An important component of the seagoing studies of Ocean Drilling Program (ODP) Leg 199 involved the geochemical analysis of bulk sediments in order to provide chemical analyses while at sea. Our sampling plan was ambitious and resulted in ~600 samples being analyzed during the cruise for a suite of 10 elements (Si, Al, Ti, Fe, Mn, Ca, Mg, P, Ba, and Sr). These analyses allowed for first-order paleoceanographic decisions (e.g., sampling the Paleocene/Eocene [P/E] boundary) to be made and drilling objectives to be optimized, while also allowing shipboard scientists to tailor their cruise and postcruise sampling requests and shore-based research. Whereas chemical analysis of the bulk sediment provides reinforcement for the large-scale lithologic changes, it can also further provide information on small-scale lithologic changes that may otherwise go unnoticed.
For many years, the analysis of major and trace elements on board the JOIDES Resolution was performed using X-ray fluorescence (XRF) spectrometry and focused primarily on igneous rocks. This instrument has been subsequently replaced by a Jobin Yvon 2000 sequential inductively coupled plasma-atomic emission spectrometer (ICP-AES) (Murray et al., 2000). General ICP-AES procedures, analyses information, and preparation procedures are described in Murray et al. (2000). The shipboard ICP-AES was first used for igneous rock (during Leg 187) and interstitial water (during Legs 188 and 189) analyses. In particular during Leg 187 (Australian-Antarctic Discordance), real-time drilling decisions were made using the ICP-AES to help select, while at sea, specific sites to drill (Christie Pederson, Miller, et al., 2001).
Despite these successes with ICP-AES analyses of igneous rocks and pore waters, until Leg 199 the ideal opportunity to use the instrument for quantitative analysis of sediment had not been realized. Shipboard major and trace element analyses provide an initial chemical characterization of the bulk sediment that can then be further expanded during shore-based analyses. For Leg 199, this chemical characterization further fuels the initial development and interpretation of mass accumulation rates (MARs), Intertropical Convergence Zone migration, and paleoceanographic changes occurring in the equatorial Pacific throughout the Paleogene. These ideas and concepts can then be revised and reinterpreted during shore-based treatment without the need to wait for basic chemical analyses. Whereas a more complete major, trace, and rare earth element analysis of the bulk sediment and eolian fraction can wait for shore-based study, analyses on board the JOIDES Resolution provide a first-order analysis useful to the entire shipboard and shore-based scientific party.
Leg 199 was particularly appropriate to use as a test bed for sedimentary ICP-AES analysis because of the variety of lithologies recovered and analytical opportunities, including analysis of the P/E boundary. Red clay, radiolarian clay, radiolarite, nannofossil ooze, nannofossil chalk, dolomite, and other sediment types were encountered. Each exhibited varying geochemical signatures. Small changes in Si or Ca concentration, for example, are easily tracked by the geochemical analyses but when viewed from the sedimentological perspective often go unnoticed. Analysis by ICP-AES is a complement to the sedimentological interpretations but also provides clues that can be easily missed.