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Sturtian
The Sturtian glaciation was a Snowball Earth glaciation, or perhaps multiple glaciations, during the Cryogenian Period when the Earth experienced repeated large-scale glaciations. The duration of the Sturtian glaciation has been variously defined, with dates ranging from 717 to 643 Ma. Stern ''et al.'' place the period at 715 to 680 Ma. According to Eyles and Young, "Glaciogenic rocks figure prominently in the Neoproterozoic stratigraphy of southeastern Australia and the northern Canadian Cordillera. The Sturtian glaciogenic succession (c. 740 Ma) unconformably overlies rocks of the Burra Group." The Sturtian succession includes two major diamictite-mudstone sequences which represent glacial advance and retreat cycles. It is stratigraphically correlated with the Rapitan Group of North America. The Sturtian is named after the Sturt Tillite, exposed in the Sturt River Gorge, near Bellevue Heights, South Australia South Australia (commonly abbreviated as SA) is a States and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Snowball Earth
The Snowball Earth hypothesis proposes that, during one or more of Earth's icehouse climates, the planet's surface became entirely or nearly entirely frozen. It is believed that this occurred sometime before 650 M.Y.A. (million years ago) during the Cryogenian period. Proponents of the hypothesis argue that it best explains sedimentary deposits that are generally believed to be of glacial origin at tropical palaeolatitudes and other enigmatic features in the geological record. Opponents of the hypothesis contest the geological evidence for global glaciation and the geophysical feasibility of an ice- or slush-covered ocean, and they emphasize the difficulty of escaping an all-frozen condition. A number of unanswered questions remain, including whether Earth was a full snowball or a "slushball" with a thin equatorial band of open (or seasonally open) water. The snowball-Earth episodes are proposed to have occurred before the sudden radiation of multicellular bioforms kno ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Marinoan Glaciation
The Marinoan glaciation, sometimes also known as the Varanger glaciation, was a period of worldwide glaciation that lasted from approximately 650 to 632.3 ± 5.9 Ma (million years ago) during the Cryogenian period. This glaciation possibly covered the entire planet, in an event called the Snowball Earth. The end of the glaciation was caused by volcanic release of carbon dioxide and dissolution of gas hydrates and might have been hastened by the release of methane from equatorial permafrost. Origin of name and history of terminology The name is derived from the stratigraphic terminology of the Adelaide Geosyncline (Adelaide Rift Complex) in South Australia and is taken from the Adelaide suburb of Marino. The term Marinoan Series was first used in a 1950 paper by Douglas Mawson and Reg Sprigg to subdivide the Neoproterozoic rocks of the Adelaide area and encompassed all strata from the top of the Brighton Limestone to the base of the Cambrian. The corresponding time period, re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cryogenian
The Cryogenian (from grc, κρύος, krýos, meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran. Cryogenian was the time of drastic biosphere changes. After the previous Boring Billion years of stability, at the beginning of Cryogenian the severe Sturtian glaciation began, freezing the entire Earth in a planetary state known as a Snowball Earth. After 70 million years it ended, but was quickly followed by the Marinoan glaciation, which was also a global event. These events are the subject of much scientific controversy specifically over whether these glaciations covered the entire planet or a band of open sea survived near the equator (termed "slushball Earth"). Ratification The Cryogenian Period was ratified in 1990 by the International Commission on Stratigraphy. In contrast to most other time periods, the b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adelaide Rift Complex
The Adelaide Superbasin (previously known as the Adelaide Geosyncline and Adelaide Rift Complex) is a major Neoproterozoic to middle Cambrian geological province in central and south-east South Australia, western New South Wales, and western Victoria. The Adelaide Superbasin consists of a thick pile of sedimentary rocks and minor volcanic rocks that were deposited on the eastern margin of Australia during the time of breakup of the supercontinent Rodinia. A number of authors have noted the similarity in these sedimentary rocks with rocks found in western North America and have suggested that they were formerly adjacent to each other in Rodinia. This is one major correlation in the SWEAT (south-west USA against East Antarctica) reconstruction of Rodinia. Particularly notable events that are preserved in the rock record of the Adelaide Superbasin are the two Neoproterozoic Snowball Earth events (the Sturtian and Marinoan Glaciations), the Neoproterozoic Oxygenation Event, the Ed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reusch's Moraine
The Smalfjord diamictite, Bigganjargga Tillite or Reusch's Moraine is a diamictite in Finnmark, northern Norway. The rock was first identified as a tillite by Hans Reusch in 1891, hence its name. The tillite overlies sandstone whose contact surface is striated. Reusch's Moraine belong to the Smalfjord Formation, a geological formation of Neoproterozoic age. The tillite possibly formed during the Sturtian glaciation in connection to a global glaciation. Reusch's Moraine was among the first sites discovered to bear evidence of Precambrian glaciations, being only preceded by findings in Scotland (1871), Australia (1884) and India (1887). The site is remarkably illustrative and Reusch's 1891 sketch has been labeled "iconic" by Paul F. Hoffman. The area has been protected by law at least since the 1960s and it is forbidden to hammer the rocks. Differing interpretations While the idea that the rocks and striations are of glacial origin have been endorsed by numerous geologists, a fe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diamictite
Diamictite (; from Ancient Greek ''δια'' (dia-): ''through'' and ''µεικτός'' (meiktós): ''mixed'') is a type of lithified sedimentary rock that consists of nonsorted to poorly sorted terrigenous sediment containing particles that range in size from clay to boulders, suspended in a matrix of mudstone or sandstone. The term was coined by Richard Foster Flint and others as a purely descriptive term, devoid of any reference to a particular origin.Flint, R.F., J.E. Sanders, and J. Rodgers (1960) ''Diamictite, a substitute term for symmictite'' Geological Society of America Bulletin. 71(12):1809–1810. Some geologists restrict the usage to nonsorted or poorly sorted conglomerate or breccia that consists of sparse, terrigenous gravel suspended in either a mud or sand matrix. Tucker, M.E. (2003) ''Sedimentary Rocks in the Field'' John Wiley & Sons, Ltd., New York, New York. 244 pp. Unlithified diamictite is referred to as diamicton. The term diamictite is often appli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is preceded by the Mesoproterozoic Era and succeeded by the Paleozoic Era of the Phanerozoic Eon. The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets may have reached the equator and formed a "Snowball Earth". The earliest fossils of complex multicellular life are found in the Ediacaran Period. These organisms make up the Ediacaran biota, including the oldest definitive animals in the fossil record. According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust. Geology At the onset of the Neoproterozoic the supercontinent Rod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canadian Cordillera
The Pacific Cordillera, also known as the Western Cordillera or simply The Cordillera, is a top-level physiographic region of Canada, referring mainly to the extensive cordillera system in Western and Northwestern Canada that constitutes the northern part of the North American Cordillera. The mountain ranges in this region were covered during the Pleistocene by the Cordilleran Ice Sheet, the extent of which gives perspective on the geographic extent of this region. The cordillera extends from the Alaska's Brooks and Alaska Ranges, southeast through most of the Yukon and British Columbia as well as the southwestern fringe of Northwest Territories and Alberta (bordered by the Mackenzie- Peel/Liard River basin and the Canadian Prairies in the east), to stretch its margin beyond the Canada–United States border with five extensive lobes reaching into the mountain valleys of Montana and Washington.D. B. Booth. (1987). Timing and processes of deglaciation along the southern margin o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unconformable
An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger layer, but the term is used to describe any break in the sedimentary geologic record. The significance of angular unconformity (see below) was shown by James Hutton, who found examples of Hutton's Unconformity at Jedburgh in 1787 and at Siccar Point in 1788. The rocks above an unconformity are younger than the rocks beneath (unless the sequence has been overturned). An unconformity represents time during which no sediments were preserved in a region or were subsequently eroded before the next deposition. The local record for that time interval is missing and geologists must use other clues to discover that part of the geologic history of that area. The interval of geologic time not represented i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glaciation
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate between glacial periods. The Last Glacial Period ended about 15,000 years ago. The Holocene is the current interglacial. A time with no glaciers on Earth is considered a greenhouse climate state. Quaternary Period Within the Quaternary, which started about 2.6 million years before present, there have been a number of glacials and interglacials. At least eight glacial cycles have occurred in the last 740,000 years alone. Penultimate Glacial Period The Penultimate Glacial Period (PGP) is the glacial period that occurred before the Last Glacial Period. It began about 194,000 years ago and ended 135,000 years ago, with the beginning of the Eemian interglacial. Last Glacial Period The last glacial period was the most recent glacial pe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, W. H. Freeman, 2nd ed, 529 pp. The term ''mudstone'' is also used to describe carbonate rocks (limestone or dolomite) that are composed predominantly of carbonate mud. However, in most contexts, the term refers to siliciclastic mudstone, composed mostly of silicate minerals. The NASA Curiosity rover has found deposits of mudstone on Mars that contain organic substances such as propane, benzene and toluene. Definition There is not a single definition of mudstone that has gained general acceptance,Boggs 2006, p.143 though there is wide agreement that mudstones are fine-grained sedimentary rocks, composed mostly of silicate grains with a grain size less than . Individual grains this size are too small to be distingui ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sturt Gorge Recreation Park
The Sturt Gorge Recreation Park is a protected area in the Australian state of South Australia located in the suburbs of Bellevue Heights, Craigburn Farm and Flagstaff Hill within the Adelaide metropolitan area about south of the Adelaide central business district. The park was established in 1973. and protects an area recognised as an area of great geological significance. It channels the Sturt River down to the Adelaide Plains. The Sturt Tillite formation was the first area in the world to provide definite evidence of Cryogenian glaciation (the Snowball Earth). It is hypothesised that the landform was created from glacial material that dropped from ice floating in the ocean which covered the area 800 million years ago. Fires of any kind are prohibited in the park. It is classified as an IUCN Category III protected area. In 1980, the recreation park was listed on the former Register of the National Estate. See also * List of protected areas in Adelaide * List of can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
