The Tertiary Sequence in North-Eastern Marlborough, New Zealand
[Read before the Wellington Philosophical Society, August 11, 1936; received by the Editor, September 24, 1936; issued separately June, 1937.]
The Sequence Of Rocks.
Deadmans Greek Beds.
Great Marlborough Conglomerate.
Table of Correlations With the Rocks of the Awatere District.
The Tertiary History of North-Eastern Marlborough.
At the conclusion of the writer's previous work on the geology of the Awatere District several major questions on the Tertiary stratigraphy of Marlborough remained unsolved. Chief of these was the relationship of the Awatere beds to the “Grey Marl” and older Tertiary deposits. Accordingly it was planned to extend the work from the Ure River southwards to the Lower Clarence. Unfortunately the full programme could not be carried out owing to the writer's departure early in 1935 for South Africa; but sufficient was done in the time available to set the major sequential questions at rest and furnish a geological sketch-map of the area between the Clarence River and Kekerangu. The structure of this block of country has proved of absorbing interest and is closely allied to that of the Middle Clarence and Awatere Districts.*
The writer's thanks are here recorded to the Royal Society of New Zealand for a grant from the Hutton Research Fund towards the cost of the investigation and to Messrs. A. J. Murray, of Wood-bank, and J. W. Trolove, of the Shades, for many kindnesses and for permission to camp upon their respective properties.
The Sequence of Rocks.
The greywackes of the area outcrop only west of the fault which strikes north-north-east along the course of the Lower Clarence and defines the eastern margin of the Seaward Kaikoura Range. Their age has not yet been definitely ascertained, but they are almost certainly in part of Maitai (Permo-Carboniferous) and in part of
[Footnote] * An account of this will be presented in a separate communication.
Jurassic age. Presumably they underlie the whole of the area between the lower Clarence and the sea; but, though this district has been subjected to intense dislocations and differential earth movements, nowhere do they outcrop within its bounds.
Rocks of Clarentian age are almost absent from the area east of the Lower Clarence. A small segment on the east bank of the Clarence River, a mile or so below the Gorge (see map), may possibly be Clarentian mudstone, but the exposure is greatly disturbed and far from typical of Clarentian material; indeed, the writer would prefer to regard it as of Tertiary age but for the facts that at the northern end of the outcrop it apparently underlies the Amuri Limestone and that the same material appears again to the east on the other side of the syncline of limestone. In any case, the outcrop is so small that it bears no comparison with the splendid development at Coverham on the other side of the Seaward Kaikoura Range. At Corner Hill, where the Clarence first comes within sight of the sea, dark volcanic sandstone, similar to that at the mouth of Limestone Creek in the Middle Awatere Valley, where McKay and the writer have individually collected Inoceramus and Belemnites, outcrops beneath the Amuri Limestone for a short distance. As noted by Jobberns (1928, p. 518) this occurrence is involved in a “powerful reversed fault.” These constitute the only known occurrences of the Clarentian in the district under review.
In the Middle Clarence Valley, Thomson has shown (1919, p. 12) from the magnificent sections exposed in the plexus of stream valleys near Coverham, that at the type locality the Clarentian mudstones, sandstones and conglomerates attain a total thickness of approximately 8000ft. It might, therefore, be anticipated that some of this very considerable thickness of strata would be represented six miles away in the coastal area; indeed, the modern conception, due originally to McKay (1886) and supported by Cotton and Thomson, the only other geologists to report on the area, that the Cretaceous and Tertiary beds once formed a continuous cover over the sites of the Seaward and Inland Kaikoura Mountains almost requires that this should be so.
Three hypotheses may be advanced to account for the facts of distribution, while still retaining the essential features of the explanation of the orogeny of the Kaikouras given by the authors mentioned: 1. That at the time of deposition the Clarentian beds were poorly developed eastward of the site of the Seaward Kaikoura Mountains. 2. That they have been subsequently removed by erosion. 3. That they have, by virtue of their general soft and incoherent nature, been crushed out by involvement in earth-movements.
In consideration of the first hypothesis, an original thinning out of the deposits by overlap to the extent of over 7500 ft. in six miles seems unlikely, especially in view of Thomson's remarks that, though it was conceivable that the surface upon which the beds were laid down was markedly uneven, yet this was not borne out by field evidence, and his further statement (1919, p. 296) that the surface
of unconformity was a “practically plane erosion surface.” His observations along the Middle Clarence Valley for a length of twenty miles, however, show (loc. cit., pp. 298–299) that there is a wide variation in the thickness and character of the Clarentian sediments even in the Middle Valley itself. Apart from the sporadic distribution of the Cretaceous volcanic deposits, he notes with reference to the normal clastics that their “thickness … varies rapidly from place to place.” Another, and equally important point in his account is that “the basal beds from the Herring River to the Bluff River are terrestrial.” From this it appears that the Clarentian beds, thinning in a distance of twenty miles along the Middle Clarence Valley from 8000 ft. at Coverham, where Thomson says the mouth of a large river must have been situated, to 3000 ft. with basal terrestrial beds at the Bluff River, may quite possibly have been subject to vastly different conditions six miles away to the east, and been scarcely, if at all, represented. The overlap hypothesis, therefore, though requiring very rapid changes in a comparatively small area, especially in view of the widespread and uniform character of the succeeding Amuri Limestone, must be regarded, in view of the facts obtainable along the length of the Middle Valley, as having definitely strong claims to consideration. One of its advantages is undoubtedly that it requires no interpolation of subsequent erosion periods or paroxysms of earth-movement to cause the removal of beds once laid down. It is also unaffected by the conformity or otherwise of the succeeding Amuri Limestone, though probably more favourable to the former.
The second hypothesis requires the interpolation of a pronounced period of erosion between the time of deposition of the Clarentian and that of the Amuri Limestone. In any consideration of this hypothesis, therefore, the relation of the Amuri Limestone to the Clarentian becomes of paramount importance. Thomson has recorded “perfect conformity” and even gradation between the Clarentian and the lower part (flint beds) of the Amuri Limestone in Sawpit Gully, Isolated Hill Creek and the Upper Ure Valley. So far as other localities are concerned, however, these observations are negatived by his recognition of unconformity at this horizon in the Herring River. Woods (1917, p. 2) has used the fact that the Amuri Limestone overlies both the Piripauan and Clarentian and is itself always followed by “Oamaruian” rocks, as an argument for its unconformity to both the underlying series. Apar from the Herring River locality, definite and incontrovertible evidence of such a period of erosion is still lacking. Unconformities within such a series as the Clarentian, however, would be very difficult to recognize, and it is quite possible that such exist and may account for the small apparent thickness in the Clarence-Kekerangu district.
Lastly, there remains the possibility that in the great earth-movements to which the Seaward Kaikouras owe their origin the soft Clarentian mudstones have acted as a comparatively non-resistant, lubricating medium, and have along the lines of movement been crushed out and lost their identity. Even so it is remarkable that practically no portions should be recognized to lend some standing
to the interpretation. Undoubtedly the movements of the Kaikoura orogeny were far more complex than has been generally recognized; the conception of more or less simple block-faulting in the Kaikoura region must soon be abandoned; but, granting all this, there still seems inadequate support for a hypothesis which relies solely upon folding and thrusting with vertical faulting to account for the removal of such [ unclear: ] quantities of material as is implied by the assumption that the Clarentian deposits east of the Clarence Gorge were ever as thick as those at Coverham to the west.
The possibility remains that none of these hypotheses is correct in itself, but that the observed condition is the result of the combination of two or three causes acting separately or in conjunction. For the present lack of corroborative evidence tells rather strongly against the third hypothesis, even admitting its adequacy to account for the known facts. While the first is extremely probable, the change in thickness seems to have taken place in a very short distance, and the suggestion of a post-Clarentian or late Clarentian period of erosion, backed by Thomson's significant observations at Herring River, must, for some time at least, command the attention of all workers in the district.
(c) Amuri Limestone.
The oldest rocks to occur in any considerable mass in the district between the Lower Clarence and the sea are the various types associated with the Amuri Limestone. In this area the limestone is in most respects akin to that in the Middle Clarence Valley, whence its lithological characters have been fully described by Thomson (1916, pp. 44–58; 1919, pp. 323–336). No further general description, therefore, need be given here.
Usually the lower part of the formation is not developed,* and on this account the flint beds, so prominent at the base of the limestone in the Middle Clarence are almost entirely absent. The only locality where they are at all well developed is to the north of Mole Hill, opposite the lower end of the Clarence Gorge, where the limestone attains a thickness of 1500ft. or more. This value is greatly in excess of any other determined by the writer, and compares with the thickness of the limestone in the Middle Valley rather than with any other section in the coastal area. Here also it is less disturbed than in any of the other exposures between the Clarence and the sea. Usually it is crushed and shattered into small lensoid masses with complete loss of stratification and in many places is ground and pulverized into a powder. These characters have been produced by a powerful series of earth-movements which have also affected the other rock-types of the district according to their particular nature.
On Jacob, the hill in the south-west bend of the Clarence, flint beds again occur, this time apparently overlying the limestone comprising the bulk of the hill, the lower portion of which consists of a calcareous sandstone. The beds thus appear to be reversed, and the lower, calcareous sandstone may be an equivalent of the Weka Pass Stone. In almost all outcrops the limestone dips steeply and at least one side of every outcrop is bounded by a fault.
[Footnote] * Compare with the Clarentian.
(d) “Grey Marl.”
This formation, like the Amuri Limestone, is present in its most typical form, a soft, grey-blue crumbling mudstone rather than a marl. Locally it contains lenses and thin beds of sandstone. Contacts with the underlying Amuri Limestone are rarely exposed and furnish little evidence of unconformity.* Not infrequently, blocks of marl appear in the upper part of the limestone (e.g., near the mouth of Deadmans Stream), but these may be faulted in. Lists of fossils have been given by Thomson (1919, pp. 337–338) and Suter (1921, pp. 32–33).
(e) The Deadmans Creek Beds.
Examination of these beds was one of the main objects of the writer's investigation, for through their fossil content correlation was expected with the fossiliferous strata of the Awatere district. The type-section, that in Deadmans Creek, was described by Thomson (1913, p. 123; 1919, pp. 343–344). The complete sequence upstream from the mouth is as follows: Great Marlborough Conglomerate (noted by McKay but overlooked by Thomson), fault, Amuri Limestone, Grey Marl passing up at the top into sandstones (Fig. 1), Great Marlborough Conglomerate (Fig. 2), grits and banded sandstones passing upwards into mudstones in the Ericaburn, a tributary of the Deadman.
Thomson gave the name “Deadmans Creek Beds” to the sandstones between the second and third outcrops of conglomerate (Fig. 3), describing them as “apparently resting on the (second) conglomerate.” Their true relation, however, is that they lie below the third conglomerate with a fault, readily demonstrable in the field, between them and the second conglomerate band. Examination of the poor section of the “Grey Marl” below the second outcrop reveals that the higher portions are sandier and similar to the Deadmans Creek beds though lacking their rich fossil content. This establishes conclusively the fact that the true position of the Deadmans Creek beds in between the “Grey Marl” and the Great Marlborough Conglomerate, and invalidates the writer's former correlation (1934, p. 30) of the Great Marlborough Conglomerate with the Medway conglomerate of the Lower Awatere. Instead, an eminently more satisfactory correlation is attained whereby the Deadmans Creek Beds still correlate palaeontologically with the Medway Series, and the succeeding conglomerates, the Great Marlborough and the Upton respectively, may be deemed to be the same. This correlation is far more natural than the earlier, which was based on the assumption that the Deadmans Creek beds overlie the conglomerate, for it permits of the identification of the two great described conglomerates with one another. The basal Medway conglomerate, altogether a smaller development, has thus no counterpart in the Kekerangu area, though the transitional beds betwen the “Grey Marl” and the sandstones of Deadmans Creek may be of the same age.
[Footnote] * Fyfe considers (1931, p.6) that an unconformity probably exists in the neighbourhood of Mount Cookson Trig., Amuri Subdivision.
The sandstones are not widely distributed, having been extensively eroded away before or during the deposition of the Great Marlborough Conglomerate. This latter formation contains a small proportion of fossiliferous sandstone blocks evidently derived from the Deadmans Creek beds, and the presence of such fossiliferous boulders over many areas where the Deadman sandstone is not now found in situ is, no evidence of the recent erosion of the formation. The Great Marlborough Conglomerate lies in many such places on an eroded surface of the “Grey Marl” without the intervention of the Deadmans Creek beds.
The following fossils have been collected by the writer:—
A. From the type-locality, Deadman sandstones above the second conglomerate outcrop, half a mile from the mouth of Deadmans Creek.
|Zeacolpus n.sp.||Glycymeris huttoni Marwick.|
|Tropicolpus albolapis (Finlay).||Cucullaea australis Hutton.|
|Struthiolaria cincta Hutton.||(?) Limopsis sp.|
|(?) Magnatica nuda Marwick.||Mactra sp. aff. discors.|
|Polinices huttoni v. Ihering.||Dosinia (Raina) sp.*|
|Polinice sp. indet.||Dosinia (Kereia) waiparaensis|
|Austrosipho crawfordi (Hutton).||Marwick.|
|Baryspira (?) robusta Marwick.||Dentalium sp. indet.|
|Glycymeris rangatira King.|
B. From a boulder on Priam's Flat, Lower Clarence River, evidently derived from the Great Marlborough Conglomerate.
|Struthiolaria cincta Hutton||Zenatia acinaces (Q. & G.)|
|Nassicola costata (Hutton.)||(?) Mactra sp.|
|(?) Waimatea sp.||Dosinia (Kereia) waiparaensis Marwick.|
|Baryspira cf. robusta Marwick.|
|Glycymeris rangatira King.||Dosina (Raina) sp.|
|Glycymeris huttoni Marwick.||Gari oamarutica Finlay.|
These records, with those already given by Thmson (1919. p. 344), are sufficient to establish fairly clearly the correlation of the Deadmans Creek beds with the sandstones of the Medway Series.
(f) Great Marlborough Conglomerate.
This formation has been extensively discussed by McKay (1886, pp. 113–122; 1890, pp. 168–179), Hector (1886, pp. xii–xxxvii), Park (1910, pp. 520–524), Cotton (1914, pp. 346–363), and Thomson (1919, pp. 340–348), while many other New Zealand geologists have also contributed to our present knowledge of the nature of the deposit. Most writers, studying the exposures at Kekerangu South Head and at Dee Gorge, have laid considerable emphasis on the great size of many of the included fragments of “Grey Marl” and Amuri Limestone. These spectacular masses, even in these localities, form
[Footnote] * Ancestral to D. nukumaruensis Marwick.
[Footnote] † May be L. lawsi King.
a very small proportion of the deposit as a whole, and attention has been drawn to them so strongly that there has been a tendency to lose sight of the fact that by far the greater part of the conglomerate consists of medium-sized greywacke pebbles and sand (Fig. 4.). The fact that the presence of such enormous angular blocks as the piece of Amuri Limestone 72ft. in diameter at Kekerangu South Head is difficult of explanation has resulted in a too-close focusing of attention upon the unusual-features, with a corresponding disregard for the more widespread and constant characters. So great, indeed, has been the insistence upon the presence of these huge masses in the Great Marlborough Conglomerate that great gravel-formations such as that forming the so-called Ancient Clarence Delta have not been recognized as Great Marlborough Conglomerate. Jobberns (1928, p. 518), while drawing attention to the fact that Otu Kaku Point, the northern prominence of this ancient salient, was composed of marl, probably the “Grey Marl,” which dipped under succeeding thick gravel beds, yet hesitated to class them as Great Marlborough Conglomerate though he was sufficiently aware of their structure to show that they could not possibly represent delta-beds of a sub-Recent cycle. The writer followed his account of the stratigraphy meticulously, and has no hesitation in agreeing with his rejection of the conception of an ancient delta, now raised considerably above sea-level, at the Clarence Mouth.
Over many square miles of country the conglomerate consists almost wholly of greywacke pebbles from two to six inches in diameter, usually very well rounded and sorted, with only rare fragments of marl and limestone. The complete elimination of these latter constituents renders the deposit indistinguishable from most outcrops of the Upton conglomerate with which it is an exact correlative. Only in rather restricted and widely separated localities do the enormous included blocks, so often referred to as typical of the deposit, occur.
McKay, in his descriptions of the component pebbles or boulders of the deposit, always referred to “a large proportion of the smaller material being hornblendic and syenitic rocks from the Tapuaenuku Range.” Cotton (1914, p. 355), Thomson (1919, p. 341), Branch and Dagger (1934, p. 123), and the writer (1934, p. 14), however, have all remarked that pebbles of such rocks are rare or absent. Such igneous pebbles as are present, and they seem to be commoner in the Clarence area than farther to the north, are of the type associated with the effusive activity which took place in Clarentian times.
The relations of the Great Marlborough Conglomerate to the underlying formations have been much discussed (see Cotton, 1914). Briefly, it may be said to rest on the formation below it, the “Grey Marl,” the Deadmans Creek beds, the Medway beds or the pre-Notocene greywackes without (except in the last case) either the violent angular unconformity of Hector and McKay or the perfect conformity of Cotton and Thomson. The section in Medway River just above the waterfall is typical of most; both formations present almost exactly the same strike and dip, but the surface of contact is undulating, truncating beds of the Medway Series only for a
limited thickness. This parallelism of strike and dip with the underlying Tertiary beds is one of the most characteristic features of the deposit, and was emphasised by Cotton and Thomson in their studies of the material in the Middle Clarence Valley where it always overlies the “Grey Marl.” Thomson (1919, p. 337) was of the opinion that an unconformity was probably present near the top of the “Grey Marl” at a horizon marked by the presence of fossiliferous boulders, an opinion which the present writer is disposed to follow, though Morgan (1910, p. 24) has described distinct unconformity elsewhere.
The age of the Great Marlborough Conglomerate is now fixed within definite limits, which must finally exclude Park's hypothesis of a glacial origin for the deposit. It lies upon the Deadmans Creek beds which are equivalent to the Medway and of Awamoan age; it is readily correlated with the Upton conglomerate, which, succeeding the Medway beds unconformably, lies below the Upton sands and mudstones of Taranakian age, just as the Great Marlborough lies below the Ericaburn beds (vide infra). Therefore it approximates to the Lower Taranakian.
The Bourne conglomerate of Fyfe (1931, p. 6; 1933, p. 7), far to the south, is probably a correlative of the Great Marlborough, its somewhat different composition being due to difference of station.
(g) Ericaburn Beds.
Passing westward through the section in Deadmans Creek, the third band of Great Marlborough Conglomerate is followed with apparent conformity by a series of mudstones and grits passing upward into thick mudstones in the Ericaburn. Thomson (1919, p. 344) was the first to record the occurrence of these beds and to observe the presence of “large calcareous concretions and a few friable fossils.” Apparently he made no collections, and the writer, who was particularly anxious to obtain specimens of the fossils, found them so tender as to preclude any attempt at extraction with the facilities available. Fossil evidence as to the age of these beds is therefore lacking, but fortunately their age may be readily defined stratigraphically. They lie, as we have seen, with apparent conformity upon the upper surface of the Great Marborough Conglomerate. In this respect they are similar to the Upton mudstones and sands of the Awatere. They consist of grits and mudstones and may thus be correlated with reasonable certainty with the true Upton beds. The higher members of the Ericaburn sequence may even be of Starborough age, as was suggested by Thomson, though if this be so the portion which belongs to the Upton Series is probably not as thick as its analogue in the Awatere Valley. Another patch of these beds, grits and mudstones containing small calcareous tubes, outcrops, striking north and south and overlying conglomerates, almost due east of Trig. Jacob.
Outside the area rocks overlying the Great Marlborough Conglomerate and probably of the same age as the Ericaburn beds have been recorded by McKay from Bluff River. Fyfe's Highfield beds may also belong here.
|Starborough Series.||(?) Ericaburn mudstones (in part).|
|Upton mudstones and sands.||Ericaburn mudstones and grits.|
|Upton conglomerate.||Great Marlborough Conglomerate.|
|Medway Series.||Deadmans Creek beds.|
|“Grey Marl.”||“Grey Marl.”|
|Amuri Limestone.||Amuri Limestone.|
|(?)Clarentian conglomerates and sandstones.||Clarentian mudstones and (?) sandstones.|
The Tertiary History of North-Eastern Marlborough.
The most recent attempt to give an account of the history of north-eastern Marlborough during Tertiary times is that by the writer (1934, pp. 28–30); but already the new facts described above require the modifications of opinions expressed such a short time ago.
In almost all sections available in the Lower Clarence area the contact of the “Grey Marl” with the Amuri Limestone is obscured by the magnitude of the earth-movements to which the coastal area has been subjected. No evidence of unconformity was obtained, but the change from one series to the next seems to be sometimes sharp and sometimes ill-defined. We may note for the purpose of our history, however, that Thomson, who believed in conformity, considered (1919, p. 349) that near the head of the Swale an erosion break was possibly present. These two formations, the Amuri Limestone and the “Grey Marl,” now occurring for the most part only in tectonically depressed areas, undoubtedly, as was realized by McKay (1886), had previously a much wider distribution, covering at one time the sites of the present Inland and Seaward Kaikoura Ranges. At present they outcrop (a) in the Middle Awatere Valley, (b) in the Middle Clarence Valley, (c) in the coastal area east and south of the Lower Clarence River, (d) sweeping in two great curves from the north-eastern end of the Middle Clarence Valley to the coast near Benmore and near the Mouth of the Ure River respectively, and (e) striking north and south along the Limestone Range Block from near the Ure River mouth to Clifford Bay. This distribution is governed by the attitudes of the various earth-blocks constituting this segment of New Zealand and represents but the remnants of a once much more extensive development.
Where the pre-Notocene greywackes and Clarentian rocks outcrop south of the Ure-Flaxbourne watershed there seems to be little doubt that the Amuri Limestone and the “Grey Marl” have been eroded from above them in fairly recent times; but to the north of this watershed, in the Lower Awatere region, later Tertiary rocks (Medway and Upton) rest upon the greywacke without the intervention of the limestone and marl formations which they follow in the southern district. Of the extension of the Amuri Limestone and “Grey Marl” at some earlier period over the Lower Awatere district there can be no doubt; the deep-water character of the deposits and their present distribution, even to the east coast of the North Island, requires such a former presence; but a period of erosion must have occurred in the northern part of Marlborough before the Medway beds were laid down.
The later deposits (i.e., post-“Grey Marl”) do not have nearly such a wide distribution and uniform character as the Amuri Limestone and “Grey Marl.” In the south, the Deadmans Creek beds rest upon the “Grey Marl” and consist of marine sandstones. In the Lower Awatere district the corresponding Medway sequence rests on greywacke, and beginning with conglomerates of a shoreline character passes upwards through sandstones to offshore mudstones, the total thickness being many times that at Deadmans Creek. As, however, the succeeding Great Marlborough Conglomerate lies above an eroded surface of the Medway beds and is probably unconformable to the Deadmans Creek beds the difference in thickness may be due to erosion. Conditions seem to have been (a) a shoreline existed near the site of the Lower Medway, (b) deeper water was in evidence in the neighbourhood of Deadmans Creek, (c) the material comprising the beds probably came from the west, (d) gradual sinking was taking place in the northern area. These conditions were brought to a close by an uplift, the visible evidence of which is the eroded surface of the Medway beds upon which rests the Great Marlborough Conglomerate.
In the south the Great Marlborough Conglomerate contains a small but fairly constant admixture of fragments of Amuri Limestone “Grey Marl”; to the north these are wholly absent and the deposit consists entirely of well-rolled greywacke pebbles with fragments of mudstone and grit from the underlying Medway Series (King, 1934, p. 13). Occasional huge blocks like those of limestone and marl so frequently noted by observers in the southern area are not found in the Awatere-Wairau district. Thus there seems reason to believe that most of the material was more or less locally derived, and that south of the Flaxbourne it was somewhat less travelled than to the north. The relation of the conglomerate to the underlying formations rather supports this conclusion, for, as we have seen, it lies in the south with conformable dip upon the “Grey Marl” and Deadmans Creek beds; in the sections in the Medway upon an eroded surface of the Medway beds; and in the neighbourhood of the upper portion of Upton Brook it rests upon a planed surface of the greywackes (King, 1934, p. 13), a contact which probably represents overlap after the post-Medway erosion interval.
Elsewhere (King, 1934, p. 14) the suggestion has been made that the conglomerate in the Awatere area was laid down close to a fluctuating shoreline and that it was in part a rewash of basal Medway conglomerate derived from an area uplifted to the southwest. This interpretation, advanced when the basal Medway conglomerate was correlated (erroneously) with the Great Marlborough, is now unnecessary though by no means incompatible with the new facts recorded above.
The absence of the conglomerate on the Seddon block north of the Haldon Hills (see King, 1934, p. 15) may require the interpolation of yet another erosion break in this locality at a time subsequent to the deposition of the conglomerate. Correspondingly the change from conglomerate to Upton mudstone in the banks of the Awatere River below the Medway junction is very sharp (King, 1934, p. 14).
The extent of the later (Upton) transgression is shown by the occurrence of beds of that age in the Lower Awatere, Ericaburn and Bluff River, while Fyfe's observations (1931, p. 6; 1933, p. 7) indicate a similar transgression (Highfield beds) in the Amuri district after the deposition of his Bourne conglomerate, which is probably a correlative of the Great Marlborough.
Broadly speaking the northern area seems to have been subjected to more pronounced fluctuations with regard to sea-level than the southern. Curiously enough this is paralleled in some respects by the formations of the south-eastern Wairarapa. On the east side of the Haurangi Mountains isolated patches of Amuri Limestone outcrop along the coast, whereas on the west this formation is absent and younger rocks overlie the greywacke. At Hurupi Creek the basal beds are coarse conglomerates succeeded by mudstones of an age equivalent to the Medway beds (King, 1933, p. 334; 1934, pp. 12–13). These are not followed by conglomerate as in the South Island but by mudstones (Onoke Series) ranging up to Nukumaruan in age (King, 1933, p. 336). The absence of the Te Aute Limestone between the Hurupi and Onoke Series in Palliser Bay is noteworthy as this formation is present throughout the length of the Wairarapa from Hawkes Bay to the Ruakokopatuna Valley.
There thus appear to have been three general provinces where conditions of sedimentation were related, but between which minor differences occur: (a) The Hawkes Bay—Wairarapa area, where the Te Aute Limestone is a constant member. (b) The Cook Strait area (Palliser Bay—Seddon), where neither the Te Aute Limestone nor the great Marlborough Conglomerate is present; in this area there is some difference in age in the uppermost beds, the Starborough in the South Island being Waitotaran, whereas the highest beds west of Lake Onoke in the North are possibly Castlecliffian. (c) The Clarence area, where the Great Marlborough Conglomerate is developed.
Branch, W. J., and Dagger, J. R., 1934. The Conglomerates of the Lower Wairau Valley, Marlborough, N.Z. Journ. Sci. and Tech., vol. 16, pp. 121–135.
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Fyfe. H.. 1931. Amuri Subdivision, N.Z.G.S. Ann. Rept., no. 25, pp. 5–6.
— 1933. Amuri Subdivision, N.Z.G.S. Ann. Rept., no. 27, pp. 6–7.
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King, L. C., 1933. Tertiary Molluscan Faunas from the Southern Wairarapa, Trans. N.Z. Inst., vol. 63, pp. 334–345.
— 1934. The Geology of the Lower Awatere District, Marlborough, New Zealand, N.Z. Dept. Sci. and Indust. Res., Geol. Mem. no. 2, 49 pp.
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— 1890. On the Geology of Marlborough and the Amuri District of Nelson, Repts. Geol. Expl. during 1888–1819, pp. 85–185.
Morgan, P. G., 1910. Notes of a Visit to Marlborough and North Canterbury, with special reference to Unconformities Post-dating the Amuri Limestone, N.Z.G.S. Ann. Rept. no. 10, pp. 17–29.
Park, J., 1910. Marlborough Coastal Moraines, Trans, N.Z. Inst., vol. 43, pp. 520–524.
Suter, H., 1921. Lists of Tertiary Mollusca from New Zealand, N.Z.G.S. Pal. Bull., no. 8, 107 pp.
Thomson, J. A., 1913. Palaeontological Report, N.Z.G.S. Ann. Rept., no. 7, pp. 122–123.
— 1916. The Flint Beds associated with the Amuri Limestone of Marlborough, Trans. N.Z. Inst., vol. 48, pp. 44–58.
— 1919. Geology of the Middle Clarence and Ure Valleys, Trans. N.Z. Inst., vol. 51, pp. 289–349.
Woods, H., 1917. The Cretaceous Faunas of the North-eastern Part of the South Island of New Zealand, N.Z.G.S. Pal. Bull., no. 4, 69 pp.
Fig. 1.—View looking upstream from near the mouth of Deadmans Creek showing Grey Marl passing upward into Sandstones beneath the ridge of Great Marlborough Conglomerate. Deadmans Creek beds occur between the two ridges of conglomerate
Fig. 2.—The south side of Deadmans Hill. showing the two ridges of Great Marlborough Conglomerate separated by a fault. Deadmans Creek flows from left to right across the centre and Deadmans Creek beds lie below the conglomerate.
Fig. 3.—Deadmans Creek sanstones disturbed by faulting in the gorge of Deadmans Creek just west of the lower conglomerate ridge. View south.
Fig. 4.—Outcrop of typical Great Marlborough Conglomerate—Saddle Camp, near the head of Rika Stream.