Figure 6. ¹⁸O and ¹³C cross plot for the same data as in Figure 5 and Table 2. Stable isotopic values for calcite, dolomite, and siderite are represented by crosses, triangles, and circles respectively. On the basis of their isotopic characteristics, carbonates from Sites 994, 995, and 997 are divided into three fields. (1) The Biogenic Calcite Field consists mostly of calcite with ¹⁸O and ¹³C values typical of biogenic calcite. (2) The Dolomite Field consists of authigenic dolomite (and some calcite), which exhibit depleted ¹³C and relatively heavy ¹⁸O values. (3) The Siderite Field is unique in that it consists solely of authigenic siderite with ¹⁸O and ¹³C values that exhibit no overlap with other carbonate phases in these sediments.