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In conjunction with increasing benthic foraminiferal 18O values at the Eocene–Oligocenetransition (EOT; ca. 34 Ma), coarse-grained ice-rafted debris (IRD; >425 μm) appearsabruptly alongside fossil fi sh teeth with continentally derived neodymium (Nd) isotope ratios( Nd) in Kerguelen Plateau (Southern Ocean) sediments. Increased Antarctic weathering fl ux,as inferred from two steps to less radiogenic Nd values, coincides with two steps in benthicforaminiferal 18O values. These results indicate that two distinct surges of weathering weregenerated by East Antarctic ice growth during the EOT. Weathering by ice sheets during aprecursor glaciation at 33.9 Ma did not produce signifi cant IRD accumulation during the fi rstNd shift. Glacial weathering was sustained during a terrace interval between the two steps,probably by small high-elevation ice sheets. A large increase in weathering signals the rapidcoalescence of small ice sheets into an ice sheet of continental proportions ca. 33.7 Ma. Rapidice sheet expansion resulted in a suppression of weathering due to less exposed area and colderconditions. Parallel changes in Antarctic weathering fl ux and deep-sea carbonate accumulationsuggest that ice-sheet expansion during the EOT had a direct impact on the global carboncycle; possible mechanisms include associated changes in silicate weathering on the EastAntarctic craton and enhanced fertilization of Southern Ocean waters, both of which warrantfurther investigation.


Scher, H. D., Bohaty, S. M., Zachos, J. C., & Delaney M. L. (2011). Two-stepping into the icehouse: East Antarctic weathering duringprogressive ice-sheet expansion at the Eocene–Oligocene transition. Geology, 39 (4), 383-386.

© Geology 2011, Geological Society of America

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