TAGGART, RALPH E. AND AUREAL T. CROSS.* Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48825. - Ecological dynamics of Eocene Lake Florissant, Colorado.
The Late Eocene (34 Ma) volcaniclastic deposits of the Florissant
Fossil Beds National Monument (Colorado) contain abundant
well-preserved remains of plants and a wide range of insect taxa.
Paleoecological analysis of the deposits, based on integration of
palynological, stratigraphic, and geochemical data, suggest that the
Florissant ecosystem was subject to chronic ecological stress. The
terrestrial vegetation was commonly devasted by holocaustic fires,
most of which probably originated in drier communities on surrounding
slopes. Precipitation was marginal, relative to the high rate of
evaporation, and lake water levels fluctuated over a wide range.
During low-water intervals the lake water was highly alkaline,
limiting aquatic biodiversity. This is consistent with the fine
preservation of fossil plant and insect material and the general
absence of an indiginous lacustrine fauna. One drop in lake level
lasted for several centuries, permitting the establishment of a
redwood/red cedar-dominated forest on the former lake bottom. A
subsequent rise in lake level resulted in the permineralization of the
bases of the standing trees, today represented by the numerous
petrified stumps throughout the Monument area.
Key words: Eocene, Florissant, Oligocene, paleobotany, paleoecology, palynology