Fossil Treasures of Foulden Maar

Plans to mine a well of diatomite in Otago hit a snag when scientists pointed out that the site contains contains a wealth of perfectly preserved examples of prehistoric Aotearoa.

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It seemed like a good plan: mine the rich diatomite deposits in a 42-hectare site near Middlemarch in Otago and export the pulverised rock as a stockfeed additive for poultry, pigs, and cattle. In 2018, a company called Plaman Global announced its intention to do just that. The activity would create regional employment, the company said, and when operations ended in 2047, a lake would be left behind “for the use of the community”.

The snag was that Foulden Maar, the unassuming place where this commercial activity was to occur, was a palaeontological site of international importance. First reported in 1875, the deposits had been quarried fitfully in the early 1940s, but the sheer scale of Plaman Global’s proposed mining operation galvanised scientists and locals into action. Dogged by resolute opposition and headlines such as ‘Turning our taonga into pet food’ and ‘Unjustifiable vandalism and grand promises’, Plaman was eventually forced to drop its plans.

In Fossil Treasures of Foulden Maar, published by the University of Otago Press, authors Daphne Lee, Uwe Kaulfuss, and John Conran explain what was at stake in the fight to save the deposits. First, some geology: a maar is a small crater formed when rising magma hits near-surface water and explodes, creating a rimmed crater.

Groundwater then seeps in to form a crater lake and, over millennia, microscopic single-celled diatoms and other algae bloom and sink, covering the lake bed in a siliceous ooze that accumulates to become diatomite. Stagnant and lacking oxygen, the deeper water of the lake preserves plant and animal remains that drift to the bottom, building through tens of thousands of undisturbed annual layers a finely calibrated record of life in the distant past.

Fossil Treasures catalogues in exquisite detail what has been found to date at Foulden Maar—everything from freshwater sponges and insects to fish and eels, and from ferns and conifers to flowering plants. Of the 10 known fossil orchid species, for example, two are from Foulden, and the insect and spider specimens found there in some cases are global firsts. Fossils from the site also include the world’s oldest known galaxiid fish and the first freshwater eel found in the Southern Hemisphere.

Foulden is especially valuable for the amount of soft tissue preserved in the diatomite, including the remnants of fish eyes and skin, and insect antennae and wing patterns. This feature, in particular, has earned the site international recognition as a Konservat-Lagerstätte deposit (Lagerstätte meaning ‘storage place’).

Invaluable though all this is, Foulden’s overriding importance today is what it can tell us about climate change. Accurately dated to 23 million years ago, its preserved leaf fossils enable scientists to reconstruct palaeotemperatures, rainfall, and changing carbon dioxide levels in the atmosphere of the early Miocene.

Tectonic stability and an absence of burrowing animals or water movement have left us with one of Earth’s most complete climate records, covering more than 120,000 years, in a site that experienced climatic influences from both tropical and polar regions. Its seasonal sedimentation rate of one millimetre a year has resulted in a chronology 10 times more detailed than equivalent deep-sea cores, and far older than Antarctic ice cores, which preserve evidence from no more than a million years ago.

One surprising discovery was that the well-preserved leaf samples from Foulden Maar showed Miocene carbon dioxide levels to have been 450-550 parts per million—similar to what is predicted to occur by 2040-50, and far higher than the widely accepted 300 parts per million that had been derived largely from calculations using marine data. The site is also the only one in the southern hemisphere to preserve a record of the El Niño Southern Oscillation in the Miocene, revealing that it was a major source of climate variability then, as now.

The authors of Fossil Treasures warn that despite the site’s scientific value, its fate remains uncertain. A similar northern hemisphere Konservat-Lagerstätte, Germany’s iconic Messel Pit, which dates to the Eocene, was mined, then destined to become a waste disposal site, until public action resulted in it being declared a UNESCO World Heritage Site in 1995. Unbelievably, Foulden Maar still lacks such legal recognition and continues to have no formal protection against mining.

Foulden Maar is helping reshape our understanding of the history of life on Earth, say the authors, and like other key fossil sites in New Zealand it should be preserved. Forty-two hectares seems a small price to pay for that.

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