Graduate Thesis Or Dissertation

 

Deciphering Quaternary Geomagnetic, Glacial, and Depositional Histories Using Paleomagnetism in Tandem with Other Chronostratigraphic and Sedimentological Approaches Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/p5547x40v

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  • Stratigraphy and chronology are essential to sedimentological study of Earth system histories. And, stratigraphy and chronology are often challenging and interesting problems themselves. The Quaternary (2.588 Ma - present) experienced paleoenvironmental and paleo-geomagnetic variability well outside the range of the recent instrumental record, providing the opportunity to place recent observations in a more complete perspective. This dissertation presents three studies that combine paleomagnetism in concert with radiocarbon, stratigraphic correlation, and/or age-depth modeling to develop stratigraphy and assign chronology. This in turn, helps to better understand the evolution of these glacial, geomagnetic, and depositional systems. The first study investigates the glacial history of the Petermann Glacier, a major outlet glacier of the Greenland Ice Sheet, over the last ~7 ka. Petermann Glacier has been remarkably stable for as long as there have been historical observations apart from two anomalously large calving events of its floating ice tongue over the last decade. This is unique when compared with many other large marine terminating Greenland outlet glaciers. Yet, our geologic evidence clearly show the Petermann Ice Tongue was not present for much of the time recorded in the sediments of Petermann Fjord. While radiocarbon and paleomagnetic methods could not constrain the sediment’s chronology alone, due to large reservoir issues and uncertain regional paleomagnetic templates, using the two methods in tandem we determine the paleoenvironmental conditions that were required to maintain the stable ice tongue of the Late Holocene. Specifically, a stable ice tongue only formed around 2-2.5 ka after sea ice conditions intensified, limiting Ekman transport of warm modified Atlantic Waters into the fjord, and surface air temperatures were within ~2o C of preindustrial conditions, slowing the subglacial run-off driven circulation of the fjord. The second study investigates the geomagnetic history of Western North America from ~35-15 ka. While the Holocene has been the focus of most studies about past directional changes of the geomagnetic field, the Late Pleistocene spans a greater range of field intensity variations that have a largely unknown relationship with field morphology. Yet, late Pleistocene sediments that could be used to investigate these questions, particularly from terrestrial archives of Western North America, are notoriously difficult to date. This makes comparison of millennial scale directional variations, like other studies have done for the Holocene, difficult. Using new data from Fish Lake, Utah and existing data from Bessette Creek, British Columbia, and Bear Lake on the Utah and Idaho Border, we construct a composite stacked record to define these variations and we account for radiocarbon and magnetic uncertainties in the stack’s chronology. We demonstrate that this PSV template can provide new insight to longstanding chronostratigraphic debates, such as the implications of various proposed chronologies of the sediments in the Wilson Creek Formation at Mono Lake, California on the outcrop’s chronostratigraphy and radiometric age estimates. The third study investigates the depositional history of the Bengal Fan over the last ~1.25 Ma. Regionally extensive hemipelagic deposits with good reversal magnetostratigraphy offer constraints on the evolution of the fan’s channel levee system through climate and sea-level transitions of the Pleistocene. Yet, it has been challenging to assign ages to the turbiditic sediments of the fan due to the absence of reliable chronostratigraphic markers. To address this issue, we model sediment accumulation rates at seven drill sites, incorporating all available age control points and integrating seismic observations to establish the stratigraphic relationships of paleo-channel-levee systems. The model results are stacked to create a composite regional signal for the Lower Bengal Fan, which, in the additional context of other regional archives, suggests growth of the spatial extent of the Bengal Fan channel-levee system along with increases in glacial-interglacial sea level amplitude.
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  • Ongoing Research
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  • 2018-06-15 to 2020-03-13

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