glacial advances in the rakaia valley, new zealand
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Glacial advances in the RakaiaValley, New ZealandJane M. Soons a & F. W. Gullentops ba Geography Department , University ofCanterbury , Christchurch , New Zealandb Instituut voor Aardwetenschappen , Leuven ,BelgiumPublished online: 14 Feb 2012.
To cite this article: Jane M. Soons & F. W. Gullentops (1973) Glacial advances in theRakaia Valley, New Zealand, New Zealand Journal of Geology and Geophysics, 16:3,425-348, DOI: 10.1080/00288306.1973.10431369
To link to this article: http://dx.doi.org/10.1080/00288306.1973.10431369
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No. 3
GLACIAL ADVANCES IN THE RAKAIA VALLEY, NEW ZEALAND
JANE M. SooNs
425
Geography Department, University of Canterbury, Christchurch, New Zealand
and
F. w. GULLENTOPS
Instituut voor Aardwetenschappen, leuven, Belgium
(Received 19 June 1972)
ABSTRACT
Re-alignment of the road near the Rakaia Gorge bridge (S82) has clearly exposed deposits of the Woodlands and younger glacial advances, and their erosional or faulted relationships. Renewed geomorphological mapping in the area indicates that the Tui Creek Advance was in three phases, not one as previously recognised, so that it may have the status of a full glaciation. New details of the deposits and geomorphology related to the three phases of the last ( Acheron) advance of the Otira Glaciation indicate greater aggradation than previously supposed, and the formation of a complex of lakes during fluctuations of the glacier.
INTRODUCTION
The magnificent terraces and the accessibility of the Rakaia valley have favoured a number of studies of its geology and geomorphology, the two most recent being those by Soons (1963) and Carryer (1967). Earlier work is summarised in Soons (1963). A sequence of glacial advances was established, based largely on geomorphological evidence, as follows:
Acheron I, II, III Youngest Major recession
Bayfield I, II Major recession
Tui Creek Interglacial
Woodlands Oldest
Carryer (1967) recognised a further advance (the Blackford) preceding Bayfield I, which is considered in this paper to be appropriatdy grouped with the Bayfield Advances. Subdivision of the advances has been based largely on the presence of moraines with outwash surfaces clearly distinguishable from each other, but no subdivision of Tui Creek was previously attempted because of the wide area covered by its morainic complex and the relatively narrow height range within which deposits occurred.
N.Z. Journal of Geology and Geophysics 16 ( 3): 425-38
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During 1970, re-alignment of State Highway 72 on the western side of the Rakaia Gorge Bridge (grid ref. 582/139585)* revealed a previously poorly exposed complex of deposits underlying one of the lowest terraces within the gorge, and also deposits underlying higher terraces, up to the level of the Bayfield II outwash surface (Soons 1963). The new exposures, re-examination of morphological features in the general area of the gorge, and new information on lake deposits and shore features near Lake Coleridge power station allow some reappraisal of the glacial sequence in the valley. The results o:f this in the gorge area are shown in Fig. 1, and include a subdivision of the Tui Creek Advance, which is now recognised as comprising three main stages.
NEW GEOMORPHOLOGICAL OBSERVATIONS
Moraines and outwash surfaces of two advances, Tui Creek II and III, are shown on Fig. 1 ; the vertical separation is about 20 m. The remnants of the Tui Creek I moraine, almost completely buried by Tui Creek II outwash, occur 5 km down the valley (grid ref. S82/202553). Remnants of a moraine and outwash surface, 15-20 m below the Bayfield I moraine and outwash surface mapped previously, are also shown on Fig. 1, on the eastern side of the river near Bayfields Homestead (grid ref. S74/124639); these have been mapped as Bayfield II.
On the opposite side of the river, near Cleardale Homestead (grid ref. 574/075667), a complex of moraine ridges ,extending through what is considered to be a large vertical range (approximately 100m) has been subdivided on the basis of height and appearance. An older set, in which few boulders are exposed, is related to the Bayfield II outwash surface, and is distinguished from an apparently younger and lower set, regarded as Acheron I. No outwash surface is associated with the Acheron I moraines. This phenomenon was discussed by Soons (1963), and was attributed to the conditions of deposition and later erosion obtaining in the early stages of formation of the present Rakaia Gorge. Gravels considered to be of Acheron age have, however, now been recognised in the newly exposed deposits at the Gorge Bridge.
Rakaia Gorge Bridge Section
The section is 'exposed in a roadside cutting running obliquely up the face of a minor terrace within the Rakaia Gorge (Fig. 2E), and is 200m long and 15-25 m high. The terrace itself is 50 m high, with its surface at an altitude of 351m a.s.l., 64m above the Gorge Bridge (see Note on height below). The cutting thus permits a total thickness of 50 m of deposits to be examined, although the full depth is nowhel'e completely visible. Further deposits are visible below road level, but are in part obscured by spoil from road construction.
':'Grid reference based on the national thousand-yard grid of the 1: 63 360 topographical map series (NZMS 1).
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FIG. 1 - Geomorphological map of the Rakaia Gorge, showing extent and age of terraces, moraines, and "Lake Cleardale" (see p. 436) shorelines.
'
j 1- "'"' .... Achuon
~Golly Bayfield
Oegrattonal surfaces
Bayfield H ~ . C k [ ~TUI fie Alluvium
~~:~a~ea;tield - . Moraines . Recent Alluvium - Acheron
Lake Cleordote Bayfield
z 9 \,.;>
C/l 0 0 z (/)
!1
~ !:"" !:"" tti z c5 "' (/)
I C') !:""
fi s: !:""
> t:l
~ z (") tti
.Vl
~ s:
""' N --.J
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428 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VoL. 16
Bayfield n aggradational surface
Post Bayfield x x degradational surface x
Possible Acheron[ .~......;-- I aggradotionol
surfaces 6<< ---
/
FIG. 2-Sketch map of terraces on the west side of the Rakaia River at the Gorge Bridge (area shown in box in Fig. 1). Scale approximate, S.H. State Highway.
The section is divided into three by two discontinuities, one a fault and the other a buried terrace face (Fig. 3, 4, and 5). Yellow-brown gravels and silts at the base of the eastern end of the section are correlated with those on the western side of the fault (Table 1), so that the throw on these beds is estimated to be about 40 m. Higher in the section, unconformably overlying gravels are displaced less, the throw being about 1 m, while the capping loess is undisturbed and has masked the fault scarp so that no trace is visible on the terrace surface, 'either on the ground or in aerial photographs. The main movement or movements appear to have taken place after the deposition of the gravels forming the buried terrace, but before that of the overlying gravels, although movement clearly continued until a 1.1elatively recent date, prior to deposition of at least part of the loess capping.
All deposits in the section are horizontally bedded, except for slope deposits along recent and buried terrace fronts. and the yellow-brown gravels at the eastern end of the section and on the up::thrown side of the fault. The slope deposits characteristically show an inclination that becomes less steep away from the cut gravel face. No disturbance of these deposits is visible, although individual boulders seem, in places, to have been reorientat,ed and incorporated into the gravels deposited against the terrace face (Fig. 5). The yellow-brown deposits at the base of the section are tilted ( 4-5°) up-valley. This may be due to local slumping, or to movement along the known fault earlier than that for which other evidence is available. Of the two silt beds, the lower, underlying the till, shows considerable internal contortion, as well as the tilt which affects all the basal yellow-brown ,gravels. The silts overlying the till are uncontorted, although equally tilted,
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c g.
·J: -1
"'
EAST
350
i ::;;:
I Fresh blue-grey gravel
Finer towards top Acheron
l
WEST lronstained gravel
} Yellowish-grey gravel up to 3m thick
1 Woodlands deposrrs
j VEX 3 300~~=-~~~~------------------~------------------------------------------~--------.--
0 200
FIG. 3-Diagrammatic representatiOn of deposits in the Rakaia Gorge Bridge section. Vertical exaggeration X 3.
z 9 \.>J
[/} 0 0 z (fJ
~
~ t"' t"' tTl z ;j '"d (fJ
I C'l t"' > ("')
s: t"'
> !;2 > z ("') tTl
"(/)
r s:
t; \0
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FrG. 4-Fault in deposits in Rakaia Gorge Bridge section. Note the drag affecting the silts (Woodlands age) on the upthrow side. PostAcheron I lag gravels and loess deposits visible above the silts.
and it is postulated that the contrast is due to the advance over the lower silts of the glacier responsible for the tiU.
The buried terrace face exemplifies the process ()f cut-and-fiii postulated for the late Pleistocene in this area (Soons 1968). Cutting of the terrace was foiiowed by reduction of the slope of the terrace face as slope deposits formed on it, and then by burial in a phase of aggradation. This appears to have been accompanied by relatively little erosion, although, as noted above, some of the slope deposits may have been incorporated in the later gravels. It is not dear whether these gravels completely over-topped the buried terrace, since the whole section has been truncated in the process of forming the present terrace (see Fig. 3 and 5). The relatively thin layer of iron-stained, current-bedded and relatively fine gravel forming the upper member of the sequence is interpreted as a lag gravel, deposited as the
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Nd. 3 SOONS & GULLENTOPS- GLACIAL ADVANCES, RAKAIA 431
FIG. 5-Buried terrace face, Rakaia Gorge Bridge section. Possible Tui Creek gravel on the right; Acheron I outwash gravel on the left. Post-Acheron I lag gravels at the top of the section.
Rakaia River was cutting down to its present level. Rather similar gravel is to be seen wherever the gravels forming other degradational terraces are exposed, but is absent from the aggradational surface af Bayfield II outwash. The lag gravel overlies most of the Rakaia Gorge Bridge section, but is absent east of a shallow gully cut along the line of a small terrace face. This gully has been in-filled with locally derived slope deposits.
Several breaks are apparent in the sequence. The upper surface of the yellow-brown gravel is clearly eroded, both at the base of the section and adjacent to the fault. The nature of the gravel above this eroded surface, with its included clasts of till derived from the yellow-brown deposits (Fig. 6), suggests strongly that it is of the same age in both places. It is yellowish-grey in colour and, at the eastern end of the exposure, passes conformably upwards into about 2 m of similarly coloured finer gravel. This in turn is unconformably overlain by about 22 m of fresh, blue-grey gravel, relatively coarse at the base but rapidly becoming finer upwards, and resting against the buried terrace face (see Fig. 5). No similar deposit is found west of the fault, where the yellowish-grey gravels are truncated by the highest bed of the sequence.
No contact is exposed between the grey gravds forming the buried terrace and the yellow-brown and yellowish-grey gravels. A small area of till, of distinctly fresher appearance than that included in the yellow-brown deposits, was briefly exposed at the base of the terrace gravels (see Fig. 3), but has been covered by debris from the slope above.
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m 0
5
10
15
20
25
30
35
TABLE 1-Deposits in the Rakaia Gorge bridge cutting
Yellowish, fine-grained silt (loess) with modern soil
Slightly iron-stained greywacke gravels, variable in size but mainly less than 15 em diameter. Current-bedded. Coarser boulders at base matrix silty-sand. Erosional contact with underlvinq deposits.
Blue-grey greywacke gravels, coarse at Yellowish grey weathered base but becoming very fine above 3-6 m greywacke gravels, approximately 6 tn from the base. Contact horizontally bedded, coarse with underlying gravels dis conformable. at base and becoming finer
towards top, but nowhere as fine as the gravels banked against the terrace face. Yellowish grey till is sometimes exposed at the base of these gravels, but may be covered by detritus; included boulders are not as weathered as those
Buried terrace face, found in the yellow till slope c.35° with downslope. ~ alternating' coarse and ::::> fine gravel deposited <( against it. lL
Coarse yellowish-grey graywacke gravel, Very large boulders at base (up to I 1 m diameter), and including clasts of till apparently derived from the underlying bed. Channelled into underlying silts.
Yellow, sandy lacustrine silts, tilted up-valley at 4-5°, Irregular bed o/ yellow till with sandy silt matrix, containing qreywacke and weathered rhyolite boulders. Yellow lacustrine sandy silts, bedding severely contorted.
Fine greywacke gravel, yellow-brown weathered. Tilted 4-5° up-valley. ; Not well stratified, possibly locally derived fan gravels.
Fine greywacke gravel, yellow-brown weathered, well-stratified. I Tilted up-valley.
Yellow sandy lacustrine silts 1 horizontally bedded but with distortion adjacent to the fault. Chann~lled
by coarse yellowish grey gravels including clasts of till.
I
.!>\,),)
N
z N
........ g ::0 z > t"
0 "%1
Cl ~ 0 t" 0
~ > z Cl
Cl ~ 0
~ [f)
(; [f)
2 t"
,..... 0\
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Nd. 3 SOONS & GULLENTOPS- GLACIAL ADVANCES, RAKAIA 433
FIG. 6-Woodlands till exposed in the Rakaia Gorge Bridge section, with o-,erlying coarse gravels, including clast of till at extre:ne right.
The contact between the topmost, slightly iron-stained and current-bedded gravel and the underlying deposits is everywhere erosional. The gravel is overlain by 1-1·5 m of fine, yellow silty material o:f loessial appearance, which although probably rather too coarse in grain size to fall within the classical definition of loess, is certainly windblown material. Charcoal of Podocarpus spicatus (matai) has been found in this deposit at the western end of the exposure (B. P. ]. Molloy, pers. comm.). The thickness of windblown material is less at the ,eastern end of the exposure, where the topmost gravel is missing because of the cutting of a low terrace (see Fig. 3).
Exposures in higher terraces
Cuttings in the higher terraces crossed by State Highway 72 (see Fig. 2, A-D) provide some information concerning the structure of these terraces. Gravel similar to that at the top of the Rakaia Gorge Bridge section is exposed in a 3 m deep cutting across terrace C, about 90 m higher than the Gorge Bridge. A buried soil has been recognised at the top of these gravels (B. P. ]. Molloy, pers. cornm.), and is overlain by 1·25m of windblown silt. Deeper exposures are visible in the cuttings by which the road climbs to terraces B (114m above the bridge) and A (128m above the bridge). These two cuttings expose about 40 m of slightly weathered grey gravd, in silty-sand matrix. The front of each terrace is reduced in angle. by roughly stratified slope deposits (Fig. 7), including silty material probably originally of windblown origin. The upper 1·5-2 m of gravel on terrace B is rather finer than the bulk of the deposit, and separated from it by a slight but distinct disconformity. The top of the gravel in both terraces is irregular,
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FIG. 7-Slope deposits en terrace face cut into Bayfield II gravel, Rakaia Gorge Bridge Section.
showing minor terraces and channels 0·6-0·9 m deep, but the terrace surfaces are smoothed by the loess cover present in both places. Terrace A is the Bayfield II outwash surface (Soons 1963 ), and B was presumably formed at an early stage of downcutting on the retreat of the Bayfield II ice.
AGE OF THE DEPOSITS
The most important problem raised, and not entirely resolved, by the exposures along the road in the Rakaia Gorge area is that of the status of the intervals between the deposits. The degree of weathering of the gravel and till at the base of the section, and of the gravel on the up-throw side of the fault, make a late ( Otira) glacial age improbable. Gravel of a similar degree of weathering is well exposed in the river cliffs a few metres downstream of the section, and has been truncated in a similar way, and at the same Ievel, by later deposits. This gravel is regarded as of Woodlands age (Soons 1963), and yellow-weathered deposits in the Gorge Bridge section are correlated with it. No silts or till have been observed in the river cliffs, and the gravel is horizontally bedded. The more complex deposits in the Gorge Bridge section were therefore probably formed when ice lay close to the present position of the Gorge Bridge. The contortions in the lower silts suggest that this ice pushed into a small pro-glacial lake, the succeeding retreat permitting the lake to extend over the till. Thefle is no evidence of the nature of the obstruction that permitted ponding, which could have been moraine or residual ice. Downstream of the present gorge, the undisturbed
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No.3 SoONS & GULLENTOPS- GLACIAL ADVANCES, RAKAIA 435
gravel is the remains of a greater thickness of outwash deposited as the Woodlands ice advanced to its maximum position 6-7 km out from the gorge, and at a higher level than the remaining deposits.
The erosional upper surface of the Woodlands deposits in the Rakaia Gorge Bridge area, and the coarseness of the overlying yellow-grey deposits, suggest a period of active down-cutting by the Rakaia River. This erosion was clearly not associated with a glacial advance, but must rather represent' an interglacial or interstadial period. There is no conclusive evidence to indicate whether this immediately succeeded the Woodlands Advance, or whether the next major advance, the Tui Creek, had taken place before down-cutting occurred, although the degree of weathering of the yellow-grey gravel suggests the earlier of these two periods'.
Of the younger deposits in the Rakaia Gorge Bridge exposure, the small remnant of till can hardly be other than of Tui Creek age. It is not as weathered as the Woodlands till, and ice of the later Bayfield advance terminat<ed 9km up-valley (Soons 1963). There is no basis for deciding to which of the Tui Creek advances this till should be attributed. It lies 150m below the lowest moraine (Tui Creek III), and could be basal till of any of the three. Its low level in relation to the moraines suggests that, as during the Woodlands Advance, the Tui Creek glacier advanced down a pre-existing valley or gorge and built up an outwash surface considerably above the level of its own base.
The grey gravel overlying the till, and forming the buried terrace, has no internal characteristics that permit it to be assigned with certainty to the Tui Creek advances. Its position immediately overlying the till suggests an origin as Tui Creek pro-glacial outwash, but the difference in weathering between the gravel and that of undoubted Bayfield age exposed in the higher terraces (Fig. 2, A and B), is slight. However, a Tui Creek age is preferred.
The fresh, blue-grey gravel resting against the terrace face represents an aggradation phase, and is so little weathered that it cannot be correlated with the Bayfield gravel 'exposed at higher levels. Its relative fineness is also a point of distinction from other gravel deposits in this area. It is therefore suggested that it is of Acheron age, probably belonging to the Acheron I Advance. Outwash deposits of this age have not previously been recognised, and no outwash surface can be distinguished. The gravel is dearly truncated, and while one or other of the minor terraces in the Gorge Bridge area (Fig. 2, C and D), may represent an aggradation surface, no exposure is available showing clearly the gravels of which these are formed.
lATER QUATERNARY HISTORY OF THE RAKAIA GORGE AREA
The additional detail of moraines and outwash surfaces provided by the re-examination of the Rakaia Gorge aDea, the exposures along the road near the Gorge Bridge, and the numerous terrace remnants within the gorge indicate a series of ice advances accompanied by the deposition of moraines and outwash gravels. Each advance was followed by a retreat phase, during which the deposits of the previous period(s) were dissected as the regime of the river changed in response to changing climatic conditions, and the
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ice-front retreated into a depression previously occupied by the glacier. At least once, a lake was ponded between the retreating ice and the deposits of its advance, as is indicated by lacustrine silts in the valley and by remnants of lake shorelines near Clear dale (see Fig. 1). During interglacial and interstadial periods the continuing down-cutting must have produced gorges almost as deep, if not as deep, as the present gorge. Four main periods of aggradation are recognisable, during the Woodlands, Tui Creek, Bayfield, and Acheron Advances. The evidence of the Gorge Bridge section suggests that periods of down-cutting between advances produced terrace sequences similar to those at present within the gorge.
The re-examination of the gorge area has revealed striking depths of erosion in the intervals between the various glacial advances as well as striking amounts of aggradation during the advances (Table 2). A major interval, amounting to a full interglacial, has been recognised between the Woodlands and Tui Creek advances, on the basis of the weathering differences between the two sets of deposits, and the obvious depth of interglacial river cutting as displayed in the river cliffs downstream from the Rakaia Gorge Bridge. The depths of erosion between later advances were not previously fully appreciated. The Tui Creek III outwash surface is at an altitude of about 460 m a.s.l., while the surface of terrace E (see Fig. 2), which may be taken as a very approximate indication of the limit of post-Tui Creek down-cutting, is at 366 m, giving an overall measure of down-cutting of about 94 m. Measured from the higher Tui Creek II surface, down-cutting is of the order of 120m. Down-cutting following the Bayfield II Advance was also important, and the post-Acheron 1 period again saw terracing within the gorge. It is not clear whether the lowest, rock-cut portion of the gorge has been cut, or merely re-excavated, in post-Acheron time.
The evidence for the existence of lakes in the Rakaia Valley is widespread, and has been subject to discussion in a number of studies (Cox 1926; Lauder 1962; Soons 1963). The relationships to glacial advances of some of the
TABLE 2-Estimates of amounts of aggradation and degradation in the Rakaia Gorge area
Glaciation
Acheron II, III, and post-Acheron Acheron I Bayfield II Bayfield I Tui Creek III Tui Creek I and II Woodlands
Aggradation (m)
22+ 45+
? c. 150
137+
Degradation (m)
60
c. 73 6+
73+ 12+
c. 120
Note: Amounts of aggradation or degradation do not indicate in any direct way volumes of gravel moved. The area affected has been progressively smaller since at least the time of the Tui Creek II maximum.
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No.3 SOONS & GULLENTOPS- GLACIAL ADVANCES, RAKAIA 437
earlier lakes, such as that in which thick silts accumulated immediately upstream of the Rakaia Gorge Bridge, ar,e not always clear, but most lakes whose existence is indicated by shoreline benches appear to have been proglacial or ice-marginal. Thus, shorelines near Cleardale Homestead (see Fig. 1) record three levels of a post-Acheron I lake at present altitudes of approximately 420, 405, and 380m. This lake is here named Lake Cleardale, and extended upstream at least as far as the limits of the Acheron II advance (Soons 1963). Remnants of lake shorelines on stable sections of the river cliffs between the Acheron I and Acheron II ice limits fall within the same height range as those at Cleardale, and indicate a lake at least 3 km long.
A series of lake shorelines is also visible on the east side of the Rakaia, between the Acheron River and Lake Coleridge power station. The lowest forms an extensive terrace on the west side of the Acheron River, crossed by the roads to the power station and to Lake Coleridge homestead, at a height of 392 m. Two exposures of the silts and gravels forming this terrace have been described by Soons (1963).
In summary, lacustrine silts at the base of a section in the terrace face (grid ref. 574/073729) are banked against till of Acheron II age, and become increasingly sandy upwards, finally passing into gravel. Fore-set beds not visible in 1963 are occasionally exposed near the top of the terrace in a 'further exposure in the roadside cutting (grid ref. 574/078729). Gravel similar to that at the top of the terrace, and at the same level, extends across a moraine of Acheron II age plastered against the face of Acheron Hill (grid ref. S7 4/071721) on the opposite side of the Acheron River. This suggests strongly that the Rakaia Lake (Lauder 1962) was lateral to the Rakaia glacier during the retreat stages of the Acheron II advance, probably representing the last in a series of ice-marginal lakes formed at a succession of levels between the valley side and the glacier. Organic remains in the silts, near the transition to gravels, have been dated at 11 650 -+- 200 years B.P. (NZ1290; C. J. Burrows pers. comm.).
This date establishes a time for the presence of ice in the Rakaia valley which is rather later than any that was previously envisaged on the basis of correlations with advanoes in other valleys of the Southern Alps. An even later date, on the basis of this evidence, must be set for the Acheron III advance and retreat.
CoNCLUSIONS
The most important modifications of previous knowledge of the Rakaia Gorge area, resulting from the work outlined above, concern the Tui Creek Advance, which is now considered to have been a major event. Three advances are recognised, together with an important amount of down-cutting in the Tui Creek-Bayfield interval, which separates the Tui CDeek Advance very clearly from later events. Also of interest is the recognition in the Gorge area of gravels regarded as of Acheron age, and the new information concerning the relatively late date at which ice must have been present in the floor of the Rakaia Valley. The increased importance of the Tui CDeek Advance calls for some re-examination of the correlation between this and
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the glacial sequence in other major valley systems of the Southern Alps. Serious attention must be given to the possibility that the Tui Creek Advance represents a distinct glaciation within the now much extended concept of the Last or Wisconsin Glaciation (Flint 1972), and that the Bayfield and Acheron Advances are the sole representatives of the Otira Glaciation in the Rakaia valley.
NOTE Heights in the Rakaia Valley
Aneroid barometer heights of terraces and outwash surfaces in the neighbourhood of the Gorge Bridge are estimated to be accurate within ± 3 m. Heights were calculated in terms of a bench mark below the Gorge Bridge, 287 · 5 m above sea level and 4-6 m above river level. Further up the valley, heights on lake terraces are estimated to be within± 10m.
ACKNOWLEDGMENTS
The writers wish to acknowledge discussions with, and suggestions from Professor M. Gage and Dr R. P. Suggate, both in the field and in preparing this paper. Grateful thanks are extended to Mr and Mrs J. R. Todhunter of Cleardale for their hospitality, and to the cartographic staff of the Geography Department, University of Canterbury, for preparing the text figures.
REFERENCES
CARRYER, S. ]. 1967: The glacial deposits along the northern flank of the Mount Hutt Range. N.Z. Journal of Geology and Geophysics 10 (4): 1136-44.
Cox, P. T. 1926: Geology of the Rakaia Gorge district. Transactions N.Z. Institute 46: 91-111.
FLINT, R. F. 1972: "Glacial and Quaternary Geology". Wiley, New York
LAUDER, W. R. 1962: Teschenites from Acheron River, Mid-Canterbury, New Zealand, with notes on the geology of the surrounding country. Transactio1JS of the Royal Society N.Z., Geology 1 (1): 109-27.
SooNs, ]. M. 1963: The glacial sequence in part of the Rakaia valley, Canterbury, New Zealand. N.Z. Journal of Geology and Geophysics 6 (5): 735-56.
---- 1968: Canterbury landscapes: a study in contrasts. New Zealand Geographer 24 (2): 115-32.
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