Cenozoic climate reconstructions via the prism of the organic geochemistry of IODP recovered sediments from the southern Pacific, northern Atlantic, and northern Indian Ocean

This thesis presents detailed geochemical, hydrocarbon and biomarker analyses carried out on cored marine sediments from three International Ocean Discovery Program (IODP) Expeditions. IODP Expedition 313, New Jersey continental shelf, U.S. middle Atlantic margin (New Jersey–Delaware–Maryland), IODP Expedition 317, Canterbury Basin, New Zealand, and IODP Expedition 355, in the Arabian Sea, Indian Ocean. The three expeditions have been a focus of attention for an extensive study of eustasy, global climatic variations, and local tectonic activity controls on the regional depositional processes. The correlation between preserved organic matter in marine sediments and climate fluctuations has been widely discussed in the scientific community. While the ability to separate between influences of local and global events on the accumulated organic matter remains challenging, the current thesis aims to look into hydrocarbon and biomarker data from the three expeditions to compare these events. The main purpose of IODP Expedition 317 was to compare the relative influence of local tectonics and global sea level changes on sediments accumulated on the continental shelf and slope off the east coast of the Southern Island of New Zealand. Cored sediments were recovered from Early Oligocene to Holocene sequences, with a particular focus on the sequence stratigraphy of the last 19 million years, when global sea level changes were dominated by glacio-eustasy. Sediments drilled in a transect of two sites on the continental shelf (Sites U1351 and U1353) and one on the continental slope (Site U1352) were used in two studies. The first study provided the first examination of the organic geochemical record from Sites U1351, U1352, and U1353 using bulk geochemistry together with hydrocarbon and biomarker distributions for early Oligocene to early Pliocene samples. Based on these it is suggested that local tectonic activity has had a rapid and significant influence on the accumulation of organic matter on the continental shelf and slope. Samples for the second study were taken from early Oligocene to Holocene sediments from the same three drilling sites, with geochemical and lipid analysis carried out to identify the source of the organic matter, and reconstruct changes in sea surface temperature (SST), soil pH, and mean annual air temperatures (MAT) in the area influenced by local tectonic activity or global climatic events. A global climatic optimum and temperature increase at the early/middle Miocene boundary, combined with the increasing land mass of the sub-continent based on an increase in sedimentation rates since the middle Miocene, suggests gradual intensification in the amount of land vegetation. Interpretation of global eustatic and climatic transformations confirms cooler Neogene SSTs were coupled with a decrease in global sea levels. A comparison study between IODP Expedition 317 Site 1352 samples and IODP Expedition 313 Sites M0027A and M0028A samples was performed. Overall, 43 samples from Expedition 313, dated from late Miocene to early Oligocene, were analysed for hydrocarbon and biomarker content. The hydrocarbon data as well as reconstructed SST, soil pH, and MAT from the New Jersey expedition were compared with results from 55 IODP Expedition 317 samples dated from early Oligocene to late Miocene. There is a decreasing SST trend from the early Miocene to the middle Miocene at both locations. Moreover, both sites show significant soil pH decreases during the mid-Miocene Climatic Optimum, and an increase in MAT during the same geological period. The last research project is based on IODP Expedition 355 drilling Site U1456 samples from the Laxmi Basin, Arabian Sea. Multi-proxy data has enabled reconstruction of the evolving provenance of deep sea sediments in the basin, by the use of heavy minerals, bulk isotopic data, bulk and molecular geochemistry, and biomarker and compound specific isotope analyses. The results show that the Indus River was the main source of the sediment into the basin for the last eight million years. Palaeothermometry of the last ten million years based on glycerol dialkyl glycerol tetraethers (GDGTs) and long chain unsaturated alkenones show SST fluctuations during this time. Our data indicate a significant increase of C3 vegetation input to the eastern Arabian Sea around 8 Ma, and increased erosion from the Himalayas around 6 Ma. Variation in precipitation patterns are shown by the δD data set as well as by other geochemical and biomarker parameters, and can be attributed to variation in Asian monsoon precipitation patterns. The results show warm water environments for the first part of the Neogene and a significant temperature decrease in the SST in the New Zealand region from ~15 Ma that can be coupled with decrease in global sea levels. Comparison between New Jersey and New Zealand samples suggest strong eustatic influence for the New Jersey region and local tectonic influence on the organic matter accumulation in New Zealand during Miocene. At the same time, the Arabian sea data shows relatively warm late Miocene that is characterised by increasing precipitation levels influenced by Asian monsoon precipitation patterns.