Foulden Maar | |
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 Foulden Maar pit as seen from Moonlight Road | |
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| Coordinates: 45°31′36″S 170°13′06″E / 45.5268°S 170.2184°E | |
| Location | Otago, New Zealand |
| Age | Miocene, ~ |
| Volcanic field | Waipiata |
Foulden Maar is a fossil site near Middlemarch in Otago, New Zealand. The fossils were deposited in the small deep crater lake of a maar formed around 23 million years ago by a volcano in the Miocene era. The crater lake existed for a period of around 130,000 years, and during this time it gradually filled up with diatomite, composed of annual layers of silica-shelled algae (diatoms). These layers of diatomite have preserved exceptional fossils of fish from the crater lake, and plants, spiders and insects from the sub-tropical forest that developed around the crater. The site is the only known maar of its kind in the Southern Hemisphere and is one of New Zealand's pre-eminent fossil sites. A 2018 proposal to mine Foulden Maar for livestock-food additive attracted significant public opposition. The mining company went into receivership in 2019, and in 2023, the Dunedin City Council reached an agreement with the receivers to purchase the land, including the surrender of the mining permits.