Basin Analysis and Play Characterization by 2rKi19t8

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									     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
                   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
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)
                   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
Langrenus: 144 km across
Apollo 8 photograph
                                     Typical
                                    Moon Crater
                                            Attributes
                                            Deep Floor
                                            Gentle Profile
                                            Ejecta Blanket
                                            Large Diameter


                               Dimensional data: Cherrington (1984)

                      2.9 km     5 km



      V.E. >25:1                                         LPI
                   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
The Modified USGS Main Sequence
   Small                                                  Large
               Crater Types (diameter in km)
   1             2&3              4            5             6
                                Walled       Small         Large
Simple         Complex
               Euler: Type 2    Plains       Basins        Basins

Moltke                                     Schrödinger   Mare Orientale

                         25          227


       10                                        320

                               Schickard
 Copernicus:
 Type 3                  93                                      930
                     Type 1 (Simple Craters)




Lunar and Planetary Institute



                                10 km

                                        Moltke
        Types 2 and 3 (Complex Craters)

                           Lunar and Planetary
                                Institute


                           Type 3 (Aristarchus)




Type 2 (Euler)




10 km                           40 km
            Types 4 and 5
   (Walled Plains and Small Basins)
Ptolemaeus (Type 4)   Schrödinger (Type 5)
        Apollo 16              Clementine




                                  150 km
          75 km

     Grimaldi Basin
         Type 5
     Wood (2003)
         Type 6 (Large Basins)
 Mare Orientale          Mare Imbrium
         Lunar Orbiter      Lick Observatory




         900 km             1,300 km

Mare Orientale
   Type 6
Wood (2003)
                   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
       Crater Degradation Index
● Empirical measurement of crater maturity
     based on presence or absence of key
     degradation factors.
● Data sources:
   Observations: >700 primarily nearside craters,
         farside craters, small basins and large basins
  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
   Crater Degradation Factors

                                            Extant?

● Subsequent impacts                         Yes
     -New craters, landslides, and ejecta

● Lava flooding                              No
     -External and internal

● Fracturing                                 No


● Degassing/Volcanism                       Maybe
      Crater Superposition and Relative Age

       Overlapping          Non-overlapping

           Theophilus

                                    Werner




Cyrillus
                                       Aliacensis

008
                            80 km      Lunar Orbiter
                                        Photograph
       Subsequent Impacts

None                        Many


   Tycho               Janssen

           80 km




                             100 km
European Southern Obs.                Lava Flooding:
                                      Mare Humorum
                                      Many large craters in
                  Gassendi         Mare Humorum are degraded
              (floor-fractured)
                                    Degradation is principally
                                       due to mare lavas


                                                         099




                         Puiseux

 Doppelmayer


                                              Doppelmayer
              Gassendi: Floor-fractured crater

European Southern Obs.




100 km




                            Apollo photograph
                 Gassendi
              Dark-Halo Craters

Pu’u O’o Firefountain

                                 Alphonsus



                                              Dark-halo
                                               craters




Nikolai Kozyrev (1958)


            USGS (1985)
                          Apollo photograph      50 km
                   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
      Crater Degradation Index
                           Low                     High
                           0         1             2

Rays or bright ejecta      Present   Not present

Rim                        Pristine Smooth or      Subdued
                           or Sharp Rounded
Floor fractured or         No        Yes
flooded by internal lava

Interior or rim flooded    No        Outer Rim     Breached
by mare lava                         Flooded or
                                     Overlapped
Major post-impact          0         1-3           >3
craters
Ejecta from other          No        Yes
craters
Albedo in full phase       Bright    Dim
Copernicus
and Stadius
                0          1             2                  100 km
Rays or         Present    Not present
bright ejecta
Rim             Pristine   Smooth or     Subdued
                or         Rounded
                Sharp

                                                    Copernicus (0)
Floor           No         Yes
fractured or
flooded by
internal lava

                                                                     Stadius (9)
Interior or  No            Outer Rim     Breached
rim flooded                Flooded or
by mare lava               Overlapped

Major post-     0          1-3           >3
impact
craters
Ejecta from No             Yes
other craters
Albedo          Bright     Dim
Degradation From Base Surge Deposits
                           (Trask and McCauley, 1972)
                0           1            2
Lunar Orbiter photograph
 Rays or    Present Not present
bright ejecta
Rim             Pristine    Smooth or    Subdued
                or          Rounded
                Sharp
Floor           No          Yes                     Riccioli   (6)
fractured or
flooded by
internal lava
Interior or  No             Outer Rim    Breached
rim flooded                 Flooded or
by mare lava                Overlapped

Major post-     0           1-3          >3
impact
craters
Ejecta from No              Yes
other craters                                             70 km
Mare Orientale
Albedo  Bright Dim
              Crater type versus C.D.I.
         10                                  n=704
          9
          8
         7
         6                                     mean
C.D.I.




         5
                                               >100
         4
                                              50-100
         3                   y=1.4x+0.6
                                               20-50
         2
                                                1-20
         1
          0
                 1   2   3   4     5      6 Type
                     C.D.I. distribution per crater type
                                         Type 1                                          Type 2
                                                                      40
                    300                  n=403                                            n=153
number of craters




                                                  number of craters
                                                                      30
                    200
                                                                      20

                    100
                                                                      10



                          0 1 2 3 4 5 6 7 8 9                              0 1 2 3 4 5 6 7 8 9
                                C.D.I.                                          C.D.I.
                                                                                           non-mare

                                                                                           mare
                     C.D.I. distribution per crater type
                                        Type 3                                          Type 4
                    20                                               10
                                        n=103                                            n=23
number of craters




                                                 number of craters
                    10                                               5




                         0 1 2 3 4 5 6 7 8 9                              0 1 2 3 4 5 6 7 8 9
                               C.D.I.                                          C.D.I.
                                                                                          non-mare

                                                                                          mare
Crater type vs. avg. # subsequent impacts
            20                               n=596
            18
               Langrenus
            16
            14
                                   Wilhelm
# impacts




            12
            10
            8                                non-mare
            6                                mare
            4
            2
             0
                   1   2   3   4   5    6 Type
                          Normalized subsequent impact data
                          10                                   n=690
                           9
# impacts/ km2 (x 10-3)



                           8
                           7                     Prevalent flooding
                           6
                           5
                           4
                           3            Sinus Iridum
                           2            Type 5
                           1
                           0
                                1   2      3    4      5   6 Type
  Lunar Crater Densities vs. Time
Number of Craters
  per 106 km2




                         Age (Billions of years)
                    Modified from Heiken, Vaniman, and French (1991)
                Arthur Scale

        ●Modified from Baldwin (1949, 1963)

Class    C.D.I. Description          Age (109 BY)

 1        0-1   Fresh rims, rays        0-2.9
 2        2     Freshest post-Mare      3.0-3.4
 3        3-4   Softened rims           3.5-3.7
 4        5-7   Heavily degraded        3.8-4.0
 5        >7    Faint outline           4.1-4.5
                        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
Clementine        framework for estimating crater
photograph        maturity.

								
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