Art. XXVII.—The Relationship of the Upper Cretaceous and Lower Cainozoic Formations of New Zealand
[Read before the Otago Institute, 5th December, 1916; received by Editors, 30th December, 1916; issued separately, 30th November, 1917.]
In vol. 48 (1915) of the Transactions of the New Zealand Institute there appear papers by Mr. P. G Morgan, Dr J. Allan Thomson, and Dr. Marshall dealing mainly with the relationship of the Lower Cainozoic marine strata of New Zealand to the Upper Cretaceous. In each of these papers my own views as to the so-called Cretaceo-Tertiary succession, and those of other New Zealand geologists, are discussed at considerable length. Of an admittedly complex problem, rendered all the more puzzling to outside geologists by the great diversity of opinion expressed at various times by many writers, Morgan's paper† embodies, to my mind, the most lucid and comprehensive exposition that has so far been placed on record. He recognizes the Miocene age of the uppermost beds at Waipara and Weka Pass,
[Footnote] † P G Morgan, Records of Unconformities from Late Cretaceous to Early Miocene in New Zealand, Trans N Z. Inst, vol 48, pp 1–18, 1916
the Upper Cretaceous age of the lowermost beds, and the apparent stratigraphical conformity of the strata from the Miocene to the Cretaceous, but finds himself, after a judicial summary of all the available evidence, unable to support the Cretaceo-Tertiary theory of the old Geological Survey. He describes the uneven corroded surface of the Amuri limestone where overlain by the Weka Pass stone in North Canterbury, and, while not placing undue stress on the magnitude of the discordance at this contact, he seems to think that the break between the Cainozoic and Cretaceous may occur at this horizon. In this he agrees with the view all along held by Hutton, and in 1912 adopted by myself* after the discovery (or rediscovery) of Cainozoic molluscs in the Weka Pass stone at Waipara by Thomson and Cotton.
In his paper† on the “Flint-beds associated with the Amuri Limestone” Thomson records the occurrence of Tertiary (Oamaruian) molluscan fauna in a bed of tuff intercalated in the Amuri limestone in the Trelissick Basin. This discovery, made by Thomson and Speight in 1915, seems destined to furnish the solution of many of the perplexities that have in the past obscured the unravelling of the relationship of the Lower Cainozoic and Cretaceous of New Zealand. The bed of tuff is overlain by 10 ft. of Amuri Limestone and underlain by 350 ft. of Amuri limestone. Of the molluscs enumerated by Thomson, 19 per cent. are Recent, and the remainder are all well-known Tertiary species, mostly Oamaruian (Miocene). Save foraminifera (mostly Globigerina), some radiolarians, and sponge spicules, the Amuri limestone itself is unfossiliferous, or, at any rate, devoid of molluscan remains; and, while recognizing the Oamaruian age of the tuffs and overlying portion of Amuri limestone, Thomson expresses the view that the portion of the Amuri limestone below the tuffs fills the hiatus between the Senonian and Oamaruian.
Marshall‡ in his paper on the “Relations between Cretaceous and Tertiary Rocks” discusses at considerable length the views of different New Zealand geologists as to the Waipara succession, and furnishes much useful information as to the relationship between the Cretaceous and Tertiary rocks in other parts of the globe. He reaffirms his belief in a Cretaceo-Tertiary succession.
I do not think that any useful object would be served by a further discussion of the various points of disagreement between myself and Dr. Marshall. The settlement of the Cretaceo-Tertiary can only be achieved by a detailed geological survey of the Middle Waipara and Weka Pass districts. The groups of beds recognized there, and their order of superposition as agreed by all geologists, are—
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|1. Greta beds|
|2. Mount Brown beds|
|3. Grey marls||Oamaruian (Miocene).|
|4. Weka Pass stone|
|5. Amuri limestone|
|6. Glauconitic greensands||Doubtful.|
|7. Saurian beds|
|9. Quartz sands with brown coal|
[Footnote] * J. Park, Tertiary Fossils in the Weka Pass Stone, New Zealand, Geol Mag., July, 1912, p 336
[Footnote] † J A. Thomson, Trans N Z Inst, vol 48, 1916, pp 48–58
[Footnote] ‡ Loc cit, pp 100–19
The Saurian beds contain Plesiosaurus and other reptilian remains of a Cretaceous facies, and are probably of Senonian age. According to Haast,* the glauconitic greensands contain Waldheimia lenticularis (which he says is also common in the Mount Brown beds), a Pecten, and a large smooth Inoceramus which he says resembles Inoceramus planus of Europe. When Lima laevigata was first reported† in the Cobden limestone it was called Inoceramus. The presence of the brachiopods and pectens inclines me to suspect that the large smooth Inoceramus of Haast may be, after all, nothing more than Lima laevigata Hutton.
The upper five members of the succession—or, at any rate, the upper four members and the uppermost portion of the fifth (Amuri limestone)— are acknowledged by all to be Tertiary. The age of the glauconitic greensands has been considered Cretaceous by all who have written on this subject, but in view of the recent discovery of an assemblage of Oamaruian molluscs in tuffs intercalated in the Amuri limestone, and the doubt as to the correctness of Haast's identification of Inoceramus, I am inclined to think that this view may have to be revised.
The opponents of the Cretaceo-Tertiary hypothesis place the unconformity between the Cretaceous and Tertiary at the close of the Amuri limestone. The discovery of Tertiary molluscs in the tuffs intercalated in the Amuri limestone leads me to conclude that the unconformity must be looked for under the Amuri limestone. Later investigation may even show that the unconformity occurs between the Saurian beds and the glauconitic greensands.
The unconformities that have been recognized between the Mount Brown and Greta beds, and between the Amuri limestone and Weka Pass stone, may prove to be local and of no palaeontological significance.
A glauconitic sandstone containing a Tertiary molluscous fauna has been reported by McKay as lying below the hydraulic limestone at Kawakawa, and a rich assemblage of molluscs was discovered by myself‡ as far back as 1885 in glauconitic greensands underlying the hydraulic limestone at Pahi, in the Kaipara district. The Pahi molluscs are undoubtedly Oamaruian. The presence of this Tertiary fauna below the hydraulic limestone has always presented one of the perplexing problems of the geology of North Auckland. The correlation of the Amuri limestone with the hydraulic limestone receives powerful support from the discovery of a Tertiary fauna in the Amuri limestone at the Trelissick Basin. The placing of the Amuri limestone in the Tertiary succession removes the most perplexing difficulty that has confronted geologists in the interpretation of the geology of the North Auckland district. What now remains to be done is to determine the relationship of the glauconitic greensands in the Middle Waipara to the overlying Amuri limestone and the underlying Saurian beds.
[Footnote] * J. Haast, Notes on the Geology of the Central Portion of the Alps, including Mount Cook, Reports of Geological Explorations during 1870–71. 1871, pp 11, 12
[Footnote] † A Mckay, Reports relative to Collections of Fossils made on the West Coast District, South Island, Reports of Geological Explorations during 1873–74, 1877, pp 80, 101; and during 1874–76, 1877, p 38
[Footnote] ‡ J. Park, On the Kaipara District, Reports of Geological Explorations during 1885, 1886, pp 164–70