The Paleocene-Eocene thermal maximum, a transient global warming event, is characterized by extensive evidence of a more active hydrological cycle. This includes a widespread pulse of kaolinite accumulation on continental margins, viewed as the by-product of either enhanced chemical weathering consistent with much more humid conditions and/or increased erosion of previously deposited laterites. The former would be more consistent with year-round humid conditions, whereas the latter might be indicative of extreme seasonal precipitation patterns. To assess these hypotheses, we present a new high-resolution clay mineral assemblage and oxygen isotope record from Bass River, a site on the New Jersey margin (east coast of North America), which shows a sharp rise in the abundance of kaolinite beginning a few thousand years before the onset of the carbon isotope excursion (CIE). The δ18O of the <2-μm-size fraction exhibits a shift toward lower values during the event. On the basis of a coeval shift in clay assemblages, the shift in δ18OClays can be explained by a shift in the relative percent of the primary clay phases rather than a change in the isotopic composition of kaolinite, as would be expected if the kaolinite had been produced primarily during the Paleocene-Eocene thermal maximum. This finding points to accelerated exhumation and erosion of kaolinitic soils, most likely Cretaceous laterites.

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