Basin Analysis and Play Characterization

1
First-Order Relationships Between Lunar Crater
Morphology, Degree of Degradation, and Relative
Age The Crater Degradation Index
William A. Ambrose
Bureau of Economic Geology John A. and Katherine
G. Jackson School of Geosciences
Apollo 17 photograph
2
Outline
? Cratering Processes
? Crater Type Versus Morphology -The USGS Main
Sequence
? Crater Degradation Processes -Fracturing, Lava
Flooding, Subsequent Impacts
? Crater Degradation Index -Statistical
Trends for Each Crater Type
? Summary and Conclusions
3
Main Sources and Acknowledgments
NASA The Lunar and Planetary Institute
-Lunar Orbiter (1966-1968), Apollo (1967-1972)
Clementine (1994), Lunar Prospector (1999)
USGS
-G. K. Gilbert, Eugene Shoemaker, and Don
Wilhelms
USAF
-Lunar Aeronautical Charts (1965)
Ralph Baldwin, The Face of the Moon (1949)
Peter Schultz, Moon Morphology (1972)
C. A. Wood, The Modern Moon (2003)
Antonín Rükl, Atlas of the Moon (2004)
4
Outline
? Cratering Processes
? Crater Type Versus Morphology -The USGS Main
Sequence
? Crater Degradation Processes -Fracturing, Lava
Flooding, Subsequent Impacts
? Crater Degradation Index -Statistical
Trends for Each Crater Type
? Summary and Conclusions
5
Langrenus 144 km across
Typical Moon Crater
Apollo 8 photograph
Dimensional data Cherrington (1984)
5 km
2.9 km
LPI
V.E. gt251
6
Outline
? Cratering Processes
? Crater Type Versus Morphology -The USGS Main
Sequence
? Crater Degradation Processes -Fracturing, Lava
Flooding, Subsequent Impacts
? Crater Degradation Index -Statistical
Trends for Each Crater Type
? Summary and Conclusions
7
The Modified USGS Main Sequence
Small
Large
Crater Types (diameter in km)
8
Type 1 (Simple Craters)
Lunar and Planetary Institute
10 km
Moltke
9
Types 2 and 3 (Complex Craters)
Lunar and Planetary Institute
10
Types 4 and 5 (Walled Plains and Small Basins)
Schrödinger (Type 5)
Ptolemaeus (Type 4)
Apollo 16
Clementine
150 km
75 km
Grimaldi Basin Type 5 Wood (2003)
11
Type 6 (Large Basins)
Mare Orientale
Mare Imbrium
Lick Observatory
Lunar Orbiter
900 km
1,300 km
Mare Orientale Type 6 Wood (2003)
12
Outline
? Cratering Processes
? Crater Type Versus Morphology -The USGS Main
Sequence
? Crater Degradation Processes -Fracturing, Lava
Flooding, Subsequent Impacts
? Crater Degradation Index -Statistical
Trends for Each Crater Type
? Summary and Conclusions
13
Crater Degradation Index
? Empirical measurement of crater maturity based
on presence or absence of key degradation
factors.
Maps and photographs ?Lunar Orbiter, Apollo,
Clementine ?Antonín Rükl, Atlas of the Moon
(2004) ?Lunar Aeronautical Charts (USAF)
Publications ?Wood (The Modern Moon,
2003) ?Westfall (Atlas of the Lunar Terminator,
2000) ?Schultz (Moon Morphology, 1972) many
others
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Crater Degradation Factors
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Crater Superposition and Relative Age
Overlapping
Non-overlapping
Theophilus
Werner
Cyrillus
Aliacensis
80 km
Lunar Orbiter Photograph
008
16
Subsequent Impacts
None
Many
Tycho
Janssen
80 km
100 km
17
Lava Flooding Mare Humorum
European Southern Obs.
Many large craters in Mare Humorum are degraded
Gassendi (floor-fractured)
Degradation is principally due to mare lavas
Puiseux
Doppelmayer
18
Gassendi Floor-fractured crater
European Southern Obs.
100 km
Gassendi
19
Dark-Halo Craters
Alphonsus
Nikolai Kozyrev (1958)
50 km
Apollo photograph
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Outline
? Cratering Processes
? Crater Type Versus Morphology -The USGS Main
Sequence
? Crater Degradation Processes -Fracturing, Lava
Flooding, Subsequent Impacts
? Crater Degradation Index -Statistical
Trends for Each Crater Type
? Summary and Conclusions
21
Crater Degradation Index
Low
High
0 1 2
Rays or bright ejecta Present Not present
Rim Pristine or Sharp Smooth or Rounded Subdued
Floor fractured or flooded by internal lava No Yes
Interior or rim flooded by mare lava No Outer Rim Flooded or Overlapped Breached
Major post-impact craters 0 1-3 gt3
Ejecta from other craters No Yes
Albedo in full phase Bright Dim
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Copernicus and Stadius
100 km
0 1 2
Rays or bright ejecta Present Not present
Rim Pristine or Sharp Smooth or Rounded Subdued
Floor fractured or flooded by internal lava No Yes
Interior or rim flooded by mare lava No Outer Rim Flooded or Overlapped Breached
Major post-impact craters 0 1-3 gt3
Ejecta from other craters No Yes
Albedo Bright Dim
Copernicus
(0)
Stadius
(9)
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Degradation From Base Surge Deposits (Trask and
McCauley, 1972)
0 1 2
Rays or bright ejecta Present Not present
Rim Pristine or Sharp Smooth or Rounded Subdued
Floor fractured or flooded by internal lava No Yes
Interior or rim flooded by mare lava No Outer Rim Flooded or Overlapped Breached
Major post-impact craters 0 1-3 gt3
Ejecta from other craters No Yes
Albedo Bright Dim
Lunar Orbiter photograph
(6)
Mare Orientale
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Crater type versus C.D.I.
10
n704
9
8
7
mean
6
5
C.D.I.
gt100
4
50-100
3
20-50
2
1-20
1
0
1
2
3
4
5
6
Type
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C.D.I. distribution per crater type
Type 1
Type 2
40
300
n403
n153
30
200
number of craters
number of craters
20
100
10
0
1
2
3
4
5
6
9
0
1
2
3
4
5
6
7
8
9
7
8
C.D.I.
C.D.I.
non-mare
mare
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C.D.I. distribution per crater type
Type 3
Type 4
20
10
n103
n23
10
number of craters
number of craters
5
0
1
2
3
4
5
6
9
0
1
2
3
4
5
6
7
8
9
7
8
C.D.I.
C.D.I.
non-mare
mare
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Crater type vs. avg. subsequent impacts
20
n596
18
16
14
12
10
impacts
8
non-mare
6
mare
4
2
0
6
5
4
3
2
1
Type
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Normalized subsequent impact data
10
n690
9
8
7
6
5
impacts/ km2 (x 10-3)
4
3
2
1
0
6
5
4
3
2
1
Type
29
Lunar Crater Densities vs. Time
Number of Craters per 106 km2
Age (Billions of years)
Modified from Heiken, Vaniman, and French (1991)
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Arthur Scale
?Modified from Baldwin (1949, 1963)
Class
Description
Age (109 BY)
0-2.9
1
Fresh rims, rays
2
3.0-3.4
Freshest post-Mare
3
3.5-3.7
Softened rims
4
3.8-4.0
Heavily degraded
5
4.1-4.5
Faint outline
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Summary
?Crater morphology is systematically related to
crater size.
?Crater degradation tends to increase with
larger crater type.
?Normalized crater-density values asymptotically
increase for crater types 1-4 lower for type 5.
?Crossplots of degree of degradation versus
crater type, plus crater- density data provide a
useful framework for estimating
crater maturity.
Clementine photograph