Last month when data started down the pipline from the hurried time of the approach to Cape York between the sites "Pathfinder Mound" and "Inaccessible Island" on Sols 2666 to 2673 I noticed interesting details about the sand and the Blueberry concretions in certain Pancams. The other day we received the remaining Pancam tricolor images which were combined into L257, L245 and R721 color images.
This unit is a weakly-indurated (-cemented) sand unit, with Blueberry concretions, that is similar to the sand in the ripples. Although the ripple sand can form a weak crust over the loose material, this undurated unit will support the weight fo the Rover's wheels but is friable enough for the wheels to leave tracks. It is clearly not the light-toned kieseritic sandstone but is apparently a weakly-indurated ripple sand. I would suppose that this unit is cemented with the sulfate salt omnipresent in this region, and suggest that it might represent a high groundwater table which saturated this sediment and left the cementing salts behind. Note that this is very low in the Burns Fm section, possibly within a few meters of the ancient Endurance surface.
Many of the Blueberry concretions are surrounded by a light-toned ring, and many of the Blueberries have popped out of the matrix, leaving a rounded pit and the light ring. This is likely a reaction zone or a weathering rim around the concretion.
There was apparently interest in this area, since this Pancam series was annotated as the "pancam_systematic_foreground_quarter_L234567Rall". I've seen occasional Pancam tricolor image sets taken just ahead of the front wheels for years and this probably has been a continuing study.
At my Photobucket Mars/Oppy site I've started a "systematic foreground" subalbum on this subject:
http://s142.photobucket.com/albums/r91/wil...ound%20Pancams/--Bill
