Newswise — All that glitters is not gold, or even fool’s gold in the case of fossils.
Researchers from The University of Texas at Austin and their partners have recently discovered that the shiny appearance of many fossils from Germany’s Posidonia shale is not caused by pyrite, commonly known as fool’s gold, which was previously believed to be the source of the shine. Instead, it is from a combination of minerals that provides information about the environment in which the fossils were formed.
The recent finding about the true source of the golden color of fossils from Germany’s Posidonia shale has significance in understanding the formation process of these fossils. These fossils are considered as some of the most well-preserved specimens of sea life from the Early Jurassic period. The discovery also sheds light on the role of oxygen in the environment during their formation.
According to Rowan Martindale, an associate professor at the UT Jackson School of Geosciences and co-author of the study, the golden fossils found in Germany's Posidonia shale are preserved as phosphate minerals with yellow calcite, instead of pyrite as previously believed. This new understanding has significant implications for comprehending how the fossils formed and the impact of environmental factors like oxygen during their formation.
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 Posidonia Shale is a collection of fossils that are around 183 million years old and include unique specimens like soft-bodied creatures including ichthyosaur embryos, squids with ink-sacs, and lobsters. The scientists aimed to understand the fossilization process that led to the exceptional preservation of these specimens and studied dozens of samples under scanning electron microscopes to analyze their chemical makeup.
“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 discovered that the fossils were mainly composed of phosphate minerals, despite the presence of microscopic clusters of pyrite crystals, known as framboids, in the surrounding black shale rock.
“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 significant finding that pyrite and phosphate were located in different regions of the specimens provides valuable insights into the fossilization environment. Pyrite is formed in the absence of oxygen, whereas phosphate minerals require oxygen. The study suggests that although an oxygen-deprived seafloor provided the necessary conditions for fossilization, the chemical reactions required for fossilization were triggered by a sudden influx of oxygen. This information sheds light on the complex interplay between oxygen availability and fossilization processes.
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-lagerstätten. However, the results of these studies contradict long-standing theories about the conditions needed for exceptional fossil preservation in the Posidonia.
According to Sinha, it has been a long-held belief that anoxia is the reason behind the remarkable preservation, but this is not entirely accurate. While anoxic conditions may help create a favorable environment for fossilization, it is the presence of oxygen that plays a key role in 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.