The continental margin around Antarctica contains large ice shelves, coastal polynyas and the Antarctic continental shelves.
Kerguelen Plateaus[edit | edit source]
The Kerguelen Plateau is an oceanic plateau and a large igneous province (LIP) located on the Antarctic Plate, in the southern Indian Ocean, a microcontinent and submerged continent, about 3,000 km (1,900 mi) to the southwest of Australia nearly three times the size of Japan, that extends for more than 2,200 km (1,400 mi) in a northwest–southeast direction and lies in deep water.
One of the largest igneous provinces (LIPs) in the world, the Kerguelen Plateau covers an area of 1,250,000 km2 (480,000 sq mi) and rises 2,000 m (6,600 ft) above the surrounding oceanic basins.
Located on the Antarctic Plate, the Kerguelen Plateau is separated from Australia by the Southeast Indian Ridge (SEIR) and from Africa by the Southwest Indian Ridge (SWIR), where these two ridges meet at the Rodrigues Triple Point or Rodriguez Triple Junction, from Antarctica by Princess Elizabeth Trough and the Cooperation Sea, the eastern margin north of the William Ridge is steep and formed during the breakup between the Kerguelen Plateau and the Broken Ridge, the southern part of the margin is separated from the Australian–Antarctic Basin by the deep Labuan Basin.
From the initial opening of the Indian Ocean until present, the Kerguelen hotspot has produced several now widely dispersed large-scale structures. The Southern Kerguelen Plateau (SKP) formed 119–110 Ma; the Elan Bank 108–107 Ma, named by Dennis E. Hayes of Lamont Doherty Easth Observatory}; the Central Kerguelen Plateau (CKP) 101–100 Ma; the Broken Ridge (connected to CKP before the Eocene breakup) formed 95–94 Ma; the Skiff Bank (east of Kerguelen archipelago) 69–68 Ma; Northern Kerguelen Plateau (NKP) 35–34 Ma; Ninety East Ridge formed 82–38 Ma north to south; the Bunbury Basalt (western Australia) formed at 137-130.5 Ma ; the Naturaliste Plateau (offshore western Australia) formed 132-128 Ma ; the Rajmahal Traps in northeast India 118–117 Ma; and finally lamprophyres in India and Antarctica 115–114 Ma.
The presence of soil layers in the basalt which included charcoal and conglomerate fragments of gneiss indicate that much of the plateau was above sea level as what is termed a microcontinent for three periods between 100 million years ago and 20 million years ago. (The charcoal was made by wildfires started by lightning or lava flows.) Large parts of the now submarine Southern (SKP) and Central Kerguelen Plateaus (CKP) were subaerial during the formation of the LIP. The SKP probably formed an island of 500,000 km2 (190,000 sq mi) with major peaks reaching 1,000–2,000 m (3,300–6,600 ft) above sea level.
The Kerguelen microcontinent may have been covered by dense conifer forest in the mid-Cretaceous.
It finally sank 20 million years ago and is now 1,000–2,000 m (3,300–6,600 ft) below sea level.
Ross Sea[edit | edit source]
The Ross Sea, a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land and within the Ross Embayment, the southernmost sea on Earth, derives its name from the British explorer James Clark Ross who visited in 1841, has to the west Ross Island and Victoria Land, to the east Roosevelt Island and King Edward VII Land, or Edward VII Peninsula, in Marie Byrd Land], while the southernmost part is covered by the Ross Ice Shelf, about 200 miles (320 km) from the South Pole with boundaries and area defined by the New Zealand National Institute of Water and Atmospheric Research as having an area of 637,000 square kilometres (246,000 sq mi).
The Ross Sea (and Ross Ice Shelf) overlies a deep continental shelf, although the average depth of the world's continental shelves (at the shelf break joining the continental slope) is about 130 meters, the Ross shelf average depth is about 500 meters. It is shallower in the western Ross Sea (east longitudes) than the east (west longitudes). This over-deepened condition is due to cycles of erosion and deposition of sediments from expanding and contracting ice sheets overriding the shelf during Oligocene and later time, and is also found on other locations around Antarctica. Erosion was more focused on the inner parts of the shelf while deposition of sediment dominated the outer shelf, making the inner shelf deeper than the outer.
Seismic studies in the latter half of the twentieth century defined the major features of the geology of the Ross Sea. The deepest or basement rocks, are faulted into four major north trending graben systems, which are basins for sedimentary fill. These basins include the Northern and Victoria Land Basin in the west, the Central Trough, and the Eastern Basin, which has approximately the same width as the other three. The Coulman High separates the Victoria Land Basin and Central Trough and the Central High separates the Central Trough and Eastern Basin. The majority of the faulting and accompanying graben formation along with crustal extension occurred during the rifting away of the Zealandia microcontinent from Antarctica in Gondwana during Cretaceous time. Paleogene and Neogene -age and faulting and extension is restricted to the Victoria Land Basin and Northern Basin.
Basement grabens are filled with rift sediments of uncertain character and age. A widespread unconformity has cut into the basement and sedimentary fill of the large basins. Above this major unconformity (named RSU-6) are a series of glacial marine sedimentary units deposited during multiple advances and retreats of the Antarctic Ice Sheet across the sea floor of the Ross Sea during the Oligocene and later.
Drill holes have recovered cores of rock from the western edges of the sea. The most ambitious recent efforts are the Cape Roberts Project (CRP) and the ANDRILL project. Deep Sea Drilling Project (DSDP) Leg 28 completed several holes (270-273) farther from land in the central and western portions of the sea. These resulted in defining a stratigraphy for most of the older glacial sequences, which comprise Oligocene and younger sediments. The Ross Sea-wide major unconformity RSU-6 has been proposed to mark a global climate event and the first appearance of the Antarctic Ice Sheet in the Oligocene.
See also[edit | edit source]
References[edit | edit source]
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