A chronostratigraphic division of the Precambrian: possibilities and challenges

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A chronostratigraphic division of the
Precambrian possibilities and challenges

• Martin J. Van Kranendonk
• Geological Survey of Western Australia
• Chair, ICS Precambrian Subcommission

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Current ICS stratigraphic chart
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Proterozoic timescale based on Supercontinent
assembly
Bleeker, 2003 Lithos 71, 99-134
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Current ICS stratigraphic chart
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Problem 4 Many significant geodynamic events
are not reflected in current timescale
e.g. appearance of first ophiolites at 2.0
Ga, reflecting what many believe is the onset of
truly modern plate tectonics.
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Problem 5 Global geodynamic events are
highly diachronous

• e.g. Archean-Proterozoic boundary
• Pilbara Craton (Australia) 2.78 Ga,
• Superior Craton (N. America) c. 2.5 Ga.

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Problem 5 Global geodynamic events are highly
diachronous

• e.g. global rifting at end of Archean

2750
2700
2650
2600
2550
2500
2450
2400
2350
Great dyke
Black Range dyke
Matachewan dykes
375 Million years!!
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Precambrian timescale revision Rationale and
aims we seek trend-related events that have
affected the entire Earth over relatively short
intervals of time and left recognizable
signatures in the rock sequences of the globe.
Such attributes are more likely to result from
events in atmospheric, climatic, or biologic
evolution than plutonic evolution.. i.e.
crust-forming events operate at 100s million
year scale, vs. biological events at lt1 million
year scale
Cloud, P., 1972. A working model of the primitive
earth. American Journal of Science 272, 537-548.
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• Precambrian timescale revision contd
• A major criticism of this approach in the 1980s
  compilation was that there was not enough
  geobiological change through the Precambrian to
  use this criterion for timescale purposes.
• However, since that time there has been a
  veritable explosion of new information pertaining
  to Precambrian geobiology in the form of
• Detailed stratigraphic sections
• High precision geochronology (U-Pb and Re-Os)
• Stable isotope geochemical data (S, C, O)
• Atmospheric/climatic modelling

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• Precambrian timescale revision contd
• Propose
• Use the wealth of new geoscientific data to erect
  a Precambrian timescale based on the extant rock
  record
• - using golden spikes where possible to reflect
  the major, irreversible processes in Earth
  evolution
• The importance of this work is to
• document major events in Earth history
• facilitate and promote communication amongst
  Earth Scientists
• convey the history of events in Earth evolution
  to the general public

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The organising principles of history are
directionality and contingency. Directionality is
the quest to explain (not merely document) the
primary character of any true history as a
complex, but causally connected series of unique
events, giving an arrow to time by their
unrepeatability and sensible sequence.
Contingency is the recognition that such
sequences do not unfold as predictable arrays
under timeless laws of nature, but that each step
is dependent (contingent) upon those that came
before, and that explanation therefore requires a
detailed knowledge of antecedent particulars.
Gould, S.J., 1994. Introduction The coherence
of history. In Bengston, S. (ed.), Early Life
on earth. Nobel Symposium 84, 1-8.
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Precambrian timescale pertinent new data
Age dates of oldest rocks
3.825 Ga
3.890 Ga
3.4 Ga
3.55 Ga
3.81 Ga
3.55 Ga
3.65 Ga
3.64 Ga
3.73 Ga
3.96 Ga
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Hamersley Basin
Hamersley Gp.
Fortescue Gp.
Trendall et al., 2004 Australian Journal of
Earth Sciences 51, 621-644.
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Stable isotope data
Major perturbation from 2.8-2.4 Ga
Johnson et al., 2008 Ann. Rev. Earth Planet.
Sci. 36, 457-493
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Great Oxidizing Event
Holland, 1994
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Melezhik, 2005 GSA Today 15, 4-11
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2.0-1.8 Ga Granular iron formation
Earaheedy Gp., Australia
Animikie Gp., N. America
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Mesoproterozoic environmental stability
Proterozoic glacial gap
environmental stability
Onset of Snowball events
Ca-sulphates
Sulphidic shales
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Climate modelling
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Hamersley Basin
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• Under high pCO2, weathering is by chemical
  processes, as a result of H2O CO2 H2CO3
  (carbonic acid)
• This results in formation of acidic waters and
  intense chemical weathering
• A predictive consequence of the geochemical data
  and this model is that residues of weathering
  should have Al2O3 and SiO2 rich horizons, and
  that indeed is exactly what occurs in Fortescue
  Group basalts

In contrast, under higher pO2, weathering is
achieved through mechanical breakdown of
material This results in the transport and
deposition of clastic sedimentary rocks.
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Hamersley Basin
Hamersley Gp.
Fortescue Gp.
Trendall et al., 2004 Australian Journal of
Earth Sciences 51, 621-644.
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Iron formation-related shales
Frere Fm., Earaheedy Gp., Australia
2 cm
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2.4 Ga glaciations
2316
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• Transition from BIF to glacials 2.4 Ga

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Summary of contingent events through time

• First crustal remnants 4.404 Ga
• First preserved rock 4.03 Ga
• First preservation of macroscopic life 3.49 Ga
• Unique and rapid growth of continental crust
  2.78-2.63 Ga
• Global deposition of BIF 2.63-2.43 Ga
• Irreversible oxidation of oceanic Fe2? rise of
  oxygen in atmosphere ? global glacial deposits
  and rise in seawater sulphate 2.43-2.25 Ga
• Lomagundi-Jatuli carbon isotopic excursion
  2.25-2.06 Ga
• Deposition of Superior-type BIFs and
  stilpnomelane shales return to reducing
  conditions 2.06-1.8 Ga
• Sulphidic shales and environmental stability
  1.8-1.25 Ga
• 10. Onset of Neoproterozoic glaciations and
  snowball Earth 750-630 Ma

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Summary of contingent events through time
2800
2600
2500
2400
2300
2200
2100
2700
Time (Ma)
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A revised Precambrian timescale possibilities
CHRONOMETRIC BOUNDARIES

• Formal definition of a Hadean Eon, from T0
  4567 Ma to age of Earths oldest rock 4030 Ma
  base of the stratigraphic column on Earth

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A revised Precambrian timescale possibilities
CHRONOSTRATIGRAPHIC BOUNDARIES
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Moving forward

• Instigate working groups for Precambrian
  timescale boundaries
• Solicit proposals for potential GSSPs in
  different countries
• Assess proposals and develop research plan to
  constrain potential boundaries
• Write formal proposals for voting by ICS members

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Glaciations
end of BIFs
2450 Ma
2630 Ma
2780 Ma
2400 Ma
2900 Ma
1840 Ma
Major crust fm. CO2 outgassing
Main BIFs and anoxic oceans
Oxidized atmosphere
Glacials and oxygenic photosynthesizers
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2.06-1.8 Ga Granular iron formation
Frere Fm., Earaheedy Gp., Australia
2 cm
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Great Oxidizing Event
Holland, 1994
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East Pilbara Terrane

• Three unconformities
• upward-younging U-Pb ages
• Distinct geochemical trends upsection
• Discrete history from neighbouring terranes

3.48 Ga stromatolites