Kear, D. 1987 Te Akau : notes on the geological map of New Zealand 1:63,360 sheet N55. Lower Hutt: New Zealand Geological Survey. Record / New Zealand Geological Survey 17 44 p.
Abstract: Te Akau District forms about a twelfth part of the western coastal region of South Auckland, where Mesozoic rocks are folded regionally into the Kawhia Syncline, and Tertiary rocks, particularly of the Te Kuiti Group, are also well exposed. The watershed between the Tasman Sea and the Waikato River system passes SE through this hilly District. Physiography strongly reflects geology. Areas of Mesozoic rocks are steeply eroded with strike ridges formed by coarser formations. The low-dipping Tertiary rocks underlie gently to moderately-steep slopes. The coarser beds form near-vertical bluffs. Coastal cliffs typically expose Tertiary rocks up to 30-35 m a.s.l., above which over 100 m of early Quaternary consolidated sands form steep coastal hills through which only the Ohuka, Waikaretu, Waimai, and Taurerei Streams have cut broad valleys. Later Quaternary sediments include: lower coastal sands still showing dune form; Waikato River alluvium in terraces up to 8 m above river level; and widespread, if narrow, flood-plain alluvium. Extinct Quaternary basalt volcanoes in the NW range from lava cones passing out of the Planeze Stage of erosion, to sea stacks in the Skeleton Stage. Formations in the following groups are described in detail: Newcastle Group, Putataka Supergroup, Rengarenga Group, Kirikiri Group, Apotu Group, Huriwai Group, Te Kuiti Group, Waitemata Group, Kaihu Sand Group, Kerikeri Volcanic Group, Tauranga Group. Economic and engineering geology of the District are described. Useful resources of sand and aggregate and ironsand exist in the area. There are no great geotechnical hazards, although some of the siltstones are liable to slumping.