Lower blue unitLong/lat: 341.46E, 23.97N

Rational: This different mineralogy reveals different conditions of formation/alteration.

Morphology & mineralogy: An outcrop in a local low on the flank of Mawrth Vallis shows on HiRISE color images light blue layers underneath the light-red layers rich in Fe/Mg-smectites. It may be the largest outcrop so close to the landing ellipse of different hydrated minerals than the large exposures of the landing site.Other smaller outcrops of the same unit may be exhumed in the vicinity on the flank of Mawrth Vallis.Similar outcrops ~65 km south of the ellipse, on the floor of Mawrth Vallis, show the presence of the sulfate bassanite.

MSL tasks: At large scale, study the layering of the outcrop, its fracturation, its relation to upper layers. At small scale, the grain structure, the mineralogy and chemistry of the rocks.

HRSC mosaic with HRSC nadir & color images

200 m

HiRISE mosaic with HRSC & HiRISE color images

A possible interlayered crater is also located at the center of this image.

The quality of the spectral datasets on the flank of Mawrth Vallis is not as good as on the top of the plateau. However this CRISM spectral ratio of the lower blue unit shows a distinct absorption band at 1.9 µm, and a possible weak one at 2.5 µm.The weakness of the bands makes the interpretation difficult, but this outcrop could be related to the Ca-sulfate detection made on the floor of Mawrth Vallis (341.6E, 22.9N) by Wray et al. (2010), also stratigraphically just under the light-red layers rich in Fe/Mg-smectites, and also light-blue on HiRISE color images.

From J. Wray