Rock varnish evidence for latest Pleistocene millennial-scale wet events in the drylands of western United States

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Rock varnish from late to latest Pleistocene geomorphic features in the drylands of the western U.S. provides evidence of nine millennial-scale wet events from 11,500–18,000 calendar yr B.P., represented by regionally replicable and approximately evenly spaced manganese- and barium-rich dark bands in varnish microstratigraphy. Preliminary radiometric age calibration indicates that these events appear to be broadly coeval with millennial-scale cooling events identified in the Greenland Ice Sheet Project 2 (GISP2) ice core record. Six of these wet events are associated with the cold intervals of the Younger Dryas and Heinrich event H1, and the other three with the short-lived cooling phases of the Intra-Allerod Cold Period, the Older Dryas, and the Oldest Dryas. These results, combined with our previous documentation of millennial-scale wet events in the Holocene varnish record for the same region, indicate that such wet oscillations in the western U.S. may be parts of regionally widespread manifestation of well-documented, pervasive millennial-scale cycles of the North Atlantic climate.