Understanding biases in reconstructing ancient marine ecosystems through the early Cambrian Sirius Passet Lagerstätte, North Greenland

Abstract

The early Cambrian (~538,8–509 Ma) marks the rapid radiation of modern animal life. ‘Burgess Shale-type’ (BST) Lagerstätte provide important windows into these early ecosystems. But how faithfully do they preserve them? Fossil assemblages have been through multiple taphonomic ‘filters’ before discovery that can each severely bias their biotas. In this thesis, I attempt to show how recognizing biases in the geologically complex and poorly understood lower Cambrian Sirius Passet Lagerstätte (North Greenland) can expose novel biological information. Each filter and its bias reflect processes that occur with different geological timing. First, I use petrographic and chemical analyses to show that quartz preserving labile soft tissues are a metamorphic replacement of originally phosphatized tissues. Then, I use a quantitative dataset of the distribution of these highly frequent phosphatized tissues to assess important controls and biases on phosphatization. I identify five controls: taxonomy, tissues, microenvironments, size, and diet. Each of them shows different biases. Then, I use an integrated bed-by-bed approach to determine the taphonomic and temporal biases of the depositional environment. I find that the benthic and pelagic components of Sirius Passet are minimally biased and capture temporal population dynamics due to highly frequent deposition. Since most macrofauna are likely preserved in Sirius Passet, I then attempt to reconstruct a qualitative food web for the pelagic biota. I find that the trophic structure has characteristics of a modern high-productivity ‘wasp-waist’ ecosystem, despite showing a significantly different taxonomic organization. Lastly, I speculate that the unique characteristics of Sirius Passet may be linked to a high-productivity paleoenvironment near a marine river plume. My thesis shows how detailed contextualization of a complex Lagerstätte (Sirius Passet) can reveal primary (biological) signals from secondary (biases/overprints) signals. Sirius Passet has potential to be a treasure trove of biological information from aftermath of the Cambrian Explosion.

Date of Award	3 Oct 2023
Original language	English
Awarding Institution	University of Bristol
Sponsors	British Geological Survey
Supervisor	Jakob Vinther (Supervisor), Philip Wilby (Supervisor), Jane Memmott (Supervisor), Tae-yoon S. Park (Supervisor) & Arne Thorshøj Nielsen (Supervisor)