Carbon isotopes and lipid biomarkers from organic-rich facies of the Shuram Formation, Sultanate of Oman

C. Lee*, D. A. Fike, G. D. Love, A. L. Sessions, J. P. Grotzinger, R. E. Summons, W. W. Fischer

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    29 Citations (Scopus)

    Abstract

    The largest recorded carbon isotopic excursion in Earth history is observed globally in carbonate rocks of middle Ediacaran age. Known from the Sultanate of Oman as the 'Shuram excursion', this event records a dramatic, systematic shift in δ13Ccarbonate values to ca. -12‰. Attempts to explain the nature, magnitude and origin of this excursion include (i) a primary signal resulting from the protracted oxidation of a large dissolved organic carbon reservoir in seawater, release of methane from sediment-hosted clathrates, or water column stratification; and (ii) a secondary signal from diagenetic processes. The compositions and isotope ratios of organic carbon phases during the excursion are critical to evaluating these ideas; however, previous work has focused on localities that are low in organic carbon, hindering straightforward interpretation of the observed time-series trends. We report carbon isotope data from bulk organic carbon, extracted bitumen and kerogen, in addition to lipid biomarker data, from a subsurface well drilled on the eastern flank of the South Oman Salt Basin, Sultanate of Oman. This section captures Nafun Group strata through the Ediacaran-Cambrian boundary in the Ara Group and includes an organic-rich, deeper-water facies of the Shuram Formation. Despite the high organic matter contents, the carbon isotopic compositions of carbonates - which record a negative δ13C isotope excursion similar in shape and magnitude to sections elsewhere in Oman - do not covary with those of organic phases (bulk TOC, bitumen and kerogen). Paired inorganic and organic δ13C data only display coupled behaviour during the latter part of the excursion's recovery. Furthermore, lipid biomarker data reveal that organic matter composition and source inputs varied stratigraphically, reflecting biological community shifts in non-migrated, syngenetic organic matter deposited during this interval.

    Original languageEnglish
    Pages (from-to)406-419
    Number of pages14
    JournalGeobiology
    Volume11
    Issue number5
    DOIs
    Publication statusPublished - Sep 2013

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