The onset of the Early Eocene Climatic Optimum, including the K/X event, at Branch Stream, Clarence Valley, New Zealand

Thursday, 18 December 2014
Benjamin S Slotnick1, Gerald R Dickens2, Chris J Hollis3, James S. Crampton3, Percy Strong3, Edoardo Dallanave4 and Andy Philips3, (1)Rice University, Houston, TX, United States, (2)Rice Univ, Houston, TX, United States, (3)GNS Science-Institute of Geological and Nuclear Sciences Ltd, Lower Hutt, New Zealand, (4)Ludwig Maximilian University of Munich, Munich, Germany
The Early Eocene Climatic Optimum (EECO), lasting from ~53-50 Ma, has been characterized as the warmest sustained interval through the Cenozoic. It was comprised of a broad temperature maximum with elevated atmospheric pCO2, noticeable shifts in carbon cycling, and a variety of faunal and floral changes. This included one, and likely additional, brief (<200 kyr) intervals of extreme warming, the K/X event. At least for the most prominent events, the long-term drop in δ13C and short-term Carbon Isotope Excursions (CIEs) have been coupled to massive fluxes of 13C-depleted carbon into the exogenic system and global climate change. However, much about EECO remains unknown because of a lack of detailed and coupled proxy records; we are currently generating useful records to better characterize lithological and geochemical signatures of EECO. Here, we help rectify this problem by presenting a new lithologic and carbon isotopic record for a ~84-m-thick section of early Eocene upper slope calcareous-rich sediments, now lithified and exposed along Branch Stream, New Zealand. Comparison of new carbon isotopic and lithologic records of this greatly expanded section to nearby Mead Stream identifies multiple negative CIEs in short succession and generally more marl during lowermost EECO (~53.3-51.7 Ma), with the most prominent of these equating to the K/X event. The early Eocene lithologic and δ13C records at Branch and Mead Streams are remarkably similar to each other, with the following distinctions: sequences at Branch Stream are thicker and generally have a wider range of δ13C across CIEs. Both expanded sections are marked by terrigenous dilution, best explained by enhanced seasonal precipitation, elevated greenhouse-gas concentrations, and likely global warming. These data indicate lowermost EECO can be described as a time with a general δ13C low superimposed by a series of short-term climate perturbations.