plankton Posted August 19, 2012 Share Posted August 19, 2012 (edited) I found this recently in Mazonia state park (Illinois). It's odd looking, but has a different texture and imprint on the one side (pic 1). Is this a fossil of some sort or just a unique piece of rock? Thanks for any feedback! Edited August 19, 2012 by plankton Link to comment Share on other sites More sharing options...
evannorton Posted August 19, 2012 Share Posted August 19, 2012 Sorry I don't see fossil just siderite. There are a few good guide books....you should also figure out if you are in an Essex or braidwood location (Essex has more jellyfish, water bugs and braidwood has more plant life), I would also look at rcfossils gallery which as good as the field museum collection. Good luck! Link to comment Share on other sites More sharing options...
Auspex Posted August 19, 2012 Share Posted August 19, 2012 It is concretionary, but it does not appear to be fossiliferous. "There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant “Try to learn something about everything and everything about something.” - Thomas Henry Huxley >Paleontology is an evolving science. >May your wonders never cease! Link to comment Share on other sites More sharing options...
Scylla Posted August 19, 2012 Share Posted August 19, 2012 Agree siderite or limonite. Are those mud crack imprints or just ridges of deposition on it? Link to comment Share on other sites More sharing options...
plankton Posted August 19, 2012 Author Share Posted August 19, 2012 Thank you all for the replies; great help! To answer Scylla's question; the lines/ridges are on the concretion. It is not deposition, because I soaked it for a while and scrubbed off all the lose material. You think those could be from mud cracks where this formed? Link to comment Share on other sites More sharing options...
Scylla Posted August 21, 2012 Share Posted August 21, 2012 Could be, if anyone has more firsthand knowledge of the local geology out there I would defer to their opinion of course. Link to comment Share on other sites More sharing options...
trilobiteruss Posted August 21, 2012 Share Posted August 21, 2012 It is a subdeltaic deposit into the bay of a distributary system that formed as seawater rose in one of flooding events that drownded the Colchester Coal swamp. It is mostly gray shale to siltstone w some sandstone distributary deposits. The siderite forms in the embayments and is typical in a number of cycles of filling, shifting, swamp and then gray shales and silts over a number of Pennsylvanian Coals in the US. Northeastern has a good book on the fauna. ESCONI. (Earth Science Club of Northern Illinois) also has some books on the fauna and flora found in the concretions. The Illinois Geological Survey where i worked for 34 years studying coal geolgy and stratigraphy and resources has a guidbook number 8 i seem to recall on this area. I did a few studies published on the low sulfur coals found below these thick embayment sub deltaic to crevasse splay deposits along deltaic rivers. Russ Link to comment Share on other sites More sharing options...
Scylla Posted August 21, 2012 Share Posted August 21, 2012 It is a subdeltaic deposit into the bay of a distributary system that formed as seawater rose in one of flooding events that drownded the Colchester Coal swamp. It is mostly gray shale to siltstone w some sandstone distributary deposits. The siderite forms in the embayments and is typical in a number of cycles of filling, shifting, swamp and then gray shales and silts over a number of Pennsylvanian Coals in the US. Northeastern has a good book on the fauna. ESCONI. (Earth Science Club of Northern Illinois) also has some books on the fauna and flora found in the concretions. The Illinois Geological Survey where i worked for 34 years studying coal geolgy and stratigraphy and resources has a guidbook number 8 i seem to recall on this area. I did a few studies published on the low sulfur coals found below these thick embayment sub deltaic to crevasse splay deposits along deltaic rivers. Russ So, um is it a mud crack? Link to comment Share on other sites More sharing options...
Missourian Posted August 21, 2012 Share Posted August 21, 2012 It looks like one of the various sideritic concretions that are common in Pennsylvanian beds. While some, such as those at Mazon Creek, contain fossils in the center, others are often barren or contain scattered fossil debris, and can take on various forms. Here in KC, such concretions can be round, irregular, or even merge into beds. They sometimes come with fossils (usually mollusk shells here), but they are usually barren. Many have septarian-like dessication cracks. Most intriguing on your specimen is the oolitic-like coarse granulation on the flat surface. Context is critical. Link to comment Share on other sites More sharing options...
trilobiteruss Posted August 22, 2012 Share Posted August 22, 2012 It looks like one of the various sideritic concretions that are common in Pennsylvanian beds. While some, such as those at Mazon Creek, contain fossils in the center, others are often barren or contain scattered fossil debris, and can take on various forms. Here in KC, such concretions can be round, irregular, or even merge into beds. They sometimes come with fossils (usually mollusk shells here), but they are usually barren. Many have septarian-like dessication cracks. Most intriguing on your specimen is the oolitic-like coarse granulation on the flat surface. I would agree that dessication cracks in the siderite are more likely than just plain mud cracks. They are typical... Link to comment Share on other sites More sharing options...
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