Michelle Fame
Research Interests
I am interested in how interactions between climate, surface processes, and tectonics act to shape landscapes over million-year, thousand-year, and modern timescales.
The research questions motivating both my past and ongoing work are largely focused on long (Ma) & Quaternary glacial-interglacial (ka) timescale landscape disequilibrium along present day passive margins and tectonically quiescent continental interiors. This work is important because (1) we can make sense of the timescales and mechanisms of future climate driven landscape change by looking to the past, (2) large areas of the world are tectonically inactive, and (3) it allows for isolated consideration of landscape response to climatic variables by removing significant tectonic uplift from the equation. Coupled with remote sensing and field observations to characterize landscapes, I quantify the timing and rates of erosion and burial averaged over the 1-100 million-year timescale using (U-Th)/He apatite and zircon thermochronology and averaged over the 10-100 thousand-year timescale using cosmogenic radionuclide (CRN), radiocarbon, and optically stimulated luminescence (OSL) dating.
Photo: Sampling a periglacial (?)boulder field near Spruce Knob, West Virginia
As the climate warms, post-glacial river systems prone to geomorphic change will become increasingly common. However, gaps in our understanding of sediment routing and floodplain morphology changes in river systems at climatic transitions remain. This project aims to increase our ability to predict whether a river system will maintain or significantly change its present morphology under a specific set of climatic changes. Quaternary aggradational and degradational river terrace successions are intermittent records of major transformations in floodplain and channel morphology as they shift between wider aggradational and narrower vertically incising endmember systems. We are undertaking an investigation into the timing, evolution and sediment routing dynamics of late Quaternary river terrace sequences in eastern Scotland as they relate to climatic shifts and glaciations of a variety of magnitudes to help fill gaps in knowledge related to river geomorphic and sedimentological responses to climate change. Eastern Scotland is an ideal location to undertake this work because it is relatively tectonically inactive, has an excellent climate chronology, has undergone both continental ice sheet and ice cap/alpine glaciation in the late Quaternary, and it contains well documented river terrace successions in our field areas of Glen Feshie, Glen Dee, and North Esk/ Westwater.
Video made by Bowdoin College undergraduate student Nora Jackson as the culmination of her summer 2020 remote research fellowship during the COVID-19 pandemic which involved identifying and mapping field sites for this project using ArcGIS.
River Feshie at the Garbhlach confluence showing at least 4 terrace levels with exposed glaciofluvial sands and gravels (Photo credit: Richard Webb, geograph.org.uk/more.php?id=5466107).
Timescales and drivers of floodplain disequilibrium at climatic transitions
What can Zircon Helium (ZHe) Thermochronology tell us about the spatial and temporal patterns of orogenic burial and erosion across the Central Appalachian Mountains?
For his undergraduate thesis at Bowdoin College I (along with Dr. Jacky Baughman, now at Humboldt State University) co-advised senior Luke Basler in measuring and interpreting ZHe thermochronology ages (closure temperature of 140- 200ï‚°C) taken from a cross-strike transect from the Appalachian foreland of West Virginia towards the Appalachian hinterland in eastern Virginia (across the Appalachian Plateau, Valley and Ridge, Blue Ridge and Piedmont provinces). A general trend of younging ZHe ages moving from the Paleozoic foreland to the hinterland constrain (1) maximum burial temperatures of Paleozoic sedimentary rocks in the Appalachian Plateau to <160ï‚°C, (2) the onset of rapid exhumation in the Valley and Ridge and western Blue Ridge to prior to 270 Ma, and (3) post-Triassic rift-related exhumation as the dominant cooling and exhumation signal in the Piedmont (Basler et al., 2021).
Photo: Bowdoin undergraduate student Luke Basler sampling for Zircon Helium dating in the Virginia Valley and Ridge Province
Holocene Glaciation in the Brooks Range, Alaska
Previous studies from the Central Brooks Range in Arctic Alaska, the ancestral homeland of the Gwich’in people, have found that Holocene maximum glacial extents were reached by 3.5 ka and 2.6 ka, prior to the Little Ice Age (1300-1850) when glaciers reached their Holocene maximum in the rest of Alaska (Pendleton et al., 2017; Calkin, 1988). If Holocene glacial extents reached their maximum in the Brooks Range prior to the Little Ice Age it would mean that local climatic conditions allowed for cooler temperatures and/or increased precipitation leading to greater ice cover earlier than in the rest of Alaska. This would shed light on important climate – glacial feedbacks in the Alaskan Arctic. In the summer of 2021, we collected a suite of 13 Holocene moraine samples in the Northeastern Brooks Range and will obtain10Be exposure ages of on a subset of those samples to determine the timing of Holocene glacial maximum. As part of her senior thesis at Bowdoin College Cameron MacKenzie will also be reconstructing the Equilibrium Line Altitude for those Holocene Glaciers to determine what degree of climatic change would be necessary to drive the observed advances.
Photo: Bowdoin undergraduate student Cameron MacKenzie sampling Holocene moraines for cosmogenic dating in the Brooks Range in the the Summer of 2021
Large boulder fields and talus slopes are ubiquitous features and likely an important means of eroding ridges comprised of resistant bedrock in the southern Appalachians. Constraining the timing of formation of these features has implications for understanding the longevity and demise of topography in ancient mountain ranges. Preliminary 10Be cosmogenic exposure ages, collected in collaboration with an undergraduate researcher at Virginia Tech, coincident with the last glacial maximum suggest that periglacial (near but outside the limits of glaciation) freeze-thaw conditions were responsible for triggering the formation of a large quartzite rock fall near Lexington, Virginia (Caton, 2017 unpublished undergraduate thesis). This suggests that intense periglacial processes affecting the southern Appalachians, far south of the glacial boundary, have important geomorphic consequences. Using new LiDAR data from southwestern Virginia (e.g., Prince, 2019), field studies, and cosmogenic dating I propose to develop a more thorough research program investigating the timing, cause, and overall geomorphic impact of the many large rock falls scattered throughout the southern Appalachians and, possibly, their connection to periglacial processes.
Above: Drone imagery of Devils Marbleyard
Timing, cause, and geomorphic impact of large (periglacial?) rock falls in the southern Appalachians
Photo: Collecting cosmogenic samples from Devil's Marbleyard, VA
In my dissertation research at Virginia Tech, under the advisement of Dr. James Spotila and in collaboration with Dr. Lewis Owen (now at NC State University), I investigated the degree to which Cenozoic changes in erosion rates, sediment budgets, and topography resulted from Quaternary glaciations versus plate boundary distal tectonic drivers in the White Mountains of New Hampshire and the Nothwest Scottish Highlands.
The main findings of the research includes:
1) Heterogeneous burial and exhumation, resulting from plate margin distal vertical crustal motions, impacted post-orogenic topographic evolution along the North Atlantic Passive Margin
(2) Cold-based and polythermal ice sheets frozen to the underlying landscape limited Quaternary glaciation’s ability to expedite passive margin erosion in some places
(3) Post-glacial sediment budgets continue to be dominated by glaciogenic sediment, >10 ka after deglaciation (Fame et al., 2019, 2018a, 2018b).
Photo: Sampling for thermochron at Mt. Washington, NH
Photo: Glacially carved ridge and cirque near Glen Nevis, NW Scotland.
Photo: Hummocky Morianes, Loch Laggan, NW Scotland around a creek