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The ejecta blanket and secondary impact craters of the mare-filled crater Archimedes (80 km in diameter) are visible on the terrain toward the viewer (south) but not on the mare surface to the crater's left and right. Yet at one time ejecta like that to the south must have completely surrounded Archimedes because similar ejecta surrounds craters such as Aristillus (upper right). Thus, the mare lavas, in addition to filling the interior of Archimedes, obviously have covered the eastern and western parts of the ejecta. In turn, ejecta from Archimedes has covered materials of the Imbrium basin like the rugged hills in the lower left of the picture. These stratigraphic relations prove that time elapsed between formation of the Imbrium basin and its filling by mare-time enough for impacts to create Archimedes, the deeply flooded crater to its right (arrow), and similar "Imbrian-age" craters elsewhere, as was pointed out by Eugene Shoemaker in 1962.
Archimedes is the first large crater described in this chapter that has no visible central peak complex. Presumably the complex exists but has been completely inundated by the mare. - Don E.Wilhelms
Report Source: NASA SP-362, Page 173, Figure 179
This web page was created by Francis Ridge
for The Lunascan Project
Section Directory 12