Fortunately, some concretions composed of microcrystalline carbonate minerals (1 cm x 4 cm) were observed at the bottom of Holes 1146A and 1146C. Two brownish concretions were collected from Samples 184-1146C-63X-7, 8-10 cm (602.88 mbsf), and 184-1146A-64X-7, 8-10 cm (606.28 mbsf), in the greenish lower Miocene sediments. XRD analyses indicate that the concretions are predominantly composed of siderite, with a small amount of rhodochrosite. The 
13C values of those two siderite concretions are -5.9
and -5.2 PDB, and 18O values are 2.5 and 2.4 PDB, respectively. Thus, the 18O and 13C values in these siderite concretions are similar to those of authigenic carbonates from Blake Ridge (Matsumoto, 1989; Pierre et al., 2000; Rodriguez et al., 2000), Cascadia (Bohrmann et al., 1998), and Guatemala Basin (Morad and Al-Aasm, 1997).
