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Laurentide Ice Sheet Retreat During the Younger Dryas: Central Upper Peninsula of Michigan, USA

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Laurentide Ice Sheet Retreat During the Younger Dryas: Central Upper Peninsula of Michigan, USA Laurentide Ice Sheet Retreat during the Younger Dryas: Central Upper Peninsula of Michigan, USA A thesis submitted to the Graduate school of the University of Cincinnati in partial fulfillment of the requirements for the degree of Masters of Science In the Department of Geology of the McMicken College of Arts and Sciences By Kent Andrew Walters B.A. Grand Valley State University April, 2011 Committee Chair: Thomas V. Lowell, Ph.D Committee Members: David B. Nash, Ph.D Timothy G. Fisher, Ph.D Abstract The response of ice sheets to climate change is of concern because of meltwater introduction to the oceans raising sea level. Yet it is uncertain how the Laurentide Ice Sheet (LIS) responded to the widely studied Younger Dryas (YD) cold interval (~12.9- 11.6 cal ka BP). In northwestern Wisconsin and the Upper Peninsula of Michigan, two sites record advances of the LIS before and near the end of the YD. The Two Creeks (~13.7 cal ka BP) and Lake Gribben (~11.6 cal ka BP) forest beds indicate that the ice sheet margin was between those sites during the YD. New geomorphic mapping and synthesis of existing and new chronology for the ice margin, document activity of the ice sheet during the YD. Combined, these data indicate that the ice sheet margin had at least six stationary positions during retreat through the YD interval and a readvance after the YD. When this pattern is compared to the isotopic record from the Greenland ice core, an apparent conflict arises. The ice sheet is retreating at a time generally thought to be cold and correlating with glacial advances. This may imply that seasonality and the corresponding warmer summers during the YD controlled the ice sheet response. Alternatively they may imply caution is needed when interpreting the ice core record. ii iii Acknowledgements: This study would like to thank the support of the Comer Science and Education Foundation’s grant to Aaron Putnam for providing this study with funding for radiocarbon dates. Putnam provided thoughtful comments on the progress and presentation of this study. We would also like to thank Robert Regis for his thoughts and information on the study region. We are grateful to Colby Smith and Paul Wilcox for their help with the sediment core collection process. Finally, I would like to thank my committee members Dr. David Nash and Dr. Timothy Fisher for their insightful comments and motivation on this project. iv Table of Contents 1. Introduction……………………………………………………………………………..1 2. Regional Setting…………………………………………………………………………2 2.1 Study Region………………………………………………………………………2 2.2 Geology…………………………………………………………………………….3 2.3 Prior Surficial Mapping…………………………………………………………...3 2.4 Existing Glacial Chronology……………………………………………………...4 3. Methods………………………………………………………………………………….5 4. Results…………………………………………………………………………………...8 4.1 Mapping…………………………………………………………………………….8 4.1.1 Subglacial Forms………………………………………………………….8 4.1.2 Ice Margin Forms………………………………………………………….9 4.1.2.1 Moraines…………………………………………………………9 4.1.2.2 Ice Contact Moraines…………………………………………..9 4.1.2.3 Moraine Spacing………………………………………………..9 4.1.3 Correlation of Refinement of Moraines………………………………...10 4.1.3.1 Late Mountain and Early Athelstane Moraine………………10 4.1.3.2 Denmark/Late Athelstane Moraine……………………………10 4.1.3.3 Intermediate Moraines………………………………………….11 4.1.3.4 Marquette Moraine………………………………………………12 4.1.4 Proglacial Deposits………………………………………………………..12 4.1.5 Meltwater Channels……………………………………………………….12 4.1.6 Non-glacial Forms…………………………………………………………13 4.1.7 Anthropogenic Forms……………………………………………………..13 4.2 Chronology………………………………………………………………………….13 4.2.1 Sagola/Saint Johns and Late Sagola/Republic Moraines…………….14 4.2.2 Denmark/Late Athelstane/Green Hills/Ishpeming Moraine…………...14 4.2.2.1 Maximum Ages………………………………………………….14 4.2.2.2 Minimum Ages…………………………………………………..15 v 4.2.3 Pembine/Hay Lake, Felch/Pike Lake and Foster City/Shag Lake Moraines…………………………………………………………………….16 4.2.4 Gwinn Moraine……………………………………………………………...16 4.2.5 Gladstone and Rapid River Moraines……………………………………17 4.2.6 Marquette Moraine…………………………………………………………17 4.2.6.1 Maximum Ages……………………………………………………17 4.2.6.2 Minimum Ages…………………………………………………....17 4.3 Timing of the Two Creeks and Marquette Moraines Refined…………………19 4.3.1 Summing Probabilities…………………………………………………….19 4.3.2 Refinement of the Green Hills/Ishpeming Moraine Formation……….20 4.3.3 Refinement of the Marquette Moraine Formation……………………...20 4.4 Interpreted Sequence of Events………………………………………………….20 4.5 Time-Distance Diagram……………………………………………………………22 4.6 Dune Sands and Lake Bottom Inorganic Sediments…………………………..23 5. Discussion……………………………………………………………………………....23 5.1 Young Minimum Ages……………………………………………………………..23 5.2 Green Hills/Ishpeming Age Assignment…………………………………………25 5.3 Laurentide Ice Sheet Retreat during the Younger Dryas………………………25 5.3.1 Step-Wise Retreat………………………………………………………...25 5.3.2 LIS Deglaciation…………………………………………………………..25 5.3.3 LIS Retreat Before or During the Younger Dryas?............................26 5.3.3.1 Ice Margin Formation…………………………………………..26 5.3.3.2 Calving Retreat………………………………………………….27 5.3.3.3 Terrestrial Retreat………………………………………………28 5.3.4 Regional Ice Sheet Comparison………………………………………...28 5.4 Marquette Advance During an Interglacial Climate…………………………….29 5.5 Contradicting Messages…………………………………………………………..30 5.5.1 Seasonality………………………………………………………………….30 5.5.2 Scandinavian Ice Sheet……………………………………………………31 6. Conclusions……………………………………………………………………………..32 vi 1. Introduction Modern day observations of glaciers and ice sheets indicate they are sensitive, and respond quickly to changes in climate (Oerlemans, 1986; Oerlemans, 1990; Oerlemans and Fortuin, 1992; Fabre et al., 1995; Lowell, 2000). Changes in ice margin position can be reconstructed from geomorphic evidence, and therefore can be used to study paleoclimatic events of rapid climate change such as the Younger Dryas cold period (YD; 12.9-11.6 cal ka BP). Much effort has been put into examining how small glaciers were affected by this rapid cooling event (Rodbell and Seltzer, 2000; Barrows et al., 2007; Ackert et al., 2008; Kaplan et al., 2010; Palmer et al., 2010; MacLeod et al., 2011; Rinterknecht et al., 2012; Young et al., 2012), but little effort has been put into the response of large ice sheets. This is especially true for the Laurentide Ice Sheet (LIS). The behavior of the LIS during the YD is poorly understood. Clayton and Moran (1986) suggested that the LIS retreated to the northern shores of Lake Superior before the onset of the YD to allow for drainage of glacial Lake Agassiz. The age and position of the Marquette Moraine in the Upper Peninsula of Michigan suggests that the LIS readvanced almost 200 km across Lake Superior during the YD. Lowell et al. (1999) refined the age of the moraine and also attributed LIS expansion to the YD cooling event. This idea was later supported and accepted after a widespread database of radiocarbon dates constraining LIS retreat was produced (Dyke, 2004). Most recently Lowell et al. (2009) dated recessional moraines refining LIS retreat near Thunder Bay, Ontario showing a step wise retreat pattern with small readvances through the Late Glacial and into the Holocene. This suggests 200 km of retreat and readvance across the Lake Superior basin was unlikely. 1 This study was undertaken to: (i) refine the pattern of LIS recession using glacial mapping and radiocarbon dates in the Upper Peninsula of Michigan; and, (ii) determine how the LIS responded during the Younger Dryas event. 2. Regional Setting 2.1 Study Region This study focuses on glacial landforms and LIS deglaciation chronology in central Upper Peninsula of Michigan (Figure 1). The study region ranges from northeast Wisconsin near Lake Winnebago into the Upper Peninsula of Michigan near Marquette. The primary study site lies between the cities of Au Train, Big Bay and Iron Mountain, MI, focusing on the glacial features southwest of Marquette, MI (red box Figure 1). Within the study region are two well-known and dated forests buried by the LIS. The first forest was buried by the LIS at 13.7 cal ka BP and is known as the Two Creeks event (Figure 1). Here, the Lake Michigan sublobe of the LIS advanced over the Two Creeks spruce forest burying it in till (Figure 1; Black, 1970). The adjacent lobe of ice known as the Green Bay lobe advanced in phase, incorporating tree remains of Two Creeks age into its sediments. A second recognized forest bed in the northern Upper Peninsula of Michigan is known as the Lake Gribben Forest, and was buried by glacial outwash during the Marquette readvance (Figure 1; Hughs and Merry, 1978; Lowell et al., 1999). It is dated to 11.6 cal ka BP (Table 1). These ages indicate that the Two Creeks and Marquette LIS advances occurred before and after YD time. Thus the behavior of the LIS can be extracted by studying the glacial features between these two 2 locations which must incorporate retreat northward from the Two Creeks site to a position north of the Marquette Moraine before readvancing to the Marquette Moraine. 2.2 Geology Two major groups of bedrock underlie the study area. In the southeast lies the Michigan basin where the bedrock consists of various limestones, Cambrian aged sandstones and few shales (Farrand, 1982). The western and northwestern landscape is controlled by Archean-aged granites, gneisses and various other volcanic or igneous rocks (Farrand, 1982). 2.3 Prior Surficial Mapping The Upper Peninsula of Michigan has had a long history of glacial investigations. Leverett (1929) interpreted the glacial history using the matrix color of tills. Much later, Black (1969) studied the glacial history using striations, drumlins, and end moraines to suggest a different glacial history of several ice lobes occupying the region. Subsequently, investigations focused on the chronology of events (Saarnisto, 1974; Drexler et al., 1983; Clayton and Moran, 1986). Two hypothesis emerged; one of slow retreat through the Upper Peninsula of Michigan (Saarnisto, 1974), and another of rapid deglaciation with a later readvance into the region (Drexler et al., 1983; Clayton and Moran, 1986). The latter was accepted as the general pattern of ice sheet recession and expansion by virtue of its inclusion in Dyke (2004).
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