AS17-150-23069 (H)

Figure 59

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Some of the strongest tonal, color, and structural contrasts among mare materials occur in Mare Serenitatis. Accordingly, it has become a classic area for studying the sequence (or stratigraphy) of mare rocks. Earlier studies of telescopic photographs seemed to provide evidence that the lighter materials in the center of the basin (top half of this view) were emplaced before the darker lavas erupted along the basin margin. However, pictures returned by Apollo 17 show that the opposite is true. The dark materials were emplaced first. They were then tilted northward and broken by faults, such as those that bound the Plinius Rilles, before the light lava flooded against them (Howard et al., 1973). The large mare ridge or wrinkle ridge deforms both light and dark mare units but is much more prominent in the lighter unit. Detailed spectral studies and visual observations by the Apollo 17 astronauts show that the lighter-toned mare is relatively browner and the darker mare is relatively bluer.  -K.A.H.