Figure 8    A generalized Holocene varnish layering sequence in the drylands of western USA and its preliminary radiometric age calibration. Age constraints are from Table 2 and the letters are keyed to those in both Fig. 7 and Table 2. The age assignments for dark layers WH1-WH12 are based on our proposed correlation between the Holocene wet events recorded in rock varnish and the Holocene millennial-scale cooling events recorded in deep sea sediments from the North Atlantic (Fig. 4; Bond et al., 1997, 1999).