Eric C. Carson, J. Elmo Rawling III, John W. Attig, and Benjamin R. Bates^§

Wisconsin Geological and Natural History Survey, Dept. of Environmental Sciences, University of Wisconsin–Extension, 3817 Mineral Point Road, Madison, Wisconsin 53705, USA

Abstract

River systems and associated landscapes are often viewed to exist in a dynamic equilibrium that exhibits a natural range of variability until and unless external driving forces cause a radical change such as abrupt drainage reorganization. Here, we reinterpret the late Cenozoic evolution of the upper Mississippi River and present evidence that the uppermost Mississippi River basin (upstream of the confluence of the Mississippi and Wisconsin Rivers) evolved as a late Cenozoic drainage system that carried water eastward into the Gulf of St. Lawrence and North Atlantic Ocean rather than to the Gulf of Mexico. Coring to determine the dip of a remnant strath surface in the lower Wisconsin River valley demonstrates that this valley was carved by an eastward-flowing river (opposite of the modern westward-flowing Wisconsin River). Geomorphic features, including the presence of numerous barbed tributaries along the lower Wisconsin River valley and the width and morphology of the Mississippi and Wisconsin River valleys, support this interpretation. GIS analysis of logs of water wells in east-central Wisconsin delineate the presence of a major buried valley system continuing east into the Great Lakes lowland. We herein refer to this ancestral drainage system as the “Wyalusing River.”

Quaternary glaciations played a significant role in reorganizing ancestral rivers in the Appalachians and eastern Great Lakes region to form the modern Ohio River as a tributary of the Mississippi River. We propose that Quaternary glaciations also played a significant role in capturing the Wyalusing drainage and routing it southward to the Gulf of Mexico. The total area diverted away from the Gulf of St. Lawrence and toward the Gulf of Mexico by Quaternary stream piracy represents at least ~420,000 km² of the modern Mississippi River basin and provides nearly one quarter of the mean annual discharge of the Mississippi River. The permanent loss of that volume of freshwater runoff into the Gulf of St. Lawrence may have had a significant impact on North Atlantic thermohaline circulation and northern hemisphere climate dynamics through the Quaternary.

^§ Current address: Dept. of Geology, University of Cincinnati, P.O. Box 210013, Cincinnati, Ohio 45221-0013, USA.

Manuscript received 21 July 2017. Revised manuscript received 29 Sept. 2017. Manuscript accepted 30 Nov. 2017. Posted online 19 Jan. 2018.

© The Geological Society of America, 2018. CC-BY-NC.

10.1130/GSATG355A.1