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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    'Golden' fossils reveal origins of exceptional preservation    
      
     Date:   
         May 2, 2023   
     Source:   
         University of Texas at Austin   
     Summary:   
         A recent study found that many of the fossils from Germany's   
         Posidonia shale do not get their gleam from pyrite, commonly   
         known as fool's gold, which was long thought to be the source of   
         the shine. Instead, the golden hue is from a mix of minerals that   
         hints at the conditions in which the fossils formed. The discovery   
         is important for understanding how the fossils -- which are among   
         the world's best-preserved specimens of sea life from the Early   
         Jurassic -- came to form in the first place, and the role that   
         oxygen in the environment had in their formation.   
      
      
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   FULL STORY   
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   All that glitters is not gold, or even fool's gold in the case of fossils.   
      
   A recent study by scientists at The University of Texas at Austin and   
   collaborators found that many of the fossils from Germany's Posidonia   
   shale do not get their gleam from pyrite, commonly known as fool's gold,   
   which was long thought to be the source of the shine. Instead, the golden   
   hue is from a mix of minerals that hints at the conditions in which the   
   fossils formed.   
      
   The discovery is important for understanding how the fossils -- which   
   are among the world's best-preserved specimens of sea life from the   
   Early Jurassic - - came to form in the first place, and the role that   
   oxygen in the environment had in their formation.   
      
   "When you go to the quarries, golden ammonites peek out from black shale   
   slabs," said study co-author Rowan Martindale, an associate professor   
   at the UT Jackson School of Geosciences. "But surprisingly, we struggled   
   to find pyrite in the fossils. Even the fossils that looked golden, are   
   preserved as phosphate minerals with yellow calcite. This dramatically   
   changes our view of this famous fossil deposit."  The research was   
   published in Earth Science Reviews. Drew Muscente, a former assistant   
   professor at Cornell College and former Jackson School postdoctoral   
   researcher, led the study.   
      
   The fossils of the Posidonia Shale date back to 183 million years ago,   
   and include rare soft-bodied specimens such as ichthyosaur embryos,   
   squids with ink-sacs, and lobsters. To learn more about the fossilization   
   conditions that led to such exquisite preservation, the researchers put   
   dozens of samples under scanning electron microscopes to study their   
   chemical composition.   
      
   "I couldn't wait to get them in my microscope and help tell their   
   preservational story," said co-author Jim Schiffbauer, an associate   
   professor at the University of Missouri Department of Geological Sciences,   
   who handled some of the larger samples.   
      
   The researchers found that in every instance, the fossils were primarily   
   made up of phosphate minerals even though the surrounding black shale rock   
   was dotted with microscopic clusters of pyrite crystals, called framboids.   
      
   "I spent days looking for the framboids on the fossil," said co-author   
   Sinjini Sinha, a doctoral student at the Jackson School. "For some of the   
   specimens, I counted 800 framboids on the matrix while there was maybe   
   three or four on the fossils."  The fact that pyrite and phosphate are   
   found in different places on the specimens is important because it reveals   
   key details about the fossilization environment. Pyrite forms in anoxic   
   (without oxygen) environments, but phosphate minerals need oxygen. The   
   research suggests that although an anoxic seafloor sets the stage for   
   fossilization -- keeping decay and predators at bay -- it took a pulse   
   of oxygen to drive the chemical reactions needed for fossilization.   
      
   These findings complement earlier research carried out by the team on the   
   geochemical conditions of sites known for their caches of exceptionally   
   preserved fossils, called konservat-lagersta"tten. However, the results   
   of these studies contradict long-standing theories about the conditions   
   needed for exceptional fossil preservation in the Posidonia.   
      
   "It's been thought for a long time that the anoxia causes the exceptional   
   preservation, but it doesn't directly help," said Sinha. "It helps with   
   making the environment conducive to faster fossilization, which leads to   
   the preservation, but it's oxygenation that's enhancing preservation."   
   It turns out, the oxygenation -- and the phosphate and accompanying   
   minerals - - also enhanced the fossil's shine.   
      
   The research was funded by Cornell College and the National Science   
   Foundation.   
      
   The Posidonia fossil specimens used in this study are now part of   
   the collections at the Jackson School's Non-Vertebrate Paleontology   
   Laboratory.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Earth_Science # Geology # Weather # Geochemistry   
             o Fossils_&_Ruins   
                   # Ancient_DNA # Fossils # Evolution # Paleontology   
       * RELATED_TERMS   
             o Fossil o Feathered_dinosaurs o Trace_fossil o   
             Recent_single-origin_hypothesis o Precambrian o Velociraptor   
             o Tyrannosaurus o Human_evolution   
      
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   Story Source: Materials provided by University_of_Texas_at_Austin. Note:   
   Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. A.D. Muscente, Olivia Vinnes, Sinjini Sinha, James D. Schiffbauer,   
      Erin   
         E. Maxwell, Gu"nter Schweigert, Rowan C. Martindale. What role does   
         anoxia play in exceptional fossil preservation? Lessons from the   
         taphonomy of the Posidonia Shale (Germany). Earth-Science Reviews,   
         2023; 238: 104323 DOI: 10.1016/j.earscirev.2023.104323   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230502155416.htm   
      
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