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Found 8 results

  1. Learning our Local Limestone

    Hi all y'all. I'm curious about learning more about our local geography to learn more about the context for fossils I find around here. I know a little bit, but not a ton and I'd love to learn more. I think I should probably start with what's exposed at the surface at my house. We're in the Balcones Fault Zone, and I've seen this spot mapped as both undifferentiated Fredricksburg Group and as Edwards Group. We've got a little intermittent creek with a deep enough valley/canyon that there's probably a 50' elevation difference between the highest and lowest areas. Being in West Austin, we do have exposed limestone cropping out at the surface. There aren't really any big cliffs, but the terrain sort of stairsteps down from the top to the bottom, with small cliffs a few feet tall interrupting the slope down. I haven't looked at all the layers closely, but it seems like there are a few layers of more porous limestone completely chock-full of shells. Would those be reef layers? This rock is a good example from one of those layers, but it seems to have more shells and bigger pieces than most of the similar layers (though it may just be less weathered...) The hard limestone exposed in the bed of the creek has what appear to be burrows, I think? The same rock layer has a few of what I believe are rudist fossils. I'm still not 100% on what rudists look like, but is this one? Higher up, there's some extensive chert/flint layers, but also some other more fossil-y layers. I'm thinking it might be a good idea to try making a stratigraphic column so I can better figure out exactly what I'm looking at, but I'm not really sure how to do that. I've got no experience in geology and would love to learn. Do any of y'all have good advice for how to go about doing this? I'm still not 100% on how to classify different carbonate rocks, so any resources you can point to for that would be greatly appreciated! I know a wee bit about our local geology, but I'd also appreciate any more in-depth resources y'all can recommend! Thanks a lot!
  2. Edwards Formation Rudist Identification

    A few weeks after my mother found her most recent cidarid in an Edwards formation check dam, I took a few minutes to swing by the same dam to see for myself what else could be found. Within minutes I dug up a cylindrical fossil that for a few weeks puzzled me due to its resemblance to a belemnite phragmocone. Then on Wednesday night I went to the DPS meeting and afterwards met briefly with Professor Andy Gale and showed him this specimen. He identified it as a rudist and immediately corroborated that with another DPS member familiar with rudists. What confused me is that it doesn't look like any of the other rudists that I have found in the Edwards. So far in my research I have found there to be 4 predominant rudist genera in the Edwards, which are listed in the tags. From pictures online I can't seem to definitively match this fragment to any of them, but it at least resembles some caprinid rudists I have seen online that are not from the Edwards. I know there must be many more rudist genera in the Edwards that I am unaware of, so I am hoping anyone more familiar with rudists than me could at least narrow it down to more than just a likely caprinid. The specimen is 3.75 cm long (Fig. 1), 4.2 cm in diameter at its concave end (Fig. 20), and 4.1 cm in diameter at its flat end (Fig. 22). I really know next to nothing about them so any help is appreciated. If anyone wants to compare this with the many other rudists that I have found from these Edwards dams, see the excessive amount of pictures in this thread. Fig. 1. Fig. 2.
  3. Edwards Check Dams

    A few weeks ago my mother, Stella (dog), and I went to a old-reliable heteromorph site in the Atco. After I dragged all my equipment to the part of the site that I was going to work, she went walking with Stella to look at some of the check-dams full of brought in Edwards limestone, chicken wire bags full of the brought in matrix put in the ditches for sediment control. In 2017 while we were at the same Atco site she was looking at a dumped pile of the Edwards and found a rare cidarid (see thread here) that compares well with Temnocidaris (Stereocidaris) hudspethensis. The sight of seeing that bizarre looking fossil just laying on the ground was quite a shock for both of us and motivation to hunt the dams more, and since then she has been casually looking over every check-dam hoping for another one. But because this Atco site is also rich in heteromorphs, I tend to focus all my attention on the chalk and neglect the Edwards dams, in these cases to my slight ire but also amazement at what she found with Stella. She did it again on the 9th, and found another cidarid that appears to be the same species as the last one from 2017, though from a different dam. I was at my Atco pile when she came over and showed it to me, completely blowing away all my finds in a very welcome way. The brought in Edwards is early upper Albian in age (about 107.6 mybp) and is a very fossiliferous crystalline limestone jammed packed with rudists and Chondrodonta sp. as well as the occasional gastropod. It makes for quite the sensory overload when trying to look for other things amongst the fossiliferous morass. The limestone is also interspersed with somewhat softer red sandstone that infills crevices in the much harder limestone and is more quickly weathered away in older exposures. I have tried so-far unsuccessfully to isolate the quarry from which the matrix originated to ask them permission to get a chance at the fossils before they are dumped in bags and hauled tens of miles to sites, damaging them. The problem is that there are multiple quarries in the nearest counties that expose the Edwards, namely Hood and Johnson counties. I have seen this matrix at sites all over North Texas, but I don't know if all that matrix is from the same quarry as the matrix from my Atco site since the Edwards is heavily quarried for fill all over the state. For now we are left to dig though the jumbled, knocked around bagged matrix, but even so the limestone is extremely hard so the fossils are not usually completely destroyed. And the site is big with lots of busted open bags. This latest cidarid is in about the same condition as the first, that being not so great but not so bad. Both specimens are missing most of their adoral sides and their apical plates are gone, leaving their circular apical scars. But they are still quite nice and intricately detailed, and also preserve some of their big mamelon tubercles, with the first specimen preserving 2 and the latest preserving 5, though there could be more under the globs of matrix stuck to them. This latest is also bigger. The first had a diameter of 52 mm at the ambitus and a preserved height of 37 mm, while the latest is 59 mm at the ambitus and 45 mm in height, though keep in mind that since they are both missing most of their adoral sides they would have had more height in life. The apical scar on the first specimen is 19 mm in diameter and on the second is 21 mm, with the crushed calcite fragments of the apical plates seen in the cavities left behind on both. I really didn't expect her to find another specimen of this rarity again, but apparently this matrix is a honey hole brought in by the truck load, making this site two honey holes in two epochs. Then on Wednesday I went by the same check dam from which this latest cidarid came and found what really appears to be a belemnite, but that is for another topic in the ID forum. Hopefully I can post that find soon. Since new Atco exposure at the site has temporarily slowed down I have an excuse to take a good hard look at the Edwards dams tomorrow afternoon. If we find anymore from the dams I will post it to this thread, so hope to see more In the mean time, here are the pictures of the echinoids, the check dam from which this latest specimen came, and a nifty Chondrodonta sp. she found in said dam. I welcome any other finds that anyone has found in the Edwards or its equivalents and any tips on how to prep limestone as hard as crystalized concrete. Also, sorry for the picture quality. My Nikon decided to die a few months ago for some reason and I have yet to get it fixed, so if anyone knows a camera repair shop that fixes Nikons in the DFW area, I am all ears. *Pictures incoming, computer acting up*
  4. On November 27 of this year my mother and I went hunting in a new housing development exposing the Austin Chalk in North Texas. The first and only site that we got to was covered in this rock that has been brought in from somewhere else. It was odd in that it looked like someone had just poured a bunch of it in an empty lot in no particular pattern. It was all next to a man made hole in the ground in the middle of the lot, but I don't see how that could be related. We have seen bags of this matrix in drainage ditches before and had also seen it variously thrown about at different Austin Chalk sites. I had found a few things in it that were intriguing, but for some reason I had largely (and very incorrectly) assumed that there was probably not much that one could find in it, so I never seriously hunted it. But my mother proved me very wrong! When we got to the site and I saw that much of it was covered in this stuff, I was somewhat annoyed since it was covering up some of the Austin Chalk. But we both got out anyways and began hunting. I went off towards the ditch where more of the Austin Chalk was exposed while she was looking around in the foreign matrix. I wasn't having much luck and she was commenting on how she was seeing some layered patterns in the matrix, pictured in F31. I didn't think much of it and kept hunting away from the pile of unknown matrix. Then less than a minute later my mother let out something along the lines of, "Hey! Hey! Hey! What is this?!" When she does that, I know she is not kidding around! So I went over there and saw her pick this up off of the ground. We both immediately knew that it was an echinoid. What made this specimen really special are the facts that this is the largest or at least second largest echinoid that we have ever found, the first echinoid from a formation other than the Austin Chalk, and our first regular echinoid all in one. Its a sad thing that it is so beat up, but then again its not surprising since it was probably hauled in a bag in the back of some guy's pickup for possibly hundreds of miles. Only two tubercles that have not been knocked off are visible, though perhaps there are one or two more buried under the chunk of matrix stuck to the side of the specimen. It is also missing most of its adoral side and most of its apical disc, with bits of the disc still in the depression that is left. Its test is pretty scuffed up in general, but at least most of it is still left and I don't think that it is too beat up to be identifiable. I took pictures of the site while I was there (pictures in F1-F4) and brought home a lot of matrix to experiment with and to photograph later to aide in identifying the formation from which it came. When I got home I consulted @Bill Thompson's book on Texas echinoids and I have been able to narrow this specimen down to the genus Temnocidaris for sure. I am hoping that you guys can help me find out what formation the matrix came from, which would greatly help to narrow down the species possibilities. Out of the four species of Temnocidaris listed in Thompson's book as being reported from Texas only two of them have there tests pictured, T. borachoensis and T. hudspethensis, with the other two species only described from their spines. Now I am not an echinoid expert by an stretch of the imagination, but I am personally leaning towards this being T. borachoensis from the Boracho Formation of Upton county or a nearby county in West Texas. My reasoning is twofold: First, to me its test much more resembles T. borachoensis than T. hudspethensis in two ways. They are that the interabulacrum tubercles are closer together than T. hudspethensis and that its test is a bit more squat than T. hudspethensis, even if it still had its base. Coincidently, just a little over a month ago @KimTexan posted for identification a Temnocidaris specimen from the Edwards Formation of Johnson county that very much resembles mine, though I can't say for sure it is the same species as mine since her specimen is missing much of its aboral side while mine is missing much of its adoral side, making a comparison between them a bit difficult. Second, from what I have seen the matrix most closely resembles the San Martine member of the Boracho Formation. If I want to learn a bit about Texas paleontology that I didn't know before I will usually look up one of @Uncle Siphuncle's Fossil hunting reports. Here is one which contains pictures of a lot of matrix and a few fossils from the Boracho formation, starting with Figure 91. The most striking resemblance I see is that the matrix has a lot of red/orange matrix streaks running through it like mine does. But because I have never hunted in the Boracho Formation other than possibly this brought in matrix, I don't know for sure. I also noticed what appears to be the same layered fossil shown in F31 in Figures 136-138. After seeing this post, I tend to think that it is oyster related material. This matrix is a lot more dense than the Austin Chalk that I am used to, making it noticeably heavier. It bubbles when I put vinegar on it indicating that it is limestone, though perhaps not as vigorously as vinegar on the Austin Chalk. I scraped some matrix with a dentist's pick in the places weakened by vinegar and places I didn't treat with vinegar, and while it did scratch the limestone matrix, the untreated matrix was harder than untreated Austin Chalk. I have tried to see if the sandy red/orange matrix bubbles, but my experiments were inconclusive because the limestone is always nearby, skewing the results. I would assume that it does not bubble on its own. After cleaning the echinoid, a few other fossils, and chunks of matrix, the toothbrush fibers had turned orange indicating that the sandstone it is not that hard, at least when wet. Also the limestone matrix is just packed full of calcite crystals, which is very noticeable in direct sunlight! The specimen its self, excluding any matrix, is 53mm in diameter by 36mm in height, though it would be taller if it still had its base. It appears to me that it is only infilled with the sandstone while there is an actual limestone chunk stuck to the side of it, shown specifically in F12. Notice the red patch on the matrix, a characteristic not unique to this chunk but seen on another chunk of matrix shown in F32. All of the pictures were taken in sunlight, so the color that you see is how it really looks. Thanks for any help in advance. F1-F4. On site photos. F2 F3
  5. Need a cidarid echinoderm ID

    I found this little jewel a while back, but never found out what species it is. Can anyone tell me what genus species it is? This is a close up of an ambulacral and pore area. I don’t think I can get much better on the close up picture quality. I do have a number of pics from other angles if needed. Thanks in advance for your input.
  6. Ammonite fragment

    I found this ammonite segment a while back in SE Johnson County in an area that is right near the Edwards Formation that is adjoined by a complex area that has Duck Creek and Ft. Worth limestone to name a few mixed in. I tend to think it may have been the complex formation, but I couldn’t tell you what part of it. I found it on top of the ground after a road was put in for a new house being built near some property I own out in the country. It is a segment of an ammonite. It weighs about 10 pounds I’d say. Is about 8 inches long and 6 inches tall or thick. Can anyone tell me about what large ammonites might be in that area?
  7. Ammonite ID 2

    Here is a 2nd ammonite found right near the first one, but a few years earlier. Can anyone tell me what the crystalline component is? This is from the Edwards Formation near Rio Vista, TX. I think it's one of my favorite ammonites because of the crystalline material. I'd kind of like to bleach the crystals to clean it up, but I'm not sure if that's possible.
  8. Ammonite ID if possible

    I found this ammonite a few years ago. Shortly after I found it a piece broke off the front revealing some of the internal structure of the ammonite. I know it is pretty worn down, but can anyone give me an idea of what kind it is? As best I can tell I found it in the Edwards formation outside of Rio Vista, TX.