175 The Neoproterozoic Earth and Life Co-evolution, Part I
This session aims to enhance discussions and foster interdisciplinary collaborations to advance understanding of the Neoproterozoic Earth and life co-evolution. Contributions from paleontologists, geochemists, sedimentologists, Earth system modelers, and related fields are highly encouraged.
Tuesday, 21 October 2025
8:00 AM - 12:00 PM
HBGCC, 304A
Exploring the environmental context of a silica-rich fossiliferous Tonian deposit
Paper number: 175-1
Program: Technical Sessions
Time: 8:05 AM – 8:20 AM
Authors
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Lucy HelmsJohns Hopkins University, Baltimore, MD
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Maelle Girard-TsuruBaltimore Polytechnic Institute, Baltimore, MD
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Frank PaviaUniversity of Washington, Seattle, WA
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Sabrina KhanJohns Hopkins University, Baltimore, MD
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Cecilia SandersUniversity of Maryland, College Park, MD
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Aibolat TalgatbekSatbayev University, Almaty
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Sezim MustapayevaSatbayev University, Almaty
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Yerkhozha MamanovSatbayev University, Almaty
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Emily SmithJohns Hopkins University, Baltimore, MD
Abstract
The Tonian is a key interval in the evolution of life and the environment, characterized by potential evolutionary and ecological shifts among eukaryotes. However, there remain questions surrounding the drivers of these biological and ecological shifts as well as the environmental context in which they occurred. This is due, in part, to the Tonian fossiliferous strata being biased towards low temperature shallow marine depositional environments. One fossiliferous Tonian deposit, the >759 Ma Chichkan Formation in southern Kazakhstan, differs from other Tonian sites globally in that it is pervasively silicified, likely the result of a distinct depositional environment. The classification and genesis of chert within the Chichkan Formation – and the implications that these hold for paleoenvironmental conditions, paleoecology, and microfossil preservation – have not been previously studied.
Here, we integrate field, petrographic, and geochemical data from the major silica-rich facies of the Chichkan Formation to classify the different types and generations of silica, explore silica formation mechanisms, and constrain the timing and conditions under which different types of silica formed. Together, our results suggest that the Chichkan Formation contains a combination of primary and diagenetic silica, indicating that this unit formed in an environment with high concentrations of dissolved silica. With our integrated petrographic and geochemical data sets, we explore alternative depositional environments for the Chichkan Formation, including hydrothermally influenced environments. By characterizing the environmental context of this Tonian deposit and the diverse microfossil assemblage that it preserves, we expand our understanding of the environmental context for Tonian eukaryotic and microbial ecosystems and the processes that facilitated fossil preservation.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-412189
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