New Zealand’s 180-million-year-old forest

Once part of the ancient supercontinent Gondwana, Curio Bay is home to one of the few accessible petrified forests on the planet and a geological phenomenon of international significance.
Take a globe and spin it to the meridian of longitude 170° East. Run your finger down to the parallels of latitude named by seafarers during the Age of Sail as the “Roaring Forties” because of their wild, westerly winds. There you will find the islands of New Zealand, set adrift like giant jigsaw pieces in the South Pacific Ocean.

There is something deeply seductive about the remote, ragged possibilities of land’s edge. I was journeying deep in New Zealand’s South Island, along its brink of raw wilderness called the Catlins, where the blustery winds and waters of Antarctica’s Southern Ocean perform alchemy on this curve of Kiwi coastline. This 100km stretch is cosseted by rugged landscapes of concert hall-sized sea caves, rock stacks, blowholes, arches and coves. Its dense temperate forests are laced with walks to fairy-tale waterfalls where bellbirds, wood pigeons, fantails and grey warblers make their presence known.

Within this curve of coast lies the clue to the birthplace of New Zealand. This magical landscape is home to the ancient geological phenomenon of Curio Bay, the site of one of the world’s finest, most accessible and rarest petrified forests.

Around 180 million years ago during the Jurassic Period, Curio Bay area was part of the eastern margin of the supercontinent Gondwana, connected to Australia and Antarctica while most of future New Zealand lay beneath the waves. Back then, the region was a broad forested coastal floodplain flanked by active volcanoes that continually destroyed the forests with massive sheets of volcanic debris. Covered with silt and mud, starved of oxygen and impregnated with silica from volcanic ash-filled floodwaters, the felled tree trunks eventually solidified and turned to rock through the process of petrification.

Most of New Zealand’s trees, ferns and flowering plants have evolved in isolation for millions of years (Credit: Marian McGuinness)

“Liquid full of dissolved silica would have permeated the buried wood, then solidified within the wood cells,” explained New Zealand palaeontologist, geologist and palaeobotanist, Dr Mike Pole. “Sometime later, the wood itself would have decayed away, and silica would have solidified in those spaces. The end result is a replacement of the wood, often right down to cell-level detail.”

Over the past 10,000 years, the sea has become an archaeologist, scraping away the layers of clay and sandstone to expose this buried forest bit by bit. What makes Curio Bay unique is the forest’s horizontal position due to its felling by volcanic ash-filled floodwaters, whereas others – such as Arizona’s Petrified Forest and Svalbard’s tropical fossil forest – are vertical. It is also one of the few in the world that is accessible. According to the New Zealand Geological Survey, “Known fossil forests of the Jurassic period are very few throughout the world and this is the most varied and remarkable of them all.”
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In addition, while most petrified forests are far removed from the modern forests that grow near them, Curio Bay’s petrified forest, which is a representation of an ancient Gondwana forest of cycads, gingkos, conifers and ferns, still has its descendants in the present-day forests found here. About 80% of New Zealand’s trees, ferns and flowering plants are native having evolved in isolation for millions of years. As well as native beech forests, there are forests of unique Southern Hemisphere conifers, called podocarp, whose species include rimu, totara, matai, kahikatea and miro, whose lineage stretches back to Gondwana.

While completing her geology studies at Victoria University in Wellington, New Zealand, Dr Vanessa Thorn concluded that this fossil forest preserved in its original growth position was rare. To study the fossil forest in its original environment, where it was volcanically buried in a geological instant, gives greater insight into its natural ecosystem, as opposed to a fossil forest ex situ, or out of place, when other factors come into play such as being disturbed by urban activities. When New Zealand was connected to the Antarctic margin of Gondwana, Thorn suggests the forest grew at approximately 75-78°S, “well within the polar circle”. The ancestors of the present-day kauri and rimu trees could fluctuate quickly between long, pitch-black winters and perpetually sunny summers of continuous light. “This is a huge difference to the present time,” said Thorn. “No trees are known to do this now.” This conundrum adds to the uniqueness and scientific importance of the Curio Bay site.

As I journeyed through this elemental landscape, I stood on an anvil-shaped headland that jutted into the sea. Today, due to its geographic isolation and nutrient-rich waters, the Catlins coast provides an extraordinary marine wildlife sanctuary for New Zealand fur seals, southern elephant seals and the native Hookers sea lions. Endemic to this area are the world’s rarest and smallest Hector’s dolphins and the world’s rarest penguin species, the yellow-eyed hoiho.


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