Recent advances in chronostratigraphy are enabling global correlation of Silurian strata at a temporal resolution of 10-100 k.y. Comparative analysis of disparate localities at this resolution is yielding surprisingly similar peculiarities of facies. Facies analysis has been traditionally regarded as a tool to investigate local paleoenvironmental conditions and reconstruct past paleoecological settings. Less frequently are aspects of facies recognized as long-distance time-correlative markers. The concept of time-specific facies, originally proposed by Walliser (1986) and recently revised by Brett et al. (2012), challenges the “strictly local” facies paradigm by emphasizing that some aspects of facies are signatures of broader oceanic-climatic processes. Their synchronous occurrence, spanning major portions of sedimentary basins to globally, represents the key distinctive factor of time-specific facies. This aspect is combined with the significance of the ecostratigraphic analysis as a tool to identify bioevents and, therefore, for improving biostratigraphic subdivisions (e.g., Boucot, 1986). Marine ironstones represent a prime example of time-specific facies. Silurian ironstones retaining microbial signatures are documented by Ferretti et al. (2012) in forms of Fe-rich oolitic horizons and ferruginous laminated structures for the Llandovery-Wenlock boundary interval (mid-late Telychian, Pt. celloni Superzone-Pt. a. amorphognathoides Zone and Sheinwoodian, Oz. s. rhenana Zone) in the Carnic Alps (Austria). Age-equivalent ironstones also occur in the Appalachian Basin of eastern North America (McLaughlin et al., 2012). Appalachian Basin ironstones collected from the New Point Stone quarry (Napoleon, Indiana) and Dawes Quarry Creek (Clinton, New York) were recently analyzed through combined analytical techniques (i.e., confocal laser Raman microscopy, X-ray diffraction, ESEM-EDX, and optical microscopy) for a geobiological characterization. Results demonstrate that the Appalachian ironstones seem to reflect the same microbially-mediated iron mineralization already documented in the Carnic Alps. Combined evidence of iron geochemistry and microbial interactions include i) the formation of planar laminated ironstones (late Telychian); ii) coeval ooidal pack- to grain-ironstones; iii) a wealth of other microbial-related morphostructures and mineralogies. The synchroneity of iron microbe activity on opposite ends of the Iapetus Ocean during the late Telychian and Sheinwoodian is inferred as a time-specific sea water redox signature associated with the Ireviken Event.

Can facies act as a chronostratigraphical tool?

CAVALAZZI, BARBARA;BARBIERI, ROBERTO;
2015

Abstract

Recent advances in chronostratigraphy are enabling global correlation of Silurian strata at a temporal resolution of 10-100 k.y. Comparative analysis of disparate localities at this resolution is yielding surprisingly similar peculiarities of facies. Facies analysis has been traditionally regarded as a tool to investigate local paleoenvironmental conditions and reconstruct past paleoecological settings. Less frequently are aspects of facies recognized as long-distance time-correlative markers. The concept of time-specific facies, originally proposed by Walliser (1986) and recently revised by Brett et al. (2012), challenges the “strictly local” facies paradigm by emphasizing that some aspects of facies are signatures of broader oceanic-climatic processes. Their synchronous occurrence, spanning major portions of sedimentary basins to globally, represents the key distinctive factor of time-specific facies. This aspect is combined with the significance of the ecostratigraphic analysis as a tool to identify bioevents and, therefore, for improving biostratigraphic subdivisions (e.g., Boucot, 1986). Marine ironstones represent a prime example of time-specific facies. Silurian ironstones retaining microbial signatures are documented by Ferretti et al. (2012) in forms of Fe-rich oolitic horizons and ferruginous laminated structures for the Llandovery-Wenlock boundary interval (mid-late Telychian, Pt. celloni Superzone-Pt. a. amorphognathoides Zone and Sheinwoodian, Oz. s. rhenana Zone) in the Carnic Alps (Austria). Age-equivalent ironstones also occur in the Appalachian Basin of eastern North America (McLaughlin et al., 2012). Appalachian Basin ironstones collected from the New Point Stone quarry (Napoleon, Indiana) and Dawes Quarry Creek (Clinton, New York) were recently analyzed through combined analytical techniques (i.e., confocal laser Raman microscopy, X-ray diffraction, ESEM-EDX, and optical microscopy) for a geobiological characterization. Results demonstrate that the Appalachian ironstones seem to reflect the same microbially-mediated iron mineralization already documented in the Carnic Alps. Combined evidence of iron geochemistry and microbial interactions include i) the formation of planar laminated ironstones (late Telychian); ii) coeval ooidal pack- to grain-ironstones; iii) a wealth of other microbial-related morphostructures and mineralogies. The synchroneity of iron microbe activity on opposite ends of the Iapetus Ocean during the late Telychian and Sheinwoodian is inferred as a time-specific sea water redox signature associated with the Ireviken Event.
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FERRETTI A.; CAVALAZZI B.; McLAUGHLIN P. I.; BARBIERI R.; EMSBO P.; FOUCHER F.; MALFERRARI D.; MESSORI F.; WESTALL F.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/479770
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