Interpreting carbon-isotope excursions: Stranglove oceans
ABSTRACT Large negative excursions in marine carbonate Î´Â¹Â³C are commonly associated with period boundaries and mass extinctions. Explanations for these events must be consistent with limitations imposed by carbon-isotope mass balance. At steady state (i.e., for excursions lasting more than 10âµ yr), the surface ocean Î´Â¹Â³C is set by the organic fraction of the total carbon burial rate and the magnitude of the photosynthetic isotope effect. The Î´Â¹Â³C of the deep ocean and the surface-to-deep isotope gradient are set by both the organic fraction of the ocean's remineralized particulate flux and the magnitude of the isotope effect. Thus it is the carbon-isotope composition of the deep ocean that is most reflective of internal oceanic processes; the surface ocean records changes in the longer term throughput of carbon in the system. The cessation of organic export from the surface ocean, such as is presumed to have caused the Strangelove ocean condition of the Cretaceous/Tertiary (K/T) boundary, leads to an isotopically homogeneous ocean in decades to centuries. If this condition persists, the ocean's isotopic composition approaches that of the riverine weathering input (in 10âµ yr). Failure to approach this value during the K/T event suggests continued production and burial of organic carbon, dominantly in either terrestrial or shallow-marine environments.
Full-textDOI: · Available from: Lee R. Kump, Feb 13, 2014
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ABSTRACT: Various environmental changes were associated with the Permian-Triassic mass extinction at 252.2 Ma. Diverse unusual sediments and depositional phenomena have been uncovered as responses to environmental and biotic changes. Lithological and detailed conodont biostratigraphic correlations within six Permian-Triassic boundary sections in South China indicate rapid fluctuations in carbonate deposition. Four distinct depositional phases can be recognized: (1) normal carbonate deposition on the platform and slope during the latest Permian; (2) reduced carbonate deposition at the onset of the main extinction horizon; (3) expanded areas of carbonate deposition during the Hindeodus changxingsensis Zone to the H. parvus Zone; and (4) persistent mud-enriched carbonate deposition in the aftermath of the Permian-Triassic transition. Although availability of skeletal carbonate was significantly reduced during the mass extinction, the increase in carbonate deposition did not behave the same way. The rapid carbonate depositional changes, presented in this study, suggest that diverse environmental changes played key roles in the carbonate deposition of the Permian-Triassic mass extinction and onset of its aftermath. An overview of hypotheses to explain these changes implies enhanced terrestrial input, abnormal ocean circulation and various geobiological processes contributed to carbonate saturation fluctuations, as the sedimentary response to large volcanic eruptions.Journal of Earth Science 04/2015; 26(2):166-180. DOI:10.1007/s12583-015-0523-1 · 0.55 Impact Factor
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ABSTRACT: A more than 2000-m-thick Cambrian^Ordovician carbonate platform succession developed on the exotic Argentine Precordillera terrane during rifting from Laurentia and drifting towards Gondwana. On base of these carbonates, a carbon isotope curve could be developed for the Cambrian^Ordovician. We measured Delta13Ccarb and Delta13Corg values on bulk rocks, selected components and diagenetic cements. Whereas the carbon isotope signals of intertidal and supratidal rocks are altered by diagenesis, most subtidal carbonates exhibit primary marine values. We can report reliable curves for the Middle^Late Cambrian transition and for the latest Cambrian to earliest Middle Ordovician. The Delta13C curve matches well with the published data from global Cambrian^Ordovician boundary sections. Excursions and shifts in the carbon isotope curve correspond to events in sequence stratigraphy. This indicates the interdependence on sea level which rules the productivity and/or preservation of organic carbon and therefore the partition between Corg and Ccarb burial.
Article: Permian–Triassic paleoceanographyGlobal and Planetary Change 06/2013; 105:1–6. DOI:10.1016/j.gloplacha.2013.03.001 · 3.71 Impact Factor