Introduction

Consolidated, unfossiliferous, wind-blown and water-laid sands, grey muds and pumiceous silts with bands of lignite form a long coastal strip in the northwestern part of Waitemata Survey District, Auckland (Fig. 1). They constitute the long peninsula that runs south from Kaipara South Head (passing below sea-level so that the basement on which they rest is not visible) and extend to south of Muriwai, where they underlie a well-defined high-level plateau and cover volcanic beds of the Manukau Breccia (lower Miocene).

Dieffenbach (1843) noted the same beds near Dargaville, and Hochstetter (1867) described similar sands and silts from the southern shores of Manukau Harbour as his Lignite Formation Cox (1881) outlined the distribution of these younger beds and named them “consolidated sands with lignite.” For the Dargaville-Rodney area Ferrar (1934) grouped these beds as the Kaihu Sands. Similar Pleistocene beds have been recorded by Searle (1944) on the northern shores of Manukau Harbour and by Gilbert (1921) on the peninsula which terminates at Manukau South Head.

The writer believes that their deposition at first took place under marine conditions but later was largely estuarine and that it began with a major rise of sea-level in the late Pliocene and was terminated by Flandrian transgression at the close of Pleistocene time. As in other parts of the world there was continuous regression of sea-level throughout the Pleistocene and in the South Kaipara district withdrawal took place from a position 550 feet higher than at present. The oscillatory effects of glacial eustasy varied the general theme of regression, and the resulting fluctuations of sea-level were reflected in the sediments of Kaihu Group by deposition of the three younger formations which are separated by erosion intervals.

suggests that extrapolation of the Otahuhu succession to the Kaipara district may not be as speculative as it appears.^* Reference to a possible Pliocene age for the basal beds of Kaihu Group or for sea-level movements is therefore made only on the tentative basis of the assumption outlined above. The rise of sea-level responsible for the deposition of Kaihu Formation, the oldest formation of Kaihu Group, at a maximum height about 600ft. above the position of the Otahuhu Pliocene beds may therefore be regarded as a continuance of late Pliocene transgression (Fig. 5). This is an extremely speculative suggestion which probably is an over-simplification of the true sequence of events; but it will serve as an hypothesis in the absence of any further information concerning this part of the Pliocene-Pleistocene history of the North Auckland area. Nevertheless, in this paper the development of the 550ft. surface of erosion and deposition is taken as Pleistocene in age.

The division of Pleistocene time into Early, Middle and Late has been carried out according to the thickness, areal extent and nature of the various formations within Kaihu Group. The basis for subdivision in this manner is fundamentally unsound since it presupposes uniform rates of sea-level rise and fall, an unvaried climate, and a constant tempo of erosion. However, the periods of time allotted to the various formations must be broadly correct.

The end of Pleistocene time is taken at the commencement of Flandrian transgression (Fig. 5); i.e., at the end of the last glacial phase when return of melt water to the ocean caused a final submergence of the North Auckland area and formed the present highly embayed coastline. The term “Flandrian “has been used by Zeuner (1950, p. 128) and Cotton (1951) in the same manner. Under this scheme all post-Flandrian events are equivalent, so that “Recent” is synonymous with “post-glacial”.