Cave sediments

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.

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.

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.

Interesting info, thanks

Quote:

---

Originally Posted by 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.

---

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!

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. :)

It was Twin.

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? :)

Quote:

---

Originally Posted by LCF

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.

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.

That "Alabama red clay", is also called "Georgia red clay". And goes at least as far west as Arkansas.

Quote:

---

Originally Posted by 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? :)

---

No, this was actually in a passage that is easily done in backmount. It's just unforgiving, even with good technique. It's small enough that any movement through it causes the bottom to stir up. It's a short passage with no off shoots until you get back into larger passage. You can usually see going through it once, but we always turn around for the full effect. It's a perfect place to expose the uninitiated to silt outs and I take all my cave students through there.

Quote:

---

Originally Posted by RN

No, this was actually in a passage that is easily done in backmount. It's just unforgiving, even with good technique. It's small enough that any movement through it causes the bottom to stir up. It's a short passage with no off shoots until you get back into larger passage. You can usually see going through it once, but we always turn around for the full effect. It's a perfect place to expose the uninitiated to silt outs and I take all my cave students through there.

---

Lulz, I know where that is :) it gets pretty after a bit..

Is this the very first jump at Twin? (before the drop off). This is a beautiful one..

Quote:

---

Originally Posted by jason

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).

---

So you don't think something within the range of observed flow is enough to account for the deposits? Is there any indication of seasonality in the laminations?

Higher rainfall locally, longer periods of low flow conditions?

It's possible that the clay layers might form during a slackwater period during spring reversals in river floods. It's also possible the clay layers could have formed under lower water table conditions during lower sea levels when the caves would had negligible flow in them (and wouldn't have functioned as springs)... Some of the clay layers are curiously capped by a hard, orange 'cemented' layer (have a look at the floor in Devil's between the Keyhole and the Hill 400 - in places this is coated by a black manganese oxide - but if you brush it off, you can see the orange crust underneath) - but we haven't analyzed it yet.

I wouldn't expect their to be seasonal differences reflected in the clays because most of the springs do not have seasonal variations water chemistry.

I was curious about this, because I knew that red colors generally indicate the presence of iron oxides, and the limestone that comprises the walls of the cave isn't an iron-rich (or red) stone. In addition, as far as I know, the Mill Pond caves don't have big reversals to siphons (Hole perhaps excepted, but this red stuff wasn't in Hole).

It was an EXTREMELY interesting and instructive experience that Rob described to us ahead of time. Interesting, because I have swum through areas in MX that were that small, and when we turned around, there was just a touch of haze in the water. This fluffy red stuff was far more unforgiving, despite the fact that we were warned, and that I was taking extreme care to be on my very, very best behavior going in. I'm glad I did it, because I'll know better than to enter anything that small in FL, unless I'm prepared for a zero viz exit.

Quote:

---

Originally Posted by SuPrBuGmAn

Lulz, I know where that is :) it gets pretty after a bit..

---

Bet you don't... See below. ;)

Quote:

---

Originally Posted by Xenia

Is this the very first jump at Twin? (before the drop off). This is a beautiful one..

---

Not that one. That is a beautiful passage, but the composition of the bottom is much different than where we went. In Skiles' passage (the first jump at Twin), the silt is tan/brown, not red. It is a very beautiful passage. A transition occurs in that passage beyond the fissure room where you come into deeper, smaller tunnel. This is where the red clay is located. But we didn't go that way. We went into a different passage that ends up connecting to that one, though.

Quote:

---

Originally Posted by RN

Not that one. That is a beautiful passage, but the composition of the bottom is much different than where we went. In Skiles' passage (the first jump at Twin), the silt is tan/brown, not red. It is a very beautiful passage. A transition occurs in that passage beyond the fissure room where you come into deeper, smaller tunnel. This is where the red clay is located. But we didn't go that way. We went into a different passage that ends up connecting to that one, though.

---

Nice. I hope I will get to see this on the next trip. We did a lot of diving at Twin on the last trip and it was so worthwhile. It is a gorgeous cave. Unfortunately I did not get any good pictures... percolation is bad even if it looks quite clean.

Quote:

---

Originally Posted by Webmaster

So you don't think something within the range of observed flow is enough to account for the deposits? Is there any indication of seasonality in the laminations?

Higher rainfall locally, longer periods of low flow conditions?

---

or the separation after deposit? stir it up and let it set and things tend to settle in like-kind layers. with millions of years to 'set' would it not layer-out - it is a kind of liquidy solid with some flow to it, right?

skip