Sediments from Lake Pepin on the Mississippi River, southeastern Minnesota, are used as provenance tracers to assess variations in hydrology and sediment-transport during the middle Holocene. Three rivers contribute sediment to Lake Pepin, and each catchment is characterized by a distinctly different geologic terrain. The geochemical fingerprint for each drainage basin was determined from the elemental composition of heavy minerals in the silt-sized fraction of modern sediment samples. Down-core elemental abundances were compared with these fingerprints by use of a chemical-mass-balance model that apportions sediment to the source areas. We observed a decreased contribution from the Minnesota River during the interval ∼6700-5500 14C yr BP, which we attribute to decreased discharge of the Minnesota River, likely controlled by a combination of precipitation, snow melt, and groundwater input to the river. This hydrologic condition coincides with the mid-Holocene prairie period recorded by fossil pollen data. The occurrence of this feature in a proxy record for hydrologic variations supports the hypothesis that the mid-Holocene prairie period reflects drier conditions than before or after in midwestern North America.
Bibliographical noteFunding Information:
The authors gratefully acknowledge the reviews of an earlier version of this manuscript by R. G. Baker, Cathy Whitlock, Walter Dean, two anonymous reviewers, and the insightful comments and suggestions of James Knox. D. Kelley is grateful for the Doctoral Dissertation Special Grant from the Graduate School of the University of Minnesota for the heavy-mineral analyses.
- Geochemical fingerprinting
- Lake Pepin
- Lake sediments
- Mass balance
- Paleoclimatic reconstruction