Ice margin and sediment fluctuations recorded in the varve stratigraphy of Lake Ojibway By Gianna Lee Evans B.S, Colorado State University 2000 A thesis Presented to the University of Cincinnati In partial fulfillment of the degree of Master of Science In the Department of Geology College of Arts and Sciences 2011 Committee Chair: Dr. Thomas V. Lowell Abstract Deglaciation of the Laurentide Ice Sheet is recorded, in part, in proglacial lake sediments. For the Lake Ojibway sequence three proxies are examined within an annual resolution framework to better understand the timing of events leading up to the final demise of the lake. Varve thickness, magnetic susceptibility (MS) and ice rafted debris (IRD) were analyzed individually and together to characterize sediment and ice margin fluctuations recorded within the varve stratigraphy. Varve thickness is a direct measurement of sediment flux. MS is a function of bulk mineralogy and grain size, and is applied here for correlation and as a proxy for the sediment source proximity. The IRD record tracks changes in the ice margin. These three properties, considered together help clarify the operation of sediment flux, water flux, and ice margin flux as the ice sheet decayed. The varve stratigraphy is compiled from sediment cores from five remnant lakes within the Lake Ojibway basin; Reid Lake, Lac Duparquet, Lac Montbeillard, Lac de Courval and Lac Wawagosic. Three prominent events in the Lake Ojibway varve sequence are explored with these proxies: varve 1528 which is thought to be the influx of Lake Agassiz water, years ~1750‐2000 which is thought to correspond to the Cochrane Advance, and the Connaught varve series from years ~2060‐2090 (Breckenridge et al., 2011, in press). Sand ripples capping the varves in Lac Montbeillard, located in the southern drainage pathway, are possibly related to overspill from the influx of Lake Agassiz water. The shift from the southern outlet to a northern drainage outlet is recorded by a cessation of varve deposition in Lac Duparquet, which is located near the arctic drainage divide. IRD and MS demonstrate that the Connaught varve series was possibly deposited as a proximal to distal series during ice margin retreat or meltwater diversion. The fluctuations in IRD from Reid Lake help refine the timing of the Cochrane advance within the varve series. The IRD may also indicate two individual surge events within the Cochrane advance. Post glacial sediments from Reid Lake located above the varve deposits were dated at 8400 ± 53 cal BP. These new data will help refine the chronology and ice margin fluctuations within the Lake Ojibway‐Laurentide Ice Sheet system prior to the final demise of Lake Ojibway. ii iii Acknowledgements I would like to thank Andy Breckenridge for his thoughts and advice on this project. I would like to thank my committee; Tom Lowell, David Nash and Aaron Diefendorf for their help editing this document. Thanks to Warren Huff, Mike Menard, Bill Honsaker and Esteban Sagredo, and others for help with lab work. Thanks also to Kristina Brady and Anders Noren for logistics and assistance at University of Minnesota‐ LRC. I would also like to thank Aaron Lingwall at the Lac Core facility at UM‐Duluth for running all the x‐ray scans on short order. Funding for this project is thanks to NSF grant EAR‐0643144. A special thanks to Kate Cosgrove for making sure that all the analytical labs were paid on time. iv Table of Contents Abstract…………………………………………………………………………………………………………… II Acknowledgements…………………………………………………………………………………………. IV Introduction…………………………………………………………………………………………………….. 1 Prior work……………………………………………………………………………………………………….. 3 General stratigraphy……………………………………………………………………………. 3 Varve thickness occurrences………………………………………………………………. 4 Varve stratigraphy………………………………………………………………………………. 7 Methods ……………………………………………………………………………………………………….. 9 Results …………………………………………………………………………………………………………… 11 Varve stratigraphy………………………………………………………………………………. 11 Magnetic Susceptibility………………………………………………………………………. 14 X‐ray Diffraction (XRD)………………………………………………………………………. 16 Ice Rafted Debris………………………………………………………………………………… 21 Chronology………………………………………………………………………………………… 31 Discussion………………………………………………………………………………………………………. 35 Magnetic Susceptibility ……………………………………………………..………………. 35 Ice Rafted Debris ………………………………………………………………………………. 39 Varve 1528 ……………………………………………………………………………………….. 40 Closing the Southern Drainage Outlet (Varve 1776) ……….……….………… 41 Cochrane Advance …….………………………………………………………………………. 42 Connaught Varve Series ……………………………..……………………………………… 44 Conclusions…………………………………………………………………………………………………… 46 References……………………………………………………………………………………………………… 48 v List of Figures and Tables Figure 1 ……………………………………………………………………………………………………. 2 Figure 2 ……………………………………………………………………………………………………. 5 Figure 3 ……………………………………………………………………………………………………. 8 Figure 4 ……………………………………………………………………………………………………. 13 Figure 5 ……………………………………………………………………………………………………. 15 Figure 6 ……………………………………………………………………………………………………. 17 Figure 7 ……………………………………………………………………………………………………. 18 Figure 8 ……………………………………………………………………………………………………. 22 Figure 9 ……………………………………………………………………………………………………. 24 Figure 10 …………………………………………………………………………………………………. 26 Figure 11 …………………………………………………………………………………………………. 27 Figure 12 …………………………………………………………………………………………………. 29 Figure 13 …………………………………………………………………………………………………. 30 Figure 14 …………………………………………………………………………………………………. 36 Table 1 ……………………………………………………………………………………………………. 32 vi Introduction: At the onset of the Holocene, approximately 12 ky BP, warming temperatures are thought to have contributed to the disintegration of the Laurentide Ice Sheet (LIS), (Alley et al., 1997; Dyke, 2004). Large meltwater lakes, such as Agassiz and Ojibway, formed in isostatically depressed basins at the ice margin during the final retreat of the LIS (Vincent and Hardy, 1979; Dyke and Prest, 1987; Veillette, 1994; Dyke, 2004). Further decay of the ice sheet led to catastrophic failure of ice dams within Hudson Bay causing an outburst of meltwater from Lake Agassiz‐Ojibway that likely drained into the north Atlantic via Hudson Straight (Teller, 1995; Clark et al., 1999; Leverington et al., 2002; Lajeunesse and St‐ onge, 2008; Haberzettl et al., 2010). Sediment sequences that formed in the ice contact Lake Ojibway basin record ice margin and meltwater fluctuations. These ice margin and meltwater fluctuations will serve to help reconstruct the basin dynamics in the Laurentide‐Lake Ojibway system, which preceded the final termination of Lake Ojibway. The chronology of these large meltwater lakes can be reconstructed through analysis of varve stratigraphy (Antevs, 1925; Antevs, 1928; Hughes, 1965; Veillette, 1994; Breckenridge et al., 2011, in press), which provides a high resolution framework. This study focuses on the stratigraphy within the ~1200 years prior to the final drainage event. Five remnant lakes within the Lake Ojibway basin (Figure 1) form a ~300 km northeast transect and connect, by way of Reid Lake, to a northwest transect from a previous study (Stroup, 2009). Varve correlations were matched to Antev’s (1925, 1928) record to provide a floating chronology of the sedimentation record (Breckenridge et al., 2011, in press). The annual resolution of the varves can be exploited to directly compare the factors controlling sedimentation and to determine if they operated in the same temporal and/or spatial context. In addition to providing a temporal framework varve sequences constitute a record of sediment flux. These can be supplemented with magnetic susceptibility (MS) and ice rafted debris (IRD), which provide 1 Location Map JAMES BAY Legend Seismic sites collected in 2008-2009 LAC WAWAGOSIC LACLakes WAWAGOSIC cored in 2008-2009 Lillabelle Lake study LACPaulen De COURVAL (2001) LAC De COURVAL Hardy (1976) LAC DUPARQUET Hughes (1965) LAC DUPARQUET REID LAKE Antevs REID LAKE LAC(1925, MONTBEILLARD 1928) Lake cores LAC MONTBEILLARD collected in km 2010 0 50 100 Cochrane limit Figure 1: Digital elevation map of the study area showing the Kinojévis phase shoreline (black line). The dashed brown line is the approximate location of the Cochrane limit. Adapted from Breckenridge, et. al (2008), Dyke (2004) and Stroup (2009). 2 additional insight about sediment source and proximity. Long term sedimentation patterns may become visible and easy to correlate from different lakes across the basin by correlating the MS data with the varve years. Because MS is a function of grain size and bulk mineralogy (Dearing, 1999) it may also be used as a proxy for terrigenous material deposited within the lake sediments (Thompson and Oldfield, 1986; Nowaczyk, 2001; Teller et al., 2008; Lennox et al., 2010). This allows the MS curve from Reid Lake, located near the paleoshoreline of Lake Ojibway (Vincent and Hardy, 1979; Veillette, 1994; Stroup, 2009), to be compared with the MS curves resulting from deep water sediments from the other remnant lakes within the Lake Ojibway basin as a proxy for water flux as well as allowing its use as a correlation tool. Ice rafted debris (IRD) was measured from X‐ray imagery in Reid Lake to assess ice margin fluctuations (Bond et al., 1992; Grousse et al., 1993; Robinson et al., 1995; Mangerud et al., 1998; McCabe and Clark, 1998; Knies et al., 2001; Stroup, 2009; Larsen et al., 2011). This multi‐proxy study of the Lake Ojibway‐Laurentide Ice Sheet system will provide a high resolution record of the events leading up to the termination of Lake Ojibway. In addition, these results will help