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Topic: Neoproterozoic

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In the News (Thu 18 Oct 18)

 Snowball Earth
Assuming volcanoes of the Neoproterozoic belched out gases at the same rate as they do today, the planet would have remained locked in ice for up to tens of millions of years before enough carbon dioxide could accumulate to begin melting the sea ice.
Similarly sharp carbon isotope excursions are associated with documented mass extinctions, though the Neoproterozoic excursions are the most extreme and of the longest duration (Knoll and Carroll 1999; Hoffman and Schrag 2000).
Thus, it is concluded that the upper diamictites in Norway (Mortenses) and Scotland (Loch na Cille) correspond to a third glaciation: the Varangerian.
www.peripatus.gen.nz /paleontology/SnoEar.html   (4762 words)

 Comings and Goings of Global Glaciations on a Neoproterozoic Carbonate Platform in Namibia
An enduring enigma of Neoproterozoic earth history is the intimate association of glacial diamictites with typical warm-water carbonates.
Spanning the late Neoproterozoic ice ages are huge positive-to-negative carbon isotopic shifts, unique in the past two billion years (Fig 2).
The long-lived strong enrichments in ¹³C indicate high proportional burial of organic carbon, consistent with late Neoproterozoic fragmentation of the supercontinent Rodinia and consequent increase in continental margins (Hoffman, 1991), which are the major repositories for organic carbon (Hedges and Keil, 1995).
www.geol.umd.edu /~kaufman/iceages.html   (6829 words)

 Palaeos Proterozoic : Neoproterozoic
The Neoproterozoic is a vast stretch of time which science is just beginning to explore.
Many may not be metazoans at all, but a competing lineage of Fungi that became extinct in the Early Cambrian.
All things considered, the Neoproterozoic is likely to be the most exciting region of spacetime to be involved with over the next decade or two.
www.palaeos.com /Proterozoic/Neoproterozoic/Neoproterozoic.html   (619 words)

 Journal of the Geological Society: U-Pb geochronology of late Neoproterozoic augen granites in the Moine Supergroup, NW ...
Abstract: Within the Caledonides of Caithness, Scotland, the Neoproterozoic metasedimentary rocks of the Moine Supergroup are intruded by minor sheets of strongly deformed granite.
Intrusion was, however, broadly contemporaneous with late Neoproterozoic extension of the Laurentian margin during continental break-up and the opening of the Iapetus Ocean.
The new data broaden the extent of this late Neoproterozoic magmatic event in the Scottish Highlands: other deformed granites that are at present undated but have been assumed to be of Caledonian age therefore require reinvestigation.
www.findarticles.com /p/articles/mi_qa3721/is_200311/ai_n9342288   (1352 words)

 [No title]   (Site not responding. Last check: 2007-11-06)
Since Eldridge Moores (1991) proposed the "SWEAT" hypothesis--that Antarctica was the Neoproterozoic conjugate rift margin to western North America--many continental reconstructions for Late Proterozoic time have been proposed (Hoffman, 1991; Kirschvink, 1992a; McKerrow et al., 1992; Dalziel, 1992; Dalziel et al., 1994).
Unfortunately, global synchroneity of Neoproterozoic glaciogenic deposits, however permissable given existing isotopic data, has yet to be demonstrated conclusively.
Nonetheless, direct paleomagnetic study of Neoproterozoic tillites can determine the severity of these glacial episodes, an issue that has been spurred by a recent debate of the Snowball Earth model (Kirschvink, 1992b; Meert and Van der Voo, 1994; Williams et al., 1995; Schmidt and Williams, 1995).
www.gps.caltech.edu /MagLab/proj_dave.html   (1321 words)

 Neoproterozoic Allochthonous Salt Tectonics During the Lufilian Orogeny
R., 2003, Neoproterozoic allochthonous salt tectonics during the Lufilian orogeny in the Katangan Copperbelt, central Africa: Geological Society of America Bulletin, v.
The Neoproterozoic Katangan rocks in the Copperbelt of Shaba (Democratic Republic of the Congo) and Zambia contain the world's largest concentration of stratiform copper-cobalt ores.
We propose that during the Lufilian orogeny, the Katangan basin was radically transformed first by extrusion of allochthonous evaporites then by orogenic shortening.
www.beg.utexas.edu /resprog/salttectonics/neoproterozoic.htm   (356 words)

 Shuhai Xiao
Nonetheless, these Neoproterozoic glaciations are expected to have had significant impact on biological evolution in the Neoproterozoic.
One of the important hurdle in the study of the interactions between climate changes and biological evolution in the Neoproterozoic is that the stratigraphic correlation of Neoproterozoic successions is rather imprecise.
The disparity between bilaterian and non-bilaterian tierers during the Neoproterozoic Cambrian transition and the delayed appearance of high tiering bilaterians is an interesting paleoecological topic.
www.geol.vt.edu /paleo/Xiao/XiaoResearchProjects.htm   (1009 words)

 Palaeos Proterozoic: Neoproterozoic: References
Allen, PA and PF Hoffman (2005), Extreme winds and waves in the aftermath of a Neoproterozoic glaciation.
Poulson, CJ, RT Pierrehumbert and RL Jacob (2001), Impact of ocean dynamics on the simulation of the Neoproterozoic "snowball Earth".
Rahn, T and JM Eiler (2000), Carbon isotope fractionation associated with adsorption of CO on mineral substrates and its relevance to the study of Mars.
www.palaeos.com /Proterozoic/Neoproterozoic/Cryogenian/References.html   (1923 words)

 Shuhai Xiao
Reliable reconstruction of the temporal and spatial distribution of Neoproterozoic biodiversity is critical to the understanding of the interactions between Neoproterozoic climate change and biological evolution.
The Quruqtagh Group in the Gobi desert of NW China is the only Neoproterozoic succession that has been cited to contain three glacial intervals.
Neoproterozoic diamictites and stable carbon isotope chemostratigraphy of the Quruqtagh Series, NW China.
www.geol.vt.edu /profs/xiao   (2523 words)

A full understanding of the Neoproterozoic, a period characterized by extreme climatic fluctuations and major biological change, has been hindered by a lack of high-precision geochronological constraints.
The close stratigraphic juxtaposition of the youngest (?) Neoproterozoic glaciogenic rocks and those preserving the earliest large animal fossils is suggestive of an environmental control on Metazoan evolution.
A highly-resolved Neoproterozoic timescale will be required to understand the significance of glaciations and their effect on ocean and atmospheric chemistry and evolution.
gsa.confex.com /gsa/2003AM/finalprogram/abstract_67490.htm   (462 words)

 Neoproterozoic glaciation may have ended with a methane gasp   (Site not responding. Last check: 2007-11-06)
Globally distributed Neoproterozoic diamictites (glacial till) are interpreted to be the result of periods of intense global glaciation, with ice extending even to tropical latitudes (Hoffman et al., 1998).
Some of the diamictites are directly overlain by thin (a few m) but persistent carbonate layers known as cap carbonates.
Other similar events are interpreted to have occurred during the Paleocene and the Jurassic, and it is not unreasonable to suggest that this could happen again in response to the current episode of climate warming.
www.mala.bc.ca /~earles/neoprot-mh-dec03.htm   (514 words)

 Inventory of Neoproterozoic and Paleozoic strata in Sonora, Mexico   (Site not responding. Last check: 2007-11-06)
This compilation is an inventory of all known outcrops of Neoproterozoic and Paleozoic strata in Sonora, Mexico.
He proposed that the emplacement of the Sonora allochthon was along a major Permian transpressional structure that was primarily a strike-slip fault with only a minor thrust component.
The inventory presented here is the product of a search of the literature for described Neoproterozoic and Paleozoic localities and our examination of a large number of the outcrops in the field.
geopubs.wr.usgs.gov /open-file/of02-97   (459 words)

 Journal of the Geological Society: ^sup 87^Sr/^sup 86^Sr chemostratigraphy of Neoproterozoic Dalradian limestones of ...
The heterolithic Neoproterozoic to Cambrian Dalradian Supergroup of Scotland and Northern Ireland was deposited on the eastern margin of Laurentia as it began to break out of Rodinia (Dalziel 1992, 1994), and was deformed and metamorphosed during the Ordovician Grampian orogeny (Harris et al.
Because the age ranges of most Neoproterozoic sedimentary successions are poorly constrained by radiometric or biostratigraphical dating, ^sup 87^Sr/^sup 86^Sr data are widely used to constrain such ages and aid correlation of Neoproterozoic sedimentary sequences in widely separated regions (e.g.
Brasier & Shields (2000) recently used the ^sup 87^Sr/^sup 86^Sr and [delta]^sup 18^O of carbonates beneath the Neoproterozoic glacigenic Port Askaig Formation in the Dalradian of the SW Scottish Highlands to propose a Sturtian (c.
www.findarticles.com /p/articles/mi_qa3721/is_200403/ai_n9392828   (1266 words)

 The Snowball Earth
Some of these organisms appeared capable of surviving global glaciation and their existence in the Neoproterozoic was unquestioned—molecular studies showed that they disproportionately represent the oldest branches in the universal tree of life.
The Neoproterozoic carbon isotopic record is very different, not only because the amounts of carbon-13 are generally much higher than modern sediments, but also because the rocks immediately surrounding the glacial deposits show huge excursions towards much lower levels of carbon-13.
In Neoproterozoic times, this region of southwest Africa was part of a vast, gently subsiding, continental shelf, located in low southern latitudes and subject to nearly unbroken carbonate sedimentation, similar to the Bahama Banks in the tropical Atlantic.
www-eps.harvard.edu /people/faculty/hoffman/snowball_paper.html   (5383 words)

 Phosphatized multicellular algae in the Neoproterozoic Doushantuo Formation, China, and the early evolution of ...
Phosphatized multicellular algae in the Neoproterozoic Doushantuo Formation, China, and the early evolution of florideophyte red algae -- Xiao et al.
Knoll A. Xiao 2003 Algae and the late Neoproterozoic evolution of macroscopic multicellularity.
Yin C. 2001 Discovery of Papillomembrana compta in Weng'an, Guizhou with discussion on the correlation of the large acanthomorphic acritarchs and the age of the Doushantuo Formation.
www.amjbot.org /cgi/content/full/91/2/214   (5881 words)

 Neoproterozoic-Early Paleozoic History of the Scottish Promontory of Laurentia
If correct, Neoproterozoic orogeny in Scotland seems doubtful and deformation in these rocks is more likely related to the assembly of Laurentia and northwestern Europe during the Early Paleozoic (consistent with other regions along the Laurentian margin).
Discounting Neoproterozoic orogeny in Scotland would simplify the pre-Caledonian history of the Scottish promontory of Laurentia in which Neoproterozoic magmas would relate to two separate phases of protracted rifting during the Riphean (~900-800 Ma) and Vendian (~600 Ma) periods.
Alternatively, confirming the existence of Neoproterozoic orogeny in Scotland may dissociate Scotland from the rest of the NE Laurentian margin, thereby inferring crustal exchange between a Gondwanide continent and Laurentia during the latest Precambrian.
www.ig.utexas.edu /research/projects/scott_prom   (485 words)

 The Neoproterozoic Play in Saudi Arabia   (Site not responding. Last check: 2007-11-06)
The Neoproterozoic succession in Saudi Arabia remains unexplored, largely due to the country’s historical abundance of shallower and more conventional plays.
Recent field studies, combined with new lithological analyses and subsurface mapping, reveal that the Neoproterozoic is also prospective in Saudi Arabia and may represent a significant unconventional play of the future.
Correlation of these Neoproterozoic strata across the Arabian Plate is critical to understanding the potential of this play in Saudi Arabia, and detailed age dating is in progress.
aapg.confex.com /aapg/sl2003/techprogram/paper_77828.htm   (307 words)

 Neoproterozoic Magmatism in the Suwannee Terrane   (Site not responding. Last check: 2007-11-06)
Neoproterozoic Magmatism in the Suwannee Terrane: Implications for Terrane Correlation
U-Pb zircon geochronology indicates a crystallization age of 552 ± 8 Ma for a dacite from this sequence, equivalent to crystallization ages of 551 Ma determined for samples of Osceola granite in central Florida, but younger than a 625 ± 2 Ma age determined for a granodiorite in the northwestern Suwannee terrane (southern Alabama).
Suwannee terrane magmatism is generally coeval with magmatism in the Avalon and Carolina terranes as well as with Neoproterozoic orogenic events in West Africa and northern South America.
www.geology.ufl.edu /manuscripts/suwannee.abst.html   (168 words)

 Carbonaceous megaremains from the Neoproterozoic Owk Shales
On the basis of the present fossil assemblage, the OSF is considered to be of the Neoproterozoic age.
The occurrence of Tawuia in the OSF assemblage is very characteristic of Neoproterozoic successions, and is helpful in establishing the age of OSF.
Hence on correlation, we presume that the Kurnool Formation is coeval to the Rewa and Bhander Groups of the Vindhyan Supergroup and the Halkal Formation of the Bhima Group.
www.ias.ac.in /currsci/may10/articles24.htm   (2388 words)

 Preliminary Digital Geologic Map of the Appalachian Piedmont and Blue Ridge, South Carolina Segment
Metamorphosed quartz diorite to diorite (Paleozoic or Neoproterozoic?)
Migmatitic paragneiss and schist of Kiokee belt (Cambrian or Neoproterozoic?)?
Felsic metavolcanic rocks and layered felsic gneiss interpreted to be metavolcanic (Ordovician to Neoproterozoic?)
geo-nsdi.er.usgs.gov /metadata/open-file/01-298/metadata.faq.html   (3382 words)

 Testate amoebae in the Neoproterozoic Era: evidence from vase-shaped microfossils in the Chuar Group, Grand Canyon -- ...
Testate amoebae in the Neoproterozoic Era: evidence from vase-shaped microfossils in the Chuar Group, Grand Canyon -- Porter and Knoll 26 (3): 360 -- Paleobiology
Testate amoebae in the Neoproterozoic Era: evidence from vase-shaped microfossils in the Chuar Group, Grand Canyon
A vaucheriacean alga from the middle Neoproterozoic of Spitsbergen: implications for the evolution of Proterozoic eukaryotes and the Cambrian explosion
paleobiol.geoscienceworld.org /cgi/content/abstract/26/3/360   (640 words)

 Stable isotopic evidence for methane seeps in Neoproterozoic postglacial cap carbonates : Nature
The most compelling criticism of the latter 'methane hydrate' hypothesis has been the apparent lack of extreme isotopic variation in cap carbonates inferred locally to be associated with methane seeps.
Here we report carbon isotopic and petrographic data from a Neoproterozoic postglacial cap carbonate in south China that provide direct evidence for methane-influenced processes during deglaciation.
This evidence lends strong support to the hypothesis that methane hydrate destabilization contributed to the enigmatic cap carbonate deposition and strongly negative carbon isotopic anomalies following Neoproterozoic ice ages.
www.nature.com /nature/journal/v426/n6968/abs/nature02201.html   (293 words)

 GSA 2003 Annual Meeting Press Release - A New Look at Neoproterozoic Earth
Bruce Runnegar, Director of the NASA Astrobiology Institute, will discuss how this period of intense interaction between Earth surface processes and the biosphere serves as a testbed for the emerging field of astrobiology.
Controversy regarding the length of time that elapsed between the last major ice age and the emergence of large animals, a significant issue of Neoproterozoic geobiology, is addressed in three talks:
During the GSA Annual Meeting, Nov. 2-5, contact Ann Cairns at the GSA Newsroom, Washington State Convention Center and Trade Center, Seattle, for assistance and to arrange for interviews: 206-219-4615.
www.geosociety.org /news/pr/03-32.htm   (328 words)

 Figure 4 | Neoproterozoic /`snowball Earth/' simulations with a coupled climate/ice-sheet model : Nature
Neoproterozoic 'snowball Earth' simulations with a coupled climate/ice-sheet model
b, Annually averaged temperature for a GCM Neoproterozoic simulation using the above ice sheets as a lower boundary condition.
A considerable area of open water exists in the tropics, though the ice sheets are almost everywhere below the melting point.
www.nature.com /nature/journal/v405/n6785/fig_tab/405425a0_F4.html   (140 words)

 Biotic enhancement of weathering, atmospheric oxygen and carbon dioxide in the Neoproterozoic
It has been suggested that biological colonization of the land surface began in the Neoproterozoic 1000–544 million years ago (Ma).
We hypothesize that this colonization involved selective weathering of P from rocks, as well as an amplification of overall weathering rates.
This in turn may have provided a necessary condition for the evolution of animals with hard skeletons seen in the ‘Cambrian explosion’;.
www.agu.org /pubs/crossref/2004/2003GL018802.shtml   (252 words)

 NAI: Year 5 Annual Report: Harvard University   (Site not responding. Last check: 2007-11-06)
Bowring, S.M., Myrow, P., Landing, E., Ramezani, J. & Grotzinger, J. Geochronological constraints on terminal Neoproterozoic events and the rise of Metazoans [Abstract].
Geochronological constraints on Neoproterozoic glaciations and the rise of Metazoans [Abstract].
Hoffman, P.F. Carbonates bounding glacial deposits: Evidence for snowball Earth episodes and greenhouse aftermaths in the Neoproterozoic Otavi Group of northern Namibia.
nai.arc.nasa.gov /year5/year4.cfm?PageAction=5&Section=7&Page=21&SortType=Project&Start=31   (635 words)

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