cave geology/hydrology and speleothems

[swadiver]

I am not a geologist, so i am looking for some info on the way Florida underwater caves have formed and why there is basically no speleothem formation in our caves. from my reading, i know they have been dry during past ice ages when sea level was much lower. not dry long enough or has the water since worn them away? why do the Mexican and Bahamian caves have formations then?
what is it about the Karst south of Orlando that has virtually no cave formation?

I am sure these are elementary questions, but any expert info would be appreciated

[Kelly Jessop]

Not a geologist,nor did I stay in a Holiday Inn Express,but my understanding is that Florida caves we dive have never had a vadose phase,but have been phreatic.

[jkaterenchuk]

Not a geologist,nor did I stay in a Holiday Inn Express,but my understanding is that Florida caves we dive have never had a vadose phase,but have been phreatic.

Thank you. Now everything is crystal clear.

[jason]

Not sure what happened to the first response I typed up and tried to submit... but here is a recap.

Caves in Florida were likely air filled at different points in the geologic past, particularly lower water tables associated with lower sea level positions. There are speleothems in caves like Warm Mineral Springs and Salt Springs which could only have formed if the caves were dry. Cores of sinkhole sediments indicate dry conditions in now underwater caves, with water levels being at least 60 m lower than present.

The reason Florida may have few speleothems, despite having had lower water levels, is that (A) they could have formed but they dissolved away or (B) the conditions for speleothem formation are rarely met in Florida. As for (A), most caves in Florida are invaded by surface water at some point (or are in environments where they would have been invaded by surface water in the recent past). Many caves reverse flow in floods and intrusion of river water is actively enlarging these caves today. If there were speleothems in these caves, they would have dissolved away. Stalactites do not dissolve away in the Yucatan or Mexico because those cave passages are (for the most part) not dissolving today. As for (B) stalactite formation requires degassing of drip waters. Drip waters accumulate CO2 in the soil zone, dissolve limestone in the rock between the soil and cave (vadose zone) and stalactites dissolve due to degassing of CO2 from dripwaters when they enter an air filled cave that has lower CO2 concentrations than the overlying vadose zone. If the CO2 concentrations in the air filled cave are too high, then stalactites will not form. Some of my research has suggested that caves in Florida may have formed at lower water tables associated with lower sea levels by inputs of vadose CO2 gas to water tables and that caves formed without initial entrances to the surface. Without an entrance to the surface, caves would have the same concentration of CO2 as the vadose zone, dripwaters would not degas and stalactites would not form.

Not a geologist,nor did I stay in a Holiday Inn Express,but my understanding is that Florida caves we dive have never had a vadose phase,but have been phreatic.

[curtschu]

I posted a really good explanation of the Florida karst features not to long ago but I can't find the post maybe if you search by my name. It is heavy on the geological terms but otherwise very interesting.

Found it

http://works.bepress.com/cgi/viewcon...%20features%22

[jason]

what is it about the Karst south of Orlando that has virtually no cave formation?

I forgot to answer this part. The main cave diving regions in Florida are located where an impermeable layer of clay and sands (the Hawthorn layer) have been removed to expose the underlying limestone. Most of Florida is covered by the Hawthorn, which prevents either prevents cave formation or covers the entrances to older caves. South of Ocala, the Hawthorn starts getting 100s of feet thick. There are a few places with small caves, for example in and around Miami, but these caves are small, air (and cockroach) filled and developed in a thin layer of limestone that was deposited on top of the Hawthorn.