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Volume 49, 1916
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Art. XXXIX.—Fossils and Age of the Hampden (Onekakara) Beds.

[Read before the Otago Institute 5th December, 1916; received by Editors, 30th December, 1916; issued separately, 7th December, 1917.]

A Preliminary reference to the Hampden beds was made by me last year.* At that time the collections that had been made had not been fully worked out, and the following species only were recorded: Avellana tertiaria Marshall, Surcula hamilton Suter, and Trigonia n. sp. A specimen of the Avellana has since been sent to M. M. Cossmann, of Paris, but he identifies the species as belonging to the closely allied genus Gilbertia, which is restricted to the Palaeocene.

That these beds of the Onekakara Beach, three miles north of Hampden, were fossiliferous was known long ago. Mantell made the first collection in 1849, and published the results in the Quarterly Journal of the Geological Society. He classed the beds as Pleistocene or newer Tertiary. Twelve species of Mollusca are listed, but this list is now of little value.

Hutton in 1875 placed the beds in the Miocene formation. He gives a list of twenty-one species of Mollusca, but possibly some of these come from neighbouring localities. In 1887 he gave a more detailed description of the locality§ A section shows the exact spot at which fossils are found. He obtained specimens of fourteen species of Mollusca, of which three species are Recent.

McKay in 1884 classed the beds as Cretaceo-Tertiary, but gave no list of fossils. He suggests that Recent species that had been placed in other lists had been embedded in the strata as a result of slipping of overlying formations. McKay further discussed the position of these beds in 1887. Again they are classed as Cretaceo-Tertiary. but it is stated that no exact list of the species can be given.

Park in 1905 classed the formation as Miocene.** He gave a list of twenty-three species of Mollusca, with a percentage of 41.5 per cent, of Recent species.

The actual rocks consist of argillaceous sands with much glauconite, in places becoming characteristic greensands. They have some concretions, both calcareous and pyritic. The fossils are poorly preserved, and are difficult to extract in a condition that admits of identification. Some four days altogether were spent in collecting.

McKay's†† statements as to the stratigraphy appear to be substantially correct. The fossiliferous beds rest directly on the strata that contain the well-known Moeraki concretions. These pass downwards into the concretionary but more sandy Kartigi beds, which in turn rest on the

[Footnote] * Trans. N.Z. Inst., vol. 48, 1916, p. 116.

[Footnote] † Vol. 6, 1850, p. 330.

[Footnote] ‡ F. W. Hutton andG. H. F. Ulrich, Geology of Otago, Dunedin, 1875, p. 57.

[Footnote] § Trans. N.Z. Inst., vol. 19, 1887, p. 426.

[Footnote] ‖ Rep. Geol. Explor. dur. 1883–84, 1884, p. 62.

[Footnote] ¶ Rep. Geol. Explor. dur. 1886–87, 1887, pp. 6, 238.

[Footnote] ** Trans. N.Z. Inst., vol. 37, 1905, p. 506.

[Footnote] †† Loc. cit., 1887.

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Shag Point conglomerates that contain the coal. The length of coast-line between the Onekakara beds and Shag Point is about twelve miles, but as it is generally parallel to the strike of the strata the actual thickness of strata exposed within this distance is small. Probably no more than 300 ft. separate these fossiliferous beds from the conglomerates at Shag Point. Above the fossil-bearing beds there are the volcanic tuffs and breccias called the Waireka tuffs, and these are sometimes associated with basaltic lava-flows. These in turn lie below the Oamaru (Ototara) limestone.

In identifying the Mollusca I am greatly indebted, as on previous occasions, to Mr. H. Suter, who kindly undertook the rather tedious task. The following is the list of species:—

  • Aturia sp.

  • Circulus n. sp.

  • Cerithidea n. sp.

  • Cerithiella n. sp.

  • Turritella symmetrica Hutton.

  • Turritella ornata Hutton.

  • Turritella n. sp. cf. aldingae Tate.

  • Struthiolaria cincta Hutton.

  • Sinum (Eunaticina) elegans Suter.

  • Ampullina waihaoensis Suter.

  • Ampullina suturalis Hutton.

  • Erato n. sp.

  • Cymatium minimum Hutton.

  • Galeodea senex Hutton.

  • Epitonium rugulosum lyratum Zittel

  • Epitonium n sp.

  • Turbonilla n. sp.

  • Dicroloma?

  • Fusinus solidus Suter.

  • Fusinus n. sp.

  • Exilia waihaoensis Suter

  • Latirus n. sp.

  • Siphonalia nodosa Martyn.

  • Siphonalia turrita Suter

  • Belophos n. sp.

  • Volutoderma n. sp.

  • Cymbiola (Miomelon) corrugata (Hutton).

  • Ancilla novae-zelandiae Sowerby.

  • Marginella n. sp.

  • Turris duplex Suter

  • Turris nexilis bicarinatus Suter.

  • Turris complicatus Suter.

  • Turris complicatus nov. var.

  • Turris regius Suter

  • Turris n. sp. cf. neglectus and regius.

  • Turris n. sp. cf neglectus.

  • Surcula hamiltoni Hutton.

  • Surcula serotina Suter.

  • Surcula n. sp.

  • Surcula n. sp. cf pareoraensis.

  • Bathytoma sulcata Hutton.

  • Terebra costata Hutton.

  • Terebra n. sp.

  • Gilbertia tertiaria Marshall.

  • Bullinella enysi Hutton.

  • Dentalium mantelli Zittel

  • Malletia n. sp.

  • Cucullaea alta Sowerby.

  • Sarepta obolella Tate

  • Sarepta n. sp.

  • Arca novae-zelandiae Smith.

  • Arca (Bathyarca) n. sp.

  • Limopsis zitelli Ihering.

  • Trigonia n. sp.

  • Lima angulata Sowerby.

  • Atrina sp.

  • Ostrea wuellerstorfi Zittel?

  • Cardium sp.

  • Cardium (Papyridea) sp.

  • Pecten huttoni Park

There are thus altogether sixty species, of which the following six are Recent: Turritella symmetrica Hutton, Siphonalia nodosa Martyn, Anclla novae-zelandiae Sowerby, Sarepta obolella Tate, Area novae-zelandiae Smith, Lima angulata Sowerby. It thus appears that no more than 10 per cent of these sixty species are Recent—a very low result when compared with those obtained by previous collectors. The following show Mesozoic affinities: Volutoderma, Dicroloma, Trigonia n. sp. The specimens referred to Dicroloma are not well preserved. The species is certainly an Aporrhaid, but not Aporrhais or Hemichenopus. To these must be added Trigonia neozelanica Suter, which was collected by Hutton.

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The following genera have been recorded from the Eocene only in those countries in which they occur: Gilbertia, Belophos. Surcula hamiltoni Suter and Exilia waihaoensis Suter have not been found above the limestone member of the Oamaru system. On the other hand, the genus Turris (Pleurotoma Lamarck), which is particularly well represented in this collection, is a Miocene genus with the single exception of one Australian species of supposed Eocene age; but there appears to be great doubt as to whether any of the Australian Tertiary formations are really older than the Oligocene, and by far the greater part of them are considered to be of Miocene age by Chapman. The genus Terebra, again, has no species in strata higher than the Miocene except in the doubtful horizons of Australia. No species of the genus Erato have yet been recorded from any formation below the Oligocene. Struthiolaria has not been found below the Miocene, though Struthiolariopsis has been found by Wilckens in the Cretaceous of South America. The same is true of Malletia.

Another point of importance is the absence of genera which are usually abundant in the Tertiary formations of New Zealand. Amongst these are Venericardia, Crassatellites, Alectrion, Calyptraea, and Crepidula. With the exception of Venericardia all of these genera are absent also from the beds of Wangaloa. In addition there is the low percentage of Recent species. Too much importance should not be attached to this, for the Onekakara material was deposited in water of considerable depth, and our knowledge of the Recent New Zealand Mollusca from any zone but the littoral is still extremely imperfect.

So far as New Zealand stratigraphy is concerned, it is probably correct to place the Onekakara beds as slightly higher than the Wangaloa horizon, though they are probably slightly older than the Chatton beds. It is extremely hard to suggest a European equivalent. The palaeontology of the Wangaloa, Onekakara, and Chatton beds strongly support the opinion that there is no geological break in the succession of the lower members of the Younger Rock series of New Zealand, elsewhere called by the author the Oamaru system. Even in these beds at Onekakara, where important Cretaceous and Eocene genera exist, there is still a great number of species that are common in the ordinary Tertiary beds of New Zealand, of which Target Gully can well be taken as a type. They also tend to show that the marginal terrigenous facies shows a variable age when different formations are compared. If the oldest sea-margin is represented in the beds of the Clarence Valley, as suggested by Thomson,* this margin appears to have extended southwards and westwards gradually. The following seems to be the approximate age of the basement beds in the different localities: Clarence Valley, Cenomanian; Amuri Bluff, Senonian; Waipara Gorge, Senonian; Wangaloa, Maestrichtian?; Chatton, Oligocene?; Wharekuri, Miocene. These Onekakara beds seemed to be more rightly classed with the Eocene than with any other European system.

The large number of species of common occurrence in the higher Tertiary rocks of New Zealand which occur also in the basement beds of the Otago localities mentioned supports the belief that deposition was continuous in

[Footnote] * Trans. N.Z. Inst., vol. 48. 1916, p. 57.

[Footnote] † Mr. C. T. Trechmann, M.Sc., F.G.S., who collected at Wangaloa with me and took a collection away with him, at first regarded the strata as of Maestrichtian age. After-wards he stated that the presence of Pugnellus appeared to justify a Danian age. (MSS. letter.)

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the New Zealand area throughout this lapse of geological time. It is noticeable that where the basement beds are of greatest age, as at the Clarence. Valley, and also at Batley, in the north of Auckland, the overlying limestone member of the series is a deep-sea ooze — globigerina, diatomaceous, or radiolarian.

While the palaeontological evidence at present available strongly supports the conclusions stated, it is certain that much still remains to be done. The collections that have already been made are capable of much extension even from the same localities, while doubtless other localities will yet be found that will add greatly to our knowledge of the fauna of the lowest members of this system of younger rocks.