IODP Expedition 330: Drilling the Louisville Seamount Trail in the SW Pacific

Deep-Earth convection can be understood by studying hotspot volcanoes that form where mantle plumes rise up and intersect the lithosphere, the Earth's rigid outer layer. Hotspots characteristically leave age-progressive trails of volcanoes and seamounts on top of oceanic lithosphere, which in turn allow us to decipher the motion of these plates relative to "fixed" deep-mantle plumes, and their (isotope) geochemistry provides insights into the long-term evolution of mantle source regions. However, it is strongly suggested that the Hawaiian mantle plume moved ~15° south between 80 and 50 million years ago. This raises a fundamental question about other hotspot systems in the Pacific, whether or not their mantle plumes experienced a similar amount and direction of motion. Integrated Ocean Drilling Program (IODP) Expedition 330 to the Louisville Seamounts showed that the Louisville hotspot in the South Pacific behaved in a different manner, as its mantle plume remained more or less fixed around 48°S latitude during that same time period. Our findings demonstrate that the Pacific hotspots move independently and that their trajectories may be controlled by differences in subduction zone geometry. Additionally, shipboard geochemistry data shows that, in contrast to Hawaiian volcanoes, the construction of the Louisville Seamounts doesn’t involve a shield-building phase dominated by tholeiitic lavas, and trace elements confirm the rather homogenous nature of the Louisville mantle source. Both observations set Louisville apart from the Hawaiian-Emperor seamount trail, whereby the latter has been erupting abundant tholeiites (characteristically up to 95% in volume) and which exhibit a large variability in (isotope) geochemistry and their mantle source components

The Response of Calcareous Nannofossil Communities to Environmental Variation During the late middle Eocene at Blake Nose, Western North Atlantic, ODP Leg 171B

Ocean Drilling Program Leg 171B Hole 1051B penetrated a continuous sequence of upper middle Eocene pelagic sediment dominated by rich calcareous nannofossil assemblages. Samples were taken at 10 cm spacing from a 20.2 meter section of the upper middle Eocene. This interval of pelagic sediment had previously been interpreted to represent ~500ky. Our revised age model, using additional data, indicates this section represents ~842ky. The Eocene Epoch was characterized by one of the most dramatic climatic transitions in the last 65 my, changing the greenhouse earth of the early Eocene to the icehouse world of early Oligocene. Here changes in calcareous nannofossils communities are observed in association with climatic variability that accompanied this transition. The relative abundance of calcareous nannofossil species was determined by conducting a count of 456 individuals for each of 203 samples. These data were analyzed using richness, diversity, and CABFAC factor analysis. This latter method showed 88.5% of the variance within the data was accounted for within two factors. Factor 1 displays a strong correlation with Shannon Diversity. The character and structure of the calcareous nannofossil communities were examined using Shannon diversity, species richness, and evenness. Shannon Diversity is shown to have statistically significant correlations to richness and evenness. Richness and evenness are negatively correlated; Richness increases slightly up-section while evenness decreases slightly. The calcareous nannofossil species present in each sample were also examined for biostratigraphic significance. It was determined that the upper middle Eocene sediments studied here are within Calcareous Nannofossil Zone CP14b. The extinction of Sphenolithus obtusus is of potential biostratigraphic value. Sphenolithus obtusus shows peak abundance of 12% in the lower portion of the section examined, a rapid decline in population followed. Assuming a constant rate of sediment accumulation (24 m/my), it is estimated to have taken approximately 126ky for S. obtusus to reach peak abundance and ~84ky to fall to 1% abundance levels where it persisted for another 100ky. Advisor: David K. Watkin