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Late Cenozoic Evolution of the Upper Mississippi River, Stream
Piracy, and Reorganization of North American Mid-Continent Drainage Systems

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 diverted away from the Gulf of St. rerouting the river roughly parallel to the
Lawrence and toward the Gulf of Mexico Marine Oxygen Isotope Stage 2 (MIS 2)
River systems and associated landscapes by Quaternary stream piracy represents at ice margin (Todd, 1914; Flint, 1949; Dyke
are often viewed to exist in a dynamic least ~420,000 km2 of the modern et al., 2002) and likely bears little resem-
equilibrium that exhibits a natural range of Mississippi River basin and provides blance to earlier Cenozoic drainage in the
variability until and unless external driv- nearly one quarter of the mean annual dis- region (Sears, 2013). The modern Ohio
ing forces cause a radical change such as charge of the Mississippi River. The per- River was formed by the blockage of sev-
abrupt drainage reorganization. Here, we manent loss of that volume of freshwater eral northward-flowing rivers by early to
reinterpret the late Cenozoic evolution of runoff into the Gulf of St. Lawrence may middle Quaternary glaciers that were
the upper Mississippi River and present have had a significant impact on North rerouted to become a tributary of the
evidence that the uppermost Mississippi Atlantic thermohaline circulation and Mississippi River (e.g., Wright, 1890;
River basin (upstream of the confluence of northern hemisphere climate dynamics Chamberlin and Leverett, 1894; Tight,
the Mississippi and Wisconsin Rivers) through the Quaternary. 1903). While some researchers have sug-
evolved as a late Cenozoic drainage system gested alternate pre-Quaternary configura-
that carried water eastward into the Gulf of INTRODUCTION tions of the upper Mississippi River (Hobbs,
St. Lawrence and North Atlantic Ocean 1997) or changes in the size of the draining
rather than to the Gulf of Mexico. Coring Over the past several decades, signifi- basin through the Quaternary (Knox,
to determine the dip of a remnant strath cant effort has been focused on constrain- 2007; Galloway et al., 2011; Cox et al.,
surface in the lower Wisconsin River val- ing the flux of freshwater from the North 2014; Cupples and Van Arsdale, 2014), it
ley demonstrates that this valley was American continent associated with the has been axiomatic that the general course
carved by an eastward-flowing river melting of the Laurentide Ice Sheet (e.g., and planform of the upper Mississippi
(opposite of the modern westward-flowing Broecker et al., 1989; Teller, 1990; River evolved through the late Cenozoic as
Wisconsin River). Geomorphic features, Licciardi et al., 1999; Wickert, 2016). This it appears today (e.g., Baker et al., 1998).
including the presence of numerous barbed flux has been linked to abrupt cooling Although some of the documented altera-
tributaries along the lower Wisconsin events during the last deglaciation as mas- tions to drainage systems have amounted
River valley and the width and morphol- sive, temporary pulses of fresh meltwater to simply repositioning a reach of a river
ogy of the Mississippi and Wisconsin off the North American continent dis- channel, other events have amounted to
River valleys, support this interpretation. rupted North Atlantic thermohaline circu- large-scale stream piracy that has redi-
GIS analysis of logs of water wells in east- lation (Condron and Winsor, 2012; rected runoff to an entirely new master
central Wisconsin delineate the presence Ivanovic et al., 2017). While much of this stream. This is particularly evident in the
of a major buried valley system continuing work has focused on abrupt climate change Ohio River basin, where rivers that flowed
east into the Great Lakes lowland. We events during the last glaciation, the ques- north to the Gulf of St. Lawrence prior to
herein refer to this ancestral drainage sys- tion of freshwater forcing on North Quaternary glaciations were rerouted
tem as the “Wyalusing River.” Atlantic thermohaline circulation also per- toward the Gulf of Mexico to become trib-
tains to longer timescales and processes utaries to the Mississippi River (Coffey,
Quaternary glaciations played a signifi- not directly related to the demise of conti- 1958). The record of late Cenozoic stream
cant role in reorganizing ancestral rivers in nental ice sheets. piracy is particularly significant in the
the Appalachians and eastern Great Lakes humid eastern portions of the North
region to form the modern Ohio River as a For more than a century, it has been doc- American mid-continent, where a dispro-
tributary of the Mississippi River. We pro- umented that the advance and retreat of portionately large amount of its freshwater
pose that Quaternary glaciations also Quaternary ice sheets in North America runoff into the oceans is derived.
played a significant role in capturing the has profoundly altered fluvial drainage
Wyalusing drainage and routing it south- patterns (Fig. 1A). The southwesterly path
ward to the Gulf of Mexico. The total area of the Missouri River is the direct result of

GSA Today, v. 28, doi: 10.1130/GSATG355A.1. Copyright 2018, The Geological Society of America. CC-BY-NC.
* Corresponding author e-mail: eric.carson@wgnhs.uwex.edu.
§ Current address: Dept. of Geology, University of Cincinnati, P.O. Box 210013, Cincinnati, Ohio 45221-0013, USA.

4 GSA Today | July 2018