Basin Groups
Basin Groups refers to 9 subdivisions of the lunar Pre-Nectarian geologic period.
Definition
[edit | edit source]The motivation for creating the Basin Groups subdivisions was to place 30 pre-Nectarian impact basins into 9 relative age groups. The relative age of the first basin in each group is based on crater densities and superposition relationships, whereas the other basins are included based on weaker grounds.[1] Basin Group 1 has no official age for its base, and the boundary between Basin Group 9 and the Nectarian period is defined by the formation of the Nectaris impact basin.
The age of the Nectaris basin is somewhat contentious, with the most frequently cited numbers placing it at 3.92 Ga, or more infrequently at 3.85 Ga.[2] Recently, however, it has been suggested that the Nectaris basin could be, in fact, much older and might have formed at ~4.1 Ga.[3] Basin Groups are not used as a geologic period on any of the United States Geological Survey lunar geologic maps. Basin Groups 1-9 and the earlier (informal) Cryptic era together make up the totality of the Pre-Nectarian period.
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Colors =
id:prenectarian value:rgb(0.823,0.302,0.380) id:nectarian value:rgb(0.898,0.329,0.071) id:imbrian value:rgb(0,0.481,0.811) id:earlyimbrian value:rgb(0,0.404,0.741) id:lateimbrian value:rgb(0,0.557,0.882) id:eratosthenian value:rgb(0.238,0.839,0.728) id:copernican value:rgb(0.5,0.5,0.5)
Period = from:-4533 till:0 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:500 start:-4500 ScaleMinor = unit:year increment:100 start:-4500
PlotData=
align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5)
bar:Period
from: -1100 till: 0 text:Copernican color:copernican from:-3200 till: -1100 text:Eratosthenian color:eratosthenian from:-3850 till: -3200 text:Imbrian color:imbrian from: -3920 till: -3850 text:N shift:(2,-5) color:nectarian from: start till: -3920 text:Pre-Nectarian color:prenectarian
bar:Epoch
from: -3200 till: 0 color:white from: -3800 till: -3200 text:Late color:lateimbrian from: -3850 till: -3800 text:Early shift:(-20,-5) color:earlyimbrian from: start till: -3850 color:white
</timeline>
References
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