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Res. 101, 11,729 42. E. R. Stofan, A. W. Brian, J. E. Guest, Icarus 173, 312 7 January 2010; accepted 25 March 2010 (1995). (2005). Published online 8 April 2010; 24. E. R. Stofan, J. E. Guest, A. W. Brian, Mapping of V-28 43. P. R. Hooper, in Large Igneous Provinces: Continental, 10.1126/science.1186785 and V-53, T. K. P. Gregg, K. L. Tanaka, R. S. Saunders, Oceanic and Planetary Flood Volcanism, J. J. Mahoney, Include this information when citing this paper. whelms the signal from primary biomass frac- Cryogenian Glaciation and the Onset tionated from contemporaneous DIC (4). We consider the large oceanic reservoir model and, on September 9, 2019 of Carbon-Isotope Decoupling as in (2), use the term DOC to collectively refer to organic carbon that is truly dissolved as well as suspended colloidal organic carbon and fine Nicholas L. Swanson-Hysell,1 Catherine V. Rose,1 Claire C. Calmet,1 Galen P. Halverson,2* POC. The buildup and maintenance of a large Matthew T. Hurtgen,3 Adam C. Maloof1† DOC pool implies low Corg remineralization— perhaps associated with low oxygen and sulfate Global carbon cycle perturbations throughout Earth history are frequently linked to changing levels—but high nutrient liberation efficiency. paleogeography, glaciation, ocean oxygenation, and biological innovation. A pronounced In such an ocean, the d13CoftheDICpoolis carbonate carbon-isotope excursion during the Ediacaran Period (635 to 542 million years sensitive to inputs (via remineralization) from the ago), accompanied by invariant or decoupled organic carbon-isotope values, has been explained 13C-depleted DOC pool that can drive negative with a model that relies on a large oceanic reservoir of organic carbon. We present carbonate and excursions. The end of the invariance in the organic matter carbon-isotope data that demonstrate no decoupling from approximately 820 to 13 d Corg record in the latter stages of the Shuram- 760 million years ago and complete decoupling between the Sturtian and Marinoan glacial Wonoka anomaly has been interpreted as the events of the Cryogenian Period (approximately 720 to 635 million years ago). Growth of the demise of the large DOC pool (2, 3). organic carbon pool may be related to iron-rich and sulfate-poor deep-ocean conditions facilitated Stratigraphically constrained coupled records by an increase in the Fe:S ratio of the riverine flux after Sturtian glacial removal of a long-lived 13 13 of d Ccarb–d Corg at sufficient detail to test this continental regolith. carbon cycle model have been available only from carbonates of Ediacaran age (2, 3). We 13 13 13 13 hroughout most of the Phanerozoic Eon variant d Corg during large changes to d Ccarb present paired d Ccarb and d Corg data from [542 million years ago (Ma) to present], across the ~580 million-year-old Shuram-Wonoka d13 paired records of carbonate carbon ( Ccarb) anomaly (Fig. 1 and fig. S1). This behavior has 1 T 13 Department of Geosciences, Princeton University, Princeton, d and coeval bulk organic carbon ( Corg) iso- been used to develop and support a model for NJ 08544, USA. 2Geology and Geophysics, University of Ade- topes are consistent with a model in which the the Neoproterozoic (1000 to 542 Ma) carbon laide Mawson Laboratories, Adelaide, SA 5005, Australia. 13 3 organic carbon in marine sediments is derived cycle in which invariant d Corg values result from Department of Earth and Planetary Sciences, Northwestern and fractionated from contemporaneous dissolved a very large oceanic reservoir of 13C-depleted dis- University, Evanston, IL 60208, USA. d13 *Present address: Department of Earth and Planetary Sci- inorganic carbon (DIC). In contrast, Ccarb and solved organic carbon (DOC) and particulate ences, McGill University, Montreal, Quebec H3A 2A7, Canada. d13 Corg records from Ediacaran (635 to 542 Ma) organic carbon (POC) (or, alternatively, sourced †To whom correspondence should be addressed. E-mail: carbonate successions (1–3) show relatively in- from a large sedimentary reservoir) that over- [email protected] 608 30 APRIL 2010 VOL 328 SCIENCE www.sciencemag.org REPORTS Fig. 1. Carbonate carbon iso- older Neoproterozoic strata: the Bitter Springs ~551 Ma Fm. tope values and organic carbon POUND Formation of the Amadeus Basin, central Aus- 700 isotope values from Neoprotero- tralia, that was deposited during the Tonian Pe- zoic carbonates of Australia with 600 riod (1000 to ~720 Ma) and the Etina-Trezona simplified lithostratigraphy. The Formations of the adjacent Adelaide Rift Com- plotted lithofacies represent the 500 plex deposited during the Cryogenian Period lithologies that dominate each (~720 to 635 Ma) (5). Together with published interval, with wider boxes corre- 400 data from the Ediacaran Wonoka Formation (1), sponding to deposition in shal- also of the Adelaide Rift Complex, these records lower water.