A Post-Tertiary Micro-Fauna in a Concretion Containing Cancer novae-zealandiae
[Read before the Otago Branch, October 12, 1948; received by the Editor, October 21, 1948.]
In the Museum of the Geological Department of Otago University is the proximal portion of a crab which bore the label Cancer cf. novae-zealandiae, Burnside. This part of the carapace and under-portions, which retains its original colouring, had been carefully freed from the less-coherent matrix in which it was embedded, but contains within the skeleton of the limbs and body-cavity a small amount of firmly cemented, grey, fine-grained matter similar to that of the uncemented Burnside mudstone near Dunedin, which is of Kaiatan (“Tahuian”) Upper Eocene age. (Finlay and Marwick, 1940, 1947.) In the absence of any record of the collector of the specimen it was not possible to check, by direct inquiry, the correctness of the locality mentioned, concerning which doubt arose. Comparison of the specimen with a modern sample of C. novae-zealandiae (Jaquinot and Lucas) substantiated the specific identification of the crab. It seemed improbable, however, that a Recent species of crab would occur in Upper Eocene Sediments Moreover, the widespread occurrence of crustacean remains in concretions in muds now accumulating on various portions of the coastline of Australia* (Etheridge and Macculloch, 1916, and Chapman, 1924) and South-Western New Guinea (van Straelen, 1928), and also in those of Auckland Harbour (Bartrum, 1917), suggested that the specimen here figured was similarly quite modern. The largest sample of the cemented matrix which could be removed from our specimen without damaging it (about a fifth of a cubic centimetre), was carefully separated from it by Professor Walsh, using a dental drill, and when crushed and examined microscopically showed the presence of sufficient determinable micro-fossils to justify the conclusion that the specimen was indeed quite modern. The following notes summarise the observations made by one of us (H. J. F.). There were present three species of foraminifera: Globigerina sp. indet., distinct from any form known in the Burnside Mudstone; Elphidium cf. advenum Cushman, resembling Recent forms of this group, but fatter and with blunter angles than those of any members of this group known in Oligocene beds; also Streblus aoteanus Finlay, a common Recent species found only in shallow water, and belonging to a genus that has not yet been found in Pre-Pliocene
[Footnote] * Among the most common of these is Thalassina anomala Herbst, which is closely allied to the Hermit crabs. “It must have swarmed over the mud flats of Northern Australia in Pleistocene times, since its remains are found in various localities in countless numbers. By the slight elevation, through coastal warping, these mud flats were drained and became beds of hardened clay with fossils” (Chapman). Specimens of these obtained at Port Darwin by one of us (W. N. B.) are in the Geological Department of Otago University.
rocks in New Zealand and is unlikely to occur in sediments deposited in water as deep as that in which the Burnside Mudstone accumulated. All three foraminifera have a glossy surface and lustre, contrasting with the dull whitish appearance of Burnside foraminifera. White porcellanous sponge spicules and echinoid spines, though common in the Burnside Mudstone, are absent from our material, which contains, however, two species of ostracods with fresh glossy surfaces, both distinct from any of the few known Burnside species. Our material yielded also fragments of mollusca, the form recognisable being a species of Lasaca, a Recent genus common in very shallow (inter-tidal) water, rarely found fossilised and but doubtfully recorded in Pre-Pliocene sediments.
In view of the consistency of the microfaunal evidence as to the age and formation-environment of the concretionary matrix of our specimen, it seems safe to conclude that it was deposited in shallow waters in relatively modern times, and that the species Cancer novae-zealandiae must be excluded from any list of Burnside fossils. Possibly the specimen was derived from the muds of Auckland Harbour, though Professor Bartrum (1917) records only that “small crabs are exceedingly common nuclei of small rounded concretions.*
Our thanks are due to Drs A. Wade, A. B. Walkom, and L. K. Ward for assistance in obtaining reference to the accounts of Recent crustacca in concretions forming in the mud about the Australian coast.
Bartrum, J. A., 1917. Concretions in the Recent Sediments of the Auckland Harbour, New Zealand. Trans. N.Z. Inst., vol. 49, pp. 425–428.
Chapman, F., 1924. Western Australian Fossils, Wade Collection. Description of Plates in Dr A. Wade's Report on the Petroleum Prospects of the Kimberley District of Western Australia and the Northern Territory. Parliamentary Reports, Commonwealth of Australia.
Etheridge, R., Jun., and Macculloch, A., 1916. Sub-fossil Crustaceans from the Coasts of Australia. Rec. Aust. Museum, vol. 12, pp. 1–14.
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.
— 1947. New Divisions of the New Zealand Upper Cretaceous and Tertiary. N.Z. Journ. Sci. Tech., vol. 28, (sec. B), pp. 230–236.
Straelen, J. van, 1928. Nova Guinea. Resultats de L'Expédition Scientifique Nécrlandaise à La Nouvelle Guinée, vol. vi, Géologie, pt. 3, p. 63. E. J. Brill, Leiden.
[Footnote] * The rapidity with which concretions may form can be illustrated by an example. The mud dredged from beside the wharves in Woolloomooloo Bay, Sydney Harbour, New South Wales, has yielded concrete-like aggregates of naturally cemented broken crockery thrown overbourd from ships. Samples of these are (or were) displayed in the Mining Museum, Sydney. The addition to the seawater of dissolved carbonates of lime with a little iron derived from the cementing matter in the sandstones surrounding the harbour may, perhaps, have favoured the rapid formation of these concretions.