Cave sediments

[LCF]

I have a question about the difference in sediments between FL and MX. I've done a lot of diving in the latter, and only a little in the forner. But today, I got a lesson in siltouts, and came out of the cave with my harness packed with fine, red clay. The passage we swam didn't look that unforgiving; I've certainly been in places in MX that were equally small, and only stirred up a little, light dust. And it wasn't ever red.

Does anybody know why the primary sediments in MX seem to be sand, limestone silt, and mung, whereas the FL caves have this red clay in them? I really haven't ever seen clay like that down south.

[Webmaster]

Huh, there's plenty of sand in FL. Some of the sediments will be from organic matter sucked in from a sink in some places. Some will be weathering products from the limestone being broken down, so you essentially have whatever more or less insoluble part is leftover. Different rocks, different sediments.

That's how the amount of rock removal from stylolites is determined, by measuring the thickness of the residue compared to the amount in a given volume of that rock.

[jason]

The red clays come from dissolution of a particular part of the sand that you see all over the surface of Florida. As an interesting aside, this sand is actually responsible for Florida being connected to mainland USA.... For much of it's 'recent' geological history, Florida was an isolated carbonate platform similar to the Bahamas. Continued erosion of the Appalachian Mountains and transport of the sand created from erosion filled in the trench that separated Florida from the mainland and eventually covered much of the state. You'll notice the land surface in the Yucatan is mostly bare limestone. This is because the Yucatan lacked a source of (siliclastic) sand (and why it doesn't have much in the way of red clay - though you'll see some red dust in places that originated from the Sahara desert). The sands in Florida weather to clays that migrate through fractures in the rock and build up in layers on cave floors during low flow conditions. Now the really interesting question is why are there are laminated clay layers indicative of low flow in high flow caves like Cow or Ginnie (or others)..... (we're working on it.... and if we figure anything out - I'll be sure to let you know). You'll also get a lot of dissolution of sand on cave floors when the springs reverse flow during large river floods.

[JamieZ]

Interesting info, thanks

The red clays come from dissolution of a particular part of the sand that you see all over the surface of Florida. As an interesting aside, this sand is actually responsible for Florida being connected to mainland USA.... For much of it's 'recent' geological history, Florida was an isolated carbonate platform similar to the Bahamas. Continued erosion of the Appalachian Mountains and transport of the sand created from erosion filled in the trench that separated Florida from the mainland and eventually covered much of the state. You'll notice the land surface in the Yucatan is mostly bare limestone. This is because the Yucatan lacked a source of (siliclastic) sand (and why it doesn't have much in the way of red clay - though you'll see some red dust in places that originated from the Sahara desert). The sands in Florida weather to clays that migrate through fractures in the rock and build up in layers on cave floors during low flow conditions. Now the really interesting question is why are there are laminated clay layers indicative of low flow in high flow caves like Cow or Ginnie (or others)..... (we're working on it.... and if we figure anything out - I'll be sure to let you know). You'll also get a lot of dissolution of sand on cave floors when the springs reverse flow during large river floods.

[LCF]

Thank you! That's fascinating. I love learning things like that, because the next time I dive in Florida, I'll be thinking about the geology, and the experience will be that much richer. Thanks again!

[JahJahwarrior]

Thank you Jason, your one paragraph answered quite a lot of the questions I had after reading a book on Floridian geology.

LCF, care you share what cave you were diving? I have yet to exit with red clay, but I have stirred up plenty of silt.

[RN]

It was Twin.

[JahJahwarrior]

Ah. I've seen clays and silts of many colours, but tend to see more gray clays here in central Florida/north central Florida. I have yet to make it up to your beautiful caves in even-more-north Florida. Jason, are more red clays found in the even-more-north Florida caves due to their closer proximity to the channel that was filled by those siliclastic sediments?

Was this during LCF's SM dive?

[gsk3]

I really haven't ever seen clay like that down south.

I learned a lot from reading the responses to this thread, but I just want to add that I grew up in Alabama and red clay is everywhere. It's actually sold to sculptors nationwide as "Alabama red clay." The stuff above ground tended to be moist and stain everything, but when dry it was an extremely fine powder.

If it originally came off the Appalachians it would make sense that it's found from AL down to FL.

[jason]

The color of the clay (at least in this instance) is primarily due to the amount of oxygen the clay has been exposed to. Red clays are colored by oxidized iron. Grey clays are typically formed in low oxygen environments (like normal Florida groundwater) and black clays generally indicate formation where no oxygen was present. If there are more red clays somewhere then it's likely an indication of greater frequency of higher oxygen contents during clay formation.... I haven't spent too much time in caves up north, so I can't really comment on specifics - but the color wouldn't have anything to do with proximity to the channel.... You just need to have siliclastic sand.