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Topic: Cryogenian

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	Cryogenian - Wikipedia, the free encyclopedia
		The Cryogenian Period (from Greek cryos "ice" and genesis "birth") is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period.
		The Cryogenian includes the Sturtian and Marinoan (formerly considered together as the Varanger) glaciations, and lasted from 850 Ma (as defined by the ICS based on radiometric chronometry) to approximately 635 Ma.
		The population of acritarchs crashed during this glaciation and it is claimed that oxygen levels in the atmosphere increased after the glaciation.
	en.wikipedia.org /wiki/Cryogenian (489 words)

	SNOWBALL EARTH
		Characteristic structures in younger Cryogenian cap carbonates (right): giant wave ripples in the Keilberg cap dolostone, NW Namibia, sea-floor cements (former aragonite crystal fans) in the Hayhook cap limestone, NW Canada.
		O) isotopic profiles of the younger Cryogenian cap-carbonate sequence and the pre-glacial Trezona anomaly, Otavi Group carbonate platform near Ombaatjie, NW Namibia.
		This contrasts with tightly clustered isotopic data from 635-Ma cap dolostones in Namibia, Svalbard and NW Canada, which are interpreted to reflect equilibrium with contemporaneous seawater.
	www.snowballearth.org /week4.html (1473 words)

	Confirming by mineral dating
		Now, we believe we have evidence that there were at least three Cryogenian glaciations, and there may have been more," says Shuhai Xiao, Ph.D., of Virginia Tech's Department of Geosciences.
		The research was supported by grants from the Chinese Academy of Sciences, China Ministry of Science and Technology, and the U.S. National Science Foundation.
		In recent years, it has been hypothesized that the earth was covered with ice and the oceans frozen to a depth of one or two kilometers during Cryogenian glaciations--a scenario known as snowball Earth.
	news-info.wustl.edu /tips/page/normal/957.html (770 words)

	Ediacaran Period - Crystalinks
		Rather, the beginning is defined by the appearance of a new texturally and chemically distinctive carbonate layer that indicates a climatic change (the end of a global ice age).
		There is an unusual depletion of 13C that marks the end of the global ice ages of the preceding Cryogenian period.
		The Ediacaran begins at the end of the last ice age of the Snowball Earth, or Cryogenian Period, a term given to a series of glaciations that covered most of our planet between 850-630 or 600 million years ago.
	www.crystalinks.com /edicaran.html (1158 words)

	Geological Society - News - Whiteout
		This late Neoproterozoic event used to be known by the name originally given it in England by the pioneering workers in the field, including Brian Harland and Tony Spencer - the Infracambrian Glaciation.
		Grooved scratch marks on this cobble were formed when it was frozen in a moving glacier and ground against the underlying pavement of the glacial valley.
		In recent years, some of them have come to believe that the entire Earth was covered with ice and the oceans frozen to a depth of one or two kilometres during these glaciations - a scenario known as “Snowball Earth”.
	www.geolsoc.org.uk /template.cfm/template.cfm?name=Snowballs (956 words)

	EO News: New Evidence Supports Three Major Glaciation Events in Distant Past - April 21, 2004
		”The Cryogenian Period is characterized by some of the worst glaciations in earth history.
		Now, we believe we have evidence that there were at least three Cryogenian glaciations, and there may have been more,” says Shuhai Xiao of Virginia Tech’s Department of Geosciences.
		Thus the combination of evidence requires at least three Cryogenian ice ages, the Sturtian, Marinoan, and Gaskiers,” says Xiao.
	earthobservatory.nasa.gov /Newsroom/MediaAlerts/2004/2004042116881.html (823 words)

	Comments (Site not responding. Last check: 2007-10-25)
		The earliest hypothesized ice age is believed to have occurred around 2700 to 2300 million years ago during the early Proterozoic Age.
		The earliest well-documented ice age, and probably the most severe of the last 1000 million years, occurred from 800 to 600 million years ago (the Cryogenian period) and it has been suggested that it produced a Snowball Earth in which permanent sea ice extended to or very near the equator.
		It has been suggested that the end of this ice age was responsible for the subsequent Cambrian Explosion, though this theory is recent and controversial.
	icedeyez87.blogdrive.com /comments?id=4 (447 words)

	Westfälische Wilhelms-Universität Münster > Geologisch-Paläontologisches Institut > Abt. Exogene ... (Site not responding. Last check: 2007-10-25)
		The geochemical results of the Cryogenian glacial succession on the Yangtze platform are viewed against the "snowball Earth" hypothesis.
		Sedimentology and environmental significance of the Cryogenian successions of the Yangtze platform, South China block.
		Palaeoenvironmental implications of sedimentological records combined with geochemical data: a Cryogenian succession on the Yangtze platform in South China, IAS glaciology conference, 2005, Aberystwyth.
	www.uni-muenster.de /GeoPalaeontologie/Geologie/Sedi/Dobrzinski_e.html (507 words)

	News Story \| Virginia Tech News \| Virginia Tech (Site not responding. Last check: 2007-10-25)
		A team of geologists from China and the United States now report evidence of at least three ice ages during that ancient time.
		"The Cryogenian Period is characterized by some of the worst glaciations in earth history," said Shuhai Xiao of Virginia Tech's Department of Geosciences.
		In recent years, it has been hypothesized that the earth was covered with ice and the oceans frozen to a depth of one or two kilometers during Cryogenian glaciations—a scenario known as snowball Earth.
	www.vtnews.vt.edu /story.php?relyear=2004&itemno=237 (1089 words)

	28th DeBeers Alex. Du Toit Memorial Lecture, 2004. On Cryogenian (Neoproterozoic) ice-sheet dynamics and the ...
		On Cryogenian (Neoproterozoic) ice-sheet dynamics and the limitations of the glacial sedimentary record -- Hoffman 108 (4): 557 -- South African Journal of Geology
		On Cryogenian (Neoproterozoic) ice-sheet dynamics and the limitations of the glacial sedimentary record
		The younger Cryogenian glaciation in northern Namibia presents
	sajg.geoscienceworld.org /cgi/content/abstract/108/4/557 (758 words)

	CHASING GLACIERS: CHEMICAL WEATHERING TRENDS IN A POSSIBLE NEOPROTEROZOIC GLACIAL SEQUENCE FROM TIGRAI, N. ETHIOPIA
		Competing hypotheses, under the popularized “Snowball/Slushball Earth” (SEH) moniker, invoke extreme variations in greenhouse gas concentrations that profoundly influenced Earth's hydrologic cycle, and therefore the intensity of chemical weathering.
		Weathering indices (WI) expressing the ratio of immobile-to-mobile cations preserved in detrital aluminosilicates should record these variations, but this potentially informative paleoclimatic tool has yet to be widely applied in Cryogenian studies.
		The Tambien Group is a metasedimentary succession of intercalated slates and limestones, capped locally (Negash) by a diamictite of probable glacial origin.
	gsa.confex.com /gsa/2006SC/finalprogram/abstract_100016.htm (468 words)

	307
		Integrated with the growing fossil record, C and Sr isotope chemostratigraphy facilitates the intra- and inter-basinal correlation of later Neoproterozoic successions.
		(pre-Varanger and post-Sturtian), and (4) the early Cryogenian (pre-Sturtian).
		For most Neoproterozoic intervals combined C and Sr isotope stratigraphy provide a much better tool for correlation than do fossils or available radiometric ages.
	www.the-conference.com /JConfAbs/1/307.html (355 words)

	History Channel Search Results
		An ice age that ended some 635 million years ago, toward the end of Precambrian time, was particularly severe.
		It occurred during the Cryogenian period of the geologic time scale, which lasted from about 850 million to 630 million years ago and gets its name from the Greek word kryos (“icy cold”).
		Some scientists believe ice may have covered the whole earth at this time—a situation dubbed “snowball earth.” It has been suggested that the glaciation that occurred more than 2 billion years ago might also be an instance of a snowball earth.
	www.historychannel.com /thcsearch/thc_resourcedetail.do?encyc_id=212493 (1251 words)

	[No title]
		The 80-km diameter center of this intrusive complex, which punched through the Laurentian craton, has been interpreted as the eruptive site of a major plume head (Higgins, 2005), with a volcanic field (now almost completely eroded) which could have been ~ 2000 km in diameter.
		Although expanded analysis of the APW paths suggests that there may have been several IITPW events in the Cryogenian â“ Cambrian interval (e.g., (Evans, 1998; Kirschvink et al., 1997), this event is constrained to be particularly rapid (ca.
		An Inertial Interchange True Polar Wander (IITPW) event on this time scale is capable of driving regional sea-level fluctuations of up to +/- 4 km (Mound et al., 1999).
	www.gps.caltech.edu /seismo/seminars/JoeKirschvink_Abstract.txt (768 words)

	EarthRef.org Reference Database (ERR) -- Kaufman & Knoll 1995
		However, integrated with the vectorial signals provided by fossils and Sr-isotopic variations, C isotope chemostratigraphy facilitates the interbasinal correlation of later Neoproterozoic successions.
		Results of these studies are evaluated in terms of four stratigraphic intervals: (1) the Precambrian/Cambrian boundary, (2) the post-Varanger terminal Proterozoic, (3) the late Cryogenian, and (4) the early Cryogenian.
		Where biostratigraphic or radiometric data constrain the age of Neoproterozoic sedimentary sequences, secular variations in C and Sr isotopes can provide a level of stratigraphic resolution exceeding that provided by fossils alone.
	earthref.org /cgi-bin/err.cgi?n=655 (283 words)

	Snowball Earth
		Snowball Earth events have been suggested as occuring at about 2.3 billion years ago and between 750 and 580 million years ago.
		According to one theory, the climate shock of the most recent snowball Earth phase, also known as the Cryogenian period, triggered the evolution of complex, multicellular life, which occurred in the Edicaran period.
		Did stardust trigger snowball Earth (Feb 10, 2005)
	www.daviddarling.info /encyclopedia/S/snowball_Earth.html (151 words)

	Glendonites in Neoproterozoic low-latitude, interglacial, sedimentary rocks, northwest Canada: Insights into the ...
		Glendonites in Neoproterozoic low-latitude, interglacial, sedimentary rocks, northwest Canada: Insights into the Cryogenian ocean and Precambrian cold-water carbonates -- James et al.
		Glendonites in Neoproterozoic low-latitude, interglacial, sedimentary rocks, northwest Canada: Insights into the Cryogenian ocean and Precambrian cold-water carbonates
		deposits imply that global ocean water during much of Cryogenian
	geology.geoscienceworld.org /cgi/content/abstract/33/1/9 (229 words)

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