HJH slide 9673

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Eons and geons a simple planetary time scale
H.J. Hofmann Dept. of Earth and Planetary
Sciences, and Redpath Museum McGill
University Montreal, QC H3A 2A7
HJH slide 9673 30 Oct 1987
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• Time
• Point, occasion, event

• Period, duration, interval

• Tempo, rhythm

• Irreversibility

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Time told by the sun
HJH slide 4845
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Time told by the animals
Pecten diegensis Dall
Merluccius bilinearis (Mitchill)
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1 cm
1 cm
H9806-22-2 062
Tidal rhythmite, Elatina Fm. (620 Ma), South
Australia
Time told by the rocks 1
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Time told by the rocks 2
Little Dal Gp. rhythmites Neoproterozoic (Geon
8-7), Mackenzie Mts., NWT. (Hofmann Aitken,
1979, CJES)
HJH slide 7758
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Graphic representation of record
Spatial section
Thickness
fit time to rock sequence
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Concepts
Rocks gaps
Sections
A B C D E F G H I J K L M N O P Q R S
Chronostrat. record
bins
incomplete, discontinuous regional
continuous, uniform universal
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Partitioning the record Nominal and interval
scales and labels
Content
Age
Albian Aalenian Artinskian Arenigian
105 Ma 180 Ma 260 Ma 480 Ma
Middle Ages Han Dynasty Satavahana Dynasty
476 AD 1453 AD 206 BC 220 AD 200 BC 236 AD
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Issue
Simple and efficient classification and
nomenclature (labels) for large pre-Cambrian time
intervals i.e., for 88 of geologic time
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(No Transcript)
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Time scale
An arrangement of events used as a measure of
the relative or absolute duration or antiquity of
a period of history or geologic or cosmic
time (Merriam-Webster, 1986)
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Time
SCALES
ASPECTS
binary nominal ordinal interval ratio
instant, event age, quality chronologic
order duration, arbitrary zero absolute zero
(no ve) evolution, change
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Time rocks
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Eons
Labels for major pre-Cambrian
divisions Archeozoic, Archean (Dana,
1872) Proterozoic (Emmons, 1888) Cryptozoic
(Chadwick, 1930) Precambrian (IUGS Prec.
Subcomm., 1969) Proterozoic divisions (IUGS
Prec. Subcomm., 1989) Precambrian/Cambrian
boundary (IGC 1992)
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Proposition
Use a universal calendar system with numerical
units appropriately large to encompass major
geological developments (basin formation,
orogenic belts, etc.) A convenient measure is a
unit of 100 million years.
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Scale of phenomena (adapted from Carey 1962, J.
Geol. Soc. India 397-105)
100 Ma
hour
day
year
Ma
sec
min
ka
Ga
Size (km)
104 km
103 km
mountain belts
102 km
sedimentary basins
glaciers
astroblemes
10 km
1 km
100 m
10 m
organisms
1 m
102
10
1
106
104
108
1010
1014
1012
1016
TIME (seconds)
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Geochrone (H.S. Williams, 1893, J. Geol.
1283-295) A standard unit of geologic
time, now obsolete, set equal to the duration of
the Eocene Paleocene Eocene of todays
scale, an interval of 31 m.y.
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Geon (H.P. Woodward, 1929, Pan-Amer. Geol.
5115-22) A unit taken to represent
either the span of the average geologic
period, or the thickness of the
average stratigraphic equivalent, a matter of
60,000,000 years, and 50,000 feet 15 km of
clastic depositions
Using 543 Ma for the base of the Cambrian, and 11
geologic periods, an updated value for Woodwards
geon is 49.4 my
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Numerical nomenclature
Units of 108 years previously considered
100 my, Ma - current geological literature (i
nien) - Chinese geological literature megacentur
y - A.F. Trendall, 1966 hectomegennium - F.E.
Wickman 1968 geocentury - P.E. Cloud,
1988 geon - H.J. Hofmann, 1990 becquerel -
P.F. Hoffman, unpublished
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Complex nomenclature
4 3 2 1
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Complex nomenclature
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5
26
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(No Transcript)
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Comparisons
100 a 1 a 1 year 101 a 1 decade 102
a 1 century 103 a 1 ka 1 milennium 106
a 1 Ma 1 megennium 107 a 108 a 1
geon 109 a 1 Ga 1 gigennium
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Geon (geological eon) (Hofmann, 1990) A
specified 100-million-year interval of geologic
time, counted backward from the present.
The geon is named for the leftmost part of the
number representing age.
Dates such as 1851 Ma and 1800 Ma belong to Geon
18 the Cretaceous extinction (065 Ma) belongs to
Geon 0
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Comparing Phanerozoic system and geon
boundaries
Period
Age
0 Ma
98.9 Ma
205.7 Ma
300 Ma
410 Ma
510 Ma
630 Ma
After Okulitch 1995, GSC Open File 3040
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Implications
Geon scale is a time scale independent of region
or planet
Phanerozoic period/system boundaries approximate
geon boundaries
The two Phanerozoic era/erathem boundaries lie
near middle of geons
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HJH slide 9673 30 Oct 1987
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100-my BINS (Geon units)
Age distribution of continental crust (Condie,
1997, Plate Tectonics and Crustal Evolution, 4th
ed.)
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18
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Changes with geologic time
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Global Precambrian stromatolite diversity (after
Semikhatov Raaben, 1996, and Hofmann, 2000)
P R O T E R O Z O I C
A R C H E A N
HJH 00
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-- -- -- Inferred SE extent of Laurentia at end
of Geon 16
Grenville Province, Geon 17-16 rocks (Rivers,
1997, Prec. Res. 86117-154)
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-- -- -- Inferred SE extent of Laurentia at end
of Geon 14
Grenville Province, Geon 15-14 rocks (Rivers,
1997, Prec. Res. 86117-154)
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TIME SLICE MAP
Grenville Province, Geon 13 rocks (Rivers, 1997,
Prec. Res. 86117-154)
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Sedimentary sequences
Grenville Province, Geon 12 rocks (Rivers, 1997,
Prec. Res. 86117-154)
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Sediments
Grenville Province, Geon 11 rocks (Rivers, 1997,
Prec. Res. 86117-154)
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Temporal classification of principal geotectonic
elements adjacent to the Slave Craton Hoffman
Hall, 1993, GSC Open File 2559
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GEON
Phanerozoic
Proterozoic
Archean
Geologic map using geon units (Hofmann, 1990,
1992)
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GEON GAP MAP
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GEON GAPS
GEON UNITS
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GEON HIATUS
Phanerozoic
Proterozoic
Archean
GEON MAP UNITS and GAPS
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Different planetary histories, same geon time
scale
GEOLOGIC TIME SCALE
LUNAR TIME SCALE
MARTIAN TIME SCALE
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Summary Why use the Geon concept?
It is numerical, direct, and simple
It is easy to learn, remember, and apply
It is necessary to learn only 1 word
It transcends language barriers
It is geopolitically neutral
It is a logical extension of the calendar system
It provides time slices of equal duration
It is versatile and facilitates quantitative
studies
It is applicable beyond Earth to planets and stars
It is helpful in communicating with non-geologists
Astronomers use light-year and parsec for large
distances, so it is appropriate to have also a
unit for large time intervals
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Geons for the Precambrian!
The Precambrian constitutes the longest part of
Earth history
Precambrian chronologic data are prevailingly
numeric, and are based on rocks
Thus, why not use large chronometric
divisions with a corresponding simple, serial
numeric nomenclature?