Clay Mineralogy and Clay Geochemistry of ODP Site 1119 - Paleoclimatic and Paleoceanographic History of the SW Pacific for the last 3.9 Ma

Ocean Drilling Program (ODP) Site 1119, off SE New Zealand, contains a ~500 m thick sedimentary record of intermediate-depth drift deposits (Canterbury Drifts) that preserve paleoceanographic and paleoclimatic events of the SW Pacific over the last 3.9 Ma. This study uses clay mineralogy, clay geochemistry, and grain size (terrigenous fractions) to unlock the paleoclimatic and oceanographic trends from the Canterbury Drift deposits. The proxies demonstrate a clear link between regional climatic and oceanographic controls on sediment deposition (e.g. glacial erosion and ocean current flow) as well as global influences (e.g. Milankovitch cycles). At the Early/Late Pliocene boundary (~3.5 Ma), the clay minerals derived from chemical weathering (mainly smectite) change to clays typical of physical weathering and increased erosion (chlorite, illite, and stilpnomelane), marking the transition into a cooler Late Pliocene environment. Shortly after this transition, a marked coarsening of the mean sortable silt fraction occurs at ~3.16 Ma that implies an increased current velocity most likely associated with the initiation of stronger Sub-Antarctic Mode Water flow. After the Late Pliocene (~3.16 Ma) the mean sortable silt fines up through the core, suggesting an overall decrease in ocean current velocity. Meanwhile, increasing chlorite and clay-sized contents up-core provide evidence for the global long term cooling trend and also suggest a stronger influence of glacial erosion processes in the South Island. Around 500 ky, trace elemental concentrations increase coincidentally with the known transition between the dominant 40 ky (Obliquity) and 100 ky (Eccentricity) orbital cycles, which establishes a relationship between the ODP Site 1119 mid-latitude record and global climate and oceanographic change. The proxy analyses from this mid-latitude location provide new information about the timing of environmental changes that are linked to both regional climatic and oceanographic events as well as to global climate change.