A total of 153 samples from the upper part of Subunit 1A of Megasequence D were taken at an average 15-cm resolution between 0 and 23.69 meters below seafloor (mbsf) in Hole 1198A (Table T1). Based on shipboard biostratigraphic datums (Shipboard Scientific Party, 2002b), this interval approximately represents the last 500 k.y. of deposition on the Marion Plateau. This period is also thought to be roughly congruous with the presence of large barrier reef systems, analogous to the present GBR, on the adjacent continental shelf during sea level highstands (International Consortium for Great Barrier Reef Drilling, 2001).
Approximately 3 cm3 of sediment was subsampled from nominally 10 cm3 of bulk sample and freeze-dried to remove pore fluids. Subsamples were crushed using a ceramic hand mortar and pestle and ground into a fine powder. From each sample, 150–250 mg of powder was weighed and utilized for the determination of bulk carbonate content following the principles of the carbonate-bomb technique (Mueller and Gastner, 1971). Duplicate sample analyses and comparisons with laboratory standards place the accuracy and precision of reported carbonate contents within a maximum of ±2.6%, with an average reproducibility of ±0.9% (Table T1).
Sediment on the northeast Australian margin comprises two basic components, terrigenous siliciclastic sediment and biogenic carbonate, with only trace amounts of other material (Harris et al., 1990; Dunbar et al., 2000; Heap et al., 2001). Consequently, within the precision of the technique, quantification of bulk carbonate content also renders accurate values for siliciclastic abundance.