Figure 54

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This picture shows the subdued, 1 50 km diameter, crater Ptolemaeus. The crater is filled to about half its original depth by the Cayley Formation, a unit with a gently undulating, nearly smooth surface. This unit forms similar smaller pools in numerous irregular depressions at various levels on the rim, flank, and wall of Ptolemaeus. The Cayley Formation consists of patches of light colored plains materials that fill most depressions peripheral to the Fra Mauro Formation (fig. 44) in the central earthside lunar uplands. Undulating surface features on the Cayley include very subtle circular depressions (d) 10 to 15 km in diameter that are more than an order of magnitude larger than the craters superposed on the Cayley, and irregular swells, swales, and scarps. Other surficial features are small, equidimensional, steep sided hills (h). The latter may have been formed on the surface of the Cayley by eruption of material from within the unit. In addition, more than 30 small craters on the Cayley have small central mounds (fig. 55). These mounds may represent relatively strong material that underlies a weak surficial layer of post Cayley regolith, indicating that the regolith is thicker here than on mare surfaces.

The deposition of the Cayley in pools indicates that it moved partly as a fluid. The distribution of the pools peripherally to a deposit of basin ejecta, the Fra Mauro Formation, indicates a related origin. The large, subdued crater forms suggest that the Cayley material is a draped blanket of fragmental material. Therefore, my colleague G. G. Schaber and I have suggested that the Cayley is a deposit of basin ejecta that became segregated from the ballistically transported ejecta that formed the Fra Mauro Formation around the Imbrium basin. The Cayley was transported separately as a fluidlike cloud that flowed along the ground across the whole region; portions were left behind to accumulate in local depressions .  R.E.E.

 Report Source: NASA SP-362, Page 64, Figure 54

This web page was created by Francis Ridge for The Lunascan Project
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