Nicholas Christie-Blick

Sedimentary Geology and Tectonics

Nicholas Christie-Blick Homepage

Neoproterozoic Earth History

The last 200 million years or so of the Neoproterozoic, from ~750-543 m.y. ago, is perhaps the most remarkable interval in the history of our planet – a time of supercontinental breakup and assembly, of the first appearance of complex animals in the fossil record, and of widespread glaciation, with continental ice sheets extending at sea level to within a few degrees of the equator. Now that the reality of low-latitude glaciation is comparatively well established, from paleomagnetic studies in Australia, an important avenue of research has to do with the conditions under which such extreme climate might arise. One of the more puzzling observations in Neoproterozoic successions is that glacial strata are widely overlain by thin layers of carbonate rock with unusually large negative carbon isotopic excursions (d¹³C values as low as -5 ⁰/00). The origin of these carbonates and their associated isotopic anomalies is currently a matter of heated debate, with one of the more startling hypotheses (the "snowball Earth") calling upon rapid post-glacial drawdown of atmospheric CO₂, which, it is supposed, reached levels as high as 120,000 ppm as result of greatly diminished continental weathering and isolation from the ocean by a virtually continuous carapace of reflective sea ice. Ongoing research casts doubt on this hypothesis, and suggests a very different scenario – that the observed isotopic anomalies are due to an addition to the ocean of isotopically depleted carbon from the degradation of gas hydrates. New carbon isotopic data from the Doushantuo cap carbonate of south China provide direct evidence for methane-related processes during deglaciation. Limestone peloids, clots and fringing cements within and above tepee-like structures are associated with highly variable d¹³C values ranging from +5 to –41 ⁰/00.

An associated issue concerns the details of the carbon isotopic record for the Neoproterozoic and the number of ice ages during that span. Recent work in the carbonate-rich succession of the Lesser Himalaya, northern India, provides perhaps the best window on the global isotopic record, as well as insights into the complexities that are undoubtedly introduced in many Neoproterozoic successions by diagenesis and metamorphism. The new data cast doubt on the hypothesis that there may have been as many as four or five ice ages rather than the two main glaciations that are generally recognized (Sturtian and Marinoan or Varanger). The new data are consistent with the interpretation of two main glaciations (Sturtian and Marinoan at ~720-675 Ma and ~650-635 Ma, respectively; Blaini Formation), and with the shorter and less extensive Gaskiers glaciation at 585-582 Ma (incised valleys within marine siltstone of the Infra Krol Formation). Carbon isotopic minima in the overlying Krol platform do not correspond in a simple way with sequence boundaries.

Recent Publications

Chandler, M.A., and Sohl, L.E., 2000. Climate forcings and the initiation of low-latitude ice sheets during the Neoproterozoic Varanger glacial interval: Journal of Geophysical Research, v. 105, p. 20,737-20,756.

Christie-Blick, N., 1997. Neoproterozoic sedimentation and tectonics in west-central Utah, in Link, P.K., and Kowallis, B.J., eds., Proterozoic to Recent Stratigraphy, Tectonics and Volcanology, Utah, Nevada, Southern Idaho and Central Mexico: Brigham Young University Geology Studies, v. 42, Part I, p. 1-30.

Christie-Blick, N., Dyson, I.A., and von der Borch, C.C., 1995. Sequence stratigraphy and the interpretation of Neoproterozoic earth history, in Knoll, A.H., and Walter, M., eds., Neoproterozoic Stratigraphy and Earth History: Precambrian Research, v. 73 (special volume), p. 3-26.

Christie-Blick, N., Sohl, L.E., and Kennedy, M.J., 1999. Considering a Neoproterozoic snowball earth (Technical Comment): Science, v. 284, p. 1087.  [Full text]

Christie-Blick, N., Williams, G.E., and Gostin, V.A., 2001. Discussion on mantle plume uplift in the sedimentary record: origin of kilometre-deep canyons within late Neoproterozoic successions, South Australia: Journal of Geological Society of London, v. 158, p. 573-576.

Jiang Ganqing, Christie-Blick, N., and Kaufman, A.J., 2002. A first order evaluation of Neoproterozoic carbon isotope data within a physical stratigraphic context: Geological Society of America, Abstracts with Programs, v. 34, No. 6, p. 355.

Jiang Ganqing, Christie-Blick, N., Kaufman, A.J., Banerjee, D.M., and Rai, V., 2002. Sequence stratigraphy of the Neoproterozoic Infra Krol Formation and Krol Group, Lesser Himalaya, India: Journal of Sedimentary Research, v. 72, p. 525-543.

Jiang Ganqing, Christie-Blick, N., Kaufman, A.J., Banerjee, D.M., and Rai, V., 2003. Carbonate platform growth and cyclicity at a terminal Proterozoic passive margin, Infra Krol Formation and Krol Group, Lesser Himalaya, India: Sedimentology, v. 50, p. 1-32.

Jiang Ganqing, Kennedy, M.J., and Christie-Blick, N., 2003. Stable isotopic evidence for methane seeps in Neoproterozoic postglacial cap carbonates: Nature, v. 426, p. 822-826.

Jiang Ganqing, Sohl, L.E., and Christie-Blick, N., 2003. Neoproterozoic stratigraphic comparison of the Lesser Himalaya (India) and Yangtze block (South China): Paleogeographic implications: Geology, v. 31, p. 917-920.

Kennedy, M.J., Christie-Blick, N., and Sohl, L.E., 2001. Are Proterozoic cap carbonates and isotopic excursions a record of gas hydrate destabilization following Earth's coldest intervals?: Geology, v. 29, p. 443-446. [See Replies to Comments, Geology v. 30, p. 287-288 and p. 763.]

Kennedy, M.J., Christie-Blick, N., and Prave, A.R., 2001. Carbon isotopic composition of Neoproterozoic glacial carbonates as a test of paleoceanographic models for snowball Earth phenomena: Geology, v. 29, p. 1135-1138.

Kennedy, M.J., and Christie-Blick. N., 2002. Isotopic and sequence stratigraphic constraints on the duration of Neoproterozoic cap carbonate deposition: Goldschmidt Conference, Abstracts, p. A374.

Levy, M., Christie-Blick, N., and Link, P.K., 1994. Neoproterozoic incised valleys of the eastern Great Basin, Utah and Idaho: Fluvial response to changes in depositional base level, in Dalrymple, R.W., Boyd, R., and Zaitlin, B.A., eds., Incised Valley Systems: Origin and Sedimentary Sequences: SEPM (Society for Sedimentary Geology) Special Publication No. 51, p. 369-382.

Link, P.K., Miller, J.M.G., and Christie-Blick, N., 1994. Glacial-marine facies in a continental rift environment: Neoproterozoic rocks of the western United States Cordillera, in Deynoux, M., Miller, J.M.G., Domack, E.W., Eyles, N., Fairchild, I.J., and Young, G.M., eds., Earth's Glacial Record: Cambridge, Cambridge University Press, p. 29-46.

Sohl, L.E., Christie-Blick, N., and Kent, D.V., 1999. Paleomagnetic polarity reversals in Marinoan (ca. 600 Ma) glacial deposits of Australia: Implications for the duration of low-latitude glaciation in Neoproterozoic time: Geological Society of America Bulletin, v. 111, p. 1120-1139.

Stewart, J.H., Gehrels, G.E., Barth, A.P., Link, P.K., Christie-Blick, N., and Wrucke, C.T., Jr., 2001. Detrital zircon provenance of Mesoproterozoic to Cambrian arenites in the western United States and northwestern Mexico: Geological Society of America Bulletin, v. 113, p. 1343-1356.

Zhang Shihong, Jiang Ganqing, Zhang Junming, Song Biao, Kennedy, M.J., and Christie-Blick, N., 2005. U-Pb sensitive high-resolution ion microprobe ages from the Doushantuo Formation in south China: Constraints on late Neoproterozoic glaciations: Geology, v. 33, p. 473-476.