Palynology of Pinedale Sediments, Devlins Park, Boulder County, Colorado

Abstract

A core of varved lake sediments from Devlins Park, Front Range, Colorado, has yielded a radiocarbon-dated pollen record of environments during the last major advance of Pinedale ice. The downstream end of Devlins Park was dammed by Pinedale ice from 22,400 to 12,180 BP, creating the lake. The pollen diagram is dominated by Artemisia (40 to 60%) and Pinus (10 to 25%). Gramineae, Chenopodiaceae-Amaranthaceae, Compositae, Juniperus, and Picea pollen are also constantly present at low percentages. Arboreal pollen percentages are low, ranging from 13 to 30%. Pollen concentration varies from 6000 to 40,000 grains cc^–1 of wet sediment. Modern pollen rain from a nearby wet depression is very different from the core pollen spectra, with greater percentages of Pinus (70%) and Picea (6%) pollen, less Artemisia (7%) pollen, and pollen concentration of 106,000 grains cc^–1.

Scattered pollen grains of tundra plants, low pine pollen percentages, and low pollen concentrations indicate that Devlins Park was above tree line during Pinedale time. Picea/Pinus ratios suggest that tree line averaged about 500 m lower than at present.