Indiana University-Purdue University Indianapolis (IUPUI) / A broad range of samples were collected from the Huron-Erie Lobe, Lake Michigan Lobe, Saginaw Lobe, and Tipton Till Plain of northern Indiana to determine the provenance of Laurentide Ice Sheet till in the Midwest U.S. during the Illinoian and Wisconsinan glaciations. U-Pb age distributions from approximately 300 detrital zircons (DZ) were used as provenance indicators for each till sample. Till from the Lake Michigan Lobe and was found to be largely homogenized. The distinct lobe DZ age distributions are the Lake Michigan Lobe till with a dominant ~1465 Ma peak, the northern Huron-Erie Lobe till with a dominant ~1060 Ma and a secondary peak at ~1450 Ma, the southern Huron-Erie Lobe till with nearly equal peaks at ~1435 Ma, ~1175 Ma, and ~1065 Ma, and the southern Saginaw Lobe till with a dominant peak at ~1095 Ma. Those four DZ age distributions were treated as endmembers in a nonlinear least-squares mixing model to calculate the contribution of each lobe to till in the Tipton Till Plain. Huron-Erie and Saginaw lobe tills were found to be the primary components of the Tipton Till Plain, and Lake Michigan Lobe till was only found in the western Tipton Till Plain. Zircons from the Saginaw Lobe till increased 39 % in the eastern Tipton Till Plain between the Illinoisan and Wisconsinan glaciations. The mixing model was also applied to relate the DZ age distributions of the lobes to bedrock within and near their flow paths. When comparing nearby bedrock to each lobe’s till, mixing model results, yield an approximate maximum transport distance between 500 and 630 kilometers for the matrix vii fraction of till in the Lake Michigan, Huron-Erie, and Saginaw lobes. Samples for the southern Huron-Erie Lobe indicate that the most of the zircon ages within the southern Huron-Erie Lobe till in Indiana were specifically entrained between Niagara County, New York and east-central Indiana. Within the model’s error, 93 – 100 % of the detrital zircons in each of the three lobes are relatable to nearby Paleozoic and Precambrian sedimentary and metamorphic bedrock formations.

Thesis advisor: Jeremy D. Shakun / The deglacial extent chronology of the southeastern Laurentide Ice Sheet as it retreated through the northeastern United States and southern Quebec has been well constrained by multiple lines of evidence. By comparison, few data exist to constrain the thinning history of the southeastern Laurentide, resulting in lingering uncertainty about volume changes and dynamics of this ice mass during the deglacial period. To address the lack of thinning information, my team collected 120 samples for in-situ `10Be exposure dating from various elevations at numerous mountains in New England and southern Quebec. Monte Carlo regression analyses using the analytical uncertainties of exposure ages from each mountain are used to determine the most-likely timing and rate of ice thinning for that location, a technique known as the ‘dipstick approach’. While this larger project is ongoing, I have processed and measured 10Be concentrations of 42 samples for this thesis and present my preliminary results and interpretation here. Exposure ages from Peekamoose Mt. in southern NY suggest ice thinning early in the deglacial period (~19.5 – 17.5 ka), near the onset of the Heinrich Stadial I cold period. Samples from Franconia Notch, NH, and Mt. Mansfield, VT, suggest ice thinning from approximately 15 – 13 ka in northern New England, roughly coincident with the Bølling-Allerød warm period. Exposure ages from each of the northern New England dipsticks are nearly identical within 1σ internal uncertainty, indicating that ice thinning was rapid. Higher elevation (>1200 m a.s.l.) samples from the northern New England mountains appear to contain inherited 10Be from previous periods of exposure, indicating a lack of glacial erosion on these surfaces. My high-elevation samples with inherited 10Be suggest that these summit landscapes were preserved beneath cold-based, non-erosive ice during the last glacial and deglacial periods. 40 samples that have yet to be processed will provide more information on ice thinning around Killington Mt., VT, Mt. Greylock, MA, Mt. Bigelow, ME, and Mt. Jacques-Cartier, Quebec. Ultimately, this information will be used to create probabilistic reconstructions of the lowering southeastern Laurentide ice surface during its retreat. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

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<p>This thesis presents a palaeoglaciological study aimed to determine the location, geometry and temporal evolution of palaeo-ice streams of the north-easternmost Laurentide Ice Sheet. The work was accomplished through the geomorphological interpretation of satellite imagery over 3.19 x 10⁶ km² of the Canadian Arctic, using a glaciological inversion scheme. Ice streams were active in this region during most of the time between the Last Glacial Maximum and the last deglaciation. A web of ice streams and inter-ice stream areas existed. Three major ice stream networks are identified: the M'Clintock Channel, Gulf of Boothia – Lancaster Sound and Hudson Strait. The M'Clintock Channel bears the most complex landform record, comprising three generations of palaeo-ice streams. Their location was weakly controlled by the subglacial topography and their geometry was determined by frozen-bed portions of the ice sheet, thus providing evidence for pure ice streams in the Laurentide Ice Sheet. In contrast, the more pronounced relief of the Gulf of Boothia – Lancaster Sound corridor supported topographically controlled ice streams. The landform record on emerged land along Hudson Strait is insufficient to support the existence of ice streams. It is therefore proposed that ice streams were constrained within the deep parts of the strait while flanked by cold-based zones on the margins. Small transient ice streams on Baffin and Prince of Wales islands drained local remnant ice caps during the collapse of the ice sheet. Analysis of the controls on the location and flow of palaeo-ice streams suggests that the interaction between the subglacial topography and thermal state of the substrate plays a more fundamental role than the geology. It is concluded that the behaviour of ice streams cannot be explained in terms of environmental controls alone, but the complex dynamics of ice stream shear margins and onset zones must be considered.</p>

This thesis presents a palaeoglaciological study aimed to determine the location, geometry and temporal evolution of palaeo-ice streams of the north-easternmost Laurentide Ice Sheet. The work was accomplished through the geomorphological interpretation of satellite imagery over 3.19 x 106 km2 of the Canadian Arctic, using a glaciological inversion scheme. Ice streams were active in this region during most of the time between the Last Glacial Maximum and the last deglaciation. A web of ice streams and inter-ice stream areas existed. Three major ice stream networks are identified: the M'Clintock Channel, Gulf of Boothia – Lancaster Sound and Hudson Strait. The M'Clintock Channel bears the most complex landform record, comprising three generations of palaeo-ice streams. Their location was weakly controlled by the subglacial topography and their geometry was determined by frozen-bed portions of the ice sheet, thus providing evidence for pure ice streams in the Laurentide Ice Sheet. In contrast, the more pronounced relief of the Gulf of Boothia – Lancaster Sound corridor supported topographically controlled ice streams. The landform record on emerged land along Hudson Strait is insufficient to support the existence of ice streams. It is therefore proposed that ice streams were constrained within the deep parts of the strait while flanked by cold-based zones on the margins. Small transient ice streams on Baffin and Prince of Wales islands drained local remnant ice caps during the collapse of the ice sheet. Analysis of the controls on the location and flow of palaeo-ice streams suggests that the interaction between the subglacial topography and thermal state of the substrate plays a more fundamental role than the geology. It is concluded that the behaviour of ice streams cannot be explained in terms of environmental controls alone, but the complex dynamics of ice stream shear margins and onset zones must be considered.

Understanding the cause of abrupt climate change in the geologic past can help assess the potential magnitude and variability of future changes in regional and global climate. The research presented here focuses on some of the first records of hydrologic variability in the central North American continent during an interval of Marine Isotope Stage 3 (24-57 thousand years before present (ka)). Sediment core MD02-2551 from the Orca Basin, northern Gulf of Mexico, is used to document the first detailed melting history of the southern margin of the Laurentide Ice Sheet (LIS) during MIS 3, and to record terrestrial inputs from the Mississippi River related to changes in evaporation-precipitation over the mid-continent, from 28-45 ka.Paired measurements of oxygen isotopes and Mg/Ca-SST on the planktonic foraminifera Globigerinoides ruber (pink) are used to calculate the oxygen isotopic composition of seawater and test one of the key hypotheses for abrupt climate change. Five rvals of freshwater input from 28-45 ka do not match the abrupt Dansgaard-Oeschger temperature oscillations recorded in Greenland ice. Rather, summer melting of the LIS may have occurred during Antarctic warming and likely contributed to sea-level variability during MIS 3. A detailed assessment over one of the meltwater events, using the oxygen and carbon isotopic composition of G. ruber and the deeper dwelling Neogloboquadrina dutertrei, demonstrate that meltwater was confined to the surface layers and likely had an impact on the biological pump in the Gulf of Mexico. A similar oxygen isotopic composition of seawater record determined from the year-round white G. ruber suggests that melting was not limited to the warmest summer months. The timing of LIS meltwater input is decoupled from an interval of enhanced wet conditions over the North American continent and increased Mississippi River discharge, as shown by a suite of organic and sedimentologic proxies. Increasing summer insolation on the orbital scale may have led to a northward migration of the Intertropical Convergence Zone and an intensification and westward shift in the conical position of the Bermuda High, which shuttles moisture to the North American continent and contributes to flooding in the Mississippi River drainage basin.

It is important to study subglacial environments in northern Canada for many reasons, such as to develop a more comprehensive understanding of glacial landscape development and to aid in mineral exploration. The purpose of this research is improve understanding of the Quaternary Geology of north central Hall Peninsula, Baffin Island, the subglacial dynamics record in particular, in order to provide industry with new knowledge, maps and interpretations to aid in mineral exploration. The glacial history of north-central Hall Peninsula, Baffin Island is very complex. By studying the subglacial landscape using both remote- and field- based techniques it was possible to develop a subglacial landscape map and a flowset map which highlighted areas with different glacial histories and basal thermal regimes. The subglacial dynamics and how they changed spatially and temporally shaped the landscape to what it is today with a mixture of cold, intermediate, and warm-based ice. Through mapping using remote sensing and field methods, seven glacial landform and striation directions were found and grouped into four ice flow events. The identified ice flows include regional flows, northern and eastern fjord influenced areas, central deglacial flows, and modern icecap flows. Subglacial erosion was investigated using several proxies including streamlined hill elongation ratios, streamlined hill density, and bedrock controlled lake density studies. These proxies together with the subglacial landscape map were overlaid to select discrete zones, termed glacial terrain zones (GTZs), in an attempt to analyze the subglacial dynamics and how different basal thermal regimes interacted with the landscape. Five glacial terrain zones (GTZs) were identified, with different spatio-temporal basal ice regimes and landform assemblages. The first zone (GTZ 1) is characterized by an expansive flowset of parallel paleo-flow indicators trending northeast. This zone has the highest degree of areal scour with thin, discontinuous and relatively unweathered till. The second zone, GTZ 2, is an area where the broad northeast flowset is crosscut locally by ice flow indicators that converge into troughs that now form a series of north trending fjords in the north of the study area. This overprinted landscape is found to propagate inland forming a channelized system, leading way to linear erosion. The modern icecap resides in GTZ 3, which inherited the broad northeast flowset, but is overprinted in valleys by eastern flows funneling into the fjords to the east, as well as western flows flowing from the modern icecap. In the central area, there is a rolling terrain of thicker till (GTZ 4) that is distinguished by its lack of subglacial features. The final contrasting landscape (GTZ 5) is characterized by southeast trending bedrock features (most likely enhanced by southeast flowing ice) and associated perpendicular moraines. GTZ 5 is also characterized by highly weathered bedrock, and locally by landform assemblages recording late deglacial readvances of thin lobes including moraines and striated outcrops. Geochemical studies for each of these landscapes lead to additional insights, characterizing the five zones further. The geochemical studies took advantage of two till sample databases taken over the study area for exploration purposes by Peregrine Diamonds LTD. The chemical index of alteration (CIA) was applied to compare erosion in the different zones. High CIA values indicate high weathering, where low CIA values low weathering. GTZ 1 is characterized by low CIA values (low weathering footprint), and GTZ 5 is characterized by high CIA value (highly weathered). To study if the GTZs had a distinct geochemical signature, as well as a signature landscape, multivariate geochemical statistics (Principal Component Analysis and Linear Discriminant Analysis) were done over the study area. Interestingly, it was found that the GTZs have geochemical signatures, which reflect the role of underlying bedrock, weathering patterns, glacial dispersal, and the complex relationships between subglacial dynamics and landscape evolution. To determine if the GTZs could be predicted by the till geochemistry, linear discriminant analysis was subsequently applied. The results indicate that the till geochemical data has a predictive capacity with an accuracy of 83.78%, which brings insight into the relationship between glacial landscapes and till composition. With this multi-proxy approach and building from previous studies, a conceptual model was developed for the study area. During the Last Glacial Maximum (LGM), the study area was inundated by the Laurentide Ice Sheet (LIS), with the Hall Ice Divide parallel to the axis of the peninsula with ice flowing from the divide to the northeast and southwest. As ice thinned, GTZ 1, an area once inundated with warm-based ice, as shown by evidence of areal scour and low CIA values, switched to being cold-based ice preserving an older landscape. Though GTZ 1 was under cold-based ice, warm-based conditions still prevailed within the channelized flow zones, which characterize GTZ 2. Evidence of this is found in the striation record, as well as the low CIA value indicative of low weathering (or high erosion). This may reflect a transition from LGM (thick-based ice) to thinner, topographically controlled ice, with cold-based ice in interfluves and hilltops, during early deglaciation. The catchment zones of the channelized system locally extend near the central area (GTZ 4) which is reflected in dispersal patterns and the striation record. As the LIS retreated, it went through a series of southeastward readvances and surges (GTZ 5). Though the ice was warm-based near the moraines in GTZ 5, prevailing cold-based conditions prevailed during most of the last glacial cycle, and the late deglacial readvances had limited erosion capacity and did not overprint the cold-based landscape significantly. This is shown by the CIA values indicative of high weathering, and lack of subglacial landforms. Series of pro-glacial lakes also formed in front of the retreating lobe. Ice is needed over GTZ 1 to prevent these lakes from draining northward. This thin ice was most likely cold-based, preserving the older GTZ 1 landscape of areal scouring. The glacial landscape of Hall Peninsula appears to record a switch from uniform warm-based LGM ice, which was laterally extensive, to localized channel flows in the fjords during deglaciation and intervening cold-based ice. The change in the geometry and basal thermo-mechanical conditions may be the prologue to the separation of the modern day ice cap from the LIS.

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