Nick might like this. I found this while doing a web search on the gas release mechanism for the origin of maars:
See the last image on this page:
Morale Claim Maar, Hopi Buttes, Arizona
http://volcano.und.nodak.edu/vwdocs/volc_images/north_america/morale_claim.html
The another link given on this page describes stratification due to differing amounts of CO2 gas in a lake. This would still require standing bodies of water though:
Lake Nyos, Cameroon
http://volcano.und.nodak.edu/vwdocs/frequent_questions/grp7/africa/question367.html
I thought this type of gas release might provide an alternative mechanism for the stratification seen in the Malin/Edgett report sedimentary layering seen near Mars equator:
Sedimentary Mars
http://science.nasa.gov/headlines/y2000/ast04dec_2.htm
Bob Clark
A CO2 origin for sedimentary layers on Mars?