Sea level controls on Ediacaran-Cambrian animal radiations

Area of Science:

• Paleontology
• Geology
• Biogeochemistry

Background:

• The causes of early animal diversification (Ediacaran-Cambrian metazoan radiations) and the reliability of the fossil record are not well understood.
• Reconstructing past environmental conditions and biodiversity requires integrating multiple geological and geochemical proxies.

Purpose of the Study:

• To investigate the drivers of Ediacaran-Cambrian metazoan radiations by analyzing changes in rock volume, biodiversity, and environmental proxies.
• To assess the influence of sea level cycles and oxygenation events on early animal evolution.

Main Methods:

• Utilized a global age framework (580-510 million years ago) to estimate marine sedimentary rock volume, reconstructed biodiversity (mean genus richness), and sampling intensity.
• Integrated carbonate carbon isotopes (δ¹³C_carb) and global redox data (carbonate Uranium isotopes, δ²³⁸U_carb) with geological data.
• Analyzed the temporal distribution of fossil assemblages (Avalon, White Sea, Cambrian) in relation to environmental changes.

Main Results:

• Sampling intensity correlated with reconstructed biodiversity before 535 million years ago.
• Global sea level cycles (transgressive-regressive) influenced the distribution of marine sedimentary rocks.
• Early metazoan radiations coincided with shallow marine oxygenation events preceding major sea level transgressions.

Conclusions:

• The fossil record of early animal life is biased, particularly for deep-marine environments.
• Despite biases, early metazoan radiations and marine oxygenation events are demonstrably linked to major sea level cycles.
• Sea level fluctuations and oxygen availability were significant factors controlling early animal evolution during the Ediacaran-Cambrian.