Murphy et al. (2000a) discussed a possible extinction mechanism for the Frasnian-Famennian (F-F) crisis based upon geochemical data from two black shales in western New York State, which correlate with the well-known Kellwasser horizons of Germany. Secular changes in the elemental and C isotope composition of organic matter from these shale levels revealed dramatic increases in the burial atomic ratios of C:N:P from Redfield-order values of ∼100:15:1 to an average of ∼5000:170:1. Murphy et al. (2000a) claimed that these shifts record increased efficiency of biolimiting nutrient recycling, resulting from fluctuating (seasonal) water-column stratification in which P is preferentially released during...

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