The geology of the Homestead stream area, Lower Hakataramea Valley, South Canterbury

Abstract

This thesis documents the geology of an area in the Lower Hakataramea Valley, some 9 miles north of Kurow, and 20 miles west of Waimate. Basement rocks include greywacke and argillite of Torlesse Supergroup (chlorite 1/2).

Hurst Lea Sandstone, possibly Cretaceous post Rangitata Orogeny debris, occurs as fault slivers.

Work centred on Notocene sediments of Oamaru Group which is subdivided into Hogburn (basal coalmeasures), Naseby (marine sediments), and Wedderburn (upper coalmeasures) Subgroups. Hogburn Subgroup includes, (1) Homestead Residual Clay (quartzose clays accumulated on Cretaceous peneplain); (2) Papakaio Formation (transgressive terrestrial Quartz sands and coal measures). Naseby Subgroup includes (1) Tapui Glauconitic Sandstone, subdivided into Incholme Glauconitic Sand (marginal marine concretionary layered, fossiliferous sands and silts) and Black Point Lens (marine, crossbedded sand barrier); (2) Kokoamu Greensand (marine, fossiliferous, calcareous greensand); (3) Otekaike Limestone, subdivided into Maerewhenua Glauconitic Limestone (well indurated, Sparsely fossiliferous limestone) and Miller Member (richly fossiliferous, concretionary, glauconitic, calcareous silts); (4) Rifle Butts Formation, subdivided into Waitoura Marl (offshore marine, richly fossiliferous, glauconitic sands and silts), Balmoral Sands (marine, bioturbated, crossbedded sand barrier), Henrys Road Greensand (lagoonal, glauconitic silts). Wedderburn Subgroup includes regressional terrestrial quartz sand.

Oamaru Group sediments represent an almost classic transgressive/regressive cycle, that reached peak transgression during Duntroonian Time (Kokoamu Greensand). Their accumulation in the mapped region was influenced by the Hakataramea High (a local area of positive relief on the peneplain): Hogburn sediments are locally missing on the high itself, and Black Point Lens (found only near the high), Otekaike Limestone (more clastic near the high), Waitoura Marl (more fossiliferous near the high), Balmoral Sand and Henrys Road Greensand (found only near the high) all show facies variation reflecting the continued influence of the high during the whole sedimentary cycle.

Pleistocene stratigraphy includes, (i) Smilie Formation (highest terrace, weather greywacke boulders), (ii) Georgetown Formation (second highest terrace, weather greywacke boulders), (iii) Morven Formation (Third highest terrace, fresh greywacke), (iv) Waikura Formation (lowest terrace, fresh greywacke).