Biomarker Preservation

Life as we know it is associated with a highly complex collection of organic matter. When an organism dies, opportunistic scavengers might come along and recycle (eat) most of the organic matter – what typically remains are hard tissues like bones from vertebrates, but occasionally remnants of soft-tissues or membranes persist in the form of molecular fossils imperceptible to the eye. These include lipids, proteins, and even genetic molecules like DNA and RNA. I investigate how lipids (components of the cell wall, tissues, fat, and signaling hormones) are preserved in their original state and undergo alteration into more stable products through a process called diagenesis. This allows us to examine organic matter in the geological record to learn how life has evolved on Earth.

Soft-Tissue Preservation in Holocene-age Capelin Concretions

Summons Lab, Bergmann Lab, Vinther Lab, & NOSAMS

Latest publication: Mojarro et al. (2021) Geobiology, PDF, https://doi.org/10.1111/gbi.12480

Determining how animal fossils form and the ways in which their soft-tissues are preserved in the geologic record has been a challenge to unravel because decay begins immediately after senescence while diagenetic alteration of organic matter continues over millions of years. Laboratory experiments running days to years provide important insights to some of the processes taking place. However, fossilization is ultimately the consequence of compounding factors, and this complexity poses various challenges for laboratory and modelling studies. Pathways of organic matter preservation are thought to not only depend on its original composition, but also contingent on the depositional setting (e.g., sedimentation rates, sedimentary composition, water chemistry, etc.), and the nature of microorganisms involved in decay. Therefore, while taphonomic experiments have significantly advanced our understanding of soft-tissue preservation, it would be ideal if fossilization could be caught in the act under natural conditions.

In recent years, carbonate concretions containing partially-to-fully decayed macroorganisms have proven to be remarkable windows into the diagenetic continuum revealing insights into the fossilization process. This is because most concretions are the result of biologically-induced mineral precipitation caused by the localized decay of organic matter which oftentimes preserve a greater biological signal relative to their host sediment.

Here we conduct a comparative lipid biomarker study investigating processes associated with soft-tissue preservation within Holocene-age carbonate concretions that have encapsulated modern capelin (Mallotus villosus). We focus on samples collected from two depositional settings that have produced highly contrasting preservation end-members.