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New Waitaki map crosses provincial lines - 25/06/2002

A new geological map of the Waitaki area shows the region in more detail than ever before.

Waitaki map

It updates existing geological maps of the area, published in the 1960s, and combines a vast amount of published and unpublished material, plus new research, to produce a valuable resource about the geology of North Otago and South Canterbury.

Geology of the Waitaki Area covers a large area of the eastern South Island, including the eastern part of Central Otago and the southern end of the Mackenzie Basin. It also extends 60km offshore over the Canterbury shelf and slope. Inland it extends as far as Middlemarch, St Bathans and Omarama.

It is the latest of a new series of geological maps covering the whole of New Zealand, published by the GNS Science Limited (GNS). Started in 1996, the series of 21 maps is scheduled for completion in 2008.

It takes the form of a 64-page well-illustrated book with a full colour folded map at 1: 250,000 scale in a sleeve in the back cover. Illustrations in the book, which include photos taken by one of New Zealand's leading landscape photographers Lloyd Homer, are accompanied by explanations that are mostly pitched at about senior secondary school level.

The map text summarises the geology and tectonic development of the Waitaki region. Much of the Otago area is underlain by schist bedrock, while north of the Waitaki River greywacke rock predominates.

The younger sedimentary rocks are rich in fossils, including remains of plesiosaurs, dolphins, sharks and many other marine animals. These fossils are of great importance for the study of ancient environments and ecology. The text also highlights aspects of economic geology and potential geological hazards.

Nine pages are devoted to the geological resources of the Waitaki region including the goldfields of the Macraes area and the historic alluvial gold workings. The Macraes gold project is one of the largest gold mines in New Zealand.

Non-metallic resources currently being extracted in this region include groundwater, limestone and marble for agriculture and industry, and building stone. There are abundant resources of greywacke aggregate in the Waitaki valley, but areas underlain by schist rocks and softer sedimentary rocks have more difficulty finding good roading materials.

Three offshore wells have been drilled for oil and gas. Although none have proved commercial, petroleum geologists consider the offshore area to have some petroleum potential.

The Waitaki region has had a low level of earthquake activity, relative to other parts of New Zealand. However, seismic instruments have recorded shaking from both local and distant earthquakes. Many faults are shown as "active", meaning that movement has occurred along them in the recent geological past. Scientists consider they have potential to move again in the future, map compiler Jane Forsyth says.

Major fault systems extend up the Waitaki, Hakataramea and Waihemo (Shag) valleys, and further active faults are known near Middlemarch, Ranfurly and Omarama. In addition, the map shows many more "inactive" faults. These are faults that have not moved in the past 100,000 years.

Other geological hazards mentioned are tsunami, coastal erosion and sea level rise, and landslides which affect many parts of the region.

Ms Forsyth says regional councils and irrigation scheme planners had already made use of the digital data from which the map was produced. Others expected to benefit from the map database include engineers, developers, scientists, and mineral exploration companies. People with an interest in geology and Otago/Canterbury mining history will also find it useful.

The map is available from the GNS Science Limited (GNS) for $25.

Contact: Jane Forsyth,
Geologist,
GNS,
Dunedin
Ph (03) 477 4050
Fax (03) 477 5232