THE SCOTTY’S PALM FLORA: A DIVERSE MEGAFLORA WITHIN 300,000 YEARS AFTER THE K-T BOUNDARY ON THE WESTERN MARGIN OF THE DENVER BASIN, COLORADO

During the Cretaceous and early Paleocene, Laramide uplift created the present eastern margin of the Front Range and began to fill the Denver Basin. Fossil plants preserved in synorogenic strata within 20 km of the western basin margin provide the opportunity to examine the orographic effect of the Front Range on the evolution of Paleocene forests. The Scotty’s Palm fossil plant site is located on the grounds of the US Air Force Academy near Colorado Springs. It was first discovered and extensively quarried in 1992-3 and censused in 2002. Preserved in an arkosic matrix, this flora occurs in the marginal portion of a large fluvial channel. Preliminary examination of the 1992-3 specimens documents 68 species, of which 58 are dicotyledonous angiosperms. High species diversity, large leaf size, a leaf margin percentage indicating a mean annual temperature of 22º C, and an abundance of fossil palm material suggest that this site is composed of leaf litter transported from a nearby tropical rainforest. Palynological analysis indicating the P1 pollen zone, paleomagnetic polarity data indicating subchron C29R, and stratigraphic analysis using well logs all suggest that the deposit formed within 300,000 years after the K/T event. Floras of this age elsewhere in the Western Interior typically contain fewer than 20 species. The Scotty’s Palm site is located 40 km south of the 64.1 mya Castle Rock rainforest, which has yielded 104 species from in situ forest floor leaf litter buried in andesitic strata. The occurrence of the Scotty’s Palm flora nearly 1 million years before the Castle Rock assemblage supports that concept that floral recovery from the K-T boundary event was rapid in the region along the eastern margin of the Laramide Front Range. It is unclear if this pattern represents increased survival of Cretaceous taxa in mountainous areas or more rapid speciation after the boundary in orographically wet areas. Dissimilarity of Scotty’s Palm taxa with local Cretaceous species suggests the latter scenario.