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Volume 75, 1945-46
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Age Revision of Tertiary Sediments at Garden Gully and Fitzgerald Creek, Near Blackball, Westland.

[Read before Wellington Branch, July 12, 1945; received by the Editor, July 13, 1945; issued separately, December, 1945.]

Summary.

A new fossil locality, probably of Bortonian age, and two lower Tertiary sections, previously considered Miocene, are described, and basal sub-bituminous coal measures correlated with bituminous Brunner coal measures of Greymouth. A brief discussion on the influence of the difference in coal rank and induration on previous correlations is extended to other West Coast sections.

Introduction.

Small areas of coal measures and overlying marine Tertiary strata mapped nearly 30 years ago in the south-east quarter of Wai-whero Survey District by Henderson (1917, Map 5), have recently been re-examined and fossils found which indicate that a revision of the earlier mapping and Tertiary classification is required. Attention is drawn to the coal, which, although belonging to the same horizon as the well-known bituminous coal of Brunner, is a low-rank subbituminous coal with as much as 19 per cent. water. The outcrops are at the foot of the abrupt eastern slopes of the Paparoa Range in Garden Gully and Fitzgerald Creek, small western tributaries of Moonlight Creek, a tributary of Grey River. Fitzgerald Creek is just over a mile south of Garden Gully and four miles north-east of the town of Blackball.

The long-abandoned alluvial diggings of Garden Gully have almost disappeared under advancing forest but can still be reached by following a five-mile formed track from Atarau on the Blackball-Ikamatua road.

Garden Gully.

The following is a composite section built up from discontinuous outcrops not far west of the old Garden Gully settlement, 60 chams from Moonlight Creek.

Feet.
Kaiatan: Soft, dark micaceous mudstone, poor fossils 50ft from base 150
Bortonian: Soft, yellow-brown, medium sand, with a thin band crowded with shell casts 20 feet from top 100
Brunner: Soft, carbonaceous sandstone 3
Coal 20
Unconformity:
Palaeozoic: Greenland Series; Leached greywacke and argillite.
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Shell casts were first discovered in iron-cemented spoil from an old water-race, but the place is neither well defined nor an obvious fossil locality. The race is a few feet below the top of the ridge between Jerry Creek and a small un-named tributary of Garden Gully to the north, and once connected with a small dam near the head of the unnamed tributary. The fossil band shows again in soft sand 20 feet below the sandstone-mudstone contact well exposed in the dam. Upstream, mudstone outcrops for 5 chains, and downstream about 100 feet vertically below the dam, the stream cascades over a conspicuous 20-foot coal exposure a few chains from Garden Gully.

Two collections of fossil casts have been examined by Dr. Marwick, who identified the following forms, indicating an Early Tertiary age, certainly pre-Whaingaroan and probably Bortonian (Mid-Eocene).

G.S. Loc. No. 2922. Waiwhero Survey District, 1.72 miles, at 105° from Trig. P. near Garden Gully.

? Nuculana n.sp. Notocorbula humerosa (IIutt.)
Glycymeris cf. subglobosa Suter Zeacolpus n.sp.
(differs towards thomsoni). ? Globisinum sp.
Lentipecten parki Marw. Buccinulid n.gen. n.sp.
Venericardia n.sp. Austrofusus n.sp. aff. acuticoslatus
Scalpomactra sp. (Suter)
Dosinia (Kakahuia) n.sp. Waimatea n.sp.
Hedecardium cf. brunneri (Hect.) Zeacuminia n.sp.
Kaitoa n.sp.

Lentipecten parki ranges from Bortonian to lower Kaiatan. Hedecardium brunneri has the same range. Kakahuia and Austrofusus acuticostatus are known only from the Bortonian, but the Garden Gully specimens are not specifically identical with the Bortonian ones. The Venericardia, the Waimatea, and the Zeacuminia suggest early rather than middle Tertiary age.

It will thus be seen that the age could be Bortonian, Tahuian, or lower Kaiatan, but no later. From general considerations, such as stratigraphic position and the foraminiferal evidence from overlying beds, a Bortonian age seems probable.

The foraminifera from the base (F. 6354), from 30 feet above the base (F. 6283), and from 50 feet above the base (F. 6284) of the mudstone are considered by Dr. Finlay to be Lower Kaiatan in age. See Appendix.

Henderson did not mention marine beds at Garden Gully, but gave a short description of coal measures both at Garden Gully and Fitzgerald Creek (1917, pp. 215–6). He also mentioned (ibid. p. 90) that Cobden limestone is fault-involved at Fitzgerald Creek.

Fitzgerald Creek.

The following steep but more complete section is intermittently exposed in the main south branch of Fitzgerald Creek upstream for 30 chains from old coal bins marked as “Hopper” on Henderson's map, and is based on age determinations by Dr. H. J. Finlay.

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Feet. (Approx.)
Waitakian: (F.6357) Soft, light grey, glauconitic and micaceous silty limestone 100 +
Whaingaroan: (F.6356) Moderately soft, light grey, calcareous mudstone, with rare leaf impressions 500
Kaiatan: (F.6355) Soft, dark, micaceous mudstone, upper contact obscured 500
Bortonian: Quartz sand, moderately coarse, few carbonaceous bands; soft enough to form rain pillars 30
Brunner: Soft, carbonaceous sandstone 1
Coal 24
Unconformity:
Palaeozoic: Greenland Series; greywacke and argillite.

Correlation.

Garden Gully is the second Bortonian locality recorded from the West Coast, the first being the “Island Sandstone” of Ten Mile Bluff eight miles north-east of Greymouth. (Finlay and Marwick, 1940, p. 106). The Island sandstone is a well defined lithologic unit as much as 500 feet thick and immediately overlies coal measures. Not previously mapped outside the Grey coalfield, it was known to extend north on the east side of the Paparoa Range to Blackball, where the coal measures have recently been re-examined, and the following section measured.

Generalized Section of Formations at Blackball.
Feet.
Waitakian: Argillaceous limestone 100
Whaingaroan: Very calcareous, light grey mudstone 800
Kaiatan:
Omotumotu: Calcareous sandstone, greywacke breccia and brown mudstone 2,750
Kaiata: Dark brown, calcareous mudstone 1,300
Bortonian: Island sandstone; medium calcareous sandstone 350
Brunner: Coal, quartz sandstone and conglomerate 50
Unconformity:
Palaeozoic: Greenland Series; greywacke and argillite.

The Brunner beds, Island sandstone and Kaiata mudstone form Morgan's Mawheraui Series, and the overlying beds part of his Greymouth Series.

Lithologic correspondence, neglecting induration, between beds of the same age at Garden Gully, Fitzgerald Creek and Blackball is so good that correlation would be possible without the fossil evidence which makes it certain. The most striking differences are the much greater induration and thickness of the Blackball section and the absence of the characteristic coarse Omotumotu facies of the Kaiatan from the Garden Gully area.

Henderson, however, mapped the coal measures of Garden Gully not as Mawheranui Series but as lower Miocene, a series which he considered to overly unconformably the Mawheranui Series, and to be about the same age as the Omotumotu beds. In this correlation he followed Morgan and Bartrum at Charleston (1915, pp. 58, 176), who, also without fossil evidence, classed as lower Miocene equally

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soft coal measures with similarly low rank coal. Induration has considerable and often sub-conscious effect on correlation. It is not often invoked as evidence in the text, but plays an important part in the field. The authors have a keen appreciation of this point, for when they first visited Garden Gully from Blackball they expected to find Mawheranui Brunner beds there, but the strikingly lower induration was sufficient to convince them temporarily of the correctness of Henderson's mapping. But for the fossils, the true age of the beds would not have been discovered, and it is to be expected that when fossils are collected from other West Coast Tertiary sections similar revision of the old lithologic mapping will be required.

Coal.

The nearest Mawheranui coal recognised by Henderson as such at Blackball is certainly much higher in rank than that at Garden Gully.

Henderson (1917, p. 216) gives the following analyses of coal from Garden Gully and Fitzgerald Creek: these are compared with the only recent analysis of Blackball coal available.

M. V.M. F.C. A. S.
(1) 16.4 48.5 34.5 0.6 4.82
(2) 17.2 46.6 35.0 0.8 4.69
(3) 17.1 47.1 35.0 0.8 3.07
(4) 19.5 43.8 34.4 2.3 4.54
(5) 17.5 46.5 34.9 1.1 4.28
(6) 3.9 49.2 45.6 1.3 5.2
(7) 4.2 49.6 45.0 1.2 5.4
(8) 3.3 51.1 44.5 1.1 5.1
(9) 3.8 50.0 45.0 1.2 5.2
  • (1) Upper 12ft of seam, Fitzgerald Creek.

  • (2) Lower 12ft of seam, Fitzgerald Creek.

  • (3) Thick seam, Jenkins' water race, Garden Gully.

  • (4) 20ft seam, township, Garden Gully.

  • (5) Average of Garden Gully and Fitzgerald Creek coals.

  • (6) Blackball Mine, top 4ft (C.S. 471)*

  • (7) Blackball Mine, middle 4ft. (C.S. 472)*.

  • (8) Blackball Mine, bottom 4ft. (C.S. 473)*

  • (9) Average of Blackball seam.

The range of the analyses is small but to facilitate comparison, averages are given for both groups. The most striking resemblances are the high-sulphur and low-ash contents, both of which are extreme values not reached by any other seams in the Grey coalfield. The high ratio of volatile matter to fixed carbon is also significant. The most striking difference is the lower water content of the Blackball group, and to a lesser extent the decrease in the ratio of volatile matter to fixed carbon. These differences are those which would be expected if the Garden Gully coal were to be metamorphosed to the rank of the Blackball coal, the large decrease in water content being accompanied by a smaller decrease in the amount of volatile matter.

It is not contended that correlation could be made solely on the basis of the similarity of analysis, but the differences are certainly not sufficient to justify placing the coals in different formations.

[Footnote] * Dominion Laboratory analyses.

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Although the present paper shows that Tertiary sediments only a few miles apart cannot be safely correlated on the basis of coal rank and induration of strata, this could not have been established without fossil evidence.

References.

Finlay, H. J. and Marwick, J., 1940. The Divisions of the Upper Cretaceous and Tertiary in New Zealand. Trans. Roy. Soc. N.Z., vol. 70, pp. 77–135.

Henderson, J.., 1917. The Geology of the Reefton Subdivision. N.Z.G.S. Bull. 18.

Morgan, P. G., 1911, The Geology of the Greymouth Subdivision. N.Z.G.S. Bull. 13.

—— and Bartrum, J. A., 1915. The Geology and Mineral Resources of the Bullet-Mokihinui Subdivision. N.Z.G.S. Bull. 17.

Appendix.
Foraminifera from Garden Gully and Fitzgerald Creek, Westland.

The microfaunas from Garden Gully and Fitzgerald Creek show that horizons from Lower Kaiatan to Upper Waitakian are represented. As elsewhere in Westland, no evidence of Bortonian age has appeared. The oldest faunas throughout this area already contain species believed to be not older than Kaiatan, and there is no sign of the key Bortonian species of the Hampden beds or the Wanstead formation. The oldest molluscan beds at Garden Gully and McKay's Monalaria sandstone from Ten Mile Creek contain no trace of microfauna. Seven samples have been examined, three in one section, three in another, and an isolated one.

Section I. Garden Gully, 38 chains at 105° from Trig. P.

F. 6354. Glauconitic base of mudstone. Very poorly fossiliferous, only Cyclammina sp. and Ditrupa tubes remaining, all calcareous forms leached out. No evidence of age.

F. 6283. Garden Gully, 30 feet above base. Well preserved fauna containing some 107 species, amongst which are:—

Arenonodosaria robusla (Stache) Bulimina pupula Stache
Arenonodosaria antipoda (Stache) Robertina n.sp.
Gaudryina reussi Stache Ceratocancris n.sp.
Gaudryina n.sp. Cerobertina kakahoica Fin.
Robulus aff. echinatus (d'Orb.) Nonion aff. pompilioides (F. & M.)
Robulus cultratus Mont. Nonion maoricum (Stache)
Vaginulinopsis hochstetteri (Stache) Anomalina aotea Fin.
Marginulinopsis spinulosus Anomalina n.sp. vitrinoda Fin.
(Stache) Anomalina eosuturalis Fin.
Siphonodosaria cf. globulifera Anomalina n.sp. aff. subnonionoides
(Kreuz.) Fin.
Siphonodosaria basicarinata n.sp. Gyroidina aff. orbicularis d'Orb.
Dentalina subcostata Chap. Gyroidina aff. neosoldani Brotz
Nodosaria aff. raphanus Linne. Gyroidina scrobiculata Fin.
Guttulina communis d'Orb. Epistomina elegans d'Orb.
Plectofrondicularia whaingaroica Halkyardia sp.
(Stache) var. Cibicides parki Fin.
Uvigerina bortotara Fin. Cibicides aff. thiara (Stache)
Bulimina truncanella Fin. Globigerinoides index Fin.
Bulimina aff. striata, d'Orb. Sphaeroidina n.sp.

This is a low Kaiatan fauna.

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F. 6284. Garden Gully, 50 feet above F. 6283, and 200 feet above coal and greywacke. 67 species mounted, amongst which are:—

Karreriella novozelandica Cush. Nonion aff. pompilioides (F. & M.)
Lestcrella cf. levis Fin. Nonion maoricum (Stache)
Arenodosaria robusta (Stache) Anomalina cosuturalis Fin.
Arenodosaria antipoda (Stache) Anomalina n.sp. aff. vitrinoda Fin.
Gaudryina reussi Stache Anomalina n.sp. aff. subnonionoides
Gaudryina n.sp. Fin.
Robulus cultratus Mont. Gyroidina cf. orbicularis d'Orb.
Vaginulinopsis hochstettery (Stache) Gyroidina scrobiculata Fin.
Dentalina subcostata Chap. Eponides ecuadorensis (C. & M.)
Bulimina truncanella Fin. Epistomina elegans d'Orb.
Bulimina aff. striata d'Orb. Cibicides parki Fin.
Bulimina pupula Stache Cibicides aff. thiara (Stache)
Cerobertina kakahoica Fin. Globigerinoides index Fin.
Ceratocancris n.sp. Fin. Sphaerodina n.sp.

Practically identical in fauna and age with the previous sample. The occurrence in both these of Cyclammina and Ditrupa specimens exactly similar in appearance to those in F. 6354 suggests that the latter is merely a basal, leached part of the Kaiata.

Section II. Fitzgerald Creek, 168 chains at 145° from Trig. P.

F. 6355. Fitzgerald Creek, 200 feet stratigraphically above the coal, i.e., about the same horizon as F. 6284. The fauna, however, is much poorer and lacks all the large species. Only the following were observed:—

Cyclammina sp. Epistomina elegans d'Orb.
Karreriella novozealandica Cush. Cibicides parki Fin.
Uvigerina bortotara Fin. Cibicides aff. thiara (Stache)
Cerobertina kakahoica Fin. Globigerinoides index Fin.
Nonion maoricum (Stache) Sphacroidina n.sp.

Also a number of Pteropods of the Lornia type. This is merely a poorer representative of the F. 6284 fauna, but is much more like the average Low Kaiatan fauna of this area. The preservation and size of the F. 6283 and F. 6284 faunas is somewhat exceptional, and plainly connects the Kaiatan with the Tahuian. There is little doubt that F. 6283 and F. 6284 are Tahuian faunas, quite similar to those from McCullough's Bridge, and the stratigraphic equivalence of F. 6284 to F. 6355, which is a normal low-Kaiatan type of fauna, indicates fairly plainly a correlation that has been suspected for some time—that the Tahuian is merely the lower part of the Kaiatan. F. 6357. Fitzgerald Creek, above F. 6355 (400 ± feet above coal).

Very poor and hard sample, few identifiable foraminifera seen:—

Robulus sp. Ehrenbergina marwicki Fin.
Nonion maoricum (Stache) Cibicides n.sp.

Little can be said about this, except that it is younger than Waitakian and probably older than Hutchinsonian.

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Isolated Sample.

F. 6356. White clayey limestone boulder, Fitzgerald Creek, 176 chains at 140° from Trig. P.

This contained a large, well preserved fauna, amongst which the following were observed:—

Valvulina pennatula (Batsch) Cerobertina kakahoica Fin.
Textularia aff. cuspis Fin. Cassidulina subglobosa Brady
Textularia aff. foliacca H.A. & E. Nonion maoricum (Stache)
Frankeina n.sp. Anomalina aotea Fin.
Gaudryina reussi (Stache) Gyroidina aff. zelandica Fin.
Arenodosaraia antipoda (Stache) Rotaliatina sulcigera (Stache)
Haeuslerella textilariformis Epistomina elegans d'Orb.
(Stache) Cibicides thiara (Stache)
Vaginulinopsis hochstetteri Cibicides aff. novozelandicus
(Stache) (Karr.)
Lagena aff. orbignyana Seg. n.var. Cibicides verrucosus Fin.
Bulimina pupula Stache Cibicides cf. collinsi Fin.
Siphogenerina striatissima (Stache) Discorbis scopos Fin.
Bolivina pontis Fin. Globigerina angipora Stache
Chilostomella aff. grandis Cush. Sphaeroidina bulloides d'Orb.
Chilostomella several spp.

This is plainly a Whaingaroan fauna, probably low down. It is almost identical with one from low in the Cobden limestone (F. 5952: 20 chains east of the bridge to Greymouth, along the main Cobden-Runanga road).