Mhunter07 Posted June 20, 2018 Share Posted June 20, 2018 Found this on a large piece of sandstone on an eastern cross timbers forest meadow in south central Denton county near the Denton landfill. Any ideas? Link to comment Share on other sites More sharing options...
DPS Ammonite Posted June 20, 2018 Share Posted June 20, 2018 I looks like an iron oxide/hydroxide (rust) cemented concretion possible following the path of a burrow or other trace fossil. However, the continuation of the wavy bedding in the sandstone into the tubular concretion in the first photo suggests that this is not a burrow but rather a pathway of iron rich water that formed the concretion. Looking at at the top of the rock, (above your hand) Mhunter06, does the bedding of the sandstone match up with the restrictions and expansions of the hemetitic tube concretion? Take a close-up picture looking down at the rock above your hand. If the the transverse lines in the tubular concretion line up with the bedding of the sandstone then this is evidence of iron rich water solutions that traveled different distances into the sandstone based on each layers porosity. I love the wavy bedding. A great rock for your yard. My goal is to leave no stone or fossil unturned. See my Arizona Paleontology Guide link The best single resource for Arizona paleontology anywhere. Link to comment Share on other sites More sharing options...
Miocene_Mason Posted June 20, 2018 Share Posted June 20, 2018 If it’s a concretion, it’s trying hard to look like an orthoconic nautiloid. “...whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” ~ Charles Darwin Happy hunting, Mason Link to comment Share on other sites More sharing options...
Mhunter07 Posted June 20, 2018 Author Share Posted June 20, 2018 Interesting, thank you for helping! I agree it would make a great ornamental piece for the yard. I also found this rock in the same area showing iron oxide concretions as well, and was wondering what the smooth white crystalization might be? Also can you offer any speculation into how these concretions formed? They are in just about every rock around here. Does it have to do with ground water? Trying to conceptualize how these crazy shapes came to be. Thanks! Link to comment Share on other sites More sharing options...
DPS Ammonite Posted June 20, 2018 Share Posted June 20, 2018 The white crystals may be gypsum since there is too much rainfall to allow salt crusts to form. The iron concretions in the Woodbine I believe were mined for iron. The concretions form where iron rich water percolates in the rock during diagenesis. Sometimes organic matter such a plant parts can act as a focal point for concretions. Your tubular iron concretion could of had a long stem or twig as a core (small enough that it did not disturb the bedding in the sandstone) that acted as a focal point for water movement and hematite deposition. My goal is to leave no stone or fossil unturned. See my Arizona Paleontology Guide link The best single resource for Arizona paleontology anywhere. Link to comment Share on other sites More sharing options...
ynot Posted June 20, 2018 Share Posted June 20, 2018 I agree that they are concretions. The "white" could be mineral salts or caliche. Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
Mhunter07 Posted June 20, 2018 Author Share Posted June 20, 2018 Thank you again for looking into this. Here is a close up of the area above my hand. I also added a photo from the other end of the concretion. Link to comment Share on other sites More sharing options...
DPS Ammonite Posted June 20, 2018 Share Posted June 20, 2018 It is hard to see perfectly the relationship between the exterior of the concretion and the bedding but, I think that the porosity of each bed did control the final exterior texture of the tubular concretion. BTW, at Grapevine Lake near Dallas, you can find impressions of toredo wood in the iron concretions from the Woodbine.The wood acted as a focal point for the concretion. I bet wood impressions can also be found in other Woodbine outcrops in north Texas. I also have found similiar iron concretions formed around wood in the Pawpaw Fm. on Lake Texoma in Oklahoma: http://www.thefossilforum.com/index.php?/topic/53577-ntx-cretaceous-is-this-a-group-of-seeds-insect-eggs-mineralgeological/&tab=comments#comment-574475 My goal is to leave no stone or fossil unturned. See my Arizona Paleontology Guide link The best single resource for Arizona paleontology anywhere. Link to comment Share on other sites More sharing options...
abyssunder Posted June 20, 2018 Share Posted June 20, 2018 Maybe we can call them Rhizoliths? " We are not separate and independent entities, but like links in a chain, and we could not by any means be what we are without those who went before us and showed us the way. " Thomas Mann My Library Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.