IS ENHANCED SILICATE MINERAL WEATHERING A PLAUSIBLE MECHANISM FOR STABILIZING ATMOSPHERIC PCO2 ON A GEOLOGICALLY-INSTANTANEOUS TIME SCALE? APPLYING MULTIPROXY PALEOPEDOLOGICAL INTERPRETATIONS TO TERRESTRIAL PETM RESEARCH

Oceanic and terrestrial records of the Paleocene/Eocene boundary reveal the coincidence of a large negative carbon isotope excursion and a transient global warming event denominated the Paleocene/Eocene Thermal Maximum. It is estimated that this event warmed temperate continental areas by as much as 5ºC and caused massive biospheric perturbations, yet the role of terrestrial weathering in this greenhouse climate has not yet been clearly discerned - in large part because evidence has often not been preserved.

Although the strata of the Williston Basin of North Dakota have long been held to have been continuously deposited throughout the PETM, workers have otherwise largely ignored this area. The geology had heretofore been described simply as a series of tectonically-controlled fluvial basin accumulations of vague provenance, but we have recognized that these sediments contain promising evidence for a well preserved terrestrial PETM signature - which manifests as a previously-unrecognized, basin-wide, deeply weathered paleultisol. Preliminary geochemical and micromorphological data and in press clay mineralogy suggest laterization processes formed this highly ferruginous kaolinitic profile. Subsequent rapid burial preserved this pedologic record indicative of a geologically-instantaneous tropical climate that persisted here into the early Eocene. In addition, the landscape has been found to contain multitudinous uncharacterized, localized paleosols that are proving to collectively yield, through a multiproxy interpretive approach, corroborative paleoenvironmental data.

Whereas continental silicate weathering as a negative feedback mechanism within greenhouse climates has traditionally been considered to occur on timescales of millions of years, our Williston Basin record suggests a far more abbreviated event. Furthermore, because little of the already-limited body of terrestrial PETM research has focused on the role of paleopedology this work is a particularly salient example of the necessity of including the paleopedological approach in the geologist's toolbox.