Controls on the evolution of Ediacaran metazoan ecosystems

Frederick Bowyer, Rachel Wood, S. W. Poulton

Research output: Contribution to journalArticlepeer-review

Abstract

A growing number of detailed geochemical studies of Ediacaran (635-541Ma) marine successions have provided snapshots into the redox environments that played host to the earliest known metazoans. Whilst previous compilations have focused on the global evolution of Ediacaran water column redox chemistry, the inherent heterogeneity evident in palaeogeographically distinct environments demands a more dissected approach in order to better understand the nature, interactions and evolution of extrinsic controls on the development of early macro benthic ecosystems. Here, we review available data of local-scale redox conditions within a palaeogeographic and sequence stratigraphic framework, in order to explore the mechanisms controlling water column redox conditions and their potential impact on the record of metazoans. The openly connected Laurentian margin, North America (632-540Ma) and Nama basin, Namibia (550-538Ma), and the variably restricted Yangtze Block, South China (635-520Ma) show continued redox instability after the first fossil evidence for metazoans, which may support opportunistic benthic colonisation during periods of transient oxygenation amidst episodic upwelling of anoxic waters beneath a very shallow, fluctuating chemocline. The first skeletal metazoans appeared under conditions of continued redox stratification, such as those which characterise the Dengying Formation of the Yangtze Block and the Nama Group. Current data, however, suggests that successful metazoan reef-building demanded more persistent oxia. We propose that cratonic positioning and migration throughout the Ediacaran Period, in combination with gradually increasing dissolved oxygen loading, may have provided a first-order control on redox evolution through regulating circulation mechanisms in the Mirovian Ocean. Some unrestricted lower slope environments from mid-high latitudes benefited from sustained oxygenation via downwelling, whilst transit of isolated cratons towards more equatorial positions stifled pervasive ventilation either through ineffective surface ocean mixing, Ekman-induced upwelling, elevated surface ocean productivity, or a combination of these processes.
Original languageEnglish
JournalGeobiology
Early online date7 Apr 2017
DOIs
Publication statusE-pub ahead of print - 7 Apr 2017

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