252-3 The Drivers of the Great Ordovician Biodiversification Event

Session: Climate Transitions in the Paleozoic

Presenting Author:

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Abstract:

The Great Ordovician Biodiversification Event (GOBE) is the largest sustained increase in marine biodiversity in Earth history. Here we outline a potential Earth System-based explanation for the event. Ecological analysis indicates that the GOBE was initiated by increased nutrient availability, most likely driven by changes in the plankton. We hypothesize that diversification was then amplified by an autocatalytic cycle wherein the increasing carbon burial that resulted from the ongoing biodiversification drew down carbon dioxide, reducing temperatures and increasing oxygen availability. This will have steadily increased ocean habitability and probably decreased the magnitude and frequency of disruptive shallow-water anoxic events, promoting further diversification. Diversification was also facilitated by re-mobilization of buried nutrients due to increased numbers of burrowing animals. Changing continental configuration, shifting ocean circulation patterns, including the development of icehouse-style circulation with cold bottom waters, also played a role in biodiversification, given that spatial environmental heterogeneity promotes speciation. The model predicts: (1) an initially accelerating increase in biodiversity as the positive feedbacks took effect; (2) a correlation between biodiversity and carbon burial, but one that was weakened as infaunalization became more prominent; and, (3) decreasing temperatures and increasing oxygen levels as biodiversity increased. Directly testing these predictions is challenging due to: uncertainties stemming from the varying spatial, temporal, and taxonomic completeness of the stratigraphic and fossil records; the necessity of relying on indirect proxy data for assessing environmental change; spatial heterogeneity in environmental conditions and thus potentially different diversity trajectories for different taxa in different regions; and, the operation of multiple feedbacks including concurrent changes in the tectonic regime that will also have effected carbon dioxide levels, etc. Nonetheless, these predictions, and thus the underlying model, find broad empirical support, inviting further analysis. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9634

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