GSA Connects 2021 in Portland, Oregon

Paper No. 42-3
Presentation Time: 2:05 PM


CRIBB, Alison1, VAN DE VELDE, Sebastiaan J.2, BERELSON, Will1, CORSETTI, Frank3 and BOTTJER, David1, (1)Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy, Los Angeles, CA 90089, (2)Biogeochimie et Modelisation du Systeme Terre, Universite Libre de Bruxelles, Brussels, Belgium; Operational Directorate Natural Environment, Royal Belgian Institute of Natural Sciences, Brussels, Belgium, (3)Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089

The Agronomic Revolution – the shift from microbial matgrounds to bioturbated mixgrounds during the Ediacaran-Cambrian transition – is believed to have been critical for the evolution of complex benthic ecosystems in the early Paleozoic. The radiation of bioturbators is thought to have increased oxygen supply to sediments by removing microbial mats and by actively mixing oxygen into the sediment, triggering an expansion of the habitable benthic zone and promoting increased tiering in early Paleozoic infaunal communities. However, hypotheses that early bioturbation caused oxygen concentrations to increase in deeper sediment tiers have generally not been tested for differences in the timing of the evolution of different bioturbation behaviors. Furthermore, the role of organic matter cycling has not been investigated, even though organic matter flux is a major driver in sedimentary oxygen dynamics and can physiologically impact the intensity of bioturbation activity.

Here, we investigate the role of biomixing (solid sediment mixing) and bioirrigation (burrow ventilation) behaviors and changes in organic matter flux to the seafloor in driving increased oxygen concentrations in deeper sediment tiers. We focused on evidence of biomixing and bioirrigation in the Ediacaran and Fortunian trace fossil records and incorporated that trace fossil data into a 1D reactive-transport model to simulate oxygen penetration depths (OPD). We find that the intensity of biomixing and bioirrigation during the Ediacaran would have had a slight shallowing effect on the OPD. Strong, modern-like levels of bioturbation could have deepened the OPD, but we find that increased organic matter fluxes, which likely co-evolved with bioturbators, significantly mute that deepening effect. Our results suggest that it was unlikely that bioturbators deepened the OPD until modern-like benthic communities evolved, but the precise impact is ultimately modulated by organic matter cycling.