University of California at Santa Cruz, United States

The pronounced global carbon-cycle perturbation and warming associated with the Paleocene-Eocene Thermal Maximum (PETM; approximately 55.5 Ma) is most parsimoniously explained by the massive sublimation and release of sedimentary methane hydrates to the ocean-atmosphere reservoir. Accurate reconstruction of the PETM requires that the chronology and completeness of stratigraphic sections be evaluated and compiled into a synoptic record of geographic and bathymetric variation. To this end, we evaluated a poorly known PETM section from ODP Site 738 ( approximately 1.3 km paleodepth, Kerguelen Plateau, Southern Indian Ocean) using cm-scale variations in bulk stable-isotopes, weight percent carbonate, and XRF-determined major elements. Stratigraphic delta (super 13) C and delta (super 18) O variations at Site 738 are broadly congruent with those at the South Atlantic Site 690 "reference section", with the following exceptions: (1) an additional short interval of intermediate delta (super 13) C values during the initial carbon isotope excursion (CIE), suggesting a more compete earliest PETM section, (2) a progressive relative decrease in sedimentation rates following the negative extrema of the CIE, and (3) a stepped approximately 0.7 per mil increase in delta (super 13) C in the latest PETM, indicating a hiatus or rapid increase in ocean-atmosphere delta (super 13) C values through accelerated carbon cycling and/or significant organic carbon burial. Weight percent carbonate values drop precipitously from >90% to approximately 70% at the onset of CIE and then gradually rise to approximately 85%, drop precipitously to approximately 75%, and finally sharply increase to >90% all prior to the CIE negative extrema. These decreases in weight percent carbonate are less extreme and shorter lived than those in deeper PETM sections and, if interpreted as a carbonate dissolution proxy, imply two distinct episodes of increased seawater corrosivity at approximately 1.3 km paleodepth, possibly through shoaling of the lysocline. Coincident with the pronounced decrease in weight percent carbonate at the onset of the CIE, XRF-scanning reveals transient increases in Fe and Mn content ( approximately 600% and approximately 400% above background, respectively). These bulk element "spikes" may reflect increased concentrations of non-carbonate phases due to dissolution and/or changes in redox conditions associated with decreased oxygenation at the onset of the PETM.