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. Problem 1: Based on round numbers, from 80’s comp., not tied to rock record. Hamersley Basin. Condie, 2004.

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A chronostratigraphic division of the precambrian possibilities and challenges

A chronostratigraphic division of the Precambrian: possibilities and challenges

Martin J. Van Kranendonk

Geological Survey of Western Australia

Chair, ICS Precambrian Subcommission


A chronostratigraphic division of the precambrian possibilities and challenges

Problem 1: Based on round numbers,

from 80’s comp., not tied to rock record

Hamersley Basin

Condie, 2004

Frequency distribution of

juvenile continental crust

Current ICS stratigraphic chart


A chronostratigraphic division of the precambrian possibilities and challenges

Proterozoic timescale based

on Supercontinent assembly

Bleeker, 2003: Lithos 71, 99-134


A chronostratigraphic division of the precambrian possibilities and challenges

Problem 2: Proterozoic system/period scheme is impractical

Problem 3: No lower limit

Current ICS stratigraphic chart


A chronostratigraphic division of the precambrian possibilities and challenges

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.


A chronostratigraphic division of the precambrian possibilities and challenges

e.g. “Classic Archean features”

= granite-greenstone crust and komatiites; typically in 2.7 Ga terranes,

but also 2.1 Ga Birimian granite-greenstone crust and 2056 Ma Lapland komatiites

<2.78 Ga volcano-sedimentary rocks

>2.83 Ga basement

3.3 Ga Olivine-bladed spinifex

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.


E g global rifting at end of archean

Problem 5: “Global” geodynamic events

are highly diachronous

2750

2700

2650

2600

2550

2500

2450

2400

2350

Black Range dyke

Great dyke

e.g.: “global rifting” at end of Archean

Matachewan dykes

375 Million years!!


A chronostratigraphic division of the precambrian possibilities and challenges

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 100’s million year scale, vs. biological events at <1 million year scale

Cloud, P., 1972. A working model of the primitive earth. American Journal of Science 272, 537-548.


A chronostratigraphic division of the precambrian possibilities and challenges

  • Precambrian timescale revision cont’d

  • A major criticism of this approach in the 1980’s 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


A chronostratigraphic division of the precambrian possibilities and challenges

  • Precambrian timescale revision cont’d

  • 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


A chronostratigraphic division of the precambrian possibilities and challenges

“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.


A chronostratigraphic division of the precambrian possibilities and challenges

Precambrian timescale: pertinent new data

4.03 Ga

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


A chronostratigraphic division of the precambrian possibilities and challenges

2450 Ma

Proterozoic

2460 Ma

2463 Ma

2490 Ma

2501 Ma

2562 Ma

2597 Ma

2630 Ma

Archean

2719 Ma

2741 Ma

2764 Ma

2775 Ma

Hamersley Basin

Hamersley Gp.

Fortescue Gp.

Trendall et al., 2004: Australian Journal of Earth Sciences 51, 621-644.


Stable isotope data

  • Coincides with unique episode

  • of crustal growth, deposition of

  • BIF and rise in atmospheric O2

Stable isotope data

Major perturbation from

~2.8-2.4 Ga

Johnson et al., 2008: Ann. Rev. Earth Planet. Sci. 36, 457-493


Great oxidizing event

8

4

33

S( / )

o

oo

0

-4

4.0

3.0

2.0

1.0

Time (Ga)

Great Oxidizing Event

Holland, 1994


A chronostratigraphic division of the precambrian possibilities and challenges

BIFs

GIF

Glacials

Melezhik, 2005: GSA Today 15, 4-11


2 0 1 8 ga granular iron formation

~2.0-1.8 Ga: Granular iron formation

Animikie Gp., N. America

Earaheedy Gp., Australia


A chronostratigraphic division of the precambrian possibilities and challenges

Mesoproterozoic environmental stability

Proterozoic glacial gap

environmental

stability

Onset of Snowball events

Ca-sulphates

Sulphidic shales


A chronostratigraphic division of the precambrian possibilities and challenges

Climate modelling

Proterozoic

Phanerozoic

100

10

%PAL

1

0.1

2.0

1.0

Time (Ga)


Hamersley basin

Hamersley Basin


A chronostratigraphic division of the precambrian possibilities and challenges

Quartz crystal ‘beds’

Pyrophyllite Al2Si4O10(OH)2

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.


A chronostratigraphic division of the precambrian possibilities and challenges

2450 Ma

Proterozoic

2460 Ma

2463 Ma

2490 Ma

2501 Ma

2562 Ma

2597 Ma

2630 Ma

Archean

2719 Ma

2741 Ma

2764 Ma

2775 Ma

Hamersley Basin

Hamersley Gp.

Fortescue Gp.

Trendall et al., 2004: Australian Journal of Earth Sciences 51, 621-644.


Iron formation related shales

Iron formation-related shales

Frere Fm., Earaheedy Gp.,

Australia

2 cm


A chronostratigraphic division of the precambrian possibilities and challenges

2220

2220

2220

2450

2432

2450

~2.4 Ga glaciations

2316


A chronostratigraphic division of the precambrian possibilities and challenges

Bedded Mn-carbonate

Dropstone in 2.4 Ga Turee Creek Gp.

Transition from BIF to glacials ~2.4 Ga


Summary of contingent events through time

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


A chronostratigraphic division of the precambrian possibilities and challenges

3. Unique and rapid growth of continental crust

4. Highly reduced atmosphere: chemical weathering and

deposition of BIF

5. Irreversible oxidation of crust and oceanic sinks (Fe2+)

→ rise of atmospheric oxygen → global glaciation and rise

in seawater sulphate

6. Lomagundi-Jatuli carbon isotopic excursion

Summary of contingent events through time

2800

2600

2500

2400

2300

2200

2100

2700

Time (Ma)


A chronostratigraphic division of the precambrian possibilities and challenges

A revised Precambrian timescale: possibilities

CHRONOMETRIC BOUNDARIES

  • Formal definition ofa Hadean Eon, from T0 = 4567 Ma to age of Earth’s oldest rock = 4030 Ma: base of the stratigraphic column on Earth


A chronostratigraphic division of the precambrian possibilities and challenges

A revised Precambrian timescale: possibilities

Neoproterozoic: onset of environmental crisis, snowball Earth, and the rise of animals; GSSP = first widespread sulphates?

Mesoproterozoic: environmental stability;GSSP = top of GIF

Archean-Proterozoic boundary at rise in atmospheric oxygen: GSSP at change from BIF to glacials

Neoarchean: widespread crust generation and onset of voluminous BIF deposition; GSSP = base of first stable flood basalts

Mesoarchean: first stable crust, with macroscopic evidence of life; GSSP = base of first stromatolitic horizon

CHRONOSTRATIGRAPHIC BOUNDARIES


Moving forward

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


A chronostratigraphic division of the precambrian possibilities and challenges

Glaciations

end of BIFs

2450 Ma

2780 Ma

2630 Ma

2400 Ma

2900 Ma

1840 Ma

Major crust fm. + CO2

outgassing

Main BIFs and anoxic oceans

Oxidized atmosphere

Glacials and oxygenic photosynthesizers


2 06 1 8 ga granular iron formation

~2.06-1.8 Ga: Granular iron formation

Frere Fm., Earaheedy Gp.,

Australia

2 cm


Great oxidizing event1

Great Oxidizing Event

Holland, 1994


East pilbara terrane

3176 Ma

3190 Ma

3240 Ma

3325 Ma

3350 Ma

3458-3427 Ma

3470 Ma

3481 Ma

3498 Ma

3508 Ma

3515 Ma

East Pilbara Terrane

  • Three unconformities

  • upward-younging U-Pb ages

  • Distinct geochemical trends upsection

  • Discrete history from neighbouring terranes

3.48 Ga stromatolites


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