Foulden Maar | |
---|---|
Coordinates: 45°31′36″S170°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.
Foulden Maar is named for the nearby farm of Foulden Hills, itself probably named after the town of Foulden in the Scottish Borders. Many other local locations—such as Kelso, Ettrick, Roxburgh, and the nearby Nenthorn—are similarly named. [1]
The landscape of the east Otago region includes a large number of volcanoes. Early studies indicated there were separate volcanic areas within the region – Waipiata Volcanic Field and the Dunedin Volcanic Group which contained the Dunedin Volcano and basaltic monogenetic volcanoes like the maar. However, later research has found that these volcanic fields overlap in both space and time. [2]
Foulden Maar is now considered to be one of around 150 volcanoes in the Dunedin Volcanic Group. Eruptions within the group began around 25 Ma near Middlemarch and finished with the youngest in the group by around 9 Ma. [2] The group is considered extinct. [3] : 20
A maar is a volcanic crater with a low rim that is formed in an explosion (known as a phreatomagmatic eruption), when magma or hot lava comes into contact with groundwater. The maar typically fills with water to become a crater lake. Foulden Maar is a maar-diatreme volcano. The diatreme is a long vertical conduit where gas-filled magma rises to the surface of the Earth during an eruption.
The Foulden Maar crater is filled with fossilised diatomite as well as sedimentary rock, debris flows, and pyroclastic rocks. [4] [5]
Two main methods have been used for dating the eruption of Foulden Maar. These are biostratigraphy and radiometric dating, based on analysis of samples from drill cores to depth of 180 metres (590 ft) taken at the site in June 2009.
Sedimentary rocks in New Zealand can be dated using analysis based on existing data about the first and last occurrences of key taxa in fossil records. Fossil pollen from the Foulden Maar drill cores has been dated at 23 Ma with reference to fossil pollen found at other fossil sites in Southland and Otago. [3] : 36
This method uses the known rate of decay of radioactive isotopes present in minerals. In this case, the analysis was based on the decay of isotopes of argon. Analysis of volcanic clast taken from a depth of 126 metres (413 ft) in the drill core indicated an age of 23.38 Ma. [3] : 37 Subsequent dating adjustment is to 23.2 ± 0.4 Ma. [2]
A geomagnetic reversal was discovered in minerals at a depth of around 107 metres (351 ft) in the drill core. A global magnetic polarity time scale shows few reversals in the general time frame indicated by other dating methods for the eruption, and the reversal found in the drill core provides supporting evidence for the age. [3] : 37
The Foulden Maar crater is approximately 1,000 metres (3,300 ft) in diameter; its diatomaceous layer is estimated to be 200 metres (660 ft) deep. [6] The Foulden Maar lake formed in a volcanic crater during the Waitakian (early Miocene), approximately 23 million years ago. [4] [7] It was deep and anoxic at the bottom, which precluded decomposition of plant and animal remains. The lake was hydrologically isolated, meaning that no rivers or streams disturbed the sedimentation, which formed multiple laminated layers. These thin layers of silica are known as diatomite, as they are composed primarily of one diatom species, Encyonema jordaniforme Krammer, that grew on submerged rocks or aquatic plants in the lake. [8] [9] As the lake gradually filled in and dried out, the diatomite layers capture a detailed fossil record of about 130,000 years. [10]
Foulden Maar is one of New Zealand's pre-eminent fossil sites, and is unique in the Southern Hemisphere for the time period it covers. [11] [12] Fossils were first discovered at the site by gold prospectors in the early 1870s and were described as "polishing powder" by the geologists Frederick Hutton and George Ulrich in 1875. [13]
Although excavations have been limited to a small area the size of a tennis court, palaeontologists have discovered hundreds of undescribed species. [14] The sediments are rich in fossil flowers, fruits, seeds, pollen, and bark from plants, as well as fungi. Several new species of plants have been discovered, and the fossil plant genus Fouldenia is named in honour of its type locality Foulden Maar. [15]
Fossilised freshwater fish are common. The earliest galaxiid fish fossil and the earliest known fossilised eel both come from Foulden Maar. [16] Numerous arthropod fossils have been found at the site, among them Araneae (spiders), Plecoptera (stoneflies), Odonata (dragonflies), Isoptera (termites), Hemiptera (true bugs), Diptera (true flies), Coleoptera (beetles), Trichoptera (caddis flies), and Hymenoptera (wasps, ants and bees). [6] The four arachnids found at Foulden Maar are the first arachnid fossils identified in New Zealand; previous spider specimens had been found in amber but were not identifiable. [17] The first fossil hymenopteran in New Zealand is an ant found at Foulden Maar. [18] Fossils of immature aquatic flies obtained from Foulden Maar are helping scientists to shed light on the ecological history of true flies in New Zealand. [19]
The fossil evidence derived from pollen and spores suggests a warm temperate or sub-tropical rain forest with canopy trees, with an understorey of shrubs, ferns and on the margins pioneer species. Climatically, the area resembled modern-day south-eastern Queensland with species that no longer occur in the New Zealand flora. [8] The lake contained small and large galaxiid fishes and eels, ducks (inferred from coprolites), and likely crocodiles as well. [20] [21]
Leaf fossils from the deposit have been used to link past spikes in carbon dioxide levels with melting of Antarctic ice, [22] [23] [24] and the variations in the laminations of the diatomite have been studied to reveal the New Zealand climate from that time. [10]
Diatomite was extracted in small quantities from the site during World War II when transport difficulties hindered access to foreign sources. [25] [26] Diatomite has a range of applications, depending primarily on purity, diatom size, and the trace elements present.
Foulden Maar is on privately owned land. The area was initially developed for mining by Featherston Resources Ltd in 1997. [27] The deposit was estimated as 5 million tonnes (Mt) by NZ Petroleum and Minerals. [28] This proved uneconomic for the company, and its assets were sold to Plaman Resources Ltd in March 2015. [27]
Plaman Resources claimed the size of the deposit was 31 Mt. [29] The shareholders for Plaman Resources are Iris Corporation, Kuala Lumpur, Malaysia (50.95 percent) and Burleigh Nominees Ltd, Douglas, Isle of Man (49.05 percent). [30] Plaman Resources' shareholders, the Iris Corporation and Burleigh Nominees, have allegedly been involved in corruption and humans-rights abuses and have unpaid debts. [31] It was unclear if Iris Corporation would remain a shareholder of Plaman if Overseas Investment Office (OIO) approval for the mine was received. [32]
Plaman held the mining rights and planned to turn all of the fossil-containing diatomite into an additive for incorporating into the food of intensively farmed animals such as ducks and pigs. [33] Initial seed funding of about US$20 million (NZ$28 million) was raised through Goldman Sachs New Zealand Holdings, the Auckland branch of New York stock-exchange listed investment bank in August 2018. [34] The financial viability of these plans was reported to hinge on the purchase of an adjoining farm, which the OIO must rule on. [11] [35] No timetable was set for the decision. [36] The proposal involved building a new $36.8m processing plant at Milton to crush the diatomite before shipping offshore from Port Chalmers or Bluff. It was estimated by the company that the trucking and processing would create 100 jobs over 27 years. [33] Plaman discussed with local councils applying to New Zealand's Provincial Growth Fund for help with the costs of building the processing plant, although no application was made. [37]
Previous mining at the site yielded low-quality diatomite only suitable for inclusion in concrete, rather than the high-quality product Plaman was marketing as "Black Pearl". [35] Plaman claimed that livestock will benefit nutritionally from Black Pearl, because the diatomite is "rich in natural organic matter (which contains humics, such as humic and fulvic acid) and other valuable nutrients, which have been shown to be beneficial in animal nutrition." [38] Animal nutrition experts expressed doubt that the product produced by Plaman will have any animal-health benefits, as there is no published data to support their claims. [39] Concerns were expressed by the New Zealand Green Party that the diatomite would be sold as fertiliser to support the production of palm oil. [27]
Plaman Resources offered to refrain from mining nearby Hindon Maar if opposition to the Foulden Maar proposal was dropped. They also offered to set aside 5 hectares (12 acres) (12–20% of the deposit) of the eastern pit at Foulden Maar for scientific research, [40] but geologists said that if the deposit is drained for mining the fossils may be lost regardless. [41]
The company was placed in receivership and voluntary liquidation in June 2019, and the OIO approval process was placed on hold. [42] [43] The Save Foulden Maar group considered crowdfunding to permanently protect the site. [44]
Some locals were opposed to the anticipated levels of dust, noise, and general disruption the proposed mine would create. [35] The Otago Regional Council granted Plaman Resources resource consent to discharge air dust for the purpose of quarrying diatomite until 1 July 2020. [45] The original mining permit was for 20 years but was extended to November 2033. [46] A wider group of people concerned about the loss of the unique fossil record described as "Dunedin's Pompeii" and an "irreplaceable treasure box" [35] [47] launched a petition to preserve the site, garnering nearly 10,000 signatures in the first month. [31] [48] [49] A leaked report by Goldman Sachs details the engagement of former Labour MP Clayton Cosgrove as a lobbyist to "secure approval" for the mine. [35]
Some locals wanted to see the area turned into a geo-park, along similar lines to other diatomite sites in Norway, Germany, and China. [47] [50] Former Prime Minister Helen Clark suggested that the site could be protected as a scientific reserve under the Reserves Act 1977, [51] saying "It just doesn't stack up. It's a question of values. Do we value knowledge? Do we value natural heritage? Do we value science and research, or do we just want to a quick dollar from a low value pit? I mean, really, it's distressing." [31] [52] [53]
MP Clare Curran voiced support for the mining proposal, saying that she had been given assurances by Plaman. [53] She argued that "misinformation" was abundant due to the slow overseas-investment-approval process and said that the resource-consent process would still need to be followed. [53] Dunedin Mayor Dave Cull, who wrote a letter of support for the mining proposal, publicly called for clarification from Plaman after hearing details of the leaked Goldman Sachs report. [54] Clutha Mayor Bryce Cadogan, who also supported the proposal, expressed frustration that commercial sensitivity prevented the release of all the information in favour of the mine. [54]
Dunedin City Council councillor Aaron Hawkins proposed that the council should "recognise the importance of Foulden Maar, and support its preservation, and protection as a scientific resource", and the council voted to do so, later formally opposing the mining proposal. [55] [56] The council made this decision after hearing from Daphne Lee, a palaeontologist and associate professor at the University of Otago, explaining the scientific importance of the site. [57] The University of Otago also formally opposed the mining proposal. [58] Sir Alan Mark, chair of the environmental group the Wise Response Society, called for the government to purchase the site and establish a geological reserve. [59]
Juliet Gerrard, the Prime Minister's Chief Science Adviser, said that "the tale is far from simple and at least two weak spots at the interface of science and policy are exposed as we dig through the complexities: there is no obvious point in central government to consider the value of a fossil record; and the science community has perhaps not previously sufficiently communicated the national and international value of this geological site." [60] The Geoscience Society of New Zealand called for the mining proposal to be stopped, with President Jennifer Eccles saying, "New Zealand’s national identity is strongly bound to its unique plants and animals. We cannot stand by and see this fountain of paleontological knowledge about where we have come from destroyed; particularly not for so little transient local and national gain." [12] [61]
In November 2019, the Dunedin City Council issued a "notice of desire" under the Public Works Act, signalling the intention to purchase the land and return it to public ownership. [62] As of September 2022, the Dunedin City Council had not proceeded with acquiring the land under the Public Works Act, and the protection of the site remained unclear. Scientists were unable to access the site. [63]
In February 2023, the Dunedin City Council reached an agreement with the receivers for Plaman Resources for the purchase 42 hectares (100 acres) of land at the site. The agreement included Plaman surrendering mining permits. The total cost of the purchase was $924,000. [64] [65]
Whakaari / White Island, also known as White Island or Whakaari, is an active andesite stratovolcano situated 48 km (30 mi) from the east coast of the North Island of New Zealand, in the Bay of Plenty. The island covers an area of approximately 325 ha, which is just the peak of a much larger submarine volcano.
Mount Tarawera is a volcano on the North Island of New Zealand within the older but volcanically productive Ōkataina Caldera. Located 24 kilometres southeast of Rotorua, it consists of a series of rhyolitic lava domes that were fissured down the middle by an explosive basaltic eruption in 1886. While the 1886 eruption was basaltic, study has shown there was only a small basalt component to the previous recent rhyolitic predominant eruptions. This eruption was one of New Zealand's largest historical eruptions, and killed an estimated 120 people. The fissures run for about 17 kilometres (11 mi) northeast–southwest.
The Auckland volcanic field is an area of monogenetic volcanoes covered by much of the metropolitan area of Auckland, New Zealand's largest city, located in the North Island. The approximately 53 volcanoes in the field have produced a diverse array of maars, tuff rings, scoria cones, and lava flows. With the exception of Rangitoto, no volcano has erupted more than once, but the other eruptions lasted for various periods ranging from a few weeks to several years. Rangitoto erupted several times and recently twice; in an eruption that occurred about 600 years ago, followed by a second eruption approximately 50 years later. The field is fuelled entirely by basaltic magma, unlike the explosive subduction-driven volcanism in the central North Island, such as at Mount Ruapehu and Lake Taupō.
A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption. A maar characteristically fills with water to form a relatively shallow crater lake, which may also be called a maar.
A volcanic crater is an approximately circular depression in the ground caused by volcanic activity. It is typically a bowl-shaped feature containing one or more vents. During volcanic eruptions, molten magma and volcanic gases rise from an underground magma chamber, through a conduit, until they reach the crater's vent, from where the gases escape into the atmosphere and the magma is erupted as lava. A volcanic crater can be of large dimensions, and sometimes of great depth. During certain types of explosive eruptions, a volcano's magma chamber may empty enough for an area above it to subside, forming a type of larger depression known as a caldera.
A volcanogenic lake is a lake formed as a result of volcanic activity. They are generally a body of water inside an inactive volcanic crater but can also be large volumes of molten lava within an active volcanic crater and waterbodies constrained by lava flows, pyroclastic flows or lahars in valley systems. The term volcanic lake is also used to describe volcanogenic lakes, although it is more commonly assigned to those inside volcanic craters.
Blue Lake Crater is a maar, or a broad, low-relief volcanic crater, in the U.S. state of Oregon. Located in Jefferson County, it consists of three overlapping craters, which hold Blue Lake. The drainage basin for Blue Lake has very steep, forested slopes and is mostly part of the explosion crater left by the volcano's eruption. The volcano lies within the Metolius River basin, which supports a wide array of plant life, large and small mammals, and more than 80 bird species. A 2009 Oregon law designated the Metolius River basin as an area of critical concern, preventing large-scale development and protecting wildlife.
The Waimangu Volcanic Rift Valley is the hydrothermal system created on 10 June 1886 by the volcanic eruption of Mount Tarawera, on the North Island of New Zealand. It encompasses Lake Rotomahana, the site of the Pink and White Terraces, as well as the location of the Waimangu Geyser, which was active from 1900 to 1904. The area has been increasingly accessible as a tourist attraction and contains Frying Pan Lake, which is the largest hot spring in the world, and the steaming and usually pale blue Inferno Crater Lake, the largest geyser-like feature in the world although the geyser itself cannot be seen since it plays at the bottom of the lake.
The volcanism of New Zealand has been responsible for many of the country's geographical features, especially in the North Island and the country's outlying islands.
Tank Farm is the name of a volcanic explosion crater on the North Shore of Auckland, New Zealand, near the approaches to the Auckland Harbour Bridge.
The geology of New Zealand is noted for its volcanic activity, earthquakes and geothermal areas because of its position on the boundary of the Australian Plate and Pacific Plates. New Zealand is part of Zealandia, a microcontinent nearly half the size of Australia that broke away from the Gondwanan supercontinent about 83 million years ago. New Zealand's early separation from other landmasses and subsequent evolution have created a unique fossil record and modern ecology.
Ōrākei Basin is a tidal basin and one of the extinct volcanoes in the Auckland volcanic field in the North Island of New Zealand. It has an explosion crater around 700 m (2,300 ft) wide, with a surrounding tuff ring. The present basin is slightly larger than the original maar crater. Sediments in the basin provided the first high-resolution palaeo-environmental reconstruction for northern New Zealand of the last 130,000 years. The basin supports recreational water sports activities for the local population.
The recently active basaltic Kaikohe-Bay of Islands volcanic field in the Northland Region of New Zealand is associated geographically with an older region of extinct volcanism to its north the Wairakau Volcanic Centre, meaning eruptions in this region have occurred over the last 20 million years. All the cones older than 2 million years have eroded away, leaving plateaus from Ōkaihau to Kerikeri and north to Whangaroa from the old andesite/dacite stratovolcanoes of the Wairakau Volcanic Centre and the ten million year old or more recent volcanoes in field towards the south. In the southern part of the field, around 12 small basaltic scoria cones, and a rhyolite dome erupted in the last 500,000 years around Kaikohe. The field is considered dormant, rather than extinct.
The Puhinui Craters are located in Auckland's Puhinui Reserve and are part of the Auckland volcanic field in the North Island of New Zealand. They were first recognised as volcanic craters in 2011. A cluster of three small maar craters like these is unique in the Auckland volcanic field. Their ages are unknown but most probably all three erupted during the same eruptive episode. They could have been associated with the eruption of nearby Matukutureia but this is speculation at present.
A crater is a landform consisting of a hole or depression on a planetary surface, usually caused either by an object hitting the surface, or by geological activity on the planet. A crater has classically been described as: "a bowl-shaped pit that is formed by a volcano, an explosion, or a meteorite impact". On Earth, craters are "generally the result of volcanic eruptions", while "meteorite impact craters are common on the Moon, but are rare on Earth".
Galaxias effusus is an extinct species of fish in the genus Galaxias, known only from 23-million-year-old fossils from New Zealand. It is named for its dramatically large dorsal, tail, and anal fins, which are much larger than those of any living New Zealand galaxiid. It is the earliest known member of the Southern Hemisphere family Galaxiiidae.
A volcanic crater lake is a lake in a crater that was formed by explosive activity or a collapse during a volcanic eruption.
Daphne E. Lee is a New Zealand geologist, palaeontologist and associate professor at the University of Otago. She is best known for her work on Foulden Maar and her research into fossils discovered at that site.
The volcanic activity in the South Island of New Zealand terminated 5 million years ago as the more northern parts of the North Island became extremely volcanically active. The South Islands surface geology reflects the uplift of the Pacific Plate as it collides with the Indo-Australian Plate along the Alpine Fault over the last 12 million years and the termination of subduction, about 100 to 105 million years ago. There is a very small chance of reactivation of volcanism in the Dunedin Volcano. This chance is made slightly higher by the observation that Southland's Solander Islands / Hautere just off the coast of the South Island were active as recently as 50,000 years old, and on a larger scale 150,000 years old.
The Dunedin volcanic group is a volcanic group that covers over 7,800 km2 (3,000 sq mi) of Otago in the South Island of New Zealand. It is a recent reclassification of the group previously known as the Waiareka-Deborah volcanic field due to common magma melt ancestries of the Dunedin Volcano with the overlapping alkali basaltic monogenetic volcanic field. Excluded from the group are a group of volcanics of different composition and older age near Oamaru, which have been given the name previously used for the Dunedin group. The older Waiareka-Deborah volcanic field overlaps the new Dunedin volcanic group geographically; though Dunedin Volcano has been well studied from the 1880s since New Zealand's first school of geology was established at the University of Otago, detailed studies of north-central volcanoes such as the Crater near Middlemarch were done much later, and high-quality composition studies still need to be done to properly classify many volcanics near Oamaru.
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