The Gippsland Bores.
Since the publication of the papers above referred to, there has appeared a very important monograph by Miss Crespin (The Stratigraphy of the Tertiary Marine Rocks in Gippsland, Vic.; Pal Bull., No. 4). No new information on the larger foraminifera is presented, but otherwise it is a comprehensive review of the Gippsland Tertiaries from Anglesean to Kalimnan, as shown in both surface and subsurface sections; all classes of fossils are discussed, and the ranges charted. Doubtless there is much unpublished molluscan evidence regarding the Victorian Tertiaries, and different opinions may arise about the conclusions reached by Miss Crespin, but an overseas author can form opinions only on the published evidence, and at the present time the Victorian Tertiary column is more adequately and more equably known from the microfauna than from the macrofauna. Since it is necessary to have a picture of the known Australian horizons before correlation can be attempted, a brief account of Miss Crespin's stratigraphic conclusions is here presented.
Core evidence is given by her for all stages from Anglesean to Kalimnan, and the practice instituted by Finlay and Marwick of nominating Standard Sections for the various New Zealand stages is continued in the Australian Tertiary. She believes (p. 5) that the fauna of Singleton's Cheltenhamian stage “has been incompletely described … suggesting a close relationship with the Kalimnan.” No other evidence is adduced for discarding the Cheltenhamian, and it may be premature to neglect it entirely. The actual passage beds met with in the bores between top Balcombian and basal Kalimnan are named by her the Mitchellian stage (p. 25), and faunas are listed. As regards the much-debated Balcombian, she notes (p. 16) that “It is impossible to support Singleton's recent view (1941) that the Batesford (Lepidocyclina) horizon is a stage directly underlying the Balcombian. Evidence from borings in Gippsland is in favour of his earlier statement (1937) that it is a facies of the Balcombian.” She therefore suggests that Balcombian be used as the stage name and proposes a threefold division into substages, with no striking lithological break between them. Her classification is as follows:–
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Maximum||thickness||240 ft.||Kalimnan||(2 zones)|
|"||"||771 "||(Bairnsdale||(2 zones)|
|"||"||857 "||Balcombian||(Batesford||(2 zones)|
|"||"||774 "||Janjukian||(2 lithologic units)|
The longest single section covering all these beds is the 3,524 ft. of the Holland's Landing Bore, and the total maximum thickness of all these stages in Australia is only some 5,200 ft.; in New Zealand, approximately all these are covered in one section south of Gisborne 20,000 ft. thick, and the total maximum amount would be far over that figure. This great disparity in formation thickness must of necessity involve different methods of attack in New Zealand, with consequent variation in viewpoint.
The name Bairnsdale is applied to the beds in all surface and subsurface sections overlying the Orbitoid horizon but underlying Mitchellian (includes the typical Balcombian of Balcombe Bay, Corio Bay, bryozoan limestone of Muddy Creek, Hamilton, etc.). Batesford is applied to the Orbitoid zone (includes the limestone of Clifton Bank. Hamilton, etc.). Longford is applied to the beds overlying the Janjukian but underlying the Orbitoid zone and is Crespin's earlier “B.1 stage” of the Holland's Landing Bore (mostly in bores, but a type surface section at Dowd's Quarry; includes little outside of Gippsland except Rocky Point, Torquay, above type Janjukian). The Kalimnan, Janjukian, and Anglesean are unaltered, but much faunal information is given on all of them. The Anglesean is shown (p. 9) to have good calcareous faunas in places, and its faunal relationship to the Janjukian is even closer than formerly believed, though no junctions are exposed in Gippsland (p. 8); it is stated to be undoubtedly still Miocene. The microfaunas quoted make it fairly evident that the Anglesean corresponds quite closely with certain facies of our basal Lower Ihungia, e.g., the Cycloclypeus Orbitoid bed at Tarakohe, discussed later in this paper. The Mitchellian stage is persistent in all bores, and shows a distinctive lithological break below the Kalimnan, but appears to grade down into Balcombian.
Examination of the evidence available to me from this and other published papers and from my own slides of Australian and New Zealand faunas indicates that the present position for correlation is as follows:—