Application of X-ray Computed Tomography to Interpreting the Origin and Fossil Content of Siliceous Concretions from the Conasauga Formation (Cambrian) of Georgia and Alabama, USA THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Jessica Kastigar Graduate Program in Geological Sciences The Ohio State University 2016 Master's Examination Committee: Loren E. Babcock (Advisor) Ann E. Cook MaryMegan Daly Copyright by Jessica Kastigar 2016 Abstract Siliceous concretions from the Conasauga Formation (Cambrian: Drumian to Guzhangian) of Georgia and Alabama, USA, yield a diverse assemblage of body and trace fossils. X-ray computed tomographic (XCT) imaging has been added to standard techniques of analysis including light microscopy, to help determine the early development and fossil content of the concretions. Most of the siliceous concretions show features consistent with biofilm-mediated early diagenesis of siliceous sponges (poriferans), primarily hexactinellids, but perhaps also including some demosponges. Leucon-grade body forms have been identified from images of the networks of canals and the spongocoels within the skeletons, and stauract spicules preserved in the concretions are consistent with a hexactinellid origin for many of the concretions. Some concretions appear to have formed from remobilized biogenic silica and nucleated around other forms of decaying organic matter, including biofilms associated with burrowing traces, fecal matter, and partially decayed remains of other organisms such as hyoliths, trilobites, and cap-shaped fossils. Most concretions probably lithified quickly but some show evidence of a longer-term process of lithification involving multiple generations of early diagenesis. XCT-scans of Holocene and post-Cambrian sponges show remarkable similarities to siliceous concretions from the Conasauga Formation, which supports the conclusion ii that many of the Conasauga Formation concretions formed around sponge skeletons. XCT-scans of siliceous, calcareous, and other concretions from various Paleozoic localities in North America, South America, and Europe show features similar to those exemplified in Conasauga Formation concretions, which implies similar microorganism- mediated early diagenesis for their origins. iii Acknowledgments This manuscript could not have been completed without the assistance of others. First and foremost, I want to thank my husband, James Knobbe, for his immense support throughout the last few years, including technical help with computer problems and Photoshop, a willingness to listen about rocks, and incredible moral support and understanding. I also want to thank my advisor, Loren Babcock, for helping me figure out what the data were trying to tell me, constantly nudging me in the right direction, and the many long conversations about these curious little concretions. I also relied heavily on my family, my parents, John and Mary Kastigar, and my father-in-law, Tom Knobbe, for their confidence in me and their support. I would also like to thank my fellow graduate students, especially Mark Peter, and faculty, including Bill Ausich, who were a source of great help, advice, and encouragement. Finally, I am grateful for the help from my committee members. Ann Cook provided access to the XCT-scanner and instructed me in its use and the use of ImageJ. Meg Daly helped me better understand the biology of sponges. Loren Babcock, Jerry Armstrong, Charles Ciampaglio, Ron Ray, and Marc Behrendt collected the Conasauga Formation concretions used in this study. Samuel Zamora provided the concretions from the Valtorres Formation, Spain. Loren Babcock provided the concretions from the Sicasica Formation, Bolivia, which were collected iv under support from a National Geographic Society Research Grant. Loren Babcock and Shanchi Peng collected the orsten-type concretion from the Huaqiao Formation, China. Dale Gnidovec provided access to specimens in the Orton Geological Museum at The Ohio State University. Access to Holocene sponge material was provided in part by Tom Watters of the Museum of Biological Diversity at The Ohio State University. v Vita 2008................................................................A.S. Geology, Heartland Community College 2011................................................................B.S. Paleontology, Northern Illinois University 2016................................................................M.A. Invertebrate Paleontology, The Ohio State University Field of Study Major Field: Geological Sciences vi Table of Contents Abstract ............................................................................................................................... ii Acknowledgments.............................................................................................................. iv Vita.. ................................................................................................................................... vi List of Figures .................................................................................................................... ix Introduction ......................................................................................................................... 1 Concretions .................................................................................................................. 2 Conasauga Formation .................................................................................................. 8 Sponge Morphology .................................................................................................. 12 Materials and Methods ...................................................................................................... 15 Research ............................................................................................................................ 18 Conasauga Concretions ............................................................................................. 18 Other Concretions ...................................................................................................... 22 Comparison of Concretions with Holocene and Fossil Poriferans ............................ 25 Figures ....................................................................................................................... 29 Discussion ......................................................................................................................... 40 vii Density Differences in Conasauga Formation Concretions ...................................... 40 Trilobites ................................................................................................................... 41 Hyoliths ..................................................................................................................... 42 Trace Fossils .............................................................................................................. 43 Poriferans in the Conasauga Formation .................................................................... 46 Generation of Concretion Development .................................................................... 49 Twinned Concretions ................................................................................................ 51 Additional Organic Material Preserved in Concretions ............................................ 51 Valtorres Formation Concretions .............................................................................. 53 Figures ....................................................................................................................... 55 References ......................................................................................................................... 66 Appendix A: Conasauga Concretions ............................................................................... 74 Appendix B: Comparative Concretions ............................................................................ 78 Appendix C: Porifera ........................................................................................................ 80 viii List of Figures Figure 1. The Coosa River Valley, northwest Georgia, and adjacent part of eastern Alabama, USA showing localities of siliceous concretions. ..................................... 17 Figure 2. Surface textures of siliceous concretions from the Conasauga Formation (Cambrian), Coosa River Valley, Georgia. ............................................................... 29 Figure 3. Twinned siliceous concretions from the Conasauga Formation. ....................... 30 Figure 4. Porosity types identified using XCT-scanning in concretions from the Conasauga Formation. ............................................................................................... 31 Figure 5. Examples of multiple diagenetic generations imaged using XCT-scanning in siliceous concretions from the Conasauga Formation. .............................................. 32 Figure 6. Low density, oval-shaped structures stretching across a siliceous concretion from the Conasauga Formation, imaged using XCT. ................................................ 33 Figure 7. Types of internal density differences identified using XCT in siliceous concretions from the Conasauga Formation .............................................................. 34 Figure 8. Stauract spicules in siliceous concretions from the Conasauga Formation.