Learning to tell Neoproterozoic time

doi:10.1016/S0301-9268(99)00067-4

Precambrian Research

Volume 100, Issues 1–3, March 2000, Pages 3-20

https://doi.org/10.1016/S0301-9268(99)00067-4 Get rights and content

Abstract

In 1989, the International Commission on Stratigraphy established a Working Group on the Terminal Proterozoic Period. Nine years of intensive, multidisciplinary research by scientists from some two dozen countries have markedly improved the framework for the correlation and calibration of latest Proterozoic events. Three principal phenomena — the Marinoan ice age, Ediacaran animal diversification, and the beginning of the Cambrian Period — specify the limits and character of this interval, but chemostratigraphy and biostratigraphy based on single-celled microfossils (acritarchs), integrated with high-resolution radiometric dates, provide the temporal framework necessary to order and evaluate terminal Proterozoic tectonic, biogeochemical, climatic, and biological events. These data also provide a rational basis for choosing the Global Stratotype Section and Point (GSSP) that will define the beginning of this period. A comparable level of stratigraphic resolution may be achievable for the preceding Cryogenian Period, providing an opportunity to define this interval, as well, in chronostratigraphic terms — perhaps bounded at beginning and end by the onset of Sturtian glaciation and the decay of Marinoan ice sheets, respectively. Limited paleontological, isotopic, and radiometric data additionally suggest a real but more distant prospect of lower Neoproterozoic correlation and stratigraphic subdivision.

Introduction

The sphinx of classical mythology was a fabulous hybrid: woman above and lion below, with the wings of an eagle. Easily enough imagined, sphinxes must nonetheless have been difficult to depict convincingly, the central challenge being to join disparate parts into a seamless whole. The geological time scale is something of a stratigraphic sphinx, and the problem of connecting a biostratigraphically conceived and chronostratigraphically defined Phanerozoic time scale to Archean and Proterozoic scales based strictly on geochronometry is one that classical artists would appreciate. The stratigraphic ‘join’ is the Neoproterozoic Era, its base designated as 1000 Ma and its top defined by the initial Global Stratotype Section and Point (GSSP) of the Cambrian Period (Plumb, 1991; Fig. 1). Of course, the Neoproterozoic Era has, itself, been divided into three periods, the geochronometrically defined (and seldom used) Tonian and Cryogenian periods and the yet to be ratified terminal Proterozoic period, or Neoproterozoic III (Plumb, 1991). Insofar as the terminal Proterozoic period will be defined as the interval between an initial boundary GSSP (not yet chosen) and the beginning of the succeeding Cambrian Period (GSSP ratified; Landing, 1994), this further specifies the ‘join’ as the initial GSSP of Neoproterozoic III.

In 1992, Knoll and Walter reviewed what was then nascent progress in understanding terminal Proterozoic stratigraphy and Earth history. Seven years later, in the wake of an extensive international research effort, it is timely to revisit the conclusions and recommendations of Knoll and Walter (1992) and to cast a critical eye backward onto earlier Neoproterozoic time.

Section snippets

Neoproterozoic III

It has long been recognized that in many parts of the world a distinctive sedimentary succession lies directly beneath basal Cambrian rocks. This package has been identified by various names, including Sinian, Vendian, Ediacaran, and Ediacarian (Harland et al., 1989), but in all cases glaciogenic rocks and Ediacaran fossils figure prominently in definition and characterization. Catalyzed by the creation of a formal working group (under the auspices of the International Commission on

How many ice ages?

The stratigraphy of the Cryogenian Period (Plumb, 1991) — the time of ice ages — lies at the heart of any effort to interpret Neoproterozoic Earth history. The Marinoan ice age may provide a suitable event for the end of the period, but it was not the first Neoproterozoic glaciation, and it may not have been the last (Hambrey and Harland, 1985, Kaufman et al., 1997; see below). Within the Neoproterozoic Era, glacial epochs appear to have been broadly synchronous on a global scale. Like the

Early Neoproterozoic (Tonian) stratigraphy and prospects for a chronostratigraphic definition of the Mesoproterozoic/Neoproterozoic boundary

The stratigraphic interval just below Sturtian glaciogenic rocks appears to be chronostratigraphically distinctive. It is marked by positive C-isotopic profiles (+5 to +8‰) in sections from Namibia (Hoffman et al., 1998), arctic Canada (Asmerom et al., 1991, Kaufman and Knoll, 1995), Australia (Walter et al., 2000), and Spitsbergen [regardless of where one places Sturtian events relative to Akademikerbreen stratigraphy (Knoll et al., 1986)] and is particularly notable for the very low ⁸⁷Sr/⁸⁶Sr

Conclusions

We know how ancient artists succeeded in sculpting the sphinx. They did it not by simply joining a female torso to a cat's loins along a line, but rather by blending the two forms through a transition zone that highlighted the compatible features of both. That, I believe, is also our best way of joining the chronostratigraphic time scale of the Phanerozoic Eon to the geochronometric scale of Earth's earlier history. Neoproterozoic rocks contain a rich record of biological and environmental

Note added in proof

Brasier and colleagues have recently reported a U-Pb zircon date of 723+16/−10 Ma for a tuffaceous horizon within the Gubrah tillite, Oman. The Oman tillites are thought to correlate with Sturtian tillites elsewhere. Thus, if the age of 660+/−15 Ma holds for pre-Varager granites in the Ural Mountains, at least three ice ages occurred during the Neoproterozoic Era. [Brasier, M., McCarron, G., Tucker, R., Leather, J., Allen, P. and Shields, G. (2000) New U-Pb zircon dates for the Neoproterozoic

Acknowledgements

The author thanks Malcolm Walter, Nicholas Christie-Blick, Alan Jay Kaufman, and other members of the ICS Subcommission on the Terminal Proterozoic Period for stimulating discussions on Neoproterozoic stratigraphy, and M.A. Fedonkin, S. Grant, S. Kolosova, and the late Y. Zhang for photographic access to some of the fossils illustrated in this paper. Jim Gehling, Malcolm Walter, John Grotzinger, and Susannah Porter made helpful comments on an earlier draft of the manuscript. This is a

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Citation Excerpt :
Similarly, the δ18O values between -1‰ and −14‰ are considered as slightly altered and values < -14‰ are considered as highly altered by diagenesis (Folling and Frimmel, 2002) (Fig. 4b, h). Sr isotopic concentrations in carbonates are highly susceptible to diagenetic alteration and thus increase the Sr isotopic ratios (Fig. 4c) in carbonates (Knoll, 2000). Carbonates affected by diagenesis show covariance and show more negative values (Fig. 4b) of O and C isotopes.
Sedimentary sequences preserve the records of changes in major controls of sedimentation namely, tectonics, climate, relative sea level and sediment production and preservation. The potential to characterize these changes in spatial and temporal scales has led to the development of the branch of chemostratigraphy. Chemostratigraphic study of sedimentary sequences commenced from recognizing identical/contrasting geochemical features across major geochronological boundaries, and evolved into one of the essential tools in exploration, characterization, and well development strategies. Chemostratigraphy incorporates applications on continuous, real-time geochemical mapping and direction of lateral drilling, and machine learning, among others. As the sedimentary systems operate on a variety of temporal scales that range from few hours (tidal cycles) to few tens of millions of years, within which many perturbations such as catastrophic and diagenetic events take place, that lead to unique geochemical signature which can be correlated at appropriate spatial and temporal scales. The application of chemostratigraphic technique in hydrocarbon exploration and reservoir characterization has gained momentum in recent years, particularly with the advent of developments in analytical instrumentation. This has also led to the integration of a variety of data from field sedimentary structures, mineralogy, major, trace and isotopic chemical compositions of whole rock, selected components of rocks, organic and inorganic components of oil and gas, etc., for reservoir characterization more accurately than ever. The geochemical fingerprinting of oil and gas reservoir components plays a major role in the identification of source rocks, discrimination of oil families, characterization of reservoir, source, and seal segments in petroleum systems. Future trends indicate the relevance and growing applications of machine learning techniques, artificial intelligence in real-time assessment, monitoring and planning of hydrocarbon exploration and production.

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Learning to tell Neoproterozoic time

Abstract

Introduction

Section snippets

Neoproterozoic III

How many ice ages?

Early Neoproterozoic (Tonian) stratigraphy and prospects for a chronostratigraphic definition of the Mesoproterozoic/Neoproterozoic boundary

Conclusions

Note added in proof

Acknowledgements

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Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Precambrian Res.

Earth Planet. Sci. Lett.

Precambrian Res.

Precambrian Res.

A review with descriptions of four unusual forms of the soft-bodied fauna of the Conception and St. John's groups (late Precambrian) Avalon Peninsula Newfoundland

Proc. Third N. Am. Paleont. Conv.

Sedimentological context of a deep-water Ediacaran fauna (Mistaken Point Formation Avalon Zone eastern Newfoundland)

Trace Fossils Small Shelly Fossils and the Precambrian–Cambrian Boundary

Bull. New York State Mus.

First Ediacaran fauna found in western Africa

Geology

A new look at evolutionary rates in deep time: uniting paleontology and high-precision geochronology

GSA Today

Calibrating rates of Early Cambrian evolution

Science

A billion years of environmental stability and the emergence of eukaryotes: new data from northern Australia

Geology

Integrated chemo- and biostratigraphic calibration of early animal evolution: Neoproterozoic–early Cambrian of southwest Mongolia

Geol. Mag.

Ediacaran sponge spicule clusters from southwestern Mongolia and the origins of the cambrian fauna

Geology

Late Vendian (Neoproterozoic III) microbial and algal communities of the Russian Platform: models of facies-dependent distribution, evolution and reflection of basin development

Rivista Ital. Paleontol. Stratigraf.

Diverse organic-walled fossils, including possible dinoflagellates, from the early Neoproterozoic of arctic Canada

Geology

Ediacaran sequence and isotope stratigraphy of the officer Basin, South Australia

Austral. J. Earth Sci.

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Acta Palaeont. Sinica

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Zircon age evidence for the Late Precambrian Acraman ejecta blanket

Austral. J. Earth Sci.

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Geol. Soc. London Q. J.

Sinian Maiohe Biota

A previously unrecognized Late Proterozoic succession: Upper Wilpena Group, northern Flinders Ranges, South Australia

Geol. Surv. S. Aust., Q. Geol. Notes

Paleoichnology of the Vendian Metazoa

New shelly fossils from Nama Group, South West Africa

Am. J. Sci.

Sr isotopic composition in Riphean, Vendian, and Lower Cambrian carbonates from Siberia

Stratigr. Geol. Correl.

Shell structure and distribution of Cloudina, a potential index fossil for the terminal Proterozoic

Am. J. Sci.

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Palaios

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Diverse calcareous Fossils From the Ediacaran-Age (550–543 Ma) Nama Group, Namibia

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Palaeontology