Lab Work: Core logs and Magnetic Susceptibility

As I wrote in my last post, when we returned from field work, I had many cores to process before selecting the cores that I am focusing on for my thesis. Each core we collected in the field had to be split, and we selected one half as a “working half” to be sampled and the other as an “archive” which will be stored for future reference. After splitting each core, I completed a core log, describing the visual properties of the sediment in addition to the length of each core section. This first step, describing changes with depth in the core, is used as a reference for sampling and identifying different units (sections of the core with similar sedimentation history) within the core.

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Field Work: Coring Lakes in Lofoten, Norway

In northern Norway, general trends of sea level lowering throughout the Holocene have been developed, with sea level in this area lowering ~10m over the past 6000 years. However, the details of this lowering are poorly constrained during the late Holocene (the past ~5000 years) (Møller, 1986). For my senior research project, I am studying sediment records from isolation basins (coastal lakes characterized by their past connection to and isolation from the sea due to relative sea level changes) in Lofoten, Norway. Using these sediment cores, I hope to better constrain the rate and magnitude of sea level lowering during the late Holocene in Norway and to understand how these changes may have affected human activity (think: Vikings) in Lofoten.

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Unfinished business

The research I have done this summer has provided the foundation for continuing into senior year. In the Geology department here at William & Mary, every senior has to complete research and write a thesis in order to graduate. I have been fortunate enough to begin this over summer and complete a great deal of preliminary research before the school year gets started. I’ve collected and reviewed many articles pertaining to my thesis and have been able to pare down superfluous information in order to concentrate on what is essential. I’ve also created multiple visuals for my research, including a geologic map, a topographic map, cross sections, a schematic of how the ophiolite and metamorphic sole were created, and a stage-by-stage walkthrough of the obduction process (see below).

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Metamorphic clues

I’ve been identifying minerals and structures within the thin sections I received last month and using them to draw conclusions on the kinds of deformation the area has undergone. The mineral assemblages in the rocks can help identify different kinds of metamorphic environments and therefore give us an idea of the scale and extent of deformation that occurred.

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Through the Looking Glass

The past month has been focused on looking at my returned thin sections under the petrographic microscope. This microscope was developed for use in optical mineralogy and is integral in identifying microstructures and the mineralogy of rock samples. There are two primary views with the petrographic microscope: plane polarized light and cross-polarized light. Plane polarized light (PPL) is when the light shining through the microscope is polarized, meaning it vibrates in a single plane. A PPL image would look something like this:

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