Glowing Golden Fossils From Early Jurassic Site Shed Light on How Exceptional Fossilization Takes Place, New Study Shows

Fossils situated in the Posidonia Shale in Germany were observed to have a golden gleam. While there have been initial assumptions about where the golden hue comes from, a new study reveals that this hue offers hints of an exceptional fossilization.

Golden Fossils

Per Live Science, experts have thought for a long time that pyrite, also referred to as "fool's gold," was the distinct component behind the unique golden hue of fossils in the Posidonia Shale in Germany.

However, according to a recent study, this might not be the case. Earlier this 2023, an international research team went to the prehistoric, early Jurassic site that is known for its remarkably fossilized marine animals. They gathered crustacean, bivalve, and ammonite samples that were as big as a palm or larger.

The researchers then analyzed the 183-million-year-old findings with a scanning electron microscope that is high-powered. As they did so, the researchers found it hard to pick up any pyrite traces in the fossils.

Rowan Martindale, a co-author of the study and an associate professor from the University of Texas' (UT) Department of Geological Sciences, explains that it has been a long-standing belief that everything in the Posidonia Shale was pyritized. The researchers gathered samples from the area that they thought were pyritized. However, they were only able to observe small bits of pyrite within them, but these were all basically yellow or phosphatized calcite. Such findings, which were published in the Earth-Science Reviews, came as a shock to the researchers and gravely affect what is currently known about this prominent fossil deposit.

Exceptional Fossilization

According to Science Daily, the fossils from the early Jurassic site date back as far as 183 million years. The remnants include squids that have inksacs, lobsters, ichthyosaur embryos, and other rare soft-bodied creatures.

As mentioned earlier, the researchers analyzed the samples they collected in order to know more about their exceptional fossilization, which fostered remarkable preservation. They observed that, on every occasion, the fossils comprised materials of phosphate, though the surrounding rocks of black shale were coated with dots of microscopic pyrite crystal clusters known as framboids.

Sinjini Sinha, a doctoral student from the Jackson School of Geosciences at UT, reportedly spent days searching for framboids across the fossils. Sinha notes that, in some specimens, around 800 framboids were observed on the matrix, while there were around three or four framboids on fossils.

Science Daily reports that the presence of phosphate and pyrite in several specimen places is vital because it holds key data regarding the fossilization environment of the specimen. While pyrite forms in environments that do not have oxygen, phosphate requires oxygen.

Hence, the research suggests that a pulse of oxygen may have been necessary to foster the necessary chemical reactions for fossilization. This comes despite how the anoxic, or oxygenless, seafloor facilitates fossilization by preventing decay and keeping predators at bay.

Sinha explains that it has been a long-standing idea that anoxia causes remarkable preservation when, in fact, it does not directly contribute to this. Rather than that, anoxia helps by making the environment more suitable for faster fossilization conditions that allow preservation. However, it is oxygenation that boosts this preservation.

The results align with the team's earlier research on geochemical conditions of areas known to hold fossils that are remarkably preserved, which are also known as konservat-lagerstätten. However, the findings contradict persisting theories regarding the condition requirements for exceptional fossilization in the Posidonia Shale.

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