256-10 Tracking Bioturbation Through Time: The Evolution of the Marine Sedimentary Mixed and Transition Layers

Session: Life and Environments Through Time and Space: Multi-Record Approaches to Stratigraphic Paleobiology, Part I

Presenting Author:

Lidya Tarhan

Authors:

Tarhan, Lidya G.¹, Pippenger, Kate Hennessy², Cribb, Alison Taveau³, Zill, Michelle⁴, Phelps, William⁵, Droser, Mary L.⁶, Bottjer, David J.⁷, Clapham, Matthew E.⁸

(1) Department of Earth and Planetary Sciences, Yale University, New Haven, CT, USA, (2) Department of Earth and Planetary Sciences, Yale University, New Haven, CT, USA, (3) School of Ocean and Earth Science, University of Southampton, Southampton, Hampshire, United Kingdom, (4) Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA, (5) Department of Geology, Riverside Community College, Riverside, CA, USA, (6) Department of Earth and Planetary Sciences, University of California, Riverside, Riverside, CA, USA, (7) Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA, (8) Department of Earth and Planetary Sciences, University of California, Santa Cruz, Santa Cruz, CA, USA,

Abstract:

Bioturbation, the excavation and mixing of sediments by burrowing animals, is one of the foremost examples of ecosystem engineering and extensively shapes the physical properties, biogeochemistry and ecology of the modern seafloor. Bioturbation is primarily recorded by homogenized sediments of the seafloor mixed layer—which today extends, on average, 5–10 cm downward from the sediment-water interface—and the underlying transition layer, which is populated by discrete burrows that, in certain settings, can exceed 1 m in depth. Although these two zones can be readily measured today, there has been limited understanding of how the mixed and transition layers evolved—and the extent to which their trajectories have been decoupled—over the Phanerozoic, since animals first began to extensively colonize the seafloor. Here we draw upon sedimentological data and a new burrow depth dataset to describe the Phanerozoic coevolution of the sedimentary mixed and transition layers. We find that deepening of the sediment mixed layer likely spanned hundreds of millions of years. In contrast, a deep transition layer was established as early as the Cambrian and did not further deepen until the Mesozoic. We also document evidence for onshore-offshore expansions in the depth of both the mixed and transition layers, mirroring evolutionary trends previously described from the body fossil and ichnodiversity records. We attribute these patterns in mixed and transition layer development to evolutionary radiations, changes in nutrient cycling and shifts in oxygen bioavailability.

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

doi: 10.1130/abs/2025AM-9246

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