All that the sediments tell us is that in the environment they formed, the activity of SO2 was much greater than that of CO2. Since liquids are much more concentrated than thin gases, an H2SO4-rich liquid will dominate the chemistry of its products, even if a thin CO2 atmosphere is present.

So you can't rule out a surface formation model.

In fact, given the extensive layering and hints of cross bedding and undulose bedding, it's hard to imagine formation in the subsurface. This *is* a surface deposit.

OTOH, it could have been significantly modified in the subsurface by recrystallisation and segregation of minerals (e.g. the "berries")