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A new geological map of the Murihiku area, including Stewart Island/Rakiura, shows the region in more detail than ever before. The map has been generated from a computer database using Geographic Information Systems (GIS) technology, which means the map data can be updated regularly as new information comes to hand. The new map replaces existing geological maps of the area, published in the 1960s, and combines a vast amount of published and unpublished material, plus new research, to produce a valuable resource about Southland geology. The large full-colour 1:250,000-scale geological map is tucked into a sleeve in the back cover of a well-illustrated 74-page companion book. This is illustrated in colour throughout, and includes photos taken by one of New Zealand's leading landscape photographers, Lloyd Homer.. Geology of the Murihiku Area covers 18,000 square
kilometres of south Otago and Southland, extending from the Catlins
west across the Waimea and Southland plains to the Takitimu Mountains
and Waiau River, and south over Foveaux Strait to Rakiura. The region's geology is dominated by 150-250 million-year-old sedimentary rocks, rich in fossils and folded into the Southland Syncline, which runs from the Catlins to Te Anau. The Waimea and Southland plains, and the Eastern Southland coalfield, lie in old river valleys across the syncline. In contrast, Stewart Island consists of granitic "basement" rocks ranging from 350 to 100 million years old. The Takitimu Mountains in the west are the remains of a chain of volcanic islands 280 million years old. The most significant advance arising from this recent mapping is in the wealth of detail shown on Stewart Island. Far from being the simple mass of granite shown on older maps, the island is now known to consist of many different rock types, separated by major fault systems. This revision of Stewart Island geology is the result of seven seasons of arduous field work by one of the authors, Dr Andrew Allibone. The onshore part of the map was compiled by GNS geologist Ian Turnbull, who has 30 years experience in mapping in the southern South Island. The map text summarises the geology and tectonic development of the Murihiku region, and highlights aspects of economic geology, including the extensive coal reserves of Eastern Southland. It lists other on-shore commodities currently being extracted as rip-rap, peat, gravel aggregate, dunite (serpentine), limestone, gold, clay and groundwater. Several pages in the text are devoted to a discussion of geological hazards in the region. The mapping has shown that Southland, far from being an earthquake-free zone, does in fact have a significant seismic hazard. Numerous active faults were identified during mapping, including a major fault line crossing the Five Rivers Plain and others around the Takitimu Mountains. Other geological hazards identified include slope instability, tsunami, ground shaking, and liquefaction, with a remote possibility of renewed activity on the volcanic Solander Island in western Foveaux Strait. Sea-floor information on the map is derived from seismic surveys by the oil and gas exploration industry and by NIWA. It shows the onshore geology in relation to the offshore Great South and Solander Basins. Onshore exploration for oil and gas in the Winton and Waiau basins has been unsuccessful to date, but geologists rate the offshore sedimentary basins as promising frontier exploration regions. Ian Turnbull said district and regional councils had already made use of some of the digital data from which the map was produced. Others expected to benefit from the map database include planners, the Department of Conservation, engineers, developers, mining companies, oil exploration companies, tourist operators, educators and scientists. People with a general interest in geology and Murihiku's history would also find it useful. The map is available from GNS for $30. Inquiries should
be sent to: sales@gns.cri.nz More information on the map will be online soon. |
