Provisional geological map of 1:50 000 sheet T21AC (Hautapu)

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Ker, D.S. 1991 Provisional geological map of 1:50 000 sheet T21AC (Hautapu). Lower Hutt: DSIR Geology & Geophysics. New Zealand Geological Survey report G 144. 19 p., 1 map

Abstract: In this part of the Wanganui-Rangitikei sedimentary basin, a later Tertiary, largely marine sequence unconformably overlies basement comprising greywacke, argillite and schist of inferred Torlesse Supergroup. The Tertiary sequence ranges from Tongaporutuan (Late Miocene) in the north to Waipipian (Middle Pliocene) in the south. Transgression was from both south and west. Sedimentary facies changes clearly show a general fining from east to west, away from the source of the Ruahine Ranges. The massive nature of the sediments indicates relatively uniform rates of deposition in depths of up to 400 m. Quaternary deposits include Murimotu Lahars in the northwest, and Hautapu Lahars in which three separate episodes can be recognised. A series of alluvial terraces is restricted in distribution, but the main aggradational surface at Taihape is correlated with the Ohakea 2 Terrace in the Rangitikei Valley. The main economic deposits are the alluvium, lahars, and cemented coquina limestone which are a local sources of material for aggregate, fill and roading. The area is one of high earthquake risk, and is close to the active volcanoes of the central North Island. Landslides are a common feature in the finer grained sediments, particularly in the west. (auth)