse tabloid to spherical concretions .

Some thin sandstone beds (5-10 em~

Obscured and slumped.

Fig. 3 Stratigraphic column of the upper Waitahaia Formation and its contact with Karekare Formation (YI6/453363). For key see Fig. 2.

- Al1ernating thin -bedded sandstone and siHstone (10-15 em). Convolu1e laminations on sandstone beds. SiHstone:sandstone 1.5:1

----

. .

I I I I I I I I I

Sil1stone-domina1ed sequence, sandstone beds (3-5 em).

Thicker sandstone beds (1 0-20 em). Ripples exposed.

Obscured. Much siHstone colluvium.

I I

-t-----u­Obscured.

A11ernating sandstone and siHstone. Sandstone beds 20 em. S and:sitt > 2:1.

Obscured.

Allernating sandstone and siHstone. Sandstone beds (20-25 em). Well-lithified, medium blue-grey medium-grained sandstone . lncompte1e Bouma sequences present

ln1erbedded siHstone is parallel lamina1ed and dark blue- grey in colour.

kare Formation at Y16/459365 (Fig. 1). The upper part of the formation is seen in Owhena Stream (Y16/462364-460363).

mation (Lillie 1953) has been applied to interbed­ded sandstones and mudstones, sometimes carbonaceous and glauconitic, distributed through­out the East Coast Deformed Belt (van der Lingen & Pettinga 1980). Owhena Formation is also equated with basal parts of the Rakauroa Forma-

Similar rocks in the Tapuaeroa Valley were assigned to the Tapuaeroa Series of Ongley & MacPherson ( 1928). The name Tapuaeroa For-

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Phillips-D. Cret. geology, Waitahaia R.

Fig. 4 Stratigraphic column of the Owhena Formation (in part after Mr P. R. Moore pers. comm.). For key see Fig. 2.

Whan~Jai Formation

Owhena Formation

0

10

20m

~ ~ c!J ~ Irregular, nodular, calcareous crystalline '-0 ,'0 concretions in hard grey bioturbated ')) <D 'i)Q mudstone.

Moderalely well bedded, hard, bluish-grey calcareous mudstone.

Hard, medium grey slightly glauconitic, micaceous · - mudstone, siky beds.

:; .. \:: ,: :(.: ··:.:·.:) 10 em very coarse sandstone-fine grit.

-;., .. , .. , ... , .. :.,,·)

o.,e.

· .. · .: : ..

,..._. : . . :. :

:.: ·,' .. : : ...... ·

. . . . . . .

. ·.·.·:.·.:.

Medium grey micaceous sandstone with thin (1-10 em) parallel laminaled, graded, glauconitic fine sandstone beds. InOceramus fragments.

Grey, highly bioturba1ed, micaeous, slightly glauconitic, gritty very fine sandstone. Poorly bedded with scal\ered concretions.

Muddy fine-very fine sandstone, micaceous, slightly glauconitic, carbonaceous. Bioturbaled with few thin lamina1ed sandstone beds.

Well-bedded allernating parallel to ripple laminaled carbonaceous sandstone.

Slightly silty sandstone to medium fine sandstone. Minor dark grey mudstone. Laminaled, graded, sandstone beds mosUy 10-30 em.

Carbonaceous laminaled sandskme beds 100 em .

--u---- '-·-··.:.·;-~j· ---u----------------Karekare ~2)~~ Concretionary Zone

Formation · · · 6 -~ - Q.:. Hard grey mudstone with thin (2-3 em)

0 - parallel-laminaled fine sandstone beds. Some concretions.

601

tion (Webb 1970; after Jablonski 1934; Moore 1978) and is equivalent to Tahora Sand (Webb 1971).

The formation consists of a thin fining-upwards sequence of sandstone, siltstone, and mudstone (Fig. 4). The top is marked by the appearance of a major nodular concretionary horizon, the base of the

overlying Whangai Formation (Lillie 1953). Basal sections are well-bedded, alternating, carbonaceous sandstone and dark grey mudstone, or carbona­ceous laminated sandstone beds. Blue-grey, muddy, highly bioturbated, micaceous, slightly glauconitic fine sandstone with scattered concretions occurs

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

above the alternating phase. The sandstone grades up into medium-grey, micaceous siltstone with thin, laminated, graded, glauconitic, fine sandstone beds containing sparse Inoceramus fragments. The upper part of the sequence is marked by a gradual fining upwards to hard, medium-grey to bluish-grey, non­calcareous, slightly glauconitic mudstone (Fig. 4).

Owhena Formation extends in a narrow band northeastwards from near Ruatahunga Station (Yl6/446347) to Waingata Stream, where it thins and disappears. The outcrop pattern closely follows that of the underlying Karekare Formation. In the southwestern comer, Owhena Formation is faulted out by the Ruatahunga Fault (Fig. I). The most complete section occurs in Waitahaia River where 100 m of sediment is present. Elsewhere only parts of the sequence are observed.

Macrofossils are rare, and only a few fragments of Inoceramus spp. were seen. Microfossil ages based on the presence of foraminifera, pollens, spores, and dinoflagellates range from Arowhanan­Haumurian (Y16/f71) to, more commonly, Piri­pauan-early Haumurian (Yl6/f165, fl66). The for­mation is possibly late Piripauan-early Haumurian in age.

WHANGAI FORMATION (Lillie 1953)

No complete sequence is known. A section in Owhena Stream from Y16j462365 to Y16/461356 incorporates most of the variations. The upper part of the sequence can be seen in Waitahaia River from Y16j471368 to Y16/475373. The contact between Owhena and Whangai Formations is conformable.

The formation consists of siliceous to calcareous, light-coloured sandstone and mudstone, greensand, and dark-coloured mudstone. Most outcrops weather creamy white with rust-coloured joints. Four distinct lithotypes can be recognised, though the precise relationship between them is difficult to define.

The base is marked by a 5-10 m thick, nodular concretionary horizon containing irregular-shaped calcareous concretions generally 15-20 em long and 5-10 em in diameter. A hard, blue-grey to grey, noncalcareous, silty mudstone to siltstone overlies the concretionary zone and is the most widespread lithotype. Local variations include dark-grey glau­conitic sandstone and blue-grey calcareous mud­stone. The top of the formation is generally represented by flaggy calcareous mudstone/siltstone.

The outcrop pattern follows that of the two underlying formations across the central portion of the study area (Fig. 1). A section of the formation, approximately 200m thick, is present in the Wai­tahaia River, but the top of the sequence is faulted out by the Owhena Fault.

Macrofossils are scarce but fish scales occur in the upper parts of the sequence. Microfossils gave dates ranging from Arowhanan to Teurian (Y16jfl74). Microfossils from a greensand in the upper part of the sequence gave a date ofpost-Hau­murian, probably Teurian (Y16jf68). The upper part of the sequence was dated as Haumurian-Teu­rian (Y16jfl67). Whangai Formation is generally regarded as Haumurian-Teurian in age (P. R. Moore pers. comm.).

Allochthonous sequence

Undifferentiated Clarence Series rocks A reference section is located within Waitahaia River from Y16j475371 to Y16/500379.

A sheared sequence of predominantly alternating sandstone and siltstone, not dissimilar to Waita­haia Formation, is above the lowest thrust plane, overlying the Whangai Formation. Sandstones are thin bedded (10-20 em) and medium grained, with some sedimentary structures. Siltstones are dark and, where severely crushed, almost black. On exposed ridges, siltstones tend to weather to a. rusty brown and often fritter out.

Several distinctive lithologies are found within the alternating sequence, though the original stra­tigraphic relationship to each other and to the alternating phases is unknown (Fig. 2).

(1) A number of large sandstone bodies occur within the Waitahaia Thrust Zone. These sand­stones are dark grey to greenish, medium grained to granular, and are generally massive. They resemble the Taitai Sandstone Member of Moko­iwi Formation (Speden 1976), but are not consid­ered to be Taitai Sandstone because Mokoiwi Formation is not present in this area (1. G. Speden pers. comm.). The sandstone bodies are generally 50 m or more thick and form bluffs at several local­ities (e.g., Y16/480384).

(2) A sedimentary breccia consists predomi­nantly of various sized, angular clasts ofTaitai-like sandstone set in a sandy matrix. Individual clasts rarely exceed 20 em in diameter and are more com­monly 5-10 em. The breccia appears to be asso­ciated with the sandstone bodies and at one locality (Y16/515380) grades into sandstone.

(3) A roundstone conglomerate consists of well­rounded polished cobbles of Torlesse Supergroup andjor Early Cretaceous sandstone. The conglom­erate occurs at a number of localities but is best exposed on Fosters Road·- New Zealand Forest Service road (Y16/473368).

The highly sheared and faulted Clarence Series rocks, and the obvious repetition of sequences caused by thrusting, make estimates of thickness unreliable. A minimum thickness of 100 m is suggested.

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Phillips-D. Cret. geology, Waitahaia R.

Fossils are sparse, though fragments of Inocer­amus spp. are common within concretions and at the base of sandstone beds. I. warakius Wellman (Yl6/fl85) has been found at one locality (J. Kenny pers. comm.). Aucellina euglypha Woods, the Motuan index fossil, was not seen in situ, but occurs within shellbed float boulders at several localities (e.g., Yl6/f240, Yl6/f241). It is uncertain whether the boulders represent clasts from conglomerates or breccias, or are from within the alternating sequence. Inoceramus fragments, some of which have affinities to I. sp. ex. gr. hakarius-fyfei (Nga­terian, Yl6/fl75) were found within the alternating sequence. Pick ( 1962) described the presence of I. tawhanus Wellman (Y16/f7523) from this unit. These rocks are considered to be Motuan-Ngater­ian in age.

TIKIHORE FORMATION (Black 1980)

This formation comprises weathered, often sheared, carbonaceous, quartzolithic, medium-grained sandstone alternating with a carbonaceous silt­stone. All outcrops are extensively weathered and have a rusty appearance. Rocks representing rem­nants of thrust sheets are found within the Wai­tahaia Thrust Zone. Because a stratigraphic sequence cannot be established, a reference section is not given. The best exposure occurs on a farm track between Y16/493340 and Y16/497346 (Fig. 1 ).

The weathered and sheared outcrops precluded sampling for microfossils, and no macrofossils were seen. The age is taken to be Arowhanan-lower Haumurian (Black 1980).

MANGATU GROUP (Wellman 1959)

Wellman (1959) described the Mangatu Group as a "great thickness of diverse but predominantly fine­grained and light coloured sediments that lie between the top of the Tapuaeroa Formation and conglomerate at the base of the Ihungia Mud­stone". The Mangatu Group was equated to three formations in Hawke's Bay-Whangai, Wanstead, and Weber (Lillie 1953). Where possible, Mangatu Group rocks within the study area have been dif­ferentiated into formational units.

WHANGAI FORMATION (Lillie 1953)

The formation consists of siliceous to calcareous shales and mudstone, greensand, and dark-coloured mudstone, which weather creamy white with rust­coloured joints. Most outcrops are extensively sheared and tectonised. Original bedding features have been generally obliterated.

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The unit is best exposed along the Waitahaia­Takapau road at the fault contact with the undif­ferentiated Clarence Series rocks (Y16/467350-447350). The intensely tectonised unit and the obvious repetition of parts of the sequence make estimates of thickness unreliable. A minimum thickness of 100 m is suggested.

The weathered and sheared outcrops precluded sampling for microfossils and no macrofossils were seen. The age is taken to be as outlined for the autochthonous Whangai Formation (i.e., Haumu­rian-Teurian).

Greensand lithotype (informal) [ = Te Waka lithofacies of Mangatu Formation (Black

1980)]

The lithotype is composed mainly of fine-medium­grained massive greensand with local, interbedded, carbonaceous siltstone lenses. The siltstone weath­ers white with a yellow efflorescence on joint sur­faces and is pale brown when fresh. A diagnostic feature of the greensand is the deep rusty-red weathering product produced by the oxidation of iron within the glauconite. The main outcrop is exposed on a ridge south of the north branch of Puniatara Stream (Y16/448326-428332). At this locality, a 50 m thick section of greensand and silt­stone is exposed.

Microfossil dating of samples gives ages of Teu­rian (Y16/f227) and Bartonian (Y16/f219).

Other lithotypes A number of other lithotypes are found within the study area, though a stratigraphic sequence cannot be established. In parts, these lithotypes equate to similar rocks mapped in the east coast region as Wanstead and Weber Formations (Lillie 1953).

The following units appear to be related in a sequence which suggests a changing environment of deposition (Fig. 2).

Limestone lithotype (informal)

A hard, white, muddy to slightly sandy limestone, with local interbeds of glauconitic sandstone is the predominant rock type. The unit is variable and is considered to be a lateral equivalent of Weber For­mation. The limestone is generally well bedded, often fiaggy, and resistant to erosion. Overall it is m]Jddy and fine grained, though locally it becomes sandy. Similarly, the interbedded glauconitic sand­stone is highly variable, from a true greensand through to a calcareous, medium-grained, glaucon­itic sandstone. Ages based on microfossils range from Whaingaroan to Duntroonian (Yl6/fl95, fl96).

The best exposure occurs below Trig. 183 Whak­oau (Y16/511366) (Fig. l) and it is also exposed at Y16/485344.

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Sandy siltstone lithotype (informal)

A calcareous, blue-grey to green-grey, slightly sandy siltstone which is generally poorly bedded forms this unit. The colour is highly variable and ranges from a dark blue-grey to a distinctive green. The green colour is attributed to glauconitisation of fine­grained particles within the matrix. Ages obtained from microfossils are Waitakian-Otaian (e.g., Yl6jf190, f220).

The blue-grey member is exposed at Y16/503348, and the greenish member is exposed at Y16/498349.

Breccia lithotype (informal)

A medium blue-grey to olive green, indurated brec­cia which contains a variety of clast sizes and shapes predominates. Clasts are predominantly sandstone similar to Taitai sandstone, with minor siltstone, calcareous siltstone, and pale sandstone. Clasts are set in a gritty matrix of sandstone and rock frag­ments, and individual clasts are generally 10-20 em in diameter. Several large ( > 50 m) blocks of Tai­tai-like sandstone occur within the breccia (e.g., Y16/499344). The breccia is well exposed in Hau­turu Stream from a contact with a large block of Taitai-like sandstone at Y16/504344 upstream as far as Y16/500347. The breccia is considered to occur as lenses within the blue-grey to green sandy siltstone.

Microfossils were not found in samples from this lithotype but the age inferred from stratigraphic relationships with other units is considered to be W ai takian-Otaian.

Conglomerate/breccia lithotype (informal)

This lithotype consists of weathered, indurated conglomerate/breccia which contains a variety of clast sizes and shapes. Clasts, unlike the breccia lithotype above, are dominated in several places by Whangai Formation rocks and include subordinate amounts of Taitai-like sandstone and other Cre­taceous-aged rock types. They are set in a gritty matrix which weathers to a rusty colour. Clast sizes range 2-50 em in diameter. The conglomerate::/ breccia is well exposed at Yl6/460339. This litho­type is considered to be a lens within the blue-grey to green sandy siltstone lithotype.

IHUNGIA FORMATION (McKay 1887)

A reference section is located in Whakoau Stream (Y16/501342-457327).

The most common rock type of the Ihungia For­mation in the study area is massive, grey to blue­grey, very fine sandy mudstone, with a variable cal­cite content. Some carbonaceous fragments are seen as fine parallel laminations on unweathered bed­ding surfaces. Alternating sandstone and mudstone

sequences are common, though not continuous, with sandstones generally 5-15 em thick, slightly calcareous, and normally graded. Upper parts are laminated, usually parallel, rarely convoluted, and grade into mudstone above.

One distinctive lithology within Ihungia For­mation is the Ihungia Igneous Conglomerate (Kenny 1980). Pebbles, cobbles, and boulders of predominantly igneous origin, together with sub­ordinate metamorphic and sedimentary rocks, con­stitute this unit. It is not considered to be a basal unit (Kenny 1980) as it occurs within mudstone several hundred metres above the base of the for­mation which is not exposed within the study area (Fig. 2). Some of the conglomerate clasts are mul­ticyclic and are hard, well rounded, and polished, while others appear to have experienced only one cycle and are softer and more angular. The con­glomerate occurs in more than one bed, its thick­ness varying between beds and thinning laterally. The overall thickness of the conglomerate unit does not exceed 10-15 m, and individual beds are 3-4 m thick. The conglomerate grades into mudstone both above and below. It is exposed in Whakoau Stream at Yl6j473332 where it is 3-4 m thick.

The thickness of Ihungia Formation within the study area is 250 m. Microfossil dating gives ages of Otaian {Y16/f229) to Altonian (Y16/f228).

STRUCTURE

Pick (1962) considered the Waitahaia area to be structurally complex and introduced the name Waitahaia Fault Zone to describe the set of faults within this region. The present study amends the nomenclature to Waitahaia Thrust Zone to avoid confusion about the major types of faults present. The study area can be subdivided into three struc­turally distinct zones (Fig. 1): (1) an autochtho­nous, structurally simple, sequence of Late Cretaceous to Paleocene sediments in the west and north; (2) a structurally complex series of thrust slices of mid Cretaceous to Lower Miocene sedi­ments forming the Waitahaia Thrust Zone; and (3) a younger, structurally simple allochthonous sheet of Miocene sediments to the south.

The autochthon The alternating sequence of the Waitahaia For­mation is folded in a series of tight folds which trend NW-NNW. Reconnaissance mapping of Ruatahunga Stream, northwest of the study area (Moore et al. 1983) indicates that the general trend of folding there (NNW-NNE) is similar to that in the immediate study area. Folds are generally asymmetric, and often one limb is displaced by a small fault close to the hinge. Minor folding occurs

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Phillips-D. Cret. geology, Waitahaia R.

Fig. 5 Oblique aerial view of the upper Waitahaia River valley, showing the general physiography and the position of the auto-chthon/allochthon boundary and part of the Waitahaia Thrust Zone.

in the Karekare Formation where fold axes trend in a similar direction to the underlying Waitahaia Formation. Within the Waitahaia River section, the degree of folding within Waitahaia Formation upstream of the KarekarejWaitahaia contact, and the overall lack of folding within Karekare For­mation in this section, indicates a major uncon­formity. In Waingata Stream, the contact is an angular unconformity.

Folding is generally absent in the Owhena or Whangai Formations, which are in a simple sequence striking northeast and dipping l 0-30° southeast.

Faulting within the autochthonous sequence is relatively minor in the western part of the study area but towards the boundary between the auto­chthon and the Waitahaia Thrust Zone the rocks become increasingly fractured. Crush zones asso­ciated with faults are in the order of 2-5 m wide. There are two distinct fault sets - one trending northwest-southeast, the other northeast-south­west. The former set is related in part to pre-Hau­murian deformation and does not offset formations above the Piripauan-Haumurian unconformity. Faults of the latter set are attributed to a later phase

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of activity. The Ruatahunga Fault is the largest of this set and is a near-vertical normal fault with a throw of c. 20 m (Fig. 5).

Waitahaia Thrust Zone (older allochthon) Structurally, this is the most complex part of the study area. Deformation is largely related to the local emplacement of allochthonous sheets con­taining rocks ranging from mid Cretaceous to early Tertiary age in a series oflow-angle, southeast-dip­ping thrust faults associated contemporaneously with the emplacement of a much larger allochthon­ous mass (Stoneley 1968). In places, deformation is so intense that original features, such as bedding, are totally obscured by the tectonic overprint of the shear fabric. The highly sheared and crushed nature of this zone, together with the occurrence of clay­rich tectonic melange, explains the high incidence of severe gully and earthftow erosion (Phillips & Pearce 1985). The lowermost thrust fault boundary separating the autochthon from allochthonous rocks varies from a low-angle ( 15-30°) to a subvertical fault. The emplacement of the lower thrust sheet has caused fracturing of underlying autochthonous rocks along a series of faults adjacent to the thrust

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

zone. The basal thrust sheet composed of undif­ferentiated Clarence Series rocks has been partly obscured by subsequent thrust sheets oflower Ter­tiary rocks, which themselves are disrupted and partly obscured by the emplacment of another major sheet comprising Ihungia Formation (lhun­gia Allochthon).

Younger (lhungia) allochthon (C. Mazengarb, New Zealand Geological Survey, pers. comm.) An extensive thrust sheet of Ihungia Formation mudstones has probably been emplaced from the NNE (J. Kenny 1984) over the upper thrust sheets of the Waitahaia Thrust Zone in the southeastern margin of the mapped area. A southward-dipping series of thrust slices of older-aged rocks and a number of minor slices of Ihungia Formation are marginal to the main younger allochthonous sheet. Internal deformation within the allochthonous sheet is minor, except for small offsets along subvertical fractures. Bedding generally strikes in an east-west direction, and dips vary from 10° to 80°S.

ENVIRONMENT OF DEPOSITION OF AUTOCHTHONOUS ROCKS

The autochthonous sequence sediments were prob­ably deposited in a large offshore basin.

The flysch-like sediments of the Waitahaia For­mation, with their abundant sole marks and incomplete Bouma sequences, were probably deposited in a shelf environment which was sub­ject to cyclic input of coarse material, probably by turbidity currents. Periods of quiescence allowed siltstones to be deposited and then be colonised by worms and epifaunal bivalves.

The massive sandstone unit may indicate dep­osition close to the centre of distributary channels within the basin, with frequent deposition of thicker sandstones by proximal turbidity currents or grain flows. Small time intervals between influxes of sand would have limited the deposition of finer grained material.

The fine grain-size of Karekare Formation sug­gests either a deepening within the basin or dep­osition where a fan channel had shifted so that the supply of coarse sediment was much reduced. The presence of thin sandstone beds near the base indi­cates that sand was occasionally supplied, but the gradual disappearance of sandstones higher in the sequence suggests that the transport mechanism or the supply of sand had shifted. The locally sandy nature of the sediment near the top of the forma­tion and the presence of I. rangatira would suggest perhaps local shallowing, possibly associated with an offshore bar. Any subsequent deposits were

probably removed during a phase of erosion before the transgression which deposited the Owhena and Whangai Formations.

The basal sandstones of Owhena Formation sug­gest a shelf situation, with a gradual deepening of the depositional basin or a reduction in supply of coarse sediment to account for the gradual fining of the sequence.

Whangai Formation siltstones and mudstones were probably deposited in a stable shelf environ­ment, possibly behind offshore barriers (Speden in Stevens & Speden 1978).

GEOLOGICAL HISTORY

A sequence of shallow-shelf sandstone and silt­stone was deposited from Motuan to Ngaterian time. Sometime within the Ngaterian, a major tec­tonic event folded and indurated the sediments of Waitahaia Formation. Local (or regional) subsid­ence then occurred and the pattern of sediment­ation resumed with deposition of the siltstones of Karekare Formation. A further cycle of uplift, fold­ing, and erosion before Piripauan-Haumurian time resulted in a regional unconformity (Moore 1978) which, in the study area, separates the Karekare and Owhena Formations. A regional transgression beginning in Piripauan-Haumurian time is sug­gested by the rapid change from the shallow, shelf sediments of Owhena Formation to the shelf deposits of Whangai Formation (Haumurian-Teu­rian). The supply of land-derived terrigenous material decreased in late Haumurian and Teurian time, as indicated by the deposition of greensand and by the increasing calcareous character of the upper Whangai Formation. Various post-Whangai sediments (Greensand lithotype; red-green argil­lites) appear to have been formed under conditions of limited supply of terrigenous sediment, but this part of the stratigraphic sequence is poorly exposed and not well understood. Landon Series sediments are dominated by glauconite-rich material interbedded with hemipelagic calcareous muds and sandy mudstones (Limestone lithotype). The sup­ply of terrigenous material increased in later Lan­don time when sandy mudstones were deposited. Deposition of coarse angular breccia as lenses within the sandy mudstone probably indicates the first major late Tertiary tectonic event-the emplacement of the thrust sheet of undifferentiated Clarence Series strata and subsequent lower Ter­tiary rocks over autochthonous Upper Cretaceous to lower Tertiary rocks. This major regional tec­tonic event is thought to have occurred between the late Waitakian and early Otaian Stages (Sto­neley 1968; Kenny 1980).

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Phillips-D. Cret. geology, Waitahaia R.

Ihungia Formation mudstones accumulated con­tinuously in outer shelf - upper slope conditions from Otaian time. Deposition was interrupted occasionally by influxes of sandy sediment. Mass­flow sediments, consisting of igneous pebbles and boulders grading up to sandstones (lhungia Igneous Conglomerate), were deposited some time in the early Altonian. Ihungia Formation rocks were indurated and gently folded after deposition ceased in the late Waiauan Stage (Kenny 1980). The younger major thrust sheet (Ihungia Allochthon) was emplaced over the Waitahaia Thrust Zone some time after Middle Miocene (Kenny 1984). Subsequent minor faulting is shown by fault traces which offset thrusts; the timing and number of phases are uncertain.

ACKNOWLEDGMENTS

I wish to thank Dr I. G. Speden and Mr P. R. Moore (New Zealand Geological Survey) for their initial guid­ance and assistance in the field and their continued sup­port of this study. Fossil identifications by Drs I. G. Speden, C. P. Strong, J. I. Raine, G. J. Wilson and Mr G. H. Scott were invaluable. For discussion and infor­mation I thank Dr A. J. Pearce, P. R. Moore, and J. Kenny. Ms Kenny is also thanked for her assistance and lively discussion in the field. Critical reading of the manuscript by A. J. Pearce, P. R. Moore, and J. Orwin contributed significantly to this paper. Miss P. Moore typed the various drafts, and maps were drawn by Car­tographic Section, Science Information Publishing Centre, DSIR. The hospitality of Mr and Mrs W. McKee (New Zealand Forest Service, Owhena) during fieldwork was greatly appreciated.

REFERENCES Black, R. D. 1980: Upper Cretaceous and Tertiary geol­

ogy of Mangatu State Forest, Raukumara Penin­sula, New Zealand. New Zealandjournal of geology and geophysics 23: 293-312.

Isaac, M. J. 1977: Mesozoic geology of the Matawai dis­trict, Raukumara Peninsula. Unpublished Ph.D. thesis, lodged in the Library, University of Auckland.

Jablonski, E. 1934: General report on the geology and oil possibilities of the Gisborne land district. Vacuum Oil Co. New Zealand Geological Survey unpub­lished open file petroleum report 119.

Kenny, J. 1980: Geology of the Ihungia area, Raukumara Peninsula. Unpublished M.Sc. thesis, lodged in the Library, University of Auckland.

----1984: Stratigraphy, sedimentology and struc­ture of the Ihungia decollement, Raukumara Pen­insula, North Island, New Zealand. New Zealand journal of geology and geophysics 27: 1-19.

Kingma, 1. T. 1965: Geological map of New Zealand 1:250 000. Sheet 6-East Cape. Wellington, New Zealand. Department of Scientific and Industrial Research.

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Lillie, A. R. 1953: The geology of the Dannevirke Sub­division. New Zealand Geological Survey bulletin 46. !56 p.

MacKay, A. 1887: On the geology of east Auckland and the northern district of Hawke's Bay. New Zealand Geological Survey reports of geological explora­tions, 1886-1887 (18): 182-219.

Moore, P. R. 1978: Geology of western Koranga Valley, Raukumara Peninsula. New Zealand journal of geology and geophysics 21: 1-20.

Moore, P. R.; Mazengarb, C.; Speden, I. G.; Phillips, C. 1. 1983: Reconnaisance survey of Waingakia and Ruatahunga Streams. (Waitahaia-Mata River Catchment). Raukumara Peninsula (Y 15). Unpub­lished New Zealand Geological Survey internal report.

Ongley, M.; MacPherson, E. 0. 1928: The geology ofthe Waiapu Subdivision. New Zealand Geological Sur­vey bulletin 30. 79 p.

Phillips, C. 1.; Pearce, A. J. 1985: Terrain stability zoning of Owhena-Mangawhero, Tokomaru State Forest. Forest Research Institute bulletin 91.

Pick, M. C. 1962: The stratigraphy, structure and economic geology of the Cretaceo-Tertiary rocks of the Waiapu district, New Zealand. Unpublished Ph.D. dissertation, University of Bristol (lodged in the New Zealand Geological Survey Library, Lower Hutt). 532 p.

Speden, I. G. 197 5: Cretaceous stratigraphy of Rauku­mara Peninsula. New Zealand Geological Survey bulletin 9/. 70 p.

---- 1976: Geology ofMt Taitai, Tapuaeroa Valley, Raukumara Peninsula. New Zealand journal of geology and geophysics 19: 71-119.

Stevens, G. R.; Speden, I. G. 1978: New Zealand. Pp. 251-328 in: Moullade, M.; Nairn, A. E. M. ed. The Mesozoic. A. The Phanerozoic geology of the World II. Amsterdam, Elsevier Scientific Publishing Co.

Stoneley, R. 1968: A lower Tertiary decollement on the east coast, North Island, New Zealand. New Zealand journal of geology and geophysics 11 : 128-156.

van der Lingen, G. 1.; Pettinga, J. R. 1980: The Makara Basin: a Miocene slope-basin along the New Zealand sector of the Australian-Pacific obliquely convergent plate boundary. Pp. 191-216 in: Ball­ance, P. F.; Reading, H. G. ed. Sedimentation in oblique-slip mobile zones. International Associa­tion of Sedimentologists special publication 4.

Webb, P. N. 1970: A preliminary statement on type material of New Zealand Upper Cretaceous, Paleocene, and Eocene foraminifera described by H. J. Finlay. New Zealand journal of geology and geophysics 13: 663-675.

---- 1971: New Zealand Late Cretaceous (Hau­murian) foraminifera and stratigraphy: A sum­mary. New Zealand journal of geology and geophysics 14: 795-828.

Wellman, H. W. 1959: Divisions of the New Zealand Cretaceous. Transactions of the Royal Society of New Zealand 87 (1 and 2): 99-163.

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