George wrote:



However, the
Muldraugh limestone in Elisabethtown, Kentucky contains huge gypsum nodules
that were believed to be formed as a secondary replacement of smaller
concretions. These gypsum nodules can be as big as 18" in diameter. All of
the cave gypsum I have seen weas formed in a dry environment out of shale or
shaley limstone with a high sulphate concentration.

ditto the gypsum info.

I think I'd go for oolitic hematite instead.



That is certainly a possibility. Only I think what I saw with the TES map
they made of the site was that the highest concentrations of hematite occurs
outside of the crater. Of course, that doesn't entirely rule out the
possibility of the spherules contain hematite. I guess we will have to wait
for them to make another announcement. One thing though, and I ask this
because although I am very familiar with Oolitic limestone formation (we
have the St. Genevieve limestone in my neck of the woods too, and I've
studied it for many years), I don't know much about oolitic hematite other
than it does occur. Does oolitic hematite form in the same way that
carbonate oolites form? If so, they would have to accrete by rolling around
on the floor of come bldy of water dure to current agitation, would they
not? I'm not saying that this isn't a possibility at the rover landing
site, I'm just trying to get a clearer picture of how hematite oolites
form. Can they form by replacement of the original carbonate with hematite
by percolation of iron-rich ground water? I don't know if this is a
possibility, but I do know that ground water in many water wells in Kentucky
and Southern Indiana that are completed in the St. Genevieve limestone have
a high iron content, yet I have never seen oolites in the St. Genevieve that
were replaced with hematite. That goes for the Illionois Fluorspar district
as well. I've never seen hematite oolites there either, even though the
iron content of the ground water there is high. I guess it may be a
question of the high Ph water keeping the iron in solution. What say you?


I'm going to say something we rarely hear around he I don't know the
mechanism of hematite oolite formation, and don't think I have the
resources around here to find out. The occurrences I know of are in
hydrothermal igneous settings, and are only sedimentary in the sense
they have been concentrated by either reheating or dissolution.