Palaeos: Palaeos Home Page The Cryogenian Period
Neoproterozoic References



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Amthor, JE, JP Grotzinger, S Schröder, & BC Schreiber (2002), Tectonically-driven evaporite-carbonate transitions in a Precambrian/Cambrian saline giant: Ara Salt Basin of South Oman. AAPG An. Mtg. WWW. (abstr.)

Awramik, SM & JP Vanyo (1986), Heliotropism in modern stromatolitesScience 231: 1279-1281.

Bartley, JK & LC Kah (2004), Marine carbon reservoir, Corg-Ccarb coupling, and the evolution of the Proterozoic carbon cycleGeology 32: 129-132.  

Beyth, M, D Avigad H-U Wetzel, A Matthews & SM Berhe (2003), Crustal exhumation and indications for Snowball Earth in the East African Orogen: north Ethiopia and east EritreaPrecam. Res. 123: 187–201.

Bodiselitsch, B, C Koeberl, S Master, & WU Reimold (2005), Estimating duration and intensity of Neoproterozoic snowball glaciations from Ir anomaliesScience 308: 239-242.  

Bottjer, DJ, JW Hagadorn & SQ Dornbos (2000), The Cambrian substrate revolution. GSA Today 10: 1-7.

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Chakraborty, PP, A Sarkar, SK Bhattacharya & P Sanyal (2002), Isotopic and sedimentological clues to productivity change in Late Riphean sea: A case study from two intracratonic basins of IndiaProc. Indian Acad. Sci. 111: 379-390.  

Corsetti, FA & AJ Kaufman (1999), At least three carbon isotope excursions/glaciations in the Neoproterozoic: Carbon isotope chemostratigraphy of Neoproterozoic-Cambrian strata, southern Great Basin, USANinth Annual V.M. Goldschmidt Conference. (abstr.)

Corsetti, FA, SM Awramik & D Pierce (2003), A complex microbiota from snowball Earth times: Microfossils from the Neoproterozoic Kingston Peak Formation, Death Valley, USAProc. Nat. Acad. Sci. USA 100: 4399-4404.  

Christie-Blick, N, LE Sohl & MJ Kennedy (1999), Considering a Neoproterozoic Snowball EarthScience 284: 1087a.  

Davidson, EH, K Peterson & RA Cameron (1995), Origin of the adult bilaterian body plans: Evolution of developmental regulatory mechanismsScience 270: 1319-1325.

Davis, SR & DM Wilkinson (2004), The conservation management value of testate amoebae as ‘restoration’ indicators: speculations based on two damaged raised mires in northwest EnglandThe Holocene 14: 135-143. 

Dornbos, SQ, DJ Bottjer & J-Y Chen (2004), Evidence for seafloor microbial mats and associated metazoan lifestyles in Lower Cambrian phosphorites of Southwest ChinaLethaia 37: 127-137.  

Dornbos, SQ, DJ Bottjer & J-Y Chen (2005), Paleoecology of benthic metazoans in the Early Cambrian Maotianshan Shale biota and the Middle Cambrian Burgess Shale biota: Evidence for the Cambrian substrate revolutionPalaeogeog. Palaeoclimat. Palaeoecol. 220: 47– 67.  

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Frimmel, HE & PG Fölling, (2004), Late Vendian closure of the Adamastor Ocean: Timing of tectonic inversion and syn-orogenic sedimentation in the Gariep BasinGond. Res. 7: 685-699.  Folling

Goodman, JC & RT Pierrehumbert (2003), Glacial flow of floating marine ice in "Snowball Earth"J. Geophys. Res. 108: 3308.

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Hagadorn, JW (1998), Restriction of a Late Neoproterozoic biotope: Ediacaran faunas, microbial structures, and trace fossils from the Proterozoic-Phanerozoic transition, Great Basin, USA.  Unpub. Ph.D. thesis, Univ. So'ern. Calif., 214 pp.

Halverson, GP, PF Hoffman, DP Schrag & AJ Kaufman (2002), A major perturbation of the carbon cycle before the Ghaub glaciation (Neoproterozoic) in Namibia: Prelude to snowball Earth?  Geochem. Geophys. Geosys. 3(6), 10.1029/ 2001GC000244.  

Hambrey, MJ & WB Harland (1981), Earth’s Pre-Pleistocene Glacial Record. Cambridge.

Harland, WB (1964), Critical evidence for a great Infra-Cambrian glaciation. Geol. Rundsch. 54: 45–61.

Harland, WB & MJS Rudwick (1964), The Great Infra-Cambrian Ice AgeScientific American, August 1964: 28-36.

Hoffman, PF & DP Schrag (1999), Considering a Neoproterozoic Snowball Earth -- ResponseScience 284: 1087a.  

Hoffman, PF & DP Schrag (2000), Snowball Earth. Scientific American, January 2000, pp. 68-75.  

Hoffman, PF & DP Schrag (2002), The Snowball Earth hypothesis: Testing the limits of global changeTerra Nova 14, 129–155.

Hoffman, PF, AJ Kaufman, GP Halverson, & DP Schrag (1998), A Neoproterozoic Snowball EarthScience 281: 1342.

Holland, HD (2003), The Geologic History of Seawater, in HD Holland & KK Turekian [eds.], Treatise on Geochemistry Elsevier, 6: 583-625.  

Huntley, JW, S-H Xiao, & M Kowalewski (2006), 1.3 Billion years of acritarch history: An empirical morphospace approachPrecambrian Res. 144: 52–68. 

Hyde, W, TJ Crowley, SK Baum & WR Peltier (2000), Neoproterozoic ‘Snowball Earth’ simulations with a coupled climate/ice-sheet modelNature 405: 425–429.

Kah, LC, TW Lyons & TD Frank (2004), Low marine sulphate and protracted oxygenation of the Proterozoic biosphereNature 431: 834-838.  

Kaufman, AJ, AH Knoll & GM Narbonne (1997), Isotopes, ice ages, and terminal Proterozoic earth historyProc. Natl. Acad. Sci. USA 94: 6600-6605.

Kennedy, MJ, N Christie-Blick & LE Sohl (2001), Are Proterozoic cap carbonates and isotopic excursions a record of gas hydrate destabilization following Earth's coldest intervals?  Geology 29: 443-446.  

Kilner, B, C Mac Niocaill & M Brasier (2005), Low-latitude glaciation in the Neoproterozoic of OmanGeology 433: 413-416.  

Kirschvink, JL (1992), Late Proterozoic low-latitude global glaciation: the Snowball Earth, in JW Schopf & C Klein [eds.] The Proterozoic Biosphere – A Multidisciplinary Study. Cambridge, pp. 51-52.

Kirschvink, JL (2002), Quand tous les Océans étaient gelésLa Recherche 355: 26-30.

Kirschvink, JL, EJ Gaidos, LE Bertani, NJ Beukes, J Gutzmer, LN Maepa, & RE Steinberger (2000), Paleoproterozoic snowball Earth: Extreme climatic and geochemical global change and its biological consequencesProc. Nat. Acad. Sci. USA 97: 1400-1405.  

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Knoll, AH (2000), Learning to tell Neoproterozoic timePrecam. Res. 100: 3-20.  

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McMechan, ME (2000), Vreeland diamictites – Neoproterozoic glaciogenic slope deposits, Rocky Mountains, northeast British ColumbiaBul. Can. Pet. Geol. 48: 246-261.

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[1]  We were embarrassed to find that there is no other full explanation of carbon isotopes in Palaeos, so here we go.  We assume no background.  


All ordinary materials are made up of atoms.  Atoms contain a very small, very dense nucleus.  The nucleus is made up of two kinds of particles: protons, which have a positive charge, and neutrons which are very similar, but have no charge.  The electric charges in the nucleus do not cause the nucleus to fly apart because these nucleons (protons & neutrons) are held together by the strong nuclear force, which is stronger than electrical repulsion at very short distances.  The nucleus is surrounded by a very much larger, but more diffuse, cloud of negatively-charged electrons.  Each electron has exactly the same charge as a proton, although it is much less massive.  This supplies overall electrical charge neutrality to the atom.

The chemical behavior of atoms is almost (remember the almost!) completely determined by the electron cloud, and the number of electrons is controlled by the number of protons in the nucleus.  So, any atom with 6 protons in the nucleus behaves about the same as any other atom with the same count.  Thus elements are defined by reference to the number of protons in the nucleus, which is also the atomic number of the element.  Any atom with 6 protons is an atom of carbon.  

Notice we have said nothing about neutrons.  For chemical purposes, they don't matter.  However, only nuclei with certain numbers of neutrons are stable for each element.  Thus, we only find carbon atoms with 6, 7, or 8 neutrons.  These different varieties of carbon atom are referred to as isotopes.  Isotopes are referred to by their total number of nucleons.  Thus, the most common type of carbon has 6 protons (by definition) and 6 neutrons and is designated 12C.  The isotope 13C is also common and is also stable.  Carbon-14, or 14C, is created in very small quantities by nuclear reactions in the upper atmosphere involving nitrogen (element 7) and cosmic rays.  14C is not stable.  One of the neutrons tends to flip back to being a proton, with the release of energy in the form of a very energetic electron.  That energetic electron is one form of radioactivity.  There is a 50% chance that this radioactive decay will happen to any given atom of 14C in 5730 years.  Thus, we say that 14C is a radioactive isotope with a half-life of 5730 years.

In the universe as a whole, 12C makes up about 99% of all carbon, while 13C is about 1%.  14C makes up a vanishingly small fraction, which we can ignore.  All atoms of carbon ought to behave in almost same way in chemical reactions.  Do you still remember the "almost"?  It becomes important here because it turns out that the enzymes involved in photosynthesis are a little biased.  They are slightly more likely to fix CO2 molecules with 12C than we would expect by chance.  Virtually all carbon in living things ultimately derives from photosynthesis.  Thus almost all organic (or biogenic) carbon, carbon which is or was part of a living creature, is isotopically light, meaning it has slightly more than the usual 99% 12C. When a great deal of carbon is tied up in organic sediments, the remaining carbon in atmospheric carbon dioxide becomes isotopically heavy.  This is called a positive excursion in 13C, or, for those wishing to be particularly obscure, a positive δ13C anomaly.  Fortunately, it is remarkably easy to measure the ratios of carbon isotopes to very high precision using mass spectroscopy (= mass spec). By examining ancient inorganic carbon, we can read the isotopic state of the atmosphere at any given time in the past.   There can be great debate about the reasons for an excursion, but the existence, and usually the magnitude, of the excursion are easily determined and quite reproducible.  

Footnote to footnote: We apologize for the stupid picture.  Do not get the idea that electrons orbit about the nucleus like a planet circling a star.  That is completely inaccurate.  Explaining why would take too long, so we'll take it up another time.

[2]  Chris's essay explains the cap carbonates here. These are calcium magnesium carbonates, or dolomite [CaMg(CO3)2], associated with the end of the major glaciations, and overlying the glacial tillite (unsorted terminal glacial rock) on all continents.  The cap carbonates are sometimes found without tillite, presumably deposited in deep water not actually reached by the continental glaciers.  

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