Precambrian Research 225 (2013) 1–6 Contents lists available at SciVerse ScienceDirect Precambrian Research journa l h omepa g e: www.elsevier.com/locate/precamres Biogeochemical changes across the Ediacaran–Cambrian transition in South China Graham Shields-Zhou a,b,∗ , Maoyan Zhu b a Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK b Key State Laboratory of Palaeobiology and Stratigraphy (LBS), Nanjing Institute of Geology and Palaeontology (NIGPAS), Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China a r t i c l e i n f o Article history: Received 10 April 2012 Received in revised form 4 October 2012 Accepted 10 October 2012 Available online 22 October 2012 Keywords: Ediacaran Cambrian Biogeochemical cycling Feedbacks Bioturbation Cambrian radiation a b s t r a c t The late Neoproterozoic successions of South China comprise some of the most complete and well- preserved records of the Ediacaran–Cambrian transition. The articles in this special issue provide a snapshot of ongoing research that is helping us to understand early stages in the development of the modern Earth system. These studies illustrate the transitional character of the Ediacaran–Cambrian inter- val from the evolution and early extinctions of the first bilaterian metazoans during the Ediacaran Period to their dominance of pelagic and benthic realms by the end of the early Cambrian. Geochemical data reveal a noisy transition of increasing baseline  13 C values punctuated by extreme isotopic oscillations. It is evident that highly negative  13 C values and large amplitude  13 C swings ceased once modern marine ecosystems had become firmly established by ∼520 Ma. We postulate that sub-surface bioturbation helped to strengthen the relationship between benthic oxidation state and P-retention, thus tighten- ing an important negative feedback that helps to stabilize productivity, climate and oxygen levels in the modern Earth system. The disappearance of negative excursions after ∼520 Ma might also suggest a key role for methanogenesis which would have declined following the rise of in-sediment sulphur cycling due to bioturbation. Further insight into this fascinating interval is needed before we can disentangle the complex interactions between biological evolution and biogeochemical cycling during the emergence of the modern Earth system. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Over the past decade, our understanding of the events lead- ing up to the expansion and diversification of animal life has improved dramatically. As a result, we know that early animal evolution was accompanied by extraordinary perturbations to cli- mate, carbon cycling, chemical weathering and tectonics as well as changes to the composition of the atmosphere and oceans. Fossil finds and geochemical data from well preserved marine succes- sions of the South China (Yangtze) Craton have fueled much of this progress, and include the first convincing fossilized animals (Xiao et al., 1998); the first putative bilaterian fossils (e.g. herein); the first evidence for predation on animals (Hua et al., 2005); and one of the most complete bio- and chemo-stratigraphic archives of the Ediacaran Period (Zhu, 2010). The contributions in this spe- cial issue were solicited to bring the reader up-to-date with recent ∗ Corresponding author at: Department of Earth Sciences, University College Lon- don, Gower Street, London WC1E 6BT, UK. Tel.: +44 207 679 7821. E-mail addresses: g.shields@ucl.ac.uk, g.shields@nigpas.ac.cn (G. Shields-Zhou), myzhu@nigpas.ac.cn (M. Zhu). developments concerning the biostratigraphy, chemostratigraphy and facies evolution through this key interval in South China. Armed with this new information, as well as recently published data from elsewhere in the world, we can begin to discuss the role that early animals played in tightening and accelerating the stabi- lizing, negative feedbacks which define the modern Earth system. During the Ediacaran–Cambrian transition, complex interactions between biological evolution and the surface environment led to a reorganization of biogeochemical cycling that was to lead to the long-term stability of Earth’s climate and atmospheric composition during the rest of the Phanerozoic Eon. 2. Advances in Ediacaran–Cambrian biostratigraphy and palaeobiology The lower Ediacaran fossil record is characterized worldwide by a group of relatively large acanthomorphic (spiny) acritarchs (LSA’s). On the South China craton, such acritarchs first appear in strata of the lower Doushantuo Formation dated to about 630 Ma (Yin et al., 2007). However, in Australia, lowermost Edi- acaran acritarchs are of the simple leiosphere type with large spiny varieties appearing only in strata deposited after the 0301-9268/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.precamres.2012.10.011