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Kawakawa Tephra in Wairarapa, NewZealand, and its use for correlatingOhakea loessA. S. Palmer aa Department of Geology , Victoria University of Wellington , PrivateBag, Wellington , New ZealandPublished online: 06 Jan 2012.

To cite this article: A. S. Palmer (1982) Kawakawa Tephra in Wairarapa, New Zealand, and its usefor correlating Ohakea loess, New Zealand Journal of Geology and Geophysics, 25:3, 305-315, DOI:10.1080/00288306.1982.10421494

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New Zealand Journal of Geology and Geophysics, 1982, Vol. 25: 305-315

Kawakawa Tephra in Wairarapa, New Zealand,and its use for correlating Ohakea loess

305

A. S. PALMERDepartment of GeologyVictoria University of WellingtonPrivate BagWellington, New Zealand

Abstract In the eastern part of Wairarapa, the20 OOO-year-old Kawakawa Tephra occurs as a 0.06­0.10 m band of coarse silt to fine sand with mediumand fine ash size glass and pumice fragments withinthe uppermost extensive loess unit. Loess enclosingKawakawa Tephra occurs mainly on alluvial fan andterrace deposits' older than the Waiohine Surface.The stratigraphic position of Kawakawa Tephrawithin the loess enables confident correlation withthe Ohakea loess of Rangitikei and Manawatu.Kawakawa Tephra and enclosing loess havecontrasting particle shape, particle packing, grain­size distribution, and mineralogy. Consequently, thedry bulk density and natural water content of thetephra, where thick and coarse, differ markedlyfrom that of the loess. The dry bulk density/naturalwater content method can usually be used to locatethe position of the tephra within the loess column atsites where the tephra is not macroscopically visible.Identification of Kawakawa Tephra is confirmed byferromagnesian mineralogy.

Keywords Kawakawa Tephra; Ohakea loess;Wairarapa; stratigraphy: correlation; dry bulkdensity; natural water content; ferromagnesianmineralogy

INTRODUCTION

The acidic c. 20 OOO-year-old Aokautere Ashmarker bed (Kawakawa Tephra, see Vucetich &Howorth (1976) for redefined name and radiocar­bon age) was originally described and named byCowie (1964a) in the Manawatu district. It occurswithin sediments previously classed as alluvial ormarine that Cowie (1964b) demonstrated to be loessderived from river flood plains. Cowie showed theloess to have been accumulating while the rivers

Received 3 July 1981, accepted 30 June 1982

4"

were aggrading during the last stadial of the Otiran(Last) Glacial. Loess deposition continued untilshortly after aggradation culminated in the forma­tion of the Ohakea Terrace (Te Punga 1952; Milne1973a, b) and river downcutting of the Holocene~poch began. Loess containing Kawakawa TephraIS found on terraces and rolling hill country olderthan the Ohakea Terrace set in the Manawatu andRangitikei districts (Milne 1973a), and is accord­ingly called Ohakea loess (Cowie & Milne 1973). InRangitikei, the base of Ohakea loess is radiocarbondated (NZ3188A) 25500 ± 800 years B.P. (old ilife; new i life is 26300 ± 800 years B.P.[NZ3188B]) and the top (NZ3165A) is 9480 ± 100years B.P. (old i life; new i life is 9760 ± 110 yearsB.P. [NZ3165B]) (Milne & Smalley 1979), consis­tent with the position of the Kawakawa Tephra inthe lower third of the loess. The lithostratigraphicand chronostratigraphic unit terminology for theloesses and climatic substages of the southwestNorth Island, inlcuding Ohakea loess (Cowie &Milne 1973), are in widespread use, but were neverformally defined at type sections. KawakawaTephra has been found within correlatives ofOhakea loess in the Wanganui (Wilde 1979),Pahiatua (Kaewyana 1980), and Wellington districts(Milne & Smalley 1979).

In Wairarapa, extensive alluvial terrace depositsolder than the Waiohine Surface (Vella 1963) aremantled by loess and tephra cover beds (Fig. 1). Theloess was mapped on a scale of 1:1 000 000 by Cowie& Milne (1973). Ghani (1974) recognised loesscontaining Kawakawa Tephra at a few places insouthern and eastern Wairarapa, overlying LastInterglacial marine benches.

Vucetich & Howorth (1976) defined 3 membersfor the Kawakawa Tephra, the oldest of these, theprominently bedded Aokautere Ash Member, has abasal layer that is a thin, distinctive, white or pinkpumiceous silt (Fig. 2). This basal marker is mostreadily seen in the field, and, together with coarserlayers, persists through Rangitikei (Milne 1973a),Manawatu (Cowie 1964a), Wanganui (Wilde 1979),Dannevirke (Rhea 1968), and Pahiatua-Eketahuna(Kaewyana 1980).

Topping & Kohn (1973), Kohn & Glasby (1978),and Howorth et al. (1980) used ferromagnesianmineralogy to distinguish late Pleistocene tephras incentral North Island. For the Kawakawa Tephra,Howorth (1976) showed that hypersthene and calcic

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306 New Zealand Journal of Geology and Geophysics, 1982, Vol. 25

• PALMERSTONNORTH

Loess cover> 1m thick

A Study sitesoI

20I

40!

60I

~N

Fig. 1 The main loess areas ineastern Wairarapa showinglocalities mentioned in the text.

hornblende were the dominant ferromagnesiancomponents at Whangamata Road, close to thesource. Data from Havelock North and Poukawa,more distant from the source, show a slight relativeincrease in hypersthene (Howorth et al. 1980). Thewriter has identified Kawakawa Tephra at manyplaces in the uppermost extensive loess inWairarapa. At some sites it is a distinct, pink-white,grey, or brown sandy layer up to 0.10 m thick, but atother sites it is mixed within loess and is difficult orimpossible to distinguish in the field.

Wairarapa loess units often lack definitivepaleosols that can be detected easily by eye, andloess morphology varies with thickness, climate, andparent material. Recognition of Kawakawa Tephrain the uppermost loess unit ensures confidentcorrelation with the Ohakea loess of the Rangitikeidistrict.

This paper establishes 2 reference localities forOhakea loess, containing Kawakawa Tephra, inWairarapa. A method is described by whichKawakawa Tephra can often be recognised quicklyand easily in the laboratory, using dry bulk density

and water content measurements. Ferromagnesianmineralogy confirms that the horizon identified isKawakawa Tephra.

SAMPLING SITES

After examination was made of surface exposures ofloess throughout Wairarapa, 4 sites, as close aspracticable to the most complete exposures of lastglaciation loess, were selected for coring (Fig. 1,Table 1). The uppermost extensive loess unit isbetween 1 and 2 m thick at these sites. At theBidwill Hill site, a sequence of loess and water-laidsediment, at least 14 m thick, was recorded on araised terrace, thought by Ghani (1978) to be of LastInterglacial (Oturian) age. At the Otaraia site, loessand water-laid sediment is at least 10 m thick on aterrace of uncertain age. The Lake Ferry site is on araised marine bench cut during the Last Interglacial(Ghani 1978). At Lake Ferry the uppermost loessunit, recognised elsewhere as enclosing KawakawaTephra, is covered by 0.6 m of localised Holocene

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Palmer-Kawakawa Tephra, Wairarapa 307

[J--';.'..; ..;.'..' .".

-~.2 CD.1:;<0Ul •

Oa.QlOO

.><:.<0.= 0>>­Ql CllC Qlc.r;Clle::0_

::.\::\.. ....•••·~:i:·~

-0­0-0-0­0-0

--o

0·1

m0·2

0-0-0­0-0-0­0-0-0­0-0-0­o-a~.~...•...•••e ••eoe•••

o

~ mg- 0·5I-<IS

~~

<IS

~ 025~

Co.~

E(;

u..

ScindeIslandAsh

to.to.

to.to.

to. Oruanuito. Breccia

to.to.

to.

.0,0.

0:0:0'0'0.

0:0'0'0.

Er

m

AokautereAsh

t] ~••• Lapilli Er-Erosion surfacePyroclastic flow -- Silt and clay ••••••

§ Ash with II Basal shower beds CJ * Grid reference0-0 chalazoidites fine sand, silt, clay ':':'::::: Sand NZMS 1

Fig. 2 Correlation columns for Kawakawa Tephra (including the Aokautere Ash of other authors) in central andsouthern North Island.

Table 1 Representative sites for Ohakea loess and Kawakawa Tephra in Wairarapa.

Grid Date Final Thickness of Depth to base ofreference drilled depth Ohakea loess! Kawakawa Tephra/

Site (NZMS 260) (sampled) (m) em) em)

Cores Bidwill Hill S27/162038 30.11.77 6.39 2.03 1.42Lake Ferry S28/901763 20.1.78 5.37 1.62 1.27Otaraia S27/056886 12.12.79 10.00 1.26 0.89Checkley Farm T26/355344 13.12.79 4.88 1.38 1.10

Sections Riverside S271181004 23.8.80 7.01 7.00 3.84Maungaraki T26/341121 10.9.80 4.00 4.00 2.50

lIncluding Kawakawa Tephra.2Depth from ground surface.

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308 New Zealand Journal of Geology and Geophysics, 1982, Vol. 25

Table 2 Abbreviated morphology of Ohakea loess and Kawakawa Tephra of reference sections.

Other features

Many fine 7.5 YR 5/8mottles.

Many fine 7.5 YR 5/8mottles and concretions.

Gammations as above.No glass.

Abundant oxide flecks andconcretions. Colour zonedgammations and mottles.

Depth Horizon Matrix lTexture 2 Consistence Structure

em. colour

1- BIDWILL CORE

0-21 Ap 10 YR 4/3 Sil Friable Fine-medium nutand granular.

21-32 Bl

10 YR 5/3 Sil Friable Fine sub blockand nut.

32-53 Bg 2.5 Y 6/4 Sicyl Firm Fine-medium7.5 Y 5/6 blocky.

53-136 Cx 10 YR 4/3 Sil Very firm Very coarseprismatic columns.

Abundant Fe, 7.5 YR 6/6mottles and concretionswith darker flecks andcutans.

Colour zoned gamrnations7.5 YR 5/6 edge to Z.5 Y7/2 centre. Veins andearthworm channels outlinedby dark cutans. Glasscontent increases towardsbase.

Pinkish cast toward base.KAWAKAWA TEPHRA.

136-142 D 2.5 Y 6/2 Sil-top Friable Graded bedding.fsl-base

142-178 C 10 YR 4/3 Sil Very firm Massive.

178-203 Cc n 10 YR 5/3 - Sicyl Firm Weak fine blocky.7.5 YR 5/3

Diffuse contact with A+B horizon of Ratan age loess

2. RIVERSIDE SECTION

375-384 D 2.5 Y 7/3 fsSil-top Friable Graded bedding2.5 Y 8/1 fsl-base fining upwards.

384-700 C3 2.5 Y 7/3 fsSil Firm Coarse prismatic10 YR 6/6 to massive.

0-12 Al 10 YR 3/3 Sil Friable

12-19 A2 10 YR 5/3 Sil Friable

19-36 A-B 2.5 Y 6/4 sil Friable- 2.5 Y 7/3

36-120 B-Cx 2.5 Y 6/4 fsSil Very firm

120-130

130-375

2.5 Y 6/2

2.5 Y 7/3

ms

fsSil

Friable

Firm

Fine crumb.

Fine crumb.

Fine weak blocky.

Coarse blocks andprismatic columns.

Weakly bedded.

Coarse prismaticcolumns.

Abundant fine rootlets.Abundant macropores.

Many pores and rootlets.

Many colour zoned gamma­tions and mottles, 7.5YR 5/6 edge to 2.5 Y 7/2centre. A few quartzpebbles.

Lensing, maximum 15crnthick. Sharp contactabove and below.

Total colour seggregationfrom 2.5 Y 8/1 to 7.5 YR5/8. Some pebbles.Gammations are thin andfaint. Glass contentincreases over last 50cm.

Pinkish lcm discontinuouslayer at base. Kawakawa Tephra.

Becomes orange towardsbase. Many Fe concre-tions and dark browncutans near base.

Sharp contact with fluvial gravels.

(Loess on nearby river cliffs is up to 20m thick).

fNote: The nomenclature in this table follows Taylor & Pohlen 1962).Colours from Oyama & Takehara (1967).

lrexture symbols: Si = silt; fs = fine sand; ms = medium sand; cy = clay; 1 loam.

loess (Palmer in press). The Checkley Farm site,north of Masterton, is on a river terrace of Porewanage.

Two other sites, at Riverside and Maungaraki(Fig. 1), were selected for sampling because the

uppermost loess is exceptionally thick. At theRiverside site the loess overlies weathered gravels ofa terrace of old, but uncertain, age, while at theMaungaraki site, southeast of Masterton, it overliesthe gravel of a terrace of Ratan age.

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Palmer-Kawakawa Tephra, Wairarapa 309

Fli. 3 A The DSIR Soil Bureau drill truck in operation. The core liner is housed within the flight auger core barrel.B The Bidwill Hill core. The Kawakawa Tephra is two-thirds of the way down the second core .e The upper part of the Bidwill Hill reference section. The Kawakawa Tephra is just below the break in the Ohakea

loess fragipan.D The Riverside section with prominent Kawakawa Tephra (100 mm pale band level with spade handle) . Nearby. the

Ohakea loess is up to 20 m thick, but the section shown is 7 m.

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310 New Zealand Journal of Geology and Geophysics, 1982, Vol. 25

METHODS

At 4 sites (Table 1) undisturbed cores were taken,using the Soil Bureau (DSIR) truck-mounted drill(Fig. 3A) fitted with a hollow-stem flight augerinside a 153 mm diameter "soil and waste" pipe.Each core is approximately 0.85 m long (Fig. 3B). A0.02-0.03 m interval between each successive pair ofcores is represented by material taken from thecutting shoe. Within a few days of drilling, thesealed cores were passed through a gamma ray scanusing an apparatus and method essentially asdescribed by Brier et al. (1969).

After extrusion on to half liners, the cores weresubsampled in duplicate, at 0.05 m intervals, todetermine water content. Dry bulk densities werecomputed from the gamma ray scan and watercontent data. Core morphology was described indetail (Palmer in press).

At sites not cored, undisturbed samples weretaken from road cuts, using thin-walled samplingtubes 0.055 m in diameter. These were weighed andthen dried at 105°C to determine water content anddry bulk density.

The Kawakawa Tephra was subsampled formineralogical analysis at 4 of the sites. Purity of thetephra component of the fine sand and coarse siltfraction was estimated visually in thin section. Theferromagnesian component of this fraction wasconcentrated using a Frantz Magnetic Separator (0.6A and 20° sideslope) and was point counted.

RESULTS

Ohakea loess in Wairarapa

The Bidwill Hill site (Table 2, Fig. 3C) is chosen as areference locality for Ohakea loess in Wairarapabecause it contains macroscopically visibleKawakawa Tephra; it has been studied previously(Pollok 1975) and it is well known by pedologists ofthe Soil Bureau, DSIR. At Bidwill Hill, Ohakealoess is exposed in a road cutting and extends fromthe ground surface to a depth of 2 m where apaleosol is developed in older loess. The KawakawaTephra is approximately 0.6 m thick, with its base1.42 m below the ground surface. The core wastaken beside the road cutting (Palmer in press).

Ohakea loess at Bidwill Hill is typical of areas inWairarapa that receive strongly seasonal rainfallwhich is less than 1100 mm/year. Usually the loess issaturated in winter and completely dried out insummer. Below a depth of about 0.6 m, andextending down to within 0.05 m of the tephra, is afragipan with coarse polygonal structures separatedby well-defined vertical cracks. Below KawakawaTephra, the loess is equally tight and compact, but

lacks polygonal structures. The loess both above andbelow the tephra is mottled, dull, yellowish brownsilt loam, that is hard when dry and deformsplastically over a small moisture range when wet.

Ohakea loess is exceptionally thick in a few smallareas immediately adjacent to source areas. Areference section for thick Ohakea loess isdesignated at Riverside (Tables 1, 2, Fig. 3D). TheRiverside site is 5 km southeast of the Bidwill Hillsite, on the eastern side of Ruamahanga River,which is the lee side with respect to the prevailingnorthwest winds. Ohakea loess enclosing KawakawaTephra extends from the ground surface to gravelsat a depth of 7 m, in the measured column, and is upto 20 m thick nearby. The loess is a fine sandy siltloam with very prominent coarse columnar struc­ture. Kawakawa Tephra, c. 0.10 m thick, is near themiddle of the loess, and this position is typical ofthick loess sections.

The greatest thicknesses of Ohakea loess inWairarapa are adjacent to the eastern side ofRuamahanga River, particularly between Mastertonand Martinborough. Most of the Ohakea loess wasblown by northwesterly winds from the aggradingOhakean age surface (Waiohine Surface, Vella1963). On the marine benches south of Pirinoa,Ohakea loess thickens toward the coast, indicatingthat southerly winds may have carried loess derivedfrom the continental shelf.

Morphology of Kawakawa Tephra

In the Bidwill Hill, Checkley Farm, Riverside, andMaungaraki columns (Fig. I), and many otherlocalities in Wairarapa, the Kawakawa Tephra isseen macroscopically as a 0.06-0.1 m thick, pinkish­white, grey, or pale-brown band of coarse silt to finesand-sized glass, with pumice fragments up to 4 mmin diameter (Fig. 2). A discontinuous, 10 mm,pinkish silty band at the base of the tephra, thatcontrasts strongly with the loess, represents part ofthe Aokautere Ash Member (Vucetich & Howorth1976).

In Wairarapa, it is not possible to identify eitherthe Scinde Island Ash Member or the upperOruanui Breccia Member described by Vucetich &Howorth (1976) (Fig. 2) and, advisedly, recognitionis at formation status. A fining-upwards sequencefrom the top of the Aokautere Ash Member isusually observed, to a total thickness of 60-100 mm,and is here termed Kawakawa Tephra. At otherlocalities, s~ch as Lake Ferry and Otaraia (Fig. 1),the Kawakawa Tephra is not prominent macroscopi­cally, but can be "felt" as a sharpness on hands orknife, and volcanic glass can be found in the coarsesilt fraction.

Where the Ohakea loess is less than 3 m thick, theKawakawa Tephra is usually found two-thirds of the

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Palmer-Kawakawa Tephra, Wairarapa

way down the loess. The position of the tephra insections of thicker loess is more variable, but isusually close to halfway down the Ohakea loess.

Dry bulk density and natural water content

Kawakawa Tephra has a much lower dry bulkdensity and higher water content than the enclosingloess. At Bidwill Hill (Fig. 4A), Riverside (Fig. 4B),and Maungaraki (Fig. 4C), the dry bulk density inthe loess above the tephra is 1.7-1.8 g/cm", and fallsto 1.4-1.5 glcm3 within the tephra. In the Ohakealoess below, dry bulk density is a maximum at 1.85g/cnr', At Checkley Farm (Fig. 1, 4D), dry bulkdensity of the loess is lower because of a differentsoil-weathering regime of higher altitude andrainfall, but the dry bulk density pattern still reflectsKawakawa Tephra in the loess, in the same way asat Bidwill Hill.

Water content is highest and bulk density lowestwhere the tephra is thickest and coarsest (Fig. 4A,B, C, D). Where the tephra is finer and indistinct,possibly through being reworked and diluted byloess, these effects are lessened. At Lake Ferry (Fig.4E) and Otaraia (Fig. 4F), Kawakawa Tephra is anindistinct layer and therefore dry bulk density andwater contents show less change.

Ferromagnesian mineralogy

In Wairarapa, Kawakawa Tephra is generally sothin that only 1 sample can be taken in any verticalsection. The ferromagnesian mineralogy of eachsample from 4 sections (Table 3, Fig. 5) is in goodagreement with that reported by Howorth et al.(1980), although preferential corrosion of somehypersthene grains indicates that mineral propor­tions may be biased towards hornblende andclinopyroxene. In Table 3 the samples are placed inorder of decreasing glass percentage in the fine sandand coarse silt fraction and thus probably in order ofreliability of ferromagnesian component counts.

DISCUSSION AND CONCLUSIONS

Kawakawa Tephra has been positively identified inthe youngest extensive loess unit in Wairarapa. Thisloess can now be confidently correlated with theOhakea loess of Rangitikei, Manawatu, andWellington which is thought to have been depositedbetween 25 000 and 9450 years ago (Milne 1973b;Milne & Smalley 1979). Because precise chronologi­cal correlation of the loess cannot be made, thestratigraphic position of Kawakawa Tephra withinOhakea loess is critical.

Water content and bulk density of a sediment arecontrolled largely by the same factors (exclusive of

311

environment of deposition), the most importantbeing particle shape, particle packing, grainsizedistribution, and mineralogy (Marshall & Holmes1979). Kawakawa Tephra in Wairarapa is relativelysandy, compared to the enclosing loess which is siltloam (Palmer in press). Volcanic glass and pumicefragments have irregular shapes and higher surfaceareas than equivalent silt-sized quartz grains.Therefore, dry bulk density of Kawakawa Tephra isexpected to be low relative to the loess. Particledensity of the tephra (glass) is similar to that of theloess (quartz and feldspar). Therefore, the tephrahas more voids able to contain and retain water, andconsequently it has a higher water content. InKawakawa Tephra, therefore, there is an inverserelationship between dry bulk density and watercontent. Dry bulk density and natural water contentprofiles clearly define the tephra within Ohakealoess, and could be used to correlate other markerbeds, deeper in the loess column.

Figure 4 shows that bulk density increases andwater content decreases systematically upwardsfrom the base of the Kawakawa Tephra as theproportion of glass shards and pumice fragmentsdecrease. At Bidwill Hill and CheckIey Farm, atephra component is detectable up to 0.5 m abovethe base of airfall material. The material directlyabove the pure tephra may be regarded as tephricloess, deposited on the loess source area as primaryairfall material, and subsequently retransported inprogressively diluted concentrations.

The water contents shown in Fig. 4 are those atthe time of coring. However, the water regime ofany near-surface soil/sediment is not static for anylength of time, even for those sediments below theapparent lowest yearly water table. The waterregime in the top few metres of loess can beexpected to show greatest variation, but the peaksand troughs in the water content curve will changeonly in magnitude and shape, and not in verticalposition. Limited data published for New Zealandsediments (Watt 1977) suggest that seasonalmoisture content changes, due to both rainfall andplant extraction, may be very small at depths below1 m.

The writer has found Kawakawa Tephra to bepresent in the uppermost extensive loess unit inWairarapa, here regarded as Ohakea loess.Kawakawa Tephra is as useful a marker bed inWairarapa as in other southern North Islanddistricts. Kawakawa Tephra is already known inMarlborough (D. Eden, pers. comm. 1982), nearNelson (Campbell 1979), and in Canterbury(Vucetich & Kohn 1973; Kahn 1979). It may enablea positive correlation of the Ohakea loess ofsouthern North Island with loess in the South Island.

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2·0

Dry bulk density (q/crn")1·2 1·4 1·6 1·8

DC

Ap88g

Cx

CcnlI uA

Horiz 1·0

omo

New Zealand Journal of Geology and Geophysics, 1982, Vol. 254a

Wa ter content (°/0 )

40 30 20 10

Kawakawa

50

312

Fig. 4A Bidwill Hill core.

4b

Fig. 4B Riverside section (nowater content data).

Dry bulk density (q/cm'')1·2 1'4 1·6 1·8 2·0

.~\

~

Kawakawa~\I

!OJ

Dry bulk density (q/crn")

Horiz 1·0 1·2 1'4 1·6 1·8 2·0

A ---4c 8 ~l8 gCx >E 2 C, ~

Kawakawa ./ Tephras: D

~~~0..Q) 3 C20 /

"

D

Fig. 4C Maungaraki section (nowater content data).

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Palmer-Kawakawa Tephra, Wairarapa 313

Dry bulk density (q/crn'')1·2 1·4 1·6 1·8 2·0

4d

oW ater conte nt (%)

40 30 20 10

L- ~K~awakawa Tep hra

I

50

Fig. 4D CheckIey Farm core.

50

Water content (%)40 30 20 10

Kawakawa

o

4eDry bul k density (q/crrr')

1·2 1·4 1'6 1·8 2·0

Fig. 4E Lake Ferry core.

Dry bu lk density (g/cm3)

1·2 ' ·4 1·6 1·8 ~oHoriz 1·0

4f

omo

Wate r content (0/0)40 30 20 10

Kawakawa

50

Fig. 4F Otaraia core.

Fig. 4 (opposite and above) Bulk density and water content plots for cores and sections of Ohakea loess and KawakawaTephra in Wairarapa.

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314 New Zealand Journal of Geology and Geophysics, 1982, Vol. 25

181 -Whangamata Road

Ell -Havelock North

/), -Poukawa

• 1-Riverside

• 2-Maungaraki

• 3-Checkley Farm

• 4-Bidwill Hill

Opx

Ca Hb

Cpx

Fig. 5 Ferromagnesian mineral­ogy of Kawakawa Tephra inWairarapa compared with the typesection (Whangamata Road) andreference localities at HavelockNorth and Poukawa (Howorth etaI. 1980).

Table 3 Mineralogical data for the Kawakawa Tephra at selected sites in Wairarapa.

Ferromagnesian mineralogy (%)Grains

Site! % Glass/ % Tephra'' counted Opx Cpx CaHb

Riverside 80 85 473 56 16 28Maungaraki 75 80 428 60.7 13.3 26Checkley Farm 70 75 422 59 13 28Bidwill Hill 65 70 408 57 16 27

!See Table 1 for NZMS 260 grid reference.2% glass of fine sand and coarse silt fraction.3An estimate of the percentage tephra component of the sample, the remainder being the loessial

component.

ACKNOWLEDGMENTS

Dr R. Northey, Mr P. Barker, Mr J. Wales, and Mr G.Schaefer (DSIR Soil Bureau) co-operated in the work. MrC. Vucetich, Professor P. Vella (Victoria University) andDr D. Milne (DSIR Soil Bureau) criticised and improvedthe manuscript. The work was supported by a U.G.c.Scholarship and the Internal Research Committee,Victoria University of Wellington.

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