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AGU: Journal of Geophysical Research, Planets

 

Keywords

  • Impact Basins
  • Impactor Populations
  • Moon
  • Stratigraphy

Index Terms

  • 1160 - Planetary and lunar geochronology
  • 5420 - Impact phenomena, cratering
  • 5455 - Origin and evolution
  • 6250 - Moon

Paper in Press

JOURNAL OF GEOPHYSICAL RESEARCH, doi:10.1029/2011JE003951

Lunar impact basins: Stratigraphy, sequence and ages from superposed impact crater populations measured from Lunar Orbiter Laser Altimeter (LOLA) data

Key Points
  • New measurements of crater statistics and stratigraphy for 30 lunar basins
  • Any transition in lunar impactor populations occurred before the mid-Nectarian
  • The oldest lunar basins are likely cratered to saturation equilibrium

Authors:

Caleb I. Fassett

James W. Head

Seth J. Jacob Kadish

Erwan Mazarico

Gregory A. Neumann

David Smith

Maria T. Zuber

Impact basin formation is a fundamental process in the evolution of the Moon and records the history of impactors in the early solar system. In order to assess the stratigraphy, sequence, and ages of impact basins and the impactor population as a function of time, we have used topography from the Lunar Orbiter Laser Altimeter (LOLA) on the Lunar Reconnaissance Orbiter (LRO) to measure the superposed impact crater size-frequency distributions for 30 lunar basins (D{greater than or equal to}300 km). These data generally support the widely-used Wilhelms sequence of lunar basins, although we find significantly higher densities of superposed craters on many lunar basins than derived by Wilhelms (50% higher densities). Our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains. The transition from a lunar impact flux dominated by Population 1 to Population 2 occurred before the mid-Nectarian. This is before the end of the period of rapid cratering, and potentially before the end of the hypothesized Late Heavy Bombardment. LOLA-derived crater densities also suggest that many Pre-Nectarian basins, such as South Pole-Aitken, have been cratered to saturation equilibrium. Finally, both crater counts and stratigraphic observations based on LOLA data are applicable to specific basin stratigraphic problems of interest; for example, using these data, we suggest that Serenitatis is older than Nectaris, and Humboldtianum is younger than Crisium. Sample return missions to specific basins can anchor these measurements to a Pre-Imbrian absolute chronology.

Received 2 September 2011; accepted 21 November 2011.

Citation: Fassett, C. I., J. W. Head, S. J. J. Kadish, E. Mazarico, G. A. Neumann, D. Smith, and M. T. Zuber (2011), Lunar impact basins: Stratigraphy, sequence and ages from superposed impact crater populations measured from Lunar Orbiter Laser Altimeter (LOLA) data, J. Geophys. Res., doi:10.1029/2011JE003951, in press.