Oliver, R.L. 1948 The Otaki sandstone and its geological history. Wellington: H.H. Tombs Ltd. Geological memoirs / New Zealand Geological Survey 7. 49 p.
Abstract: An elevation of several hundred feet of the western side of the Tararua block in the Early Pleistocene caused the rivers of the south-west Wellington coastal plain to erode deeply in the headwaters and deposit the material as extensive alluvial fans. These constitute the basal sediments of the area under discussion, and consist mainly of gravels as far as the Waikanae, Otaki, and Ohau Rivers are concerned, the Manawatu deposits being partly sand eroded from the Tertiaries. Later depression, which was associated with a reduction in supply of sediment by the rivers, submerged these coalescing alluvial deposits, enabling the sea to advance and lap the greywacke foothills of the Tararuas and extend up some of the valleys in the form of estuaries. During this time, a considerable amount of sand was being carried out by littoral wind-driven currents southward along the coast from the river mouths of South Taranaki and thereabouts and deposited by the advancing sea. At about the end of the Pleistocene the sea once again began to retreat and exposed the newly-deposited marine formation, known as the ‘Otaki Series’, or ‘Horowhenua Sandstone’. The beds are here renamed the ‘Otaki Formation’. The sea reworked the sand as it retreated, and redeposited it as beach and perhaps sand dune. The rivers and streams commenced to erode the sand and deposit alluvium. The uplift was slow, but comparatively recently the rate of uplift of the Tararua block appears to have increased markedly, causing considerable rejuvenation of the streams and rivers and supplying so much material to the waves that it has piled up as dunes. The composition of the beach and dune sands was affected in that a higher percentage than before of the sand grains was derived from the greywacke and thus reduced the proportionate number derived by littoral drift from farther north. The southern part of the plain, south of the Otaki River, does not seem to have taken part in this energetic movement, but seems to have remained more or less stationary. Perhaps it even sank a little, enabling the sea to advance and cliff the alluvium and Otaki Formation. Slight uplift again caused the sea to retreat and allowed dunes to accumulate as they were already doing farther north. This accumulation of dunes has caused the damming of the small streams and the formation of swamps. (auth)
