A RECORD OF PALEOENVIRONMENT, PLEISTOCENE FOSSILS, AND GLACIAL OUTBURST FLOODING FROM A LOESS PALEOSOL SEQUENCE IN THE PALOUSE, SOUTHEASTERN WASHINGTON

The Palouse loess deposits of the northwestern United States cover nearly 50,000 square km in southeastern Washington and parts of Oregon and Idaho to a depth of up to 75 m. The Rulo site (southeastern Washington; 46° 9' 53.79" N; 118° 30' 10.33" W; basal elevation 295 m) is a 19 m deep roadcut in the Palouse loess, revealing a total of 30 meters of Pleistocene to Holocene sediments. Paleomagnetic samples collected from the site are all normal polarity, indicating that the entire sequence was likely deposited after 781 ka. Four major unconformities, truncated clastic dikes, and extrabasinal clasts record apparent pre-late Wisconsinan glacial outburst flood events. A fossil assemblage including horse and peccary has been recovered from the basal flood sediments. More than a dozen paleosol horizons and their stratigraphic relationships are exposed. Bulk chemical weathering proxies and micromorphology reveal that most of the paleosols are minimally weathered, except for the basal paleosol at the fossiliferous horizon. This is consistent with earlier work suggesting that paleosols in the Palouse are generally an indicator of slow sediment accumulation rather than major changes in weathering intensity.