Art. 4.—On the Relation of the Oamaru Limestone and Waitaki Stone.
[Read before the Otago Institute, 8th November, 1921; received by Editor, 12th November, 1921; issued separately, 1st February, 1923]
The principal theme of a paper by Mr. Gr. H. Uttley, M.A., M.Sc, F.G.S; published in the Transactions of the New Zealand Institute* is what he calls the “ two-limestone theory of Professor Park.” Mr. Uttley's contention is that the Waitaki stone is the horizontal equivalent of the Oamaru limestone. In the beginning I may say that I am tempted to deny the gentle charge that the invention of what he calls the “ two-limestone theory ” is mine. Perhaps my disclaimer is unnecessary, since Mr. Uttley† himself supplies the correction when he tells us “ that McKay's ‘two-limestone theory’ [1877 and 1882] is radically different from Park's ‘two-limestone theory’ ”[1905 and 1918].
Mr. Uttley rightly quotes me as having written,‡ in 1887, “ Standing on the high hills surrounding Ngapara, it is quite obvious that the Ototara
[Footnote] * Trans. N.Z. Inst., vol. 52, pp. 169–82, 1920.
[Footnote] † G. H. Uttley, loc. cit., p. 139.
[Footnote] ‡J. Park. Sep. Geol. Explor. during 1886–87, p. 140, 1887.
stone at one time formed a continuous bed.” I now know how fallacious an observation made from a distant hilltop may be. Clearly, the obvious, as cogently argued by Carlyle, may easily conceal the truth.
In the summer of 1916–17 the mapping of the area lying to the west of the railway-line for the first time disclosed the error I had fallen into in 1886 in concluding from a bird's-eye view of the country that the Oamaru and Ngapara limestones were part and parcel of the same sheet.
In 1920 I spent two weeks, and in the present year four weeks, in the coastal and western parts of the Oamaru and South Canterbury districts, concerning myself mainly with the position of the Lioihyrella boehmi horizon and the relationship of the Oamaru and Waitaki stones. I again traced the Waitaki stone to Ngapara and Tokarahi, and examined the country between Enfield, Windsor, Big Hill, and Ngapara. I satisfied myself that I was right (1904, 1910, and 1918) in regarding the Waitaki, Maruwhenua, Ngapara, and Tokarahi stones as part and parcel of the same sheetr; and, of no less importance, confirmed my survey of 1918, which showed, that the Oamaru stone does not connect with, or come within many miles of, the Ngapara limestone.
Among other places I revisited this year was the high ground overlooking Windsor Junction. From this elevation the Oamaru—stone, escarpment behind Cormack's is seen to approach Enfield, whence with its cover of Kakanui limestone it sweeps northward to_. Teaneraki Cliffs and. beyond this to Table-top Hill. The escarpment now trends north-west in the direction of Big Hill, giving the impression as viewed in perspective that the Oamaru stone forms the cap of Big Hill itself and of the scarp-bounded mesas lying between Big Hill and Ngapara.
As shown by my mapping (1918), the Oamaruian strata are arranged in a flat anticline, the axis of which runs north-eastward from Elderslie to the west of Big Hill. In consequence of the slight tilt of the strata, first the Waiareka tuffs, and then the quartz-conglomerates of the Upper Ngaparan, emerge to the north of Table-top Hill from below the Oamaru stone. The Waiareka tuffs form the escarpment as far as the head of Horse Gully, while to the north and west the quartz—conglomerates occupy the summit of Big Hill, where the dip is still to the south—east. The isolated mesas around Ngapara are also capped by conglomerates, which are horizontal or dip gently to the north-west.
Along the eastern or coastal fringe of the anticline the strata are bent into minor synclinal and anticlinal folds. The best developed of these is the Awamoan syncline, a N.W.-S.E. fold which closes to the north-west, where it gradually merges into the eastern limb of the major anticline.
I have recently examined many of the fine natural sections in the Waihao area, and find myself in agreement with Mr. McKay and Dr. Thomson that the Mount Harris or Elephant Hill beds rest conformably on the Waihao stone. On palaeontological grounds these observers have assigned the Mount Harris beds to the Awamoan. With this view both Mr. Uttley and I agree. But the contention of Dr. Thomson and Mr. Uttley that the Waihao stone is the horizontal equivalent of the Oamaru stone implies the absence of the whole of the Hutchinsonian in South Canterbury. As urged by me in 1918.* such a hiatus would mean an unconformity between the Waihao-stone and the Mount Harris beds. Of this, however, there is no evidence. Clearly, if the Mount Harris beds are Awamoan, the Waihao stone must be Hutchinsonian.
[Footnote] * J. Park, The Geology of the Oamaru District, N.Z. Geol. Surv. Bull. No. 20 n.s.), p. 110, 1918.
When dealing with analogous conditions at Otiake Mr. Uttley gets over the difficulty by the simple expedient of combining the Hutchinson and Awamoan beds in what he calls*the “ Hutchinsonian-Awamoan horizon.” But each of them taken by itself is a series of fossiliferous beds of great thickness. How then, may I ask, can the two when combined form one horizon?
Mr. Uttley attempts to justify his view on physical and palaeontological grounds. He rightly quotes my statement that there is no sharp line of demarcation between the Hutchinsonian and Awamoan. The close stratigraphical relationship of the two series has always been recognized by New-Zealand geologists, but surely this cannot be regarded as a valid reason for the creation of a “ Hutchinsonian-Awamoan horizon.” Following this line of argument, we might as well deny the separation of the Ordovician and Silurian, Triassic and Jurassic, Miocene and Pliocene; or deny the right of historians to divide historic time into periods.
During my survey of the Oamaru district in 1916–17 I discovered a hitherto - unknown fossiliferous horizon in the Upper Hutchinsonian at Target Gully, containing many casts of Pachymagas parki, and separated from the overlying Target Gully Awamoan shell—bed by about 20 ft. of soft glauconitic sandstone. From the friable glauconitic sandstone of this horizon (bed c, fig. 35, Geol. Surv. Bull. No. 20, p. 80) I collected seventy-two species of Mollusca. Mr. H. Suter, who made the identifications, recognized twenty-nine of these as living species, equal to 40–3 per cent. Mr. Uttley argues that because some 33 per cent, of the three hundred species of Mollusca from the overlying Awamoan beds in the Oamaru district are Recent “ there would seem to be no justification for separating these beds from the Awamoan horizon.”
I do not think Mr. Uttley's † argument is sound; and if we followed it to its logical conclusion we should get curious results. It is well known that station exercises a powerful influence on the distribution of molluscan life. Of the few molluscs recorded from the Oamaru stone none are Recent, while the overlying tufaceous beds contain about forty-five molluscs of which about 31 per cent, are still living. The marly green-sands under the Kakahu limestone contain 37 per cent, of Recent species‡; whereas collections from the Pareoran (Awamoan) of South Canterbury contain only 27 per cent, of living forms.§
The grouping and correlation of horizons based on small collections must always be regarded with suspicion. Frequently they give results that are altogether erroneous.
In his latest paper Mr. Uttley∥ seems to have modified or receded from his “ Hutchinsonian-Awamoan ” hypothesis. He says: “ (6.) The occurrence of Awamoan fossils in the beds (Otiake beds) above the limestone of the Waitaki Valley, and the fact that the Awamoan and Hutchinsonian are ‘part and parcel of the same series,’ as Hutton, McKay, and Park have asserted, further strengthens the argument that this limestone [Otiake] is Ototaran.”
[Footnote] * G. H. Uttley, (1) Tertiary Geology of the Area between Otiake River (Kurow District) and Duntroon, North Otago; (2) Tertiary Geology of the Area between Wharekuri and the Otiake River, North Otago, Trans. N.Z. Inst., vol. 52, pp. 151, 153, 154, 164, 167, 1920.
[Footnote] †Trans. N.Z. Inst., vol. 52, p. 174, 1920.
[Footnote] ‡N.Z. Geol. Surv. Pal. Bull. No. 8, p. 54, 1921.
[Footnote] §Loc. cit.' p. 58.
[Footnote] ∥Trans. N.Z. Inst., vol. 52, p. 182, 1920.
Perhaps I may say that the phrase “ the same succession ” would express my own and McKay's meaning better than the words “ the same series ” quoted above.
Mr. Uttley immediately continues: “(7.) Nevertheless, the brachiopod fauna of the greensands in the Oamaru coastal district enables a clear line of demarcation to be drawn in that area between the Hutchinsonian and Awamoan.” “With this I am in complete agreement. But my bed c of fig. 35 at Target Gully, previously referred to, contains an abundance of brachiopods (see Geol. Surv. Bull. No. 20, p. 81), while the hard brown glauconitic sandstone stratum (bed d) which underlies the Awamoan and closes the Hutchinsonian contains casts of Pachymagas parki in great abundance. Therefore, according to Mr. Uttley's own view quoted above, bed c of fig. 35 cannot be regarded as Awamoan.
I am of the opinion that if the new horizon (bed c) at Target Gully were opened up a rich harvest of molluscs would be obtained. Experience has shown that exhaustive collecting in the Cainozoic formations tends to decrease and not increase the proportion of. living forms. Apart from further discoveries, the presence of so many brachiopods in beds c and d proves that Mr. Uttley has failed in his contention that “ there would seem to be no justification for separating these beds from the Awamoan horizon.”
In 1918 I described a section a quarter of a mile east of Flume Creek* in which a yellowish-brown calcareous slightly glauconitic sandstone intercalated with harder bands contains the coral Isis in abundance. This rock conformably overlies a greyish-white limestone that in its upper part is hard and semi-crystalline, and rests on volcanic tuffs and mineral breccias. These tuffs were first described as occurring in this area by Mr. Uttley. An assemblage of bracbipods in which Liothyrella boehmi Thomson is prominent occurs at the base of the glauconitic sandstone and upper part of the mineral tuffs. If any reliance is to be placed on the zonal value of the brachiopod fauna it is evident that what I have classified as the upper band of Oamaru stone† must be grouped with the Deborah (or Kakanui) limestone lying above it. The importance of this section is second only to that at the mouth of Flume Creek. Mr. Uttley states that he “was unable to find it.”
I have examined the section in question twice in the present year and found that the Isis band, as I stated in 1918, does underlie the brown glauconitic sandstone with the intercalated hard limestone layers. I now find that the coral I called Isis is the related Mopsea.
Mr. Uttley in discussing this section continues, “ Even if the glauconitic sandstone (bed g of fig. 28) does occur as shown in section above no evidence has been presented to show that it is the equivalent of the limestone of the Waitaki Valley near Duntroon.” He himself does not hesitate to correlate the so-called Otiake limestone with the Maruwhenua limestone, notwithstanding that the former occurs as an isolated down-faulted block lying between two ridges of Palaeozoic rock, one of which separates it from the Otekaike limestone, the nearest Cainozoic rock, which. may or may not be the horizontal equivalent of all or a part of the Maruwhenua stone.
Mr. Uttley maintains that the Waitaki stone near Duntroon is a limestone as pure in many parts as the typical Ototaran (Oamaru) limestone.
[Footnote] * J. Park, N.Z. Geol. Surv. Bull. No. 20 (n.s.), p. 65, 1918.
[Footnote] †Loc dt., p. 66.
But in saying this he has fallen into an error. The Oamaru stone is essentially a polyzoan limestone of high but even grade, the calcium-carbonate content seldom falling below 90 per cent, except where mingled with volcanic ash. Its distribution shows that it is local, and that it accumulated as an off-shore reef or bank where no terrigenous matter was being deposited. On the other hand, the Waitaki stone is a low-grade arenaceous limestone of extremely variable composition.
As a rule, the typical Oamaru building-stone is so soft that it can be cut with a saw as readily as a log of pinewood’. I have examined 110 sections of Oamaru stone from Gay's Weston quarry, and forty-two from Totara, Teschemaker's, and Deborah. The Polyzoa range from 28 to 94 per cent., the difference from 100 being made up for the most part by Foraminifera with some echinoderm plates and rarely shell-fragments. The average sample contains about 60 per cent, of Polyzoa and 30 per cent, of Foraminifera. Dr. P. Marshall* has described a sample of Oamaru stone as composed of'Polyzoa, echinoderm plates, and Foraminifera in about equal proportions. I am satisfied that the sample examined by Dr. Marshall was not representative.
The Waitaki stone, as typically developed near Duntroon, is an impure arenaceous limestone intercalated with thin layers of higher-grade limestone that weather out in the escarpment-faces as prominent bands. The analysis† quoted by me, and referred to by Mr. Uttley,‡ is that of a sample collected from several of the highly calcareous bands mentioned above. It may be said that these bands taken altogether comprise less than 20 per cent, of the Duntroon stone.
Mr. Uttley§ also refers to the Bortonian stage, the existence of which is based on the occurrence of an assemblage of molluscs of an ancient Cainozoic type at Black Point, near Borton's, in the Waitaki Valley. The first collection at this place was made by Mr. McKay ∥ in 1876, who reported, among other forms, the occurrence of A.ncyloceras and Scaphiles. No Secondary cephalopods were found by me in 1904 or 1918; but the collections made by McKay (1876) and by me (1918) contained three genera new to the New Zealand fauna, and several gasteropods of an ancient type, fully justifying my old colleague in placing these beds in the so-called Cretaceo-Tertiary system of the First’ Geological Survey.
The fossils from near Windmill Creek and Papakaio were provisionally referred by me to the Bortonian. The limitations mentioned by Mr. Uttley were clearly recognized by me, hence the separate lists of fossils I gave in 1918.¶ Till Mr. Uttley is able to furnish some new facts about the horizon of the fossils occurring near Windmill Creek and Papakaio we may, I think, let the provisional correlation stand. Dr. Thomson has said that most of the fossils from Black Point occur as casts. That statement can refer only to the forms obtained from the weathered skin of the concretionary masses. The fossils from the middle of the boulders are mostly testiferous and well preserved.
In a note to my paper “ On the Age and Relations of the New Zealand Coalfields ” I stated that I had obtained evidence in north Otago and south Canterbury confirming my view that the Pareora beds underlie the
[Footnote] * Trans. N.Z. Inst., vol. 48, p. 92, 1916.
[Footnote] †N.Z. Geol. Surv. Bull. No. 20 (n.s.), p. 115, 1918.
[Footnote] ‡Trans. N.Z. Inst., vol. 52, p. 178, 1920.
[Footnote] §Loc. cit., pp. 178–79.
[Footnote] ∥Rep. Geol. Explor. during 1876–77, p. 52, 1887.
[Footnote] ¶N.Z. Geol. Surv. Bull. No. 20 (n.s.), pp. 34, 35, 1918.
Oamaru stone and therefore belong to the Oamaru series.* I need hardly say that the “ Pareora beds ” I referred to belonged to the Pareora series of Hutton. It was to eliminate the confusion arising from the application of this name by some observers to beds below, and by others to beds above, the limestone that in 1905 I adopted the name “ Awamoa ” in preference to “ Pareora” when dealing with beds definitely known to overlie the Mount Brown (or Hutchinsonian) beds.†
My classification‡ of 1905, with “ a. Waitaki stone ” deleted, still represents the stratigraphical succession of the Lower Cainozoic formations of New Zealand as we know them to—day. The inclusion of the Waitaki stone was an attempt to reconcile Captain Hutton's views with those of the Geological Survey.
The Liothyrella boehmi assemblage of brachiopods previously alluded to underlies the Kakanui (or Deborah, Waitaki, Maruwhenua, Ngapara, Tokarahi) limestone, but overlies the Oamaru building—stone. I can only repeat that if, as claimed by Dr. Thomson and Mr. Uttley, this assemblage possesses zonal value, we must admit that the Waitaki limestone is not the horizontal equivalent of the Oamaru stone, but occupies a higher position in the Cainozoic succession of south Canterbury and north Otago, being separated from the Oamaru stone by the Liothyrella boehmi horizon.
The Oamaruian succession in the Oamaru coastal area and in the Waitaki-Ngapara area is shown below:—
|Stage.||Coastal Area.||Waitaki-Ngapara Area.|
|Awamoan||Awamoa beds||Awamoa beds.|
|(Deborah limestone||Waitaki limestone.|
|Hutchinsonian||L. boekmi band||Lm boehmi band.|
|Ototaran||Mineral tuffs||(a)“Grey sandy beds.|
|Oamaru stone||(b) Bortonian.|
|Ngaparan||Ngapara grits, sands, &c.||Ngapara grits, sand, &c.|
[Footnote] * Trans. N.Z. Inst., vol. 36, p. 418, 1904.
[Footnote] †Trans. N.Z. Inst., vol. 37, p. 492, 1905.
[Footnote] ‡J. Park, loc. cit., p. 492.