The New Caledonian archipelago is a microcontinental island chain which originated as a fragment of Zealandia, a nearly submerged continent or microcontinent which was part of the southern supercontinent of Gondwana during the time of the dinosaurs. The Grande Terre group of New Caledonia, with Mont Panié at 1,628 meters (5,341 ft) as its highest point, is the most elevated part of the Norfolk Ridge, a long and mostly underwater arm of the continent. While they were still one landmass, Zealandia and Australia combined broke away from Antarctica between 85 and 130 million years ago. Australia and Zealandia split apart 60–85 million years ago. Although biologists consider it contrary to the evidence of surviving Gondwanan lineages, geologists consider the logical possibility that Zealandia may have been completely submerged about 23 million years ago. While a continent like Australia consists of a large body of land surrounded by a fringe of continental shelf, Zealandia consists almost entirely of continental shelf, with the vast majority, some 93%, submerged beneath the Pacific Ocean. This viewpoint is not universal. Pelletier argues that Grande Terre was completely submerged for millions of years, and hence the origin of the flora may not be local in nature, but due to long distance-dispersal.
Zealandia is 3,500,000 km² in area, larger than Greenland or India, and almost half the size of Australia. It is unusually slender, stretching from New Caledonia in the north to beyond New Zealand's sub-Antarctic islands in the south (from latitude 19° south to 56° south, analogous to ranging from Haiti to Hudson Bay or from Sudan to Sweden in the northern hemisphere). New Zealand is the greatest part of Zealandia above sea level, followed by New Caledonia.
Given its continental origin as a fragment of Zealandia, unlike many of the islands of the Pacific such as the Hawaiian chain, New Caledonia is not of geographically recent volcanic provenance. Its separation from Australia at the end of the Cretaceous (65 MYA) and from New Zealand in the mid-Miocene has led to a long period of evolution in near complete isolation. New Caledonia’s natural heritage significantly comprises species whose ancestors were ancient and primitive flora and fauna present on New Caledonia when it broke away from Gondwana millions of years ago, not only species but entire genera and even families are unique to the island, and survive nowhere else.
Since the age of the dinosaurs, as the island moved north due to the effects of continental drift, some geologists assert that it may have been fully submerged at various intervals. Botanists, however, argue that there must have been some areas that remained above sea-level, serving as refugia for the descendants of the original flora that inhabited the island when it broke away from Gondwana. The isolation of New Caledonia was not absolute, however. New species came to New Caledonia while species of Gondwanan origin were able to penetrate further eastward into the Pacific Island region.
Read more about this topic: Geography Of New Caledonia
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