Timing, provenance, and implications of two MIS 3 advances of the Laurentide Ice Sheet into the Upper Mississippi River Basin, USA

doi:10.1016/j.quascirev.2021.106926

Quaternary Science Reviews

Volume 261, 1 June 2021, 106926

https://doi.org/10.1016/j.quascirev.2021.106926 Get rights and content

Highlights

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Radiocarbon ages place Keewatin-sourced ice in the Mississippi Basin during MIS 3.
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The southwestern Laurentide Ice Sheet reached ∼42°N around 42 and 30 ka.
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Advances of the Des Moines Lobe provided source sediment for MIS 3 loess.
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Loess deposits and records in the Gulf of Mexico show signals of these advances.
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There was likely no ice west of the Des Moines Lobe during MIS 3.

Abstract

Evidence for a glacial advance into the Upper Mississippi River Basin between Marine Isotope Stage (MIS) 2 and MIS 6 has been debated for over a century. New sedimentological and chronological data provide evidence for two advances of the Laurentide Ice Sheet (LIS) into Iowa during MIS 3 to the east and west of the local glacial maximum margin. The lithology of the MIS 3 till is similar to the MIS 2 Des Moines Lobe till, which suggests both tills were sourced from the Keewatin Dome. A synthesis of new and previously collected radiocarbon ages indicate the two advances reached their terminus near 42⁰ N around 42 ka and 30 ka. A comparison of this record with published loess chronology and provenance studies suggests that these advances were likely a glacial source for the Mississippi Valley Roxana Silt and the Pisgah Formation loess in the Missouri River Valley. The apparent discrepancy between the basal ages of the Roxana and Pisgah loesses may be due to the timing of Des Moines Lobe entering the Mississippi River watershed before the Missouri River watershed. The results of this study demonstrate that the LIS advanced much farther south during MIS 3 than previously recognized, which has significant implications for ice sheet and paleoclimate modeling.

Introduction

Knowledge of glacial extent and timing are necessary to model Laurentide Ice Sheet (LIS) dynamics during its build up, acme, and decline. Unfortunately, terrestrial records of North American glaciation leading up to the Last Glacial Maximum (LGM, 19–26.5 ka, Clark et al., 2009) are sparse (Stokes et al., 2012). Because the LIS was more extensive in most areas during MIS 2 (12–27 ka) than during MIS 3 (27–57 ka) (Lisiecki and Raymo, 2005; Siddall et al., 2008), older records of glaciation tend to be buried or eroded by the younger ice and subsequent sediment deposition. A primary indicator of glacial activity within the Upper Mississippi River Basin during MIS 3 has been the loess record, although the initial glacial source in Illinois, the ‘Altonian’ phase, was shown to not be time corelative with the Roxana (Willman and Frye, 1970; Leigh and Knox, 1993; Leigh, 1994; Curry, 1998; Grimley, 2000; Curry and Grimley, 2006). The timing, distribution, and extent of MIS 3 ice are critical parameters to constrain the initial conditions of the MIS 2 LIS. Therefore, the physical record of MIS 3 ice in North America is important for ice sheet reconstruction and modeling ice dynamics, as well as indicating the glacial correlation with loess records in the Midcontinent.

Understanding ice center development in North America leading up to the LGM is a crucial component of global sea level reconstructions, as Euroasian ice centers during MIS 3 were largely confined to alpine settings (Gowan et al., 2021). Whether the Labradoran dome in the east and the Keewatin dome in the west were connected during MIS 3, i.e. if Hudson Bay was glaciated, is a matter of ongoing debate. Previous studies have put forth LIS configurations that cover most of the Canadian Shield (Vincent and Prest, 1987; Dredge and Thorleifson, 1987; Gowan et al., 2021). However, radiocarbon (¹⁴C) and optically stimulated luminescence (OSL) ages from the Hudson Bay lowlands gathered by Dalton et al. (2016) suggest an unglaciated marine-terrestrial transition area during MIS 3 that was later buried by ice. This interpretation suggests that the LIS was not as extensive as previously assumed during this interval (Dalton et al., 2019). Pico et al. (2017) paired this reduced ice reconstruction with additional sea level indicators to conclude that the eastern LIS developed rapidly between 50 and 35 ka. Newly published North American MIS 3 ice sheet margin reconstructions also suggest a significant reduction in ice sheet extent during this interval when compared with previous estimations (Dalton et al., 2019; Batchelor et al., 2019). However, the interpretation of an ice-free Hudson Bay lowland has been questioned due to an abundance of “greater than” ¹⁴C ages and discordance between some OSL and finite ¹⁴C results within the equivalent units (Miller and Andrews, 2019). Subsequently, additional records of the LIS during MIS 3 are critical for modeling ice sheet buildup to the LGM. This data could help clarify apparent signals of dome asynchroneity between eastern and western sourced lobes advancing to their local last glacial maximum (Heath et al., 2018) and the MIS 3 loess records in the Mississippi and Missouri River Valleys (Leigh and Knox, 1993).

The activity of the Des Moines Lobe (DML, Fig. 1) during MIS 2 and 3 is an important indicator of overall behavior of the LIS during this interval. In this paper, the term DML is used to represent the lobe of ice that descended north to south from Manitoba, Canada (Keewatin Sector) into Iowa at any time during the last glacial period (MIS 5–2). The DML is considered to be an ice stream of the LIS (Clark, 1994; Patterson, 1997), and Margold et al. (2015) ranks it as one of the longest ice streams in the world— it is around 1400 km from its presumed source at the Saskatchewan River to its terminus at Des Moines, Iowa. During MIS 2, Dalton et al. (2020) propose the DML was actively advancing and retreating between 22 and 14 ka, reaching its southern limit around 18 ka. In contrast, Heath et al. (2018) suggest the DML advanced 200 km in under one thousand years to reach its terminus around 15 ka, after which it retreated nearly as rapidly. In both models, the DML reached its maximum extent thousands of years after ice lobes to the east (Heath et al., 2018) (Fig. 1). The low-relief till plain left by the MIS 2 DML also contrasts with land systems formed by lobes to the northeast, which consist of drumlins, high-relief moraines, low-relief hummocks, and ice thrust terrains (Colgan et al., 2005). The difference between the DML's timing and style of glaciation when compared with lobes to the east is likely explained by the DML being an ice stream moving mainly across a poorly lithified to unlithified, deformable bed by ice sourced from a different dome (Clark, 1994; Clayton et al., 1985, Patterson, 1997, 1998; Hooyer and Iverson, 2002; Margold et al., 2015). In addition, the DML does not encounter deep water lakes or basins like the eastern Labrador sourced lobes, e.g. the Superior, Green Bay, or Lake Michigan lobes which may have acted as a reservoir of ice for eastern lobes (Fig. 1; Cutler et al., 2000). Detailing DML activity prior to the LGM may aid in understanding the contrast between eastern and western lobes, driving mechanisms across the LIS, as well as the timing of ice dome growth during MIS 3.

Records from other lobes are also necessary to better understand the chronology and behavior of the LIS. Recent studies have placed ice within Wisconsin during MIS 3 (Carlson et al., 2018; Ceperley et al., 2019), but notably not Illinois, (Curry and Pavich, 1996). Additional evidence for MIS 3 glaciation includes glacial outwash (Carson et al., 2019) and loess in the Mississippi River Valley (Willman and Frye, 1970; Leigh and Knox, 1993; Leigh, 1994 Curry, 1996; Grimley, 2000; Forman and Pierson, 2002; Curry and Grimley, 2006). The loess record in major river valleys is important as it can be used to indicate lobe advance into the basin over time (e.g. Curry and Grimley 2006; Muhs et al., 2018). In the Gulf of Mexico, sediment core evidence such as records of meltwater pulses, chemical weathering proxies, detrital zircon geo-thermo-chronology, and shifts in clay mineralogy suggests that the ice was present somewhere within the Upper Mississippi River or Missouri River basins during MIS 3 (Tripsanas et al., 2007; Sionneau et al., 2013; Fildani et al., 2018).

Presented here are new radiocarbon ages and stratigraphic relationships from drill cores and outcrops that document two glacial diamictons deposited in northern Iowa during MIS 3, called the Sheldon Creek Formation (Fig. 2, Bettis et al., 1996). These ages, together with a synthesis of previously published and new data, provide new insights into the extent and timing of LIS advances and demonstrate the presence of two Keewatin-sourced ice advances within the Upper Mississippi River Basin during MIS 3. These advances represent a glacial source for the Roxana Silt within the Mississippi basin and the Pisgah Formation loess in the Missouri River Valley.

Section snippets

Regional setting and past work

The glaciated portion of the Upper Mississippi River Valley (Fig. 1) has been influenced by multiple advances of the Quaternary LIS. These advances left a palimpsest of deposits and landforms, with the most recent deposits being best preserved, and the older units being progressively difficult to recognize and interpret. This record has been of interest to geologists since the 19th century and remains important for Quaternary research as discoveries from the stratigraphic record in the Central

Lithologic description

This study was conducted using continuous drill cores collected from across north-central Iowa, as well as outcrops and quarry exposures (Fig. 3 inset). The majority of cores were collected in plastic sleeves using either a Central Mine Equipment drill rig or a truck mounted Giddings™ probe. Other cores were retrieved using a trailer mounted Giddings™ in unlined core barrels that were wrapped after collection. Cores were described and subsampled in a laboratory facility under fluorescent

Results

The new and legacy radiocarbon ages from across the study area (Table 1) are shown geographically in Fig. 3 and with stratigraphic context in Fig. 5, Fig. 6, Fig. 7. Fig. 5 shows cores and sections collected on the MIS 2 till plain while Fig. 5 shows cores collected to the east of the Bemis moraine on the IES. Stratigraphic (Fig. 7) and chronologic (Fig. 4) results point to the potential for two advances and will be discussed below. Based on this evidence, ages are be subdivided into four

Discussion

To inform the theoretical ice advance model, the MIS 2 DML is used as an analogue for the behavior of the MIS 3 ice. Since the DML was streaming during parts of MIS 2, it is likely that it behaved similarly during MIS 3. The factors that lead to ice streaming as defined in Winsborrow et al. (2010) – meltwater routing, bed roughness, geothermal heat flux, topographic step, and topographic focusing – were likely also present during MIS 3. By the analogy with the MIS 2 DML, thin ice likely

Conclusions

The synthesis of new and previously published ages presented here demonstrates that the Sheldon Creek Formation in Iowa was deposited during MIS 3. Two distinct ice advances within this interval are separated in some localities by weathering horizons or weakly developed soils. The Fort Dodge and Lehigh phases reached their terminal position around 42 and 30 ka, respectively. The behavior of the DML during MIS 3 is assumed to reflect the fast, streaming style of its MIS 2 iteration (Clark, 1992;

Sources of funding

This work was partially supported by the USGS National Cooperative Geological Mapping Program under STATEMAP award numbers G16AC00196 (2016), G17AC00258 (2017), & G18AC00194 (2018). Funding for undergraduate researchers on this project was partially supported by a National Science Foundation Award: Improving Undergraduate STEM Education Grant GP-IMPACT-1600429.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was partially supported by the USGS National Cooperative Geological Mapping Program under STATEMAP award numbers G16AC00196 (2016), G17AC00258 (2017), and G18AC00194 (2018). Funding for undergraduate researchers on this project was partially supported by a National Science Foundation Award: Improving Undergraduate STEM Education Grant GP-IMPACT-1600429. We thank the numerous landowners who allowed us to collect samples over the years, especially Martin Marietta and US Gypsum for

References (126)

R.G. Baker et al.
Mid-Wisconsinan environments on the eastern Great plains
Quat. Sci. Rev.
(2009)
E.A. Bettis et al.
Landscape evolution, alluvial architecture, environmental history, and the archaeological record of the Upper Mississippi River Valley
Geomorphology
(2008)
A.E. Carlson et al.
Rapid Laurentide ice-sheet advance towards southern last glacial maximum limit during marine isotope stage 3
Quat. Sci. Rev.
(2018)
P.U. Clark
Unstable behavior of the Laurentide ice sheet over deforming sediment and its implications for climate change
Quat. Res.
(1994)
B.B. Curry
Evidence at Lomax, Illinois, for mid-Wisconsin (∼40,000 yr B.P.) position of the Des Moines lobe and for diversion of the Mississippi river by the lake Michigan lobe (20,350 yr B.P.)
Quat. Res.
(1998)
B.B. Curry et al.
Absence of glaciation in Illinois during marine isotope stages 3 through 5
Quat. Res.
(1996)
B.B. Curry et al.
Quaternary glaciations in Illinois
A.S. Dalton et al.
Constraining the late pleistocene history of the Laurentide ice sheet by dating the missinaibi formation, Hudson Bay lowlands, Canada
Quat. Sci. Rev.
(2016)
S.L. Forman et al.
Chronologic evidence for multiple periods of loess deposition during the late pleistocene in the Missouri and Mississippi river valley, United States: implications for the activity of the Laurentide ice sheet
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(1992)
D.A. Grimley et al.
Modern, Sangamon and Yarmouth soil development in loess of unglaciated southwestern Illinois
Quat. Sci. Rev.
(2003)

G.R. Hallberg

Pre-Wisconsin glacial stratigraphy of the central plains region in Iowa, Nebraska, Kansas, and Missouri

Quaternary Science Reviews- Quaternary Glaciations in the Northern Hemisphere

(1986)

G.R. Hallberg et al.

Stratigraphy and correlation of the glacial deposits of the Des Moines and James lobes and adjacent areas in north Dakota, south Dakota, Minnesota, and Iowa

Quaternary Science Reviews- Quaternary Glaciations in the Northern Hemisphere

(1986)

B. Hallet et al.

Rates of erosion and sediment evacuation by glaciers: a review of field data and their implications

Global Planet. Change

(1996)

S.L. Heath et al.

Pattern of southern Laurentide ice sheet margin position changes during heinrich stadials 2 and 1

Quat. Sci. Rev.

(2018)

P.M. Jacobs et al.

Pedogenesis of a catena of the farmdale–sangamon geosol complex in the North central United States

Palaeogeogr. Palaeoclimatol. Palaeoecol.

(2009)

W.H. Johnson et al.

Source and origin of Roxana silt and middle wisconsinan midcontinent glacial activity

Quat. Res.

(1989)

D.S. Leigh et al.

AMS radiocarbon age of the upper Mississippi Valley Roxana silt

Quat. Res.

(1993)

T.V. Lowell

The application of radiocarbon age estimates to the dating of glacial sequences: an example from the Miami sublobe, Ohio, USA

Quat. Sci. Rev.

(1995)

M. Margold et al.

Ice streams in the Laurentide Ice Sheet: identification, characteristics and comparison to modern ice sheets

Earth Sci. Rev.

(2015)

H.W. Markewich et al.

Paleopedology plus TL, Be-10, and C-14 dating as tools in stratigraphic and paleoclimatic investigations, Mississippi River Valley, USA

Quat. Int.

(1998)

J.A. Mason

Transport direction of peoria loess in Nebraska and implications for loess sources on the central Great plains

Quat. Res.

(2001)

J.A. Mason

Up in the refrigerator: geomorphic response to periglacial environments in the Upper Mississippi River Basin, USA

Geomorphology

(2015)

J. Mason et al.

Middle to Late Pleistocene loess record in eastern Nebraska, USA, and implications for the unique nature of Oxygen Isotope Stage 2

Quat. Sci. Rev.

(2007)

G.H. Miller et al.

Hudson Bay was not deglaciated during MIS-3

Quat. Sci. Rev.

(2019)

D.R. Muhs et al.

Geochemical variations in peoria loess of western Iowa indicate paleowinds of midcontinental north America during last glaciation

Quat. Res.

(2000)

D.R. Muhs et al.

Chronology and provenance of last-glacial (peoria) loess in western Iowa and paleoclimatic implications

Quat. Res.

(2013)

D.R. Muhs et al.

Geochemistry and mineralogy of late quaternary loess in the upper Mississippi river valley, USA: provenance and correlation with Laurentide ice sheet history

Quat. Sci. Rev.

(2018)

C.J. Patterson

Southern Laurentide ice lobes were created by ice streams: Des Moines lobe in Minnesota, USA

Sediment. Geol.

(1997)

L.B. Railsback et al.

An optimized scheme of lettered marine isotope substages for the last 1.0 million years, and the climatostratigraphic nature of isotope stages and substages

Quat. Sci. Rev.

(2015)

W.C. Alden et al.

The iowan drift, a review of the evidences of the iowan stage of glaciation

Iowa Geological Survey Annual Report

(1917)

H.F. Bain

Relations of the Wisconsin and Kansan drift sheets in central Iowa, and related phenomena

Iowa Geological Survey Annual Report

(1897)

R.G. Baker et al.

Mid-Wisconsinan stratigraphy and paleoenvironments at the St. Charles site in South-central Iowa

Geol. Soc. Am. Bull.

(1991)

G. Balco et al.

Absolute chronology for major pleistocene advances of the Laurentide ice sheet

Geology

(2010)

G. Balco et al.

The first glacial maximum in North America

Science

(2005)

G. Balco et al.

Dating Plio-Pleistocene glacial sediments using the cosmic-ray-produced radionuclides 10Be and 26Al

Am. J. Sci.

(2005)

C.L. Batchelor et al.

The configuration of Northern Hemisphere ice sheets through the Quaternary

Nat. Commun.

(2019)

E.A. Bettis

The Deforest Formation of Western Iowa: Lithologic Properties, Stratigraphy, and Chronology

(1990)

E.A. Bettis et al.

Complex response of a midcontinent North America drainage system to Late Wisconsinan sedimentation

J. Sediment. Res.

(1997)

E.A. Bettis et al.

Last Glacial loess in the conterminous USA

Quat. Sci. Rev.

(2003)

J. Boellstorff

North american pleistocene stages reconsidered in light of probable pliocene-pleistocene continental glaciation

Science

(1978)

J.D. Boellstorff

Chronology of some Late Cenozoic deposits from the central United States and the ice ages

Transactions of the Nebraska Academy of Science VI

(1978)

S. Calvin

Iowan drift

Geol. Soc. Am. Bull.

(1899)

S. Calvin

The Iowan drift

J. Geol.

(1911)

E.C. Carson et al.

LATE MIS 3 ONSET TO LARGE-SCALE AGGRADATION ON THE UPPER MISSISSIPPI RIVER VALLEY, USA

(2019)

E.G. Ceperley et al.

The role of permafrost on the morphology of an MIS 3 moraine from the southern Laurentide Ice Sheet

Geology

(2019)

T.C. Chamberlain

The classification of American glacial deposits

J. Geol.

(1895)

T. Chamberlin

Supplementary hypothesis respecting the origin of the loess of the Mississippi valley

J. Geol.

(1897)

P.U. Clark

Surface form of the southern Laurentide ice sheet and its implications to ice-sheet dynamics

Geol. Soc. Am. Bull.

(1992)

P.U. Clark et al.

The last glacial maximum

Science

(2009)

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Citation Excerpt :
Over North America, there is some indirect proxy evidence suggesting a moderately large continental ice sheet during MIS 3. However, this evidence can be explained by non-glacial processes and/or the brief ice extension noted by Kerr et al. (2021). Notably, the eolian-sourced Roxana Silt (and correlatives, e.g. Gilman Canyon Formation) is spatially ubiquitous in the mid-continental United States and was deposited from 55 ka to 30 ka (Bettis et al., 2003; Follmer, 1996; Forman and Pierson, 2002; Leigh, 1994).
There is disagreement in the Quaternary research community in how much of the marine δ¹⁸O signal is driven by change in ice volume. Here, we examine this topic by bringing together empirical and modelling work for Marine Isotope Stage 3 (MIS 3; 57 ka to 29 ka), a time when the marine δ¹⁸O record indicates moderate continental glaciation and a global mean sea level between −60 m and −90 m. We compile and interpret geological data dating to MIS 3 to constrain the extent of major Northern Hemisphere ice sheets (Eurasian, Laurentide, Cordilleran). Many key data, especially published in the past ~15 years, argue for an ice-free core of the formerly glaciated regions that is inconsistent with inferences from the marine δ¹⁸O record. We compile results from prior studies of glacial isostatic adjustment to show the volume of ice inferred from the marine δ¹⁸O record is unable to fit within the plausible footprint of Northern Hemisphere ice sheets during MIS 3. Instead, a global mean sea level between −30 m and − 50 m is inferred from geological constraints and glacial isostatic modelling. Furthermore, limited North American ice volumes during MIS 3 are consistent with most sea-level bounds through that interval. We can find no concrete evidence of large-scale glaciation during MIS 3 that could account for the missing ~30 m of sea-level equivalent during that time, which suggests that changes in the marine δ¹⁸O record are driven by other variables, including water temperature. This work urges caution regarding the reliance of the marine δ¹⁸O record as a de facto indicator of continental ice when few geological constraints are available, which underpins many Quaternary studies.
Evolution of the Laurentide and Innuitian ice sheets prior to the Last Glacial Maximum (115 ka to 25 ka)
2022, Earth-Science Reviews
Citation Excerpt :
Our maximum ice extent also considers evidence suggesting a short-lived, dramatic extension of the Keewatin Dome southward into the continental United States via a low-lying topographic corridor in Manitoba. The timing and extent of this advance (between ~34 ka and ~30 ka; known as the Lehigh Advance) is based on radiocarbon dating of wood contained within, overlying and underlying this till unit associated with the Keewatin Dome (Kerr et al., 2021). Along the Atlantic coastline, the ice margin is drawn at midway between the present-day coastline and the continental shelf edge.
The Laurentide Ice Sheet was the largest global ice mass to grow and decay during the last glacial cycle (~115 ka to ~10 ka). Despite its importance for driving major changes in global mean sea level, long-term landscape evolution, and atmospheric circulation patterns, the history of the Laurentide (and neighbouring Innuitian) Ice Sheet is poorly constrained owing to sporadic preservation of stratigraphic records prior to the Last Glacial Maximum (LGM; ~25 ka) and a case-study approach to the dating of available evidence. Here, we synthesize available geochronological data from the glaciated region, together with published stratigraphic and geomorphological data, as well as numerical modelling output, to derive 19 hypothesised reconstructions of the Laurentide and Innuitian ice sheets from 115 ka to 25 ka at 5-kyr intervals, with uncertainties quantified to include best, minimum, and maximum ice extent estimates at each time-step. Our work suggests that, between 115 ka and 25 ka, some areas of North America experienced multiple cycles of rapid ice sheet growth and decay, while others remained largely ice-free, and others were continuously glaciated. Key findings include: (i) the growth and recession of the Laurentide Ice Sheet from 115 ka through 80 ka; (ii) significant build-up of ice to almost LGM extent at ~60 ka; (iii) a potentially dramatic reduction in North American ice at ~45 ka; (iv) a rapid expansion of the Labrador Dome at ~38 ka; and (v) gradual growth toward the LGM starting at ~35 ka. Some reconstructions are only loosely constrained and are therefore speculative (especially prior to 45 ka). Nevertheless, this work represents our most up-to-date understanding of the build-up of the Laurentide and Innuitian ice sheets during the last glacial cycle to the LGM based on the available evidence. We consider these ice configurations as a series of testable hypotheses for future work to address and refine. These results are important for use across a range of disciplines including ice sheet modelling, palaeoclimatology and archaeology and are available digitally.

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