500,000 Year-old Stable Isotopic Record from Devils Hole, USGS OFR-97-792

Table 1 lists only 284 samples because a sample taken at 114.28 mm was eliminated when post-1994 reanalysis of its delta 18O value indicated an error in the earlier determination. Carbon isotopic ratios are reported in per mill relative to VPDB, defined by assigning a delta 13C of +1.95 per mill to the reference material NBS 19 calcite. Oxygen isotopic ratios are reported relative to VSMOW reference water on a scale normalized such that SLAP reference water is -55.5 per mill relative to VSMOW reference water.

The oxygen isotopic fractionation factors employed in this determination are those listed in Coplen and others (1983). The delta 18O value of the isotopic reference material NBS 19 on this scale is +28.65 per mill. The ± 1 sd (standard deviation) error for the delta 18O and delta 13C analyses is ±0.07 and 0.05 per mill, respectively.

Ages were estimated by linear interpolation between age control points taken at key intervals in the core and analyzed by TIMS 230Th-234U-238U dating. The age estimates in Table 1 are based on the original 21 control points (see Table 2 in Ludwig, et al., 1992, and Figure 2 in Winograd, et al., 1992) as well as for the recently obtained TIMS age of 143.8±0.9 ka (2 sd analytical error) at 51.5 mm (Winograd, et al., 1997).

The later sample was taken specifically for additional control in a critical portion of the core. Errors in the ages vary but are bounded by the errors in the appropriate control points. (See Table 2 in Ludwig, et al., 1992.)