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Stratigraphy and Paleoecologyof the Productus Creek Group,South Island, New ZealandLucy M. Force aa 218 Madison Street, Herndon , Virginia 22070 ,U.S.A.Published online: 05 Jan 2012.

To cite this article: Lucy M. Force (1975) Stratigraphy and Paleoecology of theProductus Creek Group, South Island, New Zealand, New Zealand Journal of Geologyand Geophysics, 18:3, 373-399, DOI: 10.1080/00288306.1975.10421544

To link to this article: http://dx.doi.org/10.1080/00288306.1975.10421544

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N.z. Journal of Geology and Geol'hysics Vol. 18, No. 3 (1975): 373-99

STRATIGRAPHY AND PALEOECOLOGY OF THE PRODUCTUS CREEK GROUP, SOUTH ISLAND,

NEW ZEALAND

Lucy M. FORCE

218 Madison Street, Herndon, Virginia 22070, U.5.A.

ABSTRACT

In middle and late Permian time, the Productus Creek area of South land, New Zealand, was the site of simultaneous accumulation of shallow marine, biogenic carbonate and immature volcanogenic sediments. The prismatic shell fragments of the bivalve Atomodesma formed the major limestones; this suggests a well-established bank environment. Less extensive calcareous Bryozoa banks succeeded the Atomodesma banks, and were covered in turn by a prograding conglomerate in late Permian time.

Trends in fossil assemblages, clay mineralogy, sediment sizes, and sediment thicknesses suggest a nearby Permian shore line north-west of Productus Creek.

Two hypothetical transgression-regression models of the Productus Creek Group are discussed: (a) a migrating delta and (b) eustatic sea-level variation which takes into account contemporaneous glacial events in Australia and elsewhere.

One new informal formation, the Weetwood Formation, is named, and the Mangarewa, Elsdun, and Hawtel Formations are redefined.

INTRODUCTION

The middle and upper Permian section at Productus Creek, in the Wai­raki Hills north of Ohai (Fig. 1, inset), is relatively unmetamorphosed, well exposed, and easily accessible. The section is part of a discontinuous belt of shallow marine Permian sediments and volcanics along the western margin of the New Zealand Geosyncline and the west limb of the South­land Syncline.

Early geologic work in the Pro ductus Creek area was by Rout (Rout & Willett 1949; discovery of first fossils) and Fletcher et al. (1952; des­cription of fossils). Mutch (1964) mapped the Productus Creek area at a scale of 1: 63 360. His map shows the Productus Creek Group as a simple north-trending homoclinal sedimentary sequence dipping eastward. It forms a lobe of middle and upper Permian rocks on the east flank of the lower Permian Takitimu Group. The latter consists of volcanogenic rocks and forms the Takitimu Mountains (Figs 1, 2). Surrounding the Productus Creek Group on the north, east, and south are fossiliferous Triassic sedi­ments. Mutch, aided by Waterhouse and others, collected fossils from numerous localities in the Takitimu and Pro ductus Creek Groups. Water­house (1958; 1963a-d; 1964a-c; 1965; 1967; 1968) subsequently des­cribed most of the faunas.

The present paper presents the results of the writer's field and laboratory study of the area in 1967-70.

Received 16 January 1973; revised 23 October 1973.

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374 N.z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 18

NEW FIELD WORK

Two detailed tape and compass traverses were made in the Pro ductus Creek area. Contacts were checked at many points or walked out, and lateral lithologic relationships were examined. Fossil counts were made at a few localities.

Field work resulted in a few modifications of the original structural and stratigraphic interpretations in Mutch (1964). The Glendale Limestone Member (of the Elsdun Formation) terminates just south of Productus Creek; its position is taken by volcanogenic sandstone. North of the northern traverse, the Glendale Limestone Member also ends abruptly against a volcanogenic sandstone (cf. Mutch 1972, fig. 28 and Force 1972).

Waterhouse's paleontological determinations led to the distinction between the Letham and Mangarewa Formations. The two cannot be distinguished in the field, however, and the present writer mapped them as one unit, called the Mangarewa Formation. The name "Letham Formation" was left without a rock unit and is therefore omitted here. Further work may prove the Letham and Mangarewa Formations lithologically distinct.

Mutch (1968 pers. comm.) referred to a "Weetwood ·Member",des­cribing it as a tuff. It appears to be a mafic-poor micro-diorite or perhaps an andesite. Because its lithology is distinctive and its boundaries sharp (Fig. 1) rather than gradational, the unit should be raised to formational status (Force 1972). In this paper it will be referred to as the Weetwood Formation. Its relationship with the surrounding sediments is not com­pletely understood but it is tentatively excluded from the Pro ductus Creek Group because it is probably intrusive. Mutch now (1972) refers to this unit as part of the "Park Intrusives"

STRATIGRAPHY

The stratigraphic nomenclature of Mutch (1964) has been retained wherher practical to avoid the confusion of renaming rock units. Figure 3 indicates the differences in terminology.

MANGAREWA FORMATION

The Mangarewa Formation consists mainly of volcanogenic biocalcarenite; lenses of biocalcirudite (coquinite; Coral Bluff Member of Mutch 1972; see also Fletcher et al. 1952 and Waterhouse 1964c) and volcanogenic sandwacke increase in abundance toward the north.

The Mangarewa Formation overlies the Takitimu Group (Fig. 1). There are several volcanogenic conglomerate lenses toward the top of the Takitimu Group which resemble the less' fossiliferous parts of a conglomerate present locally along the base of the Mangarewa Formation. Where the conglomerate is missing, the base is characterised by dark, volcanogenic biocalcarenite, which in several places contains distinctive trace fossils. The immediately underlying Takitimu Group sediments are not calcareous. In spite of the conglomerate lenses, the dips in the Mangarewa Formation and adjacent Takitimu Group strata suggest only a slight or local unconformity.

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d G((}phYJics Vol. 18 Nc. 3 (197)) !,;''z.]IJI{fna/Q/GeolOlJdrl

l

PO.st-!Gl~::rlsl,,~ ... ut'lofood FDroatiC):l.

'r'ri-tHie ~U:.li!"ret'eDti:Jte4 ----~v.J.inU Bre.ecia

'y~H,J.\ltel Fo:-~ti(Q:

l~ir~;~~~e Hllto:.

"

"

.rer:-. t.:l ~ " s.1.n4stone , Gle~.le ~ i .~~. -. nsdun Z'or=atiO:J.:

~ . Liu>atone I coz:glca.

~~Y.:s. l'U.r:.gl::"e~ F~tiQ;]:: ; .~ . N!)ds eon.e , lbutooe ... c>o::glOl"!.erat.e

~rnit i."'IU Group

:,;',2. jlJl{fnaf Qf Geolol.J arid G((}phYJics Vol. 18 ]'iQ. 3 (197))

"

FORCE - PRODUCTUS CREIK GROUP

Loc.al itJ ~p ElI'!.I. .... 1'IO!<

~8 --.... t.cOYQ and dhU.:et co:lit.act 0 !l!lIb No~t!l ... - -- J.uu:e4 or p-adationll (:ont.a.c.~ ~,,~ .atti~. , l'oo.."!.gi.D.g ~ ~ E..o.-oor.:l fau lt ~ to--..:ard tiet

=;_J.uu:e4 t.u1t + Re~r::::.(,.:!)t , natl00al

~ l;' 4<1 8reec:i3. 0 }} 5U;i>le lGu.11t,

~ Pe~ent .mu ? LitbolGg1 or C.':oat.act UDkuown .... ..1 b ten:lt teDt :ltH&.:I HCS (!iUS }516) Glouopteril ap .

I'",

FIG. I- Geological map of the Productus Creek area.

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N,Z. JOURNAL Of GEOLOGY AND GEOPHYSICS

Triassic

Permian upper and

middle

lower

Malakoff

Hill Group

Productus

Creek

Group

Takitimu

Group

FIG. 2-Stratigraphic framework of the Proouctus Creek Group.

MUlCh (1964; 1972) This paper

Wairaki Breccia Wairaki Breccia

Hawtel Fm. Hawtel Fm, Hilton Limestone Mem, Hilton Limestone Mem.

Hawtel Mudstone

Elsdun Fm. Elsdun sandstone

Elsdun Fm. Glendale Limestone Mem, Glendale Limestone Mem. Elsdun conglomerate

Mangarewa Fm.

Letham Fm.

Mangarewa Fm. Mangarewa sandwacke Mangarewa limestone Mangarewa Conglomerate

Lithologic description

Fossil-bearing volcanogenic conglomerate

Bryozoan-echinodermal biocalcarenlte lenses surrounded by mudstone (leached biocalcarenite, in part); volcanogenic

~:z~~~:t~~~ ~~~~oa~k~lc surrounding Atomodesma biocalcarenite; conglomerate lenses at base

Volcanogenic biocalcarenite interbedded with volcanogenic sandwacke and shell beds; fossiliferous volcanogenic conglomerate lenses primarily at base

FIG. 3-Productus Creek Group nomenclature and lithology. base ;'

lPI)

(PI)

(PI)

10 25 top

metre6J~et

.., 0 50

:.;:1 20 75 I!!

~ (Bc)

(f)

"'() C

'" Z c 'iii "'()

E E LL

FIG. 4-Produetus Creek. stratigraphie column. Symbols are explained in key on Fig. 5.

Triassic

Malakoff

Hill Group

N,Z. JOURNAL OF GEOLOGY AND GEOPHYSICS

Permian upper and

middle

Wairakl BreCCla

Hawlel Formation

Elsdun Formation

Mangarewa Formation

Productus

Creek

Group

lower

Takitimu

Group

FIG. 2-Stratigraphic framework of the Proouctus Creek Group.

MulCh (1964; 1972) This paper

Wairaki Breccia Wairaki Breccia

Hawtel Fm. Hawtel Fm, Hilton Limestone Mem, Hilton Limestone Mem.

Hawtel Mudstone

Elsdun Fm. Elsdun sandstone

Elsdun Fm. Glendale Limestone Mem, Glendale Limestone Mem. Elsdun conglomerate

Mangarewa Fm.

Letham Fm.

Mangarewa Fm. Mangarewa sandwacke Mangarewa limestone Mangarewa Conglomerate

Lithologic description

FOSSil-bearing volcanogenic conglomerate

Bryozoan-echinodermal biocalcarenlte lenses surrounded by mudstone (leached biacalcarenite, in part); volcanogenic

Very immature volcanogenlc sandstone and sandwacke surrounding Atomodesma biocalcarenite; conglomerate lenses at base

Volcanogenic biocalcarenite interbedded with volcanogenic sandwacke and shell beds; fossiliferous volcanogenic conglomerate lenses primarily at base

FIG. 3-Productus Creek Group nomenclature and lithology.

/,

~I/ I

u/

-' ' -, ' ... I \~

(lOOm)

base

~ "8

~ ~

;'

(M)

lPI}

(PI)

(PI)

'" c

~ "0

iijlZCl) Cl) "0

~~

10 25 top

metre6J~et

.., 0 50

~Jr 20 75

'" 1 Cl) "0 C

'" Z

~ EI~

LL

Cl) "0 iij

Z Cl) Cl)

(Bc)

5 (Bel

(Bc)

FIG. 4-Productus Creek, stratigraphic column. Symbols are explained in key on Fig. 5.

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FORCE - PRODUCTUS CREEK GROUP

5 (M)

l c 0 .~

E ... 0 u.

.. o IBa)

·f.

(:)c:i6o~ DJ O();o 5 base

'Il:"?", \=)

? ;.J.

DJ,Obol(l(o,M) c···· ()

C :::J

-0 (J)

[jJ

5 1

= =

E u. Qi

'3 cO I

(J) (J)

§ (lOOm) -0

GJIPI,Ba).!!!. 1 W

~PIF 01

G

:s: limestone, most particles larger than 1 mm ~ limestone, most particles smaller than 1 mm

(limestones composed of Atomodesma prisms unless otherwise noted)

= calcareous 000 conglomerate (particles mostly larger than

2 mm)

,f sand (f= particles ;~ - ;;6 mm) ="- silt (116-;256 mm) ~ mud (particles less than ;16 mm) -> :-' igneous rock

scona .. cross bedding

G graded bedding ____ sheared

~ fissile

~ contorted 1 grey 5 olive grey

burrow or trail PI plant 9 body fossil M mollusc other than Atomodesma

= Atomodesma Ba brachiopod Br bryozoan E echinoderm columnal c coral

o no outcrop L-J lOOm omitted strata ,.-.,

!f1'1* . Idd bl h . I

~':7 Inc u e sym 0 s s ow typlca .( 20 stratlQrapny for the Interval, too ~.. mm thinly oeaded to be drawn to ::J, scale smaller than that indicated

FIG. 5-Productus Creek (north traverse), stratigraphic column, Scale as for Fig. 4. Lithologic symbols within asterisks (*) show typical stratigraphy for the interval, too thinly bedded to be drawn to a scale smal!er than that indicated.

N.Z. /ollmal of Geology and GeophYJics Vol. 18 1'10.3 (1975)

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No. 3 FORCE - PRODUCTUS CREEK GROUP 375

The thickness of the Mangarewa Formation is partly accounted for by the irregular shape of the Weetwood Formation but, in general, the Manga­rewa Formation is thicker toward the north, reaching roughly 180 m at Coral Bluff. The lithology in a south-facing cliff just north of the map area resembles Coral Bluff samples, and the vegetation and lineaments in air photos also suggest that the formation continues northward.

Bed thicknesses change laterally within a few metres from 20 to 40 mm. The bed surfaces are commonly marked by trace fossils and more rarely by brachiopod and mollusc shells. Size sorting is evident in some beds, and compositional and size grading are suggested by differential weathering in other beds. In the latter, coarser volcanogenic material is followed by more soluble and finer-grained Atomodesma (bivalve) prisms mixed with vol­canogenic silt.

Most of the calcite is Atomodesma prisms. The calcite content, deter­mined by at least 200 point counts per thin section, ranges from 0 to 75%. The average is probably somewhat less than 50%.

Most other primary minerals and lithic fragments appear to have been derived from a volcanic source. They are discussed in detail below.

ELSDUN FORMATION

The EIsdun Formation can be divided into three members, only one of which has been formally named.

(1) The Elsdun conglomerate (oldest) is a distinctive polymictic con­glomerate with a few granitic pebbles, which occurs at the base on the north traverse.

(2) The Glendale Limestone Member (Mutch 1972) comprises most of the formation and directly overlies the Mangarewa Formation at several points south of Coral Bluff.

(3) The Elsdun sandstone member comprises sandstone, sandwacke, and upper conglomeratic units which occupy positions lateral to and over­lying the Glendale Limestone. South of the southern end of the limestone, the sandstones and sandwackes are found in contact with the Mangarewa Formation and Takitimu Group, respectively.

The Elsdun Formation is 365 m thick at Productus Creek, and 430-460 m at the north traverse (Figs 4, 5). The upper contact is not exposed at the north traverse, and the maximum thickness was derived by projection of the contact at Productus Creek along a coincident break in slope. The Elsdun sandstone member averages 45 m thick where it overlies the Glen­dale Limestone Member, and about 140 m north and south of the limestone.

Calcite Atomodesma prisms comprise 0--95% of Glendale Limestone Member beds; typically the carbonate content is well over 50%. Trace fossils are rar~ and usually small. The colour of both fresh and weathered surfaces of Glendale Limestone Member is lighter than that of the Manga­rewa Formation. In most samples of Mangarewa limestone the colour is between N4 and 5Y 4/1 (Goddard et al. 1963); Glendale Limestone samples range between N5 and 5Y 6/1. Light brownish yellow staining gives the impression of a predominance of iron oxides in the lower part

Geology-2

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376 N.z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 18

of many beds, particularly toward the base of the Glendale Limestone Member.

The volcanogenic and occasional metamorphic and granitic particles which are the source of the limonite are the same size or larger than the abundant Atomodesma prisms. Size and composition grading is very common in the Glendale Limestone Member along Productus Creek, but is rare on the north traverse, and apparently absent farther north. Conversely, cross­bedding is more common toward the north; whole Atomodesma and large fragments are also more common northward. These trends support north­ward shallowing in the depositional basin. Graded beds are 20-100 mm thick and are laterally continuous for tens of metres. Cross-bedding occurs in 50-100-mm-thick beds which usually pinch out in less than 3 m. Ripples are very rare.

Fifty-five metres from the top of the Glendale Limestone Member is a fossiliferous conglomerate 0·6-1·3 m thick overlain by a scoriaceous basalt 0·6 m thick. The conglomerate, which can be traced for several tens of metres south of Productus Creek, is composed of mafic volcanic pebbles, brachiopods, echinoderm columnals, bryozoans, and Atomodesma limestone pebbles and boulders up to 300 mm long containing echinoderm and bryozoan fragments.

Volcanic activity in Glendale time is indicated by the presence of the scoria. The close association of the fossiliferous volcanogenic conglomerate and the scoria suggests a causal relationship. The volcanic pebbles in the conglomerate are andesitic and basaltic and so may have been derived partly from flows just preceding deposition of the overlying scoria. Most of the fossils in the conglomerate are not similar to the Mangarewa fauna and so may have been contemporaneous with volcanism. If this interpreta­tion is correct, the assemblage represents a community which lived within or between Atomodesma banks or colonies.

Evidence favouring lateral equivalence 6f Elsdun sandstone member and Glendale Limestone Member is the petrographic similarity of sandstone within and beside the Glendale Limestone Member, and the obvious inter­fingering of Glendale Limestone and Elsdun sandstone beds just east of the southern end of the Weetwood Formation (Fig. 1).

Part of the Elsdun sandstone member directly overlies the Glendale Limestone. There is no apparent lithologic break or rapid change between the Elsdun sandstone beds lateral to the Glendale Limestone and those overlying both the limestone and the lateral sandstone beds.

HAWTEL FORMATION

The Hawtel ·Formation overlies the Elsdun Formation. In this paper the name Hawtel Formation is given to only the muddy unit which contains lenses of bryozoan-echinodermal limestone which Mutch (1972) designated the Hilton Limestone Member. The unit here called the Elsdun sandstone member was included by Mutch (1964) in his Hawtel Formation because he did not recognise it as a partial facies equivalent of the Glendale Limestone Member. As defined here, the Hawte1 Formation (Fig. 1) extends from north traverse, where it contacts the overlying Wairaki

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No. 3 FORCE - PRODUCTUS CREEK GROUP 377

Breccia, almost to the southern end of the map area, where 1t 15 overlain by the Triassic. The thickness is 45-90 m at north traverse and 75 m at Productus Creek, and it increases southward.

Most outcrops of the Hawtel Formation have either a crushed or a spongy appearance. Close examination reveals the biogenic nature of the cavities. Holes approximately 1 mm across in curving rows are Bryozoa moulds; others, up to 17·5 mm in diameter, are moulds of echinoderm columnals. Calcite, presumably the original mineral (Lowenstam 1963), is still present in some of the less weathered material. Bedding is indistinct in areas which are presently less calcareous.

The limestone lenses are up to 6 m thick and over 30 m long. Individual beds are 20-50 mm thick. Units 0·6-1·0 m thick are highly contorted in places, due either to irregular primary deposition controlled by fenestellid bryozoan growth pattern, early post-depositional slumping on oversteepened bedding planes, or tectonic disturbance. Because of contortion of the beds, lateral continuity is difficult to determine. Polished specimens of the lime­stone show a tight framework filled with biogenic fragments and secondary calcite. This structure has been called "biolithite" (Folk 1962); the term implies that the Bryozoa actually constructed the framework.

Judging from the ubiquitous biogenic features in this formation, the Productus Creek area was the site of thriving echinoderm and bryozoan communities in Hawtel time.

W AlRAKI BRECCIA

The youngest sedimentary unit in the Productus Creek Group is the fossiliferous, volcanogenic Wairaki Breccia. This is properly a conglomerate as most of the pebbles are rounded. It extends from just south of Productus Creek to the northern end of the main outcrop belt. The basal contact of Wairaki Breccia is distinct where it is directly underlain by the Hawtel Formation. North of the Hawtel Formation, however, the Elsdun sand­stone appears to grade upward into conglomerate without a distinct break.

Bedding is vague, especially in the coarser part of the formation. The total thickness is at least 60 m on both traverses. The formation is thickest at the north of the map area and thins southward.' Wairaki Breccia beds are more nearly parallel to the overlying Triassic beds to the north than to the south.

WEETWOOD FORMATION

The Weetwood Formation crops out in a short, irregular lens between the Mangarewa and Elsdun Formations from just south of Productus Creek to the first creek north of Productus Creek (north traverse). At Productus Creek, the body is 180 m thick, and it is thicker just to the south.

The rock type is a distinctive mafic-poor micro-diorite or andesite. Pebbles derived from the Weetwood Formation have not been recognised in over­lying Permian strata.

Distinct internal variations, in such characteristics as crystal shape, size, composition, or orientation, were looked for but not observed. Primary

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378 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 18

layering is absent, although jointing parallel to the regional strike occurs in some places. One sectioned specimen suggests chilling at the lower edge of the body.

In view of the homogeneity of the formation, the absence of this rock type as detritus in upper Permian sediments, and the presence of small intrusions of Triassic age within a few kilometres of the Productus Creek area, the Weetwood Formation is tentatively interpreted as a Triassic intrusion. As such it is not included in the Productus Creek Group.

Summary of Stratigraphy

The Productus Creek Group is a northward-thinning wedge of fine­grained sedimentary rock, surrounded by a partial envelope of coarse­grained rock which closes around the north end of the wedge of fines.

The fine wedge consists of the Hawtel Formation and the Glendale Limestone Member of the Elsdun Formation. The Hawtel Formation is absent in the north and is thicker to the south. The fine particle size characteristic of the Glendale Limestone is controlled to a large extent by the breakdown of Atomodesma shells to component calcite prisms, rather than by hydrography. But trends in grading, which is more common to the south, and scour and fill as well as whole shells, which are more prevalent to the north, suggest a northward shoreline for the Glendale Limestone. The wedge shape of the Hawtel Formation also indicates a northward shore.

The coarse envelope is defined by the Mangarewa Formation, Elsdun sandstone member, and the Wairaki Breccia. The conglomeratic part of the Mangarewa Formation is much thicker at Coral Bluff than farther south. Overlying the Mangarewa Formation at Coral Bluff, the Elsdun sandstone forms the closure of the envelope and coarsens upward into the Wairaki Breccia. The Wairaki Breccia is thickest in the north and does not cover the Hawtel Formation in the south.

LITIJOLOGIC AND MINERALOGIC TRENDS

Framework Grains

The major trend apparent in the field is the change in calcite content. Aragonite, dolomite, and other carbonates were not found. The carbonate is generally in the form of biogenic framework grains. Framework grains are clastic particles which are mostly larger than 0'06 mm and which touch each other. Lithic, primarily volcanogenic fragments, and detrital crystals of mainly plagioclase, pyroxene, quartz, and magnetite are the other important framework grains.

Volcanic Fragments

In this paper, the term tuff is applied only to rocks known to contain "glass" shards. Other volcanogenic particles include particles eroded from flows older than or penecontemporaneous with the time of deposition;

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No. 3 FORCE - PRODUCTUS CREEK GROUP 379

primary pyroclastic debris not including glass shards; and grains, other than glass shards, eroded from a primary pyroclastic deposit.

The most abundant volcanogenic rock types represented in the sediments are fresh and altered andesite, and basalt. Original essential minerals in­clude plagioclase and clinopyroxene; minor and accessory minerals are magnetite and quartz. The mafic minerals have locally altered to chlorite, hematite, and limonite, and the plagioclase has locally altered to mont­morillonite, albite, laumontite, heulandite, and analcime.

Feldspar

Detrital plagioclase crystals over 0·5 mm are commonly euhedra with normal and oscillatory zoning or albite twinning; smaller crystals seldom show zoning. Slender twin-pair laths predominate in the lithic fragments with fine groundmass and oriented phenocrysts. The composition, altera­tion, zoning, twinning, and habit of the detrital plagioclase crystals and the plagioclase phenocrysts in lithic fragments were found to be similar in a given specimen. They were therefore considered to have the same origin; that is, the detrital crystals were derived from the lithic fragments. Most plagioclase feldspar compositions were determined on detrital crystals, using a modified Rittman method (flat stage). Potash feldspar was identified by comparison with thin section mounting medium. The calcium content of plagioclase generally falls in the range An30-oo , although extremes of AnI and An7l were found. A rough upward trend from predominantly labora­dorite to predominantly oligoclase in the Mangarewa Formation-Elsdun Formation sequence may reflect a change from an andesitic to a dacitic source; more calcic plagioclase at the Elsdun Formation-Hawtel Formation contact (locality 34b; Fig. 1) is possibly due to uncovering of an older source, uncovering of the Mangarewa Formation, or reoccurrence of an de­sitic volcanism. In the Mangarewa and Glendale biocalcarenites, the detrital plagioclase content is usually less than 10% of the total rock volume (by thin section estimation). In the Eldsun sandstone member, the average is 10-15% and the range is 1-25%. The maximum was noted in two samples south of the Glendale Limestone. Very little microcline and orthoclase have been identified, and no sanidine.

Pyroxene

Pyroclastic clinopyroxene, mostly in the Mangarewa Formation, and clastic clinopyroxene throughout the section are diopsidic augite, on the basis of maximum extinction angle.

A few prismatic concentrations of chlorite may be pseudomorphic after orthopyroxene. Clinopyroxene in the same thin sections appears fresh.

Quartz

Detrital quartz occurs in at least three habits: low quartz pseudomorph after high quartz; aggregates which are quartzose sandstone or quartzite, and quartzose schist; and single anhedra which may be either broken pseudomorphs or low quartz derived from a granitic source. Generally, the most abundant habit is the pseudomorph, evidently from silica-saturated

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380 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 18

ash or flow rocks. However, within the basal zone of the Glendale Lime­stone, and the lower half of the Elsdun sandstone member immediately south of the limestone, there are more anhedra than euhedra. This is also the only zone where quartz comprises more than 10% of the total rock. Granitic fragments and sericite are also notable. The quartz anhedra are presumed to have been derived from a granitic source.

Other Minerals

Magnetite, identified by magnetic and reflection properties and X-ray diffraction pattern, is ubiquitous and usually comprises 1-3% of the rock. It exceeds 5% in at least two zones (localities 725c, 33, 34b) in the Elsdun sandstone member just above and south of the Glendale Limestone (Fig. 1). Large and small crystals are common in volcanic rock fragments and as single grains.

Analcime, heulandite (clinoptilolite), laumontite, montmorillonite, and chlorite are the main alteration products of the primary minerals. Mont­morillonite is discussed in the section on clays.

Chlorite has replaced glass, pyroxene, and the centres of calcic plagio­ciase grains, and rarely the entire matrix of a sandwacke. The habit is invariably "books" of bent crystals which appear as short, radiating fibres in thin section. The juxtaposition of scoria and chlorite-rich beds near the top of the Glendale Limestone Member suggests some causal relation­ship between them. One possible explanation is that an ash shower pro­vided a large amount of ferric glass which later altered to chlorite.

Strongly reducing conditions would not have been appropriate for the formation of chlorite (Berner 1964). Some chlorite may have formed at the surface prior to burial where burrows indicate aerobic conditions; much of the chlorite, however, probably formed during burial metamorphism.

Authigenic sphene, pyrite, and hematite are accessory constituents in almost every thin section. Sphene is in volcanic fragments. The limestones release H 2S during grinding or solution in acid, indicating the presence of finely disseminated pyrite. Pyrite may have formed just after deposition, when the large mass of organic carbon contributed by dead Atomodesma and other organisms would have resulted in a reducing environment at or below the water-sediment interface.

Matrix

The amount and composItIOn of matrix (particles interstitial to frame­work grains; usually finer than 62 [lm) are clues to both sedimentation­particularly the water motion-and diagenesis. The predominantly sandy rocks were divided into sandstones and sandwackes on the basis of matrix content; 15% was chosen as the dividing line (Pettijohn 1957). Consider­ing the labile nature of the minerals and mineraloids comprising the frame­work grains, the writer assumes the original matrix grains were at least as unstable. Under any likely depositional conditions fine volcanogenic particles would tend to alter rapidly. The resulting matrix may thus be related only indirectly to the original detrital matrix (Cummins 1962; Hawkins &

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No. 3 FORCE - PRODUCTUS CREEK GROUP 381

Whetten 1969; Dickinson 1970). The framework grains are touching rather than "floating", so they do not appear to have been replaced by "pseudo-matrix"; the distinction between better sorted sands tones and more poorly sorted sandwackes is therefore still useful as an indicator of sedi­mentary conditions.

The Glendale biocalcarenites and interbedded sandstones are noticeably free of matrix, but sandwackes occur in the contemporaneous non-calcareous unit (Elsdun sandstone member). Silt or mud comprises more than 50/0 of the non-calcareous rocks but does not exceed 350/0, even in the peripheral areas, below the Hawtel Formation. Increase in matrix southward in the Elsdun sandstone member suggests quieter water toward the south during deposition.

Paradoxically, fine sediment predominates in the Hawtel Formation, whereas the thriving encrusting Bryozoa communities incorporated in it suggest moderate water speed and slow sedimentation.

In Wairaki Breccia time, coarse sediment was dumped onto the shelf faster than finer material could be supplied to fill the interstices. The resulting pores remained empty or were filled with calcite. Some of the calcite is probably "inorganic" cement, and some appears to be crushed shell materia!.

Clay Fraction

The clay fraction of 40 Productus Creek samples was separated by crushing, centrifuging, and settling in a still water column. Carbonate was removed with dilute HC!. Clay size particles were pipetted onto glass slides and analysed by X-ray diffractometry. Samples with 14A peaks were vapour­glycolated to determine if montmorilIonite was present.

MontmorilIonite, chlorite, ilIite, quartz, feldspar, laumontite, and heu­landite (clinoptilolite) were detected (Fig. 6). A 7 A peak which moved slightly in some samples after glycolation is probably iron-rich chlorite interlayered with montmorillonite (Carroll 1970; J. R. Boles pers. comm.).

Areas under peaks on smoothed diffractograms were estimated by count­ing the graph paper squares. Unweighted areal proportions within each sample were computed by averaging two to four subsamples. The primary use of the data is to compare one phase in several samples. Different phases in one sample cannot be rigorously compared.

Although serial samples through a single bed (102-105b) do not reveal significant variations, the Productus Creek section as a whole does exhibit some trends.

Montmorillonite

A mixed-layer clay with a high proportion of montmorillonite and some chlorite (Carroll 1970) is present in the Mangarewa Formation. Mont­morilIonite is also the predominant constituent of the clay fraction through­out most of the Elsdun Formation and it decreases slightly upward. The Hawtel Formation apparently lacks montmorillonite.

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field no.

4 35

512_ 34a

776_ 513_

7

8 9

31-

10 10a 12 24 '25b 26b 27 11

717-

526-55

62 64 68

533-80a 84 86a 86b

105 a 105b 104 103 102

99 120 539-

554 558 543-

montmorillonite chlorite

[J rn [J m [J m

m rn m [J

m m [J p

[J m m [J

[] rn p rn p m

[J [J

[J [J - -[J [J

ill [J

m [J

m [J

m m [J m

rn m m m

m m [J m - -

ITl [J

[J [J

n, rn CD [J

[J rn rn rn

[J rn [J [J

rn [J

rn [J

rn [J

W IW rn [J

rn [J

rn m [J m

~

0 5 10 0 5 proportional scale

chlorite illite and illite rn rn rn m [J m m m m m m m m m m m m []

[] rn [] rn

p [J

[] [J

m m -m m m m [J m [J m

m m [] m

rn ,m [J m

m rn rn m

-m rn m [J

rn rn [J rn m rn rn rn rn rn [J rn [J rn rn III [J rn

W IW [J rn m m m m m rn

10 0 5 6 5

quartz feldspar laumontite ciinoptilolite

[J [J [J [) -c <Do

[J m [J ~-[J ",Cii m [J m [JIE

m m m [J J: [J [J [J m

[J [J [J []

[] [J [J []

[] [] [J []

[] [J [] []

[] [J [] [) [] [] p p

[J [J [] []

[J [] [J [] c [] [J m m 0

I[] .~ -[] III [J E [J [] m [J 0

LL

[l [J m p [J [J [J p [J' [J Im p

m m [] p c III m m [J ~

"0 [J I[] [J [J

(fJ

ill m I [J p p

III [J [J [J -

[J [J t~ p [J rn I[J p

[J [] [J p [] [] [J p

[] [] rn p

rri rn [J p [J m rn p [J [] [J [J

[J [J [] p

rn [] rn p [J [J rn p

rn [IT Irn p '" rn [J [J p3c <DO

[J

I~ I~ p ~-E

m pc E "'~ m p~J:

75 5 0 5 0 '5 10 0 5

FIG, 6-Stratigraphic variations In the proportions of phases in the clay-size fraction of Productus Creek Group rocks. A "+" after field number designates a sample off the main Productus Creek traverse. "P" indicates the presence of a phase in undetermined amount.

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Quartz

Clay-size quartz is somewhat more abundant in the Mangarewa Forma­tion than at the base of the Elsdun Formation. It increases in abundance slightly from the base of the Elsdun through the Hawtel Formation. As the samples were not analysed in stratigraphic order, sample preparation is not a major factor in the quartz trend.

Chlorite and Illite In the Pro ductus Creek Group, chlorite and iIlite are most abundant in

the clay fraction of the Hawtel Formation, with significant increase upward. Chlorite in the Glendale Limestone is important only in a bed near the volcanic lens. Chlorite appears in a sample of Elsdun sandstone member which may be the lateral equivalent of the Glendale volcanic lens. It is also noteworthy that the three Elsdun Formation samples containing abun­dant chlorite contain less montmoriIlonite than predicted by the trend.

Summary of Assemblaxes and Interpretation of Trends

Mineral assemblages characteristic of the Productus Creek Group clay­size fraction are: Mangarewa Formation = montmoriIlonite-quartz-laumon­tite-clinoptilolite; Elsdun Formation = montmoriIlonite-quartz-laumonbite­clinoptilolite; and Hawtel Formation = chlorite-illite-quartz-Iaumontite (Fig. 6).

The most striking change in the clay-fraction mineralogy occurs at the boundary between the Elsdun and Hawtel Formations, i.e., a decrease in montmorillonite accompanied by an increase in chlorite and illite. Illite and chlorite may form in the marine environment by addition of K+ and Mg+, respectively, to montmorillonite (Grim & Johns 1954). The distribu­tion of montmorillonite, chlorite, and iIlite suggests a more seaward posi­tion for the Hawtel Formation; this supports the stratigraphic interpreta­tion presented above in which the Hawtel Formation is seen as the core of a seaward-thickening wedge of fines. Alternatively, the Glendale Lime­stone Member may have been deposited the same distance from shore as the Hawtel Formation but nearer a river mouth, estuary, or delta distribu­tary.

DISTRIBUTION OF FOSSILS

Fossils comprise most of the Glendale Limestone and a large part of the Hawtel Formation. At the base (Mangarewa Formation) and top (Wairaki Breccia) of the Productus Creek Group are two other fossiliferous zones.

All the fossiliferous units contain Atomodesma prisms, volcanogenic rock fragments, and authigenic minerals, but the range of proportions differs. Fossil assemblages are distinct for each unit, but within one formation lateral faunal variations are as great as vertical variations.

Lists of fossils which the writer identified in each formation appear in the Appendix with estimates of their abundance. Fossil localities are shown on the stratigraphic columns (Figs 4, 5) and are listed separately elsewhere (Force 1972).

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North South

Brachiopods / /,,,,:0: / 4! + Not

Molluscs /B"ch;~:'/ Present

+ // /7a

/

~I:'" / / / /

/+ / Brachiopods + Molluscs

Bryozoans / /B~O;O~S / / / / /

Top

Base

FIG. 7-Diagrammatic stratigraphic distribution chart of commonest fauna I groups in the Mangarewa Formation; Atomodesma is present in the lined areas.

MANGAREWA FORMATION

Where brachiopods are not present, Atomodesma makes up most of the fauna. North of north traverse, brachiopods occur with gastropods, bivalves, and bryozoans throughout the formation (Fig. 7). In north traverse, brachio­pods, molluscs, and bryozoans occur in the lower two-thirds of the forma­tion; no brachiopods or bryozoans occur in the upper third. At Productus Creek and farther south, brachiopods, molluscs (mainly biva1ves), and minor concentrations of bryozoans occur in the lower third but only a few molluscs occur in the upper two-thirds. Whole Atomodesma shells are not abundant north of north traverse except in the lower part of the section, In summary, there is an inverse relationship between an Atomodesma-other mollusc-dominated assemblage and a more diverse brachiopod-mollusc­bryozoan assemblage. The former is found in more of the section to the south, whereas the latter increases in importance northward. This pattern is part of the evidence on which the discussion of the geohistory of the Productus Creek area is based (see below) .

Similar Australian Fauna

Coleman (1957) noted two faunal associations in the Permian of Western Australia: dense colonies of either productids or Calceolispongia. Both associations were interpreted as neritic or epineritic, and appear to have preferred a silty substrate. The productids are of the subfamilies Productinae and Strophalosiinae. Coleman reported that while a species from each subfamily might live in close proximity, more than one species of a single subfamily did not cohabit an area. He concluded that the lateral and vertical distribution of the species was governed more by ecology than evolution. Rarely, young productids were found attached to Calceolisponf(ia. Asso­ciated with mature productids were other brachiopods, such as Neospirifer, Streptorhynchus, Cleiothyridina, Chonetes, and Dielasma; small, simple corals and T hamnopora; and a parasitic worm.

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No. 3 FORCE - PRODUCTUS CREEK GROUP 385

Notably absent from both the Australian and New Zealand deposits are fusulinids (present in the Alpine belt, east of the Hokonui belt), algae (widespread in Permian rocks elsewhere; Konishi 1954), and ammonoids (Waterhouse 1964a).

No other Permian faunal assemblage known to the writer resembles those in the Mangarewa Formation as closely as the Western Australian assem­blages, although Wass (1971) has found similar assemblages in eastern Australia. A shallow water communication between the two land masses at least during the lower Permian seems likely.

Water Motion in Mangarewa Time

The more delicate brachiopods (Eehinolosia, Terrakea) are usually found in fine to medium sand with few plant fragments. Except at one locality, they are very rare in the Productus Creek section where coarse sediments and plants are abundant. This suggests that the spiney brachiopods congre­gated in the quieter areas, probably away from the plant-bearing fresh­water ( ?) distributaries.

A fossil count at locality MfS (Fig. 1; same as NZGS 3616; details in Force 1972) indicates that there are few small benthonic molluscs and a relative abundance of more mobile or resistant forms (pectenids, neo­spiriferids, Ambikella, and Plekonella). The large number of T errakea is attributed to transport from quieter areas, possibly by longshore current. The ventral to dorsal valve ratio at locality MfS is 16/1; at locality 735 it is 9/1 to 3/1. The larger ventral valve would tend to be transported beyond the dorsal valve, and the increasing proportion of ventral valves toward Productus Creek may reflect such a process. The contemporaneity of localities MfS and 735 has not been established, however. They are both highly fossiliferous zones and appear to be approximately along strike, but it was not possible to trace actual bedding planes in the field between the two localities.

At locality MfS, 75-80% of the disarticulated brachiopod whole valves are convex toward the stratigraphic top of the beds. Ambikella, usually articulated, is always found with the ventral valve up-presumably the reverse of the life position; zaphrenthid corals are usually in the plane of bedding; large spiriferids are more often posterior up than down, again, the reverse of the life situation. Plekonella, a small spiriferid, usually occurs as coquinas in channels 20-50 mm deep. The shell orientations (van Straaten 1952; Muller 1958; Emery 1968), the presence of shallow shell-filled channels, and the fossil assemblages (Coleman 1957) suggest the neritic zone. While the wave capacity at times was adequate to move cobbles at locality MfS, the presence at locality 735 of some productids in life posi­tion, with spines braced downward, precludes very vigorous water motion there. The more usual hash of spines and broken shells at locality 735 may be due to post-depositional compaction, but probably was at least partly a result of comminution by waves or currents some distance from the site of burial.

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Feeding Habits ot Organisms in Mangarewa Time

There are at least three feeding habits of the Mangarewa organisms. Epifaunal suspension feeders include Atomodesma and the other large bivalves, brachiopods, corals, Bryozoa, sponges, and echinoderms. Small, mobile molluscs apparently foraged at the surface or in the top 10 mm of sediment; palaeotaxodonts used labial pal ps as gatherers (Morton 1967; Stanley 1969); pleurotomariids selectively ingested food·containing sedi­ment as they passed over it.

Although the mobility of the palaeotoxodonts cannot be proved con­clusively, Stanley (1969) makes a good case for the part that the fine chevron ornamentation on some Tellinacea and Lucinacea played in burrow­ing. Some New Zealand Permian palaeotaxodonts also have chevron orna­mentation, and a mobile life is at least a possibility.

As the major competitors for food in suspension, brachiopods and Atomodesma probably tended toward mutual exclusion. During deposition of Mangarewa sediment, in which brachiopods are abundant, Atomodesma did not flourish as prolifically as during deposition of the brachiopod-free Glendale Limestone Member of the Elsdun Formation. Atomodesma was capable of completely dominating a community whereas other taxa appa­rently were not. Therefore, Atomodesma probably had greater influence than did other taxa on the composition of any community of which it comprised a notable proportion.

Predation in Mangarewa Time

Little evidence of predation was found in any of the Productus Creek taxa. Pachydomids at locality MfS may possibly have supported parasitic clams, bryozoans (cf. Boekschoten 1966, fig. 10), and sponges. Etheripecten may have some bryozoan or sponge damage. Possible fish predation of Atomodesma is suggested by concentrations (pods) of small or large "plates" of shell. Direct evidence such as teeth or bitten shells is absent.

Preservation of Body Fossils

Preservation of the body fossils provides several clues about deposition and shallow burial. Atomodesma and brachiopods produced shells which were predominantly calcite. Their shells and shell fragments are well pre­served in fresh specimens. Thin sections usually show that the regular prisms and tangential fibres have undergone very little recrystallisation, although original shell "thickening" (in brachiopods) and laumontitisation have obscured some detail. The external features of rugose corals are well preserved, but internal structure is obliterated by recrystallisation in most specimens. The original mineralogy of the coralla was probably aragonite (Fairbridge et al. 1967). The good preservation of uncrushed specimens of Mangarewa fenestellid Bryozoa suggests their shells were originally calcite (a general characteristic of fenestellids; Lowenstam 1963). Recent echinoderm tests are composed of somewhat porous plates of Mg-calcite (Donnay & Pawson 1969), a mineral which tends to dissolve incongruently to form calcite and an Mg-rich fluid (Land 1967). The transition from Mg.calcite is usually rapid enough to preserve the structure of the shell and

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No. 3 FORCE - PRODUCTUS CREEK GROUP 387

this may account for the preservation of echinoderm columnals in the Mangarewa Formation as well as in the Hawtel Formation.

Most gastropods and bivalves are present in the Mangarewa Formation as chlorite casts. Most modern gastropod and bivalve shells contain at least some aragonite, and many are primarily aragonitic. Land (1967; also Winland 1968) showed experimentally that the aragonite-calcite "inver­sion" can involve a "complete", slow dissolution of the aragonite. This reaction, in contrast to the rapid, incongruent dissolution ("incomplete" in the sense that a solid phase is always present) of the Mg-calcite to calcite transition, tends to permit replacement of the aragonite by a non­calcareous phase such as chlorite.

The order of stability of commonly occurring natural biogenic carbonates was experimentally determined by Chave et al. (1962) as calcite (most stable), aragonite, Mg-calcite. However, due to the processes described above, the "order of fossil preservation" is often found to be calcite, Mg-calcite, aragonite. This appears to be true in the Mangarewa Forma­tion: calcite skeletons (e.g., brachiopods and Atomodesma) are fresher than Mg-calcite skeletons (e.g., echinoderm columnals) which are fresher than aragonite skeletons (e.g., molluscs other than Atomodesma). The chlorite which replaces the shells may be pseudomorphic after an authigenic phase such as chamosite (James 1966) which formed after the aragonite dissolved and before the void collapsed. This restricts "chamosite" crystallisa­tion to very soon after burial.

The flattened appearance of the pleurotomariids indicates that the shell shapes were altered or altering during compaction.

Trace Fossils

Trace fossils are abundant in the Mangarewa Formation in both the limestones and the sandstones; they are most obvious on weathered surfaces and polished hand specimens. Trails and burrow fillings are, respectively, parallel to and at sharp angles to bedding planes. There are at least two types of trails: sinuous lines of segmented, nested dark and light arcuate bands up to 5 mm wide and 60 mm long; and sinuous, continuous (un­segmented) trails of the same uimensions. They are similar to Recent trails of gastropods and bivalves (Lessertisseur 195·5, figs 10, 11) and were probably made by palaeotaxodonts, pleurotomariids, and scaphopods on the water-sediment interface. A discontinuous motion with back-filling is suggested by the arcuate bands, and some consolidation soon after con­struction is indicated in both types of trails.

The burrows may be "Chondrites" (Seilacher 1964, fig. 3) and were probably formed by soft-bodied organisms which were not preserved. None of the shelled fossils collected from the Mangarewa Formation are believed to have burrowed more than 10-20 mm into the substrate. Trails and burrows appear to belong to Seilacher's ethological groups "Pasichnia" (grazing movement) and "Repichnia" (directional movement).

Surface trails, burrows, and sessile benthonic organisms are proof of aerobic conditions above and immediately below the sediment-water inter­face (Seilacher 1964) in the Mangarewa Formation. The preservation of

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TABLE I-Distribution of trace fossils (T) and plant fossils (PI) in the Elsdun Formation. Percentages calculated with (w) and without (w/o) samples con­taining only Atomodesma (A).

A (-T, -PI) A, T (-PI) A, PI (-T) A, T, PI Other fossils

N of N traverse No. of w w/o samples (%) (%)

4 o o 1 o

80 0 o 0 o 0

20 100

N traverse No. of w w/o samples (%) (%)

13 5 3 5 3

50 0 19 38 12 23 19 38

Productus Creek No. of w w/o samples (%) (%)

25 40 15 17 12

26 0 41 55 15 21 18 24

"carbonised" plants and ubiquitous fine-grained pyrite suggest anaerobic conditions soon after burial.

ELSDUN FORMATION

Atomodesma fragments are present in almost every sample of Glendale Limestone in the Productus Creek and north traverse sections. Table 1 shows that trace fossils are less common to the north, and plants occur more frequently with trace fossils than alone. At times the influx of plant material coincided with the obscuring of traces, or possibly with inhibition of organisms responsible for them; during other periods of plant deposition animal traces are abundant. Because most of the plant fragments are merely dark brown laths with little relict structure, identification even on a gross level is not usually possible. One good leaf specimen from locality MfS (NZGS 3616) was identified as Glossopteris sp. (Mildenhall 1970).

Remains of palaeotaxodonts and pleurotomariids are absent in the Glen­dale Limestone Member although there are traces similar to those attributed to small molluscs in the Mangarewa Formation. The greater purity of the Glendale Limestone suggests that the chemical constituents of a suitable replacement mineral were not present or at least not abundant; this would permit the moulds resulting from dissolution of aragonite shells to collapse.

A series of 21 samples in the upper 150 m of the Glendale Limestone reveals a trend of upward decreasing bioturbation, as estimated from the amount of bedding retained. Apparently the organisms were unable to keep up with sedimentation. This was probably due to increased rate of deposition, decreased number of burrowers, decreased ability to burrow, or a combination of these factors.

At a few localities in the Elsdunsandstone member there are limonitic tubes resembling the trace fossil "Planolites ophthalmoides" (Seilacher 1964, fig. 6). These have not been found in other formations, and the organism that formed them is unknown.

Fossils other than Atomodesma, traces, and plants are rare in the Glen­dale Limestone Member. Lunucammina, a nodosarian foraminifer, occurs in at least three localities. It must be fairly abundant, at least locally, to have been discovered in thin section. The bryozoan concentrations (locality

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No. 3 FORCE - PRODUCTUS CREEK GROUP 389

14) and underlying fossiliferous conglomerate (locality ISb) associated with the scoria are the only non-Atomodesma shell beds in the Elsdun Forma­tion. The almost total absence of other organisms supports the idea that Atomodesma Jived in colonies or banks.

Comparison of the ManJ;arewa and Elsdun Formations

Conditions for deposition of the Elsdun Formation probably did not differ radically from those for the Mangarewa Formation, but there were several variations. The most important difference is in the general pattern of deposition. The "heart" of the Elsdun Formation, the Glendale Lime­stone Member, interfingers with sandstone and sandwacke to the north and south. The changes in lithology are abrupt, with very little evidence of gradational units in between. The sandstone is thick north and south of the Glendale Limestone, and thin stratigraphically above it, so that the total thickness through the Elsdun Formation is fairly constant over its length. The shape of the Glendale Limestone and its relationship to the surrounding sandstone are the same as Merriam (1962), Mudge (1957), and Harbaugh (1959; 1960) described for the late Paleozoic limestone "buildups" of the central United States. Furthermore, marked changes in attitude of beds in the lower part of the Glendale Limestone Member along Productus Creek (Fig. 1) recall the "large-scale cross beds ... on the flanks" of these "buildups" (Merriam 1962). Breccias were noted at the base of two beds at the north end of the Glendale Limestone, and one of the breccias directly overlies conglomerate; this is also indicative of flank deposition.

Beds in the Glendale Limestone are about the same thickness as in the Mangarewa Formation but include few burrows and more graded units, cross-beds, and scour and fill structures. Biota other than plants and Atomodesma is minor, in contrast to the diverse and abundant biota of the Mangarewa Formation.

The differences between the Mangarewa and Elsdun Formations may be related to the greater influence of Atomodesma banks or colonies on the deposition of the Elsdun Formation. The almost complete separation of carbonate from non-carbonate "facies" and the paucity of fossils other than Atomodesma would be expected in the situation where overlapping biogenic banks form slight topographic rises which divert non-biogenic debris. Biologically, the main difference between the two formations was the relative lack of vigor of the Atomodesma colonies contributing to the Mangarewa Formation, with the resultant lower level of prism production and topographic control.

HAWTEL FORMATION

Fenestellid bryozoans are found in most samples of the Hawtel Forma­tion. Less abundant but widespread are abraded Atomodesma fragments and echinoderm columna Is. This specialised fauna and the lenses of con­torted bryozoan limestone strongly suggest bryozoan reefs. Shallow water is indicated by the low number of species present (Schopf 1969).

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Bryozoan Banks During the last decade the aSSOcIatIOn described above, but without

Atomodesma, has been recognised in Carboniferous rocks in Europe (Schwarzacher 1961; Lees 1964) and North America (Cotter 1965). It is sometimes referred to as "Waulsortian-type reef" after the epoch (lower Carboniferous) of the type locality in western Eire. The authors concluded that the "reefs" were actually "banks", where the framework of bryozoans and echinoderms was not rigid and probably incapable of wave resistance. Where the growth was densest the dominant organisms apparently trapped carbonate mud by slowing the sediment-moving currents; in this respect the Waulsortian banks are similar to modern "grassy" carbonate banks. The Carboniferous bank complexes have several penecontemporaneous growth centres with overlapping, sheet-like "flank deposits". The number of growth centres contained in each Hilton Limestone lens was not deter­mined, but the calcareous mudstone surrounds all of the limestones and is therefore analogous to the overlapping flank deposits of the Carboniferous banks.

Bedding is less distinct in the Hawtel flank deposits than in the banks proper. The bedding, which is delineated by cavities formed by the dis­solution of small echinoderm columnals and bryozoan fragments, is irregular and in many places is sheared beyond recognition.

Brachiopod-bivalve lenses, also surrounded by calcareous mudstones, may represent a bank-edge or interbank facies. They occur only near the top of the Hawtel Formation and, although the forms are somewhat similar to those at the base of the Productus Creek Group, their lack of repre­sentation throughout most of the column suggests either isolation, migration away from the area for most of the time span, or reworking from a deposit younger than the Mangarewa which was not observed.

Much of the Hawtel mudstone is very porous due to the dissolution of calcite and subsequent shearing. Muddy matrix is evident in thin sections of the Hilton Limestone, in and among bryozoan zoaria, indicating that mud was present. The micro-environment was apparently clear enough to support vigorous life. Although mudstone surrounds the Hilton Limestone lenses, contacts are quite sharp and indicate the isolation of the Bryozoa colonies.

C. A. iandis (pers. comm.) suggests the limestones are possibly alloch­thonous blocks in the incompetent calcareous mudstones. This is supported by contortion and shearing and the abrupt contacts between the two litho­logies. As the fauna is distributed in the typical Waulsortian pattern, however, it seems unlikely that the limestones moved from one "ecological zone" to another.

W AlRAKI BRECCIA

The fauna of the Wairaki Breccia, like that of the Mangarewa Forma­tion, is more diverse than that of the Hawtel Formation, and it contains several undescribed genera and species. All of the forms are either small or in some other way abrasion resistant. Conglomerate pebbles 5-20 mm in diameter, with calcite cement and coarse sand matrix indicate a vigorous

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No. 3

Walraki Breccia ______

...____Hawtel Fm.

Elsdun Fm.

Mangarewa

Fm.

FORCE - PRODUCTUS CREEK GROUP

North South

Non-bank faunas Bank fauna

?

No fauna ? Bank

Non-bank faunas

FIG. 8-Faunal affinities in the Productus Creek Group.

391

Top

Base

environment. The presence in at least one sample of large pebbles of Mangarewa lithology indicates the uplift or perhaps the uncovering of the basal unit by the end of the Permian. Of particular interest are a bivalve and a "mentzeliopsid" brachiopod which do not resemble any previously described New Zealand Permian fossils.

Summary of Faunal Distribution in the Prodtlctus Creek Group

In the Productus Creek Group, brachiopod-mollusc-bryozoan assemblages form an envelope around a wedge of bank-forming faunas (Fig. 8). The faunal pattern corresponds closely to the lithologic pattern (see Figs 9, 10) discussed in the next section.

HYPOTIlETICAL GEOHISTORY OF TIlE PRODUCTUS CREEK GROUP

The pattern formed by the distribution of fossils, sediment sizes, and thickness trends (Figs 1, 4, 3, 7, 8; Table 1) is a rough wedge of one facies surrounded by an envelope of another facies (Fig. 9). It appears to record a major transgression and regression. Some aspects of this pattern are repeated in many other Permian areas of the Hokonui belt (Force 1972).

Two models which account for the pattern and variations will be pre­sented. The migrating delta model applies only to the Productus Creek sequence; the eustatic sea-level model applies to the whole Hokonui belt Permian sequence.

Migrating Delta Model

Interfingering of the Hawtel Formation and the Glendale Limestone Member, constituting the bank facies, with the Elsdun sandstone member defines a possible delta front. Other evidence favouring a delta are the upward gradation of Elsdun sandstone into Wairaki Breccia, the thickening

Geology-3

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~ volcanic range

- --=::::-----")----coastal

I

A accretlng delta r

..... -_..... -~ r_":::::::- __ ...!:t- __ --__ -

........ @:_-.> ~:'A~'::;

B accreting J /' -_, ___ d~':.. _J _ _ ... /

rejuvenated volcanic terrane

---""'~~~

1,/f1 I"", c

/ I

/

/ I

Hawtel Fm

D

/

I~ ,

/ I ~, I / '

Wairaki Breccia

Glendale Lst Mem

Elsdun ss

mem

seaward

coarse

WiN S E

landward

coarse 00

10

0000

VOL. 18

o o

ic

FIG. 9-Migrating delta model, a'nd sedimentary patterns in the Productus Creek Group. (A) Northward delta migration during Mangarewa time: fossiliferous sediments are interbedded with land-derived ( ?) volcanogenic siltstones and sandwackes; Coral Bluff zone is overridden by deltaic deposits. Reversal during EIsdun time could account for the upward transition (north of Glendale Lime­stone Member and Hawtel Formation) from Mangarewa-type sediments through EIsdun sandstopes and sandwackes to the conglomerates of the Wairaki Breccia. (B) Southward delta migration during Hawtel time: Hawtel mud is derived from peneplained hinterland and pyroclastic volcanism. (C) Coarse sediment shed by rejuvenated land during Wairaki Breccia time overrides Hawtel mud. Abraded Atomodesma fragments in both the Hawtel and Wairaki Breccia suggest reworking of the Glendale or Mangarewa calcareous beds. At = Atomo­desma, Br= Bryozoa. (D) and (E) show the units which constitute the coarse and fine facies; a northward shoreline is inferred from thinning directions of Hawtel Formation and Wairaki Breccia, and from distribution of sedimentary structures and fossils.

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No. 3 FORCE - PRODUCTUS CREEK GROUP 393

of the Hawtel Formation toward the south, and the lack of a significant erosional unconformity at the base of the Mangarewa Formation (Fisk 1955). For the delta to have formed the wedge pattern, it must have migrated north and then south along the subsiding Productus Creek basin (Fig. 9A-C).

Bustatic Sea-Level Variation Model

This transgressive-regressive model (Fig. lOA-F) takes into considera­tion the probable sea-level variations caused by upper Carboniferous and Permian glaciations in Australia and elsewhere.

Figure loA shows the hypothetical situation in the Productus Creek area during early Mangarewa time. The northward transgression of the near­shore zone is recorded in the Mangarewa conglomerate. The basal conglo­merate mixed with large and small plant fragments (Figs 7, lOA) gives way to a fossiliferous zone (Fig. lOB) in which turbulent and quiet water environments are reflected in the distribution of fossils (N eospirifer and Plekonella, and spiney brachiopods, respectively). A predominantly mollus­can assemblage succeeds the brachiopod-dominated unit (Fig. 10C).

Figure 10D depicts Atomodesma banks shedding carbonate debris which constitutes the Glendale Limestone. Muddy sand was deposited at the dis­tributary mouth, but the fines were winnowed in several places and re­deposited with bypassed sand. Graded bedding is rare in the north but common in the south, indicating that redeposition was southward. A mafic ash shower blanketed this area near the end of Glendale time (there is little montmorillonite and abundant chlorite in the clay fraction of samples from localities 10, lOa, 31; Fig. 6).

Sedimentary conditions changed at the beginning of Hawtel time. The biogenic limestones and surrounding calcareous mud stones were deposited on a marine shelf with migrating topographic rises adjacent to shallow depressions (Fig. 1 OE). The rises were occupied and possibly built by fenestellid bryozoans and the fine non-carbonate material accumulated mainly in the depressions. Large echinoderms lived singly within the bryozoan banks; smaller echinoderms were more gregarious and' tended to occupy interbank positions. Elsdun sandstones and sandwackes occur to the north, and presumably interfinger with the Hawtel mudstone and limestone. There is some evidence that the depositional shelf was shallower to the north in Glendale time (see above) and this bottom configuration was probably maintained through Hawtel Time. As the sandy and muddy lithologies (Elsdun and Hawtel Formations) are not gradational, a topographic or hydrodynamic barrier such as a submarine rise or longshore current may have existed between their areas of accumulation.

The abrupt transition from the Hawtel Formation to the Wairaki conglo­merate records the destruction of the bryozoan colony environment by a flood of coarse clastics (Fig. 1 OF). Because the Wairaki Breccia thins to the south, and the Hawtel Formation thins and interbeds(?) with the Elsdun sandstone member to the north, it is likely that the source for both was north of Productus Creek and that water was deeper to the south-east.

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N

\ 0

0 0

Distributary 0

PI

0 0

PI

I 0

Land Sea

A B Terrakea

0 E

PI plants ~ spiney brachiopods C> At Atomodesma qp ~ spiriferid brachiopods Br Bryozoa 'f echinoderm

III

VOL. 18

)\t (&\

C

F

'~ I PI

o

o o

o o o

molluscs other than Atomodesma trails and burrows

probable erosion

FIG. IQ-Sea-Ievel vanatlOn model of (A-D) transgression and (E, F) regression. (A) Basal fossiliferous volcanogenic conglomerate (Mangarewa Formation) is followed by (B, C) successive faunas (Mangarewa Formation) climaxing in (D) prolific Atomodesma banks (Glendale Limestone Member of the Essdun Forma­tion). (D, E) The seaward thickening wedge of fines (Glendale Limestone Member plus Hawtel Formation), the core of the sequence, is overridden by (F) coarse sand and conglomerate (Wairaki Breccia) in late regression. Circles indicate conglomerate.

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No. 3 FORCE - PRODUCTUS CREEK GROUP 395

CONCLUSIONS

The Permian stratigraphic section of Productus Creek may be broken into four parts.

(1 ) Mangarewa Formation (as used in this paper) contains a basal unit of fossiliferous conglomerate, succeeded by volcanogenic Atomodesma biocalcarenite interbedded with volcanogenic sandstone and sandwacke.

(2) Elsdun Formation comprises a thick lens of fine-grained, relatively pure Atomodesma biocalcarenite (Glendale Limestone Member) surrounded by partially contemporaneous low- to non-carbonate volcanogenic sandstone and sandwacke.

(3) Hawtel Formation (as used in this paper) comprises thin lenses of bryozoan-echinodermal biolithite (Hilton Limestone Member) within a sheared volcanogenic biocalcareous mudstone.

(4) Wairaki Breccia is a fossiliferous volcanogenic conglomerate which may be partly Triassic.

A fifth unit, the Weetwood Formation (diorite) is tentatively referred to the Triassic.

Abrupt terminations and other features of the biocalcarenites in the Elsdun and Hawtel Formations suggest that they were formed by the accumulation of carbonate debris in a bank environment. The Bryozoa banks of the Hawtel Formation retained some internal biogenic structure but the Atomodesma banks of the Elsdun Formation did not. Non-carbonate, vol­canogenic sediments comprising the Elsdun sandstone member and the Hawtel mudstone were deposited beside the banks.

Trends in clast size and thicknesses of finer and coarser sedimentary units indicate a shore line north of Pro ductus Creek. The sedimentary strike of the shore line was approximately north-east.

The presence of a sedimentary wedge indicates a transgressive-regressive history. Two depositional models are possible: one involving a migrating delta, and the other related to contemporaneous eustatic sea-level variations. Evidence more strongly favours the latter model.

ACKNOWLEDGMENTS

I thank the Department of Geology of Otago University, the Paleontological Branch of the New Zealand Geological Survey, and the Department of Geological Sciences of Lehigh University for their material help and advice in this project. A Fulbright-Hays grant, a fellowship awarded by the American Association of University Women, and a Lehigh Universtiy grant are much appreciated. The dissertation on which this paper is based was reviewed extensively by Drs C. A. Landis, ]. M. Parks, and ]. D. Ryan; I wish to express to them my special thanks. Suggestions by two anonymous reviewers and Eric R. Force have improved the clarity of the paper.

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BOEKSCHOTEN, G. ]. 1966: Shell borings of sessile epibiontic organisms as palaeoeco­logical guides (with examples from the Dutch coast). Palaeogeography, Palaeoclimatology, Palaeoecology 2: 333-79.

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CARROLL, D. 1970: Clay minerals: a guide to their X·ray identification. Geological Society of America Special Paper 26. 80 p.

CHAVE, K. E.; DEFFEYES, K. S.; WEYL, P. K.; GARRELS, R. M.; THOMPSON, M. E. 1962: Observations on the solubility of skeletal carbonates in aqueous solutions. Science 137: 33-4.

COLEMAN, P. ]. 1957: Permian Productacea of Western Australia. Australian Bureau of Mineral Resources Bulletin 40. 189 p.

COTTER, E. 1965: Waulsortial·type carbonate banks in the Mississippian Lodgepole Formation of central Montana. Journal of Geology 73: 881-8.

CUMMINS, W. A. 1962: The greywacke problem. Liverpool-Manchester Geological Journal 3: 51-72.

DICKINSON, W. R. 1970: Interpreting detrital modes of graywacke and arkose. Journal of Sedimel1tary Petrology 40: 695-707.

DONNAY, G.; PAWSON, D. L. 1969: X-ray diffraction studies of echinoderm plates. Science 166: 1147-50.

EMERY, K. O. 196R: Position of empty pelecypod valves on the continental shelf. Journal of Sedimentary Petrology 38: 1264-9.

FAIRBRIDGE, R. W.; CHILINGAR. G. V.; BISSELL, H. J. 1967: Introduction. Pp. 1-28 1n CHILINGAR, G. V.; BISSELL, H. ].; FAIRBRIDGE, R. W. (Eds): "Car­bonate Rocks". Vo!. 1. Elsevier, New York. 471 p.

FISK, H. N. 1955: Sand facies of Recent Mississippi Delta deposits. Proceedings of the 4th World Petroleum Congress, Rome, 1955: 377-9R.

FLETCHER, H. 0.; HILL, D.; WILLETT, R. W. 1952: Permian fossils from Southland. N.Z. Geological Survey Paleontological Bulletin 19. 30 p.

FOLK, R. L. 1962: Spectral subdivision of limestone types. Pp. 62-84 in HAM, W. E. (Ed.): Classification of carbonate rocks. American Association of Petroleum Geologists Memoir 1. 279 p.

FORCE, L. M. 1972: Atomodesma limestones of the Hokonui belt Permian South Island, New Zealand. (Unpublished Ph.D. dissertation, Lehigh University, Bethlehem, Pennsylvania.)

GODDARD, E. W.; TRAsK, P. D.; DE FORD, R. K.; ROVE, O. N.; SINGEWALD, ]. T. JR.; OVERBECK, R. M. 1963: "Rock-col or Chart". Geological Society of America, New York.

GRIM, R. E.; JOHNS, W. E. JR. 1954: Clay mineral investigation of the sediments from northern Gulf of Mexico. National Academy of Science Publication 327: 81-103.

HARBAUGH, ]. W. 1959: Marine bank development in Plattsburg Limestone (Pennsyl­vanian), Neodesh-Fredonia, Kansas. Kansas Geological Survey Bulletin 134: 289-331.

1960: Petrology of marine bank limestones of the Lansing Group (Penn­sylvanian), south-east Kansas. Kansas Geological Surz;ey Bulletin 142: 1R9-234.

HAWKINS, ]. W.; WHETTEN, ]. T. 1969: Graywacke matrix minerals: hydrothermal reaction with Columbian River sediments. Science 166: R68-70.

JAMES, H. L. 1966: Chemistry of the iron rich sedimentary rocks. US. Geological Survey Professional Paper 440-W. 60 p.

KONISHI, K. 1954: Succodium, new codiacean genus, and its algal associates in the late Permian Kama Formation of southern Kyushu, Japan. Faculty of Science Journal, Tokyo University III (9): 225-40.

LAND, L. S. 1967: Diagenesis of skeletal carbonates. Journal of Sedimentary Petrology 37: 914-30.

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No. 3 FORCE - PRODUCTUS CREEK GROUP 397

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WATERHOUSE, ]. B. 1958: The occurrence of Atomodesma Beyrich in New Zealand. N.Z. Journal of Geology and Geophysics 1: 166-77.

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1%4a: A Permian ammonoid from New Zealand. Joumal of Paleontology 38: 149-50.

1964b: Permian brachiopods of New ZeaJa~d. N.Z. Geological Survey Paleontological Bulletin 35. 287 p.

1964c: Permian stratigraphy and faunas of New Zealand. N.z. Geological SlIITey Bulletin 72. 101 p.

1965: Palaeotaxodont bivalves from the Permian of New Zealand. Palae· ontology 7: 630-55.

1967: Upper Permian (Tatarian) brachiopods from New Zealand. N.Z. JOllmalof Geology and Geophysics 10: 74-118.

1968: The classification and descriptions of Permian Spiriferida (Brachio­poda) from New Zealand. Palaeontographica 129: 1-94.

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APPENDIX

DISTRIBUTION OF PERMIAN BIOTA AT PRO DUCTUS CREEK, SOUTHLAND

A = abundant on two or more bedding planes or at two or more localities; C = common on two or more bedding planes or at two or more localities; R = few individuals on one or two bedding planes or at one or two localities; 0 = present at more than two localities. abundance not estimated.

MANGAREWA FORMATION (65 localities)

Brachiopods Echinolosia rIlClxll'e!li E. sp. T errakea spp. Callcrinella magl1it,/ica Stellocisma papilio Neochonetes beatusi Lissocholletes brel,isulcus StrefJtorhYl1chus pelicallensis Cleio/hyridina laqueata Middalya cf. joh1lstonei Maorie!asma impera/um N eospirifer wairakiensis N. sp. N %spirifer micros/ria/lIs N. sp. Spiriferjna cristCl/a cf. Spirifer rajah Martinia cf. glabra Ambikella cos/a/a A. diHimilis A. sp. P!ekonella sou/h/andellsis P. mu!ticos/ata P. actl/a P. camp belli P. sp. At/enua/ella inCUfl'ata

Echinoderms Aesiocrilllls cf. 110dos1ls

o C A R R C R R R R R C R R o R R R C R R A R A R o R

C

Corals T hamnopora sp. zaphrenthid

Foraminifera L1I1l1lcammina cf. Robllloides sp.

Ostracodes Gastropods

Platyteichum iora/um P. spi1'OlaxlIm Glabrocing1l11lm camp belli Pertlvispira imbricata P. sp. Spiroralum sp. 117 arthia perspecta TV. sp. MOllrlonia sp. Glyp/ospira sp.

Bivalves Atomodesma sp. large fragments prisms

Praell11dll!omya sllbe/ongata Numlopsh imperta N. sp. Nuc1l1zdata prolonga N. obliqua N. sp.

R C

R R R

o R R R o R R R R R

R A R R C R R R

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No. 3 FORCE - PRODUCTUS CREEK GROUP

Glyptoleda flexuosa Vamnella sp. Uncinella sp. Pyramus sp. ?Collocardium sp. Etheripecten sp. Astartila obscllra Paleo/llc;lla sp.

R Scaphopods R Plagioglypta sp. R Bryozoans R lacy R cylindrical R Incertae sedis, tubes R Trace fossils R Plant fossils

ELSDUN FORMATION (more than 118 localities) Brachiopods

Ambikella sp. Terrakea cf. brachythaera Notospirifer microstriatus? Spiriferella supplanta

Echinoderms Foraminifera Ltl11ucammina indet.

Ostracodes

HAWTEL FORMATION (17 localities)

Brachiopods chonetid

Echinoderms Corals

WAIRAKI BRECCIA (4 localities)

Brachiopods chonetid dielasmid Neos/lirifer sp. lvfartiniopsis sp. Ambikella sp. Plekonella sp. Psilocamara saginata

Molluscs R Atomodesma sp. R pleurotomariid R Bryozoa

R Dyscritella? s.

R Sa/fordotaxis sp. Polypora? sp.

Sponge spicules R Incertae sedis, tubes R Trace fossils R Plant fossils

Molluscs R Atomodesma sp. A Bryozoa R

IP airakiella rostrata R mentzeliopsid(?) R Echinoderms R Corals R Molluscs C Atomodesma sp. R Bryozoa R

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