Significance of Fossils from the Huiroa Oil-bore, Taranaki.
[Read, by permission of the Director of the N.Z. Geological Survey, before the Wellington Philosophical Society, 10th October, 1923; received by Editor, 6th October, 1924; issued separately, 31st March, 1926.]
Three shells from between the depths of 4,550 ft. and 4,760 ft. in the Huiroa oil-bore (twenty-four miles south-east of New Plymouth, or fifteen miles by a road north-east of Stratford), forwarded to the Geological Survey in 1916 by Mr. J. Henchman, and identified by Mr. H. Suter, * are now classed by Dr. Marwick † as—
Aethocola cliftonensis Marwick,
Streptopelma henchmani Marwick,
Turritella carlottae Watson (still living).
These fossils can be used to refer the beds from which they came to their place in the Tertiary succession recognized in Taranaki (see p. 317). The most important for this purpose is Streptopelma henchmani, ‡ which has been collected by the writer on the coast between Pukearuhe and the mouth of Onairo Stream—the only locality besides the bore in which it is known to occur—in beds belonging to the lower 1,400 ft. of the Onairo series. Aethocola cliftonensis ranges from the Onairo series down to the underlying Tongaporutu series, and the Recent species Turritella carlottae, according to Dr. Marwick, also ranges down to the Tongaporutu series. The above evidence thus indicates that the bottom of the well, at 4,921 ft. (or about 4,250 ft. below sea-level), is probably still in the Onairo series, though possibly in the Tongaporutu series. The stratigraphical evidence tends to place the bottom of the bore at least as low as the base of the former series.
Since at New Plymouth only the Onairo beds have yielded oil—deep boring into older strata having so far proved unsuccessful—a knowledge of the position of the base of the Onairo series will be of use in testing this known petroliferous series in other parts of Taranaki. About 2,000 ft. of Onairo beds is exposed on the coast as far west as a point six miles east of the mouth of the Waitara; and if roughly the same dip is maintained, and no big faults displace the strata, the base of the series lies at about 4,000 ft. below sea-level at New Plymouth. A line drawn south-east from New Plymouth to a point a little to the north-east of the Huiroa bore is believed to indicate approximately the base of the Onairo series at 4,000 ft. below sea-level. To the north-east it lies at shallower depths, reaching sea-level at the southern end of White Cliffs.
Any fossils, even if fragmentary, obtained during drilling in Taranaki are of interest, and some may be of value in determining the position of the beds penetrated.
[Footnote] * N.Z. Geol. Surv. Pal. Bull. No. 8, p. 24, 1921.
[Footnote] † For description of the first two species see paper by Dr. Marwick at page 321.
[Footnote] ‡ Termed Verconella n. sp. in N.Z. Geol. Surv. 17th Ann. Rep., Parliamentary Paper C.—2c, p. 8, 1923.