Silicate weathering machine at work: Rock magnetic data from the late Paleocene-early Eocene Cicogna section, Italy

Dallanave, E, Tauxe L, Muttoni G, Rio D.  2010.  Silicate weathering machine at work: Rock magnetic data from the late Paleocene-early Eocene Cicogna section, Italy. Geochemistry Geophysics Geosystems. 11

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atmospheric carbon-dioxide, clay-mineral, Eocene, equatorial pacific, evidence, geomagnetic-field, global warming, hematite, isotope excursion, maghemite, negative feedback, Paleocene, silicate weathering, stable-isotopes, surface-temperature, thermal maximum, waisted hysteresis loops


We describe a scenario of climate forcing on sedimentation recorded in the late Paleocene-early Eocene Cicogna marine section from the Belluno Basin ( NE Italy). Previously published magneto-biostratigraphic data revealed that the similar to 81 m Cicogna section extends from Chron C25r to Chron C23r spanning the NP7/NP8-NP12 nannofossil zones (similar to 52.2-56.6 Ma). Using previously published rock magnetic data, augmented by data from this study, we describe and thoroughly discuss a pronounced increase of hematite ( relative to maghemite or magnetite) between similar to 54.9 and 54.6 Ma immediately above the Paleocene-Eocene boundary, followed by a second, long-term increasing trend from similar to 54 Ma up to similar to 52.2 Ma in the early Eocene. This hematite is essentially of detrital origin, insofar as it is associated with a strong shallow bias of paleomagnetic inclinations, and is interpreted to have formed on land by the weathering of Fe-bearing silicates and other primary minerals. We speculate that the warm and humid climate typical of the Paleocene-Eocene thermal maximum (PETM, similar to 54.9 Ma) as well as of the warming trend leading to the early Eocene climatic optimum (EECO; similar to 52-50 Ma) enhanced continental weathering of silicate rocks with the consequent production, transport, and sedimentation of detrital hematite grains. This hypothesis is confirmed by a statistical correlation between the rock magnetic properties and global climate as revealed by a standard benthic oxygen isotope record from the literature. Our temporal coupling between oxidation state of sedimentary magnetic phases and global climate is therefore consistent with the existence in the Paleocene-Eocene of the silicate weathering negative feedback mechanism for the long-term stabilization of the Earth's surface temperature.






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