The geology of the Dannevirke Subdivision

(Inc. GST)
(Ex. GST)
Write a Review

Lillie, A.R. 1953 The geology of the Dannevirke Subdivision. Wellington: Department of Scientific and Industrial Research. New Zealand Geological Survey bulletin 46 156 p.

Abstract: A major furrow or trough which existed during the Cretaceous and Tertiary periods was subjected to minor movements and oscillations of the sea floor, filled with sediments, and at the close of Tertiary time uplifted, folded, and faulted by a principal orogeny - the Kaikoura orogeny. The sediments of Cretaceous and Early Tertiary age, as measured compositely in these areas where the sequence is most complete, have a thickness of at least 13,000 ft. The lithology is often very monotonous and beds of very different age may be lithologically identical. The width of the furrow during the Cretaceous period cannot be determined, but a region of shallowing, probably a major anticlinal belt, existed on the site of the present coast. During most of the Tertiary period the trough was bounded to the west by a coast-line situated a short distance east of the present Ruahine watershed. In the east the anticlinal belt on the site of the present coast was mobile and occasionally emergent. During the Early Tertiary the axis and region of deepest sedimentation in the trough coincided with the tectonic axis of the present Whangai Range. The trough was elongated and comparatively narrow - some twenty-four to thirty miles wide. The commencement of the final folding and faulting was marked by preliminary uprise and warping along the former axis of deepest sedimentation. As a result of these preliminary movements the axis of principal sedimentation was shifted to the west, where a further 8000-9000 ft of Late Tertiary (Pliocene) strata were deposited before the whole region finally became emergent at the end of Pliocene time. The crustal shortening induced by the Tertiary movements over the whole region was probably about one-seventh to one-eighth of the original unfolded width. The region of the coast is described as having been an anticlinal belt, since there was mobility and emergence at several time intervals but no evidence that the emergence was very widespread or that the region was an eastern limiting frame of great dimensions for the Cretaceous-Tertiary deposition. It is more probable that this coastal region constituted a welt over which the sea transgressed periodically, and that the Dannevirke Subdivision as a whole was a trough within a larger geosyncline that extended far to the east of the anticlinal belt and the present coast-line. The Late Tertiary folding movements were not so intense as those often associated with large mountain structures, but there was a definite underthrust from the east or south-east directed towards the major geanticline of the Ruahines. Later faulting has continued intermittently up to the present day, producing the tilted peneplain remnants and earthquake scarplets prominent in the subdivision. (auth)