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

Devils Hole is a tectonically formed cave developed in the discharge zone of a
regional aquifer in south-central Nevada. (See Riggs, et al., 1994.) The walls
of this subaqueous cavern are coated with dense vein calcite which provides an
ideal material for precise uranium-series dating via thermal ionization mass
spectrometry (TIMS). Devils Hole Core DH-11 is a 36-cm-long core of vein
calcite from which we obtained an approximately 500,000-year-long continuous
record of paleotemperature and other climatic proxies. Data from this core were
recently used by Winograd and others (1997) to discuss the length and stability
of the last four interglaciations. These data are given in table 1
(http://pubs.usgs.gov/of/1997/ofr97-792/)

These records have provided information that has posed several challenges to
the orbital theory of the causation of the Pleistocene glaciations, suggested
insights regarding the duration of current Holocene climate, provided a new
chronology for the Vostok, Antarctica, ice core paleotemperature record, and
yielded insights on the age of the groundwater in the principal aquifer of
southern Nevada (http://pubs.usgs.gov/of/2002/ofr02-266/)

Carbon and oxygen stable isotopic ratios were measured on 285 samples cut at
regular intervals inward from the free face of the core (as reported in
Winograd et al. ,1992, and in Coplen et al., 1994). 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.)