GEOMORPHOLOGY AND ENVIRONMENTAL GEOCHEMISTRY OF SELECTED FENS IN THE SAN JUAN MOUNTAINS, COLORADO: A PRELIMINARY ASSESSMENT

The San Juan Mountains have a complex geologic history along with a varied history of intense mining throughout the 18^th and 19^th centuries. A regional study of this environment calls for an evaluation of the geomorphic processes that shape the present landscape as well as the fate of various heavy metals associated with both mining and present day sources. Higher than normal concentrations of aluminum, cadmium, copper, iron, manganese, and zinc are known to occur throughout the wetlands of the San Juans. Lead is also thought to occur in high concentrations. Less is known about exact levels of lead, and how various competing contaminant sources contribute to its deposition.

The intense glaciation of the San Juans created geologic niches for fen development, which occur throughout the area. Thus, a variety of fens, which act as heavy metal sinks, were sampled to provide for an evaluation of the regional environmental geochemistry. We developed a core-collection tool using PVC pipe, a fence post driver, and an attachable handle for extraction. Unfortunately, the device worked with limited success; driving of the sampling core resulted in compaction of fen sediments. Ultimately, we were forced to use a sharpshooter shovel to extract samples from the fens. Six profiles were extracted; all were ~34 cm depth. Each profile was sampled at 2 cm intervals. In the lab, a central core of each sample was removed with acid-washed plastic utensils to minimize contamination. We also attempted to extract cores from a tarn, but this was not successful.

In addition to collecting core samples, we mapped geomorphic features associated with the fens. Fens are situated along the floors of glaciated valleys and adjacent to cols. Forms bordering the fens include polished bedrock, moraines, avalanche cones, talus cones, rock glaciers, and river terraces. A geomorphic map at a scale of 1:10,000 of each fen location was created.

Future fieldwork will require a greater spatial sampling as well as vibracore sampling to a greater depth.