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Protracted development of bioturbation through the early Palaeozoic Era


Bioturbation, the physical and chemical mixing of sediment by burrowing animals, exerts an important control on the character of modern marine sediments and biogeochemical cycling1,2,3,4,5,6,7,8,9. Here we show that the mixing of sediments on marine shelves remained limited until at least the late Silurian, 120 million years after the Precambrian–Cambrian transition. We present ichnological, stratigraphic and taphonomic data from a range of lower Phanerozoic siliciclastic successions spanning four palaeocontinents. The protracted development of the sediment mixed layer is also consistent with sulphur data and global sulphur model simulations. The slow increase in the intensity of bioturbation in the sediment record suggests that evolutionary advances in sediment colonization outpaced advances in sediment mixing. We conclude that ecosystem restructuring caused by the onset of significant infaunal mobile deposit feeding (‘bulldozing’) occurred well after both the Cambrian Explosion and the Great Ordovician Biodiversification Event.

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Figure 1: Lower Palaeozoic trace fossil preservation and ichnofabrics.
Figure 2: Lower Palaeozoic changes in bed thickness.
Figure 3: Relative abundance of ichnofabric indices (ii) for each chronologic interval.
Figure 4: Modelled results of the impact of early Palaeozoic bioturbation on contemporaneous marine sulphate concentrations [SO4].


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This research was supported by an NSF Graduate Research Fellowship, Amherst College John Mason Clarke Fellowship, Janet M. Boyce Memorial Fellowship and grants from the Society for Sedimentary Geology, Geological Society of America, Paleontological Society, American Museum of Natural History, Sigma Xi, InfoQuest Foundation, Evolving Earth Foundation and the Community Foundation (L.G.T.), as well as the NSF Earth-Life Transitions Program and NASA NAI UCR node (N.J.P.) and NASA NAI MIT node (D.J.T.). Permitted access to sections was provided by the Fortune Head Ecological Reserve (Canada) and Death Valley National Park (USA). Fieldwork was facilitated by D. Auerbach, E. Conrado, R. Dahl, J. Esteve, T. Garlock, J. Gehling, E. Haddad, C. Hall, L. Hancock, S. Jensen, L. Joel, T. Johnston, K. Keenan, N. McKenzie, A. Miller, P. Myrow, A. Ruiz, A. Sappenfield and R. Thomas. This paper benefited from discussion with D. Hardisty and C. Reinhard.

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L.G.T. conceived the study, with input from all authors. L.G.T. collected all field data and performed analyses. L.G.T. and N.J.P. developed the bioturbation-dependent sulphate model, with input from D.T.J. L.G.T. wrote the manuscript with input from all authors.

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Correspondence to Lidya G. Tarhan.

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Tarhan, L., Droser, M., Planavsky, N. et al. Protracted development of bioturbation through the early Palaeozoic Era. Nature Geosci 8, 865–869 (2015).

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