The fossil forest of Curio Bay

Heather Wilson (New Zealand)

The 180 million year old fossilised forest at New Zealand’s Curio Bay is of international geological significance. When I visited the area recently, the wind was blowing a gale and there were high seas. There is a two-minute walk from the car park to a lookout and then a series of steps down to the beach. When the rocks and fossilised trees are wet, they are slippery, so you need good footwear.

This is a protected area. When I visited, there was a representative from the Department of Conservation guarding the beach. There are also video cameras keeping an eye on the fossilised forest, making sure it doesn’t gradually vanish as a result of tourists and rock hounds making off with specimens.

This is one of the most extensive and least disturbed examples of a Jurassic fossil forest in the world. The area within which it is found stretches for about 20km, from Curio Bay, south-west to Slope Point. When the forest was living (during the Middle Jurassic epoch), New Zealand was part of the eastern margin of the ancient super-continent known as Gondwana. North of Curio Bay, most of the country’s future land area was beneath the sea.

The fossilised trees occur in green sandstones, alternating with blue shaley clays containing plant impressions. Silica has entirely replaced the woody structure of the trees and rendered them extremely resistant to erosion. Therefore, they withstand the action of the sea much longer and better than the surrounding rocks and are exposed in relief by erosion. The sandstones lie almost flat and, at low tide, form wide shelving ledges over which are strewn many tree stumps and prostrate trunks.

On occasion, many trunks over 20m in length have been measured and some have exceeded 30m. Fossil wood has also been obtained at intervals along the Waikawa coast over  an 11km stretch, and also inland, near Waimahaka, indicating that the fossil forest beds are most likely of considerable extent. The blue shaley clays associated with the fossil forest have yielded abundant impressions of fern plants. In the past, erect tree trunks have been found standing in the face of the sea cliffs, with their entire root systems exposed in the underlying beds. Inland ditches and streams also contain fossilised wood, fern stems and imprints of leaves.

The forest predominantly consisted of trees that formed a low canopy over an undergrowth dominated by ferns. Some of the fossil trees are related to the modern kauri and the Norfolk Island pine

Massive sheet floods of volcanic debris, perhaps triggered by heavy rain on a barren volcanic mountain, are believed to have destroyed the forest. It eventually grew back only to be flooded by volcanic debris once again. This happened at least four times over a period of about 20,000 years and the sequence of events is clearly recorded by distinct bands of fossilised tree stumps and wood, exposed today in the cliff face.

This area is well worth a look and you can take as many photographs as you wish. However, there is a definitive “NO” where the question of taking the fossilised wood away is concerned.

New Zealand’s Curio Bay is situated on the Catlins coast, about 88km south-east of Invercargill and 7km south of Waikawa. It is signposted from the Southern Scenic Route that follows State Highway 92 through the Catlins from Invercargill to Balclutha.