PALEOENVIRONMENTAL INDICATORS IN A PEAT BOG FROM ALLEGAN COUNTY, MICHIGAN

High-resolution analysis of a core in a peat bog in Allegan County, Michigan demonstrates variably in past environmental conditions. Examined proxies include organic bulk density (OBD), sand concentrations, charcoal, plant macrofossils, and sponge spicules. Charcoal analysis was done every 0.5 cm, OBD every 1 cm, sand concentrations every 1 cm, and plant macrofossils and sponge spicules at selected locations. Preliminary plant macrofossil analysis suggests four ecological divisions. Samples are highly-decomposed in the top 167 cm of the core (~0 – 3100 cal. YBP), corresponding to high OBD values indicative of progressive terrestrialization of the bog. Sponge spicules are abundant in sediments deposited before 3000 cal. YBP, but are absent in younger sediments suggesting that the center of the bog became emergent after 3000 cal. YBP. Well-preserved Sphagnum and abundant Cyperaceae seeds are noted at 210 – 242 cm (~4000 – 4600 cal. YBP). OBD values show moderate fluctuations along a plateau during much of this time period, suggesting moderate climatic changes. Cyperaceae seeds, but no Sphagnum, are noted at 260 – 380 cm (~5000 – 7300 cal. YBP). High decomposition and abundant roots were noted in this interval hindering analysis. OBD values show large fluctuations, including two large increases in value, indicative of drier conditions. This could have contributed to the poor preservation of these samples. Well-preserved Sphagnum is again noted at 380 cm (~7300 cal. YBP), corresponding to low OBD values indicative of wetter periods. Peaks in sand concentrations in sediments deposited after 8000 cal. YBP indicate episodic increases in the flux of sand into the bog with peak spacing ranging from 80 to 400 years. Charcoal analysis for the portion of the core deposited between 2460 – 3260 cal. YBP reveals that charcoal concentration peaks are coincident with sand concentration peaks. The bog was emergent at this time and the main pathway of sand into the bog was probably aeolian. Thus it appears that increases in both fire and windblown sand may have been controlled by the same climatic factors. OBD peaks are broader than charcoal peaks and may reflect longer term variations in moisture. Further data collection needs to be done to determine if there is a correlation between OBD and charcoal abundance.