A volcanic ash origin for the Meridiani bedrock has been proposed.
There was recently some rather public back-biting between MER scientists arguing the bedrock is evaporitic and a team suggesting the bedrock is from compacted volcanic ash.
A volcanic environment for bedrock diagenesis at Meridiani Planum on Mars.
Thomas M. McCollom & Brian M. Hynek
NATURE|Vol 438|22/29 December 2005
http://www.ifa.hawaii.edu/~meech/NAIJC/papers/MeridianiPlanum_Nature2005_Volcanic.pdf
IS THE CHEMISTRY OF THE BEDROCKS AT MERIDIANI PLANUM INDICATIVE OF A VOLCANIC OR SEDIMENTARY/EVAPORITE ORIGIN?
T. M. McCollom and B. M. Hynek,
Laboratory for Atmospheric and Space Physics, UCB392, University of Colorado, Boulder CO 80309. *****@lasp.colorado.edu.
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2023.pdf
Bob Clark