61st Annual Report on Research 2016

The first major activity for this study was to hire two undergraduate research students (Dan Conrad and Chad Arnhold). The students spent ~10 hrs/week working on the project during the academic year. Their first major task was to improve their ArcGIS skills, learn how to integrate Matlab and ArcGIS to run stream profile analysis, perfect their knickpoint selection process, and integrate that work with Google Earth to check the chosen knickpoints against the geomorphology of the study site. Once confident in their abilities to run the software and select knickpoints effectively and efficiently, the students processed all the major drainage networks across southwestern Norway. These data provided them with two opportunities in preparation for summer fieldwork: (1) Each individual knickpoint was categorized as glacial or non-glacial using Google Earth high-resolution imagery along with ArcGIS and Matlab. These data were then compiled and compared, and twelve of the most interesting knickpoints were selected for detailed fieldwork. (2) The Matlab output data (stream profiles, channel steepness, and knickpoints data) were analyzed in detail, comparing "glacial" versus "non-glacial" knickpoints in order to test whether such identification is possible without the need for imagery. This second task is ongoing. Additionally, the students spent significant time analyzing Matlab code in order to run chi-plot fluvial analysis for the region and compare that method with the channel steepness method. Dan and Chad presented their work at two Geological Society of America regional conferences.

The second major activity performed for this study was to prepare and implement 3 weeks of fieldwork in July/August of 2016. Fieldwork was coordinated with collaborator Tim Redfield of the Norwegian Geological Survey (NGU) who accompanied me and the two undergraduate students for the duration of the fieldwork. Tim Redfield, who has lived in Norway for >15 years and has studied similar problems during his time there, provided us with a thorough understanding of regional context and previous work completed (including insider knowledge into failed projects and unsuccessful work). The field season had two major focuses: (1) understanding the processing driving the formation of the selected knickpoints, especially processes indicating Cenozoic differential uplift along faults, and (2) add to existing thermochronology work by sampling for (U-Th)/He apatite thermochronology across known faults and at a specific elevation across the region. The first goal was carried out by detailed exploration of each selected knickpoint in the field and geomorphic mapping each locale, paying special attention to glacial versus fluvial process signatures in the landscape. Several distinctly different types of knickpoints were identified during fieldwork. Several of the knickpoints were identified as caused by processes not believed to be related to the current work (large volume landsliding / transient migration into a high-elevation paleosurface) and no further work is planned regarding those knickpoints at the current time. The remaining knickpoints consist of two types: (1) 3 knickpoints mark a dramatic transition from relatively undisturbed glacial landscape to deeply incised gorges indicative of fast fluvial incision, and (2) a forth knickpoint coincides with a newly mapped fault trace. The first type can all be found in the footwall of strands of the Møre Trøndelag fault complex (MTFC) where the drainages defined by the knickpoints are distinctly different from drainages located in the hanging wall. Detrital samples were collected from drainages on both sides of the MTFC for catchment-averaged cosmogenic erosion rates to compare rates of process across the fault (total of 9 samples). Additionally, bedrock samples were taken on either side of one of knickpoints for (U-Th)/He thermochronology. At the knickpoint that coincides with a previously unmapped normal fault, fault gouge samples were taken from the fault zone for SEM analysis and rock samples were taken from the footwall and hanging wall of the fault for comparative (U-Th)/He thermochronology across the structure. To address the second goal of the fieldwork we first collected 12 samples at the same elevation across the region (400 m above sea level) to add to previous studies of apatite fission track dates collected at 0 m and 1000 m elevation. Secondly, a suite of 15 bedrock samples were collected across the Laerdal Gjende fault system and the Nord Fjord Sogn detachment zone which will be used to examine differential exhumation across the structures.

The third major activity is ongoing sample processing. The two students who completed fieldwork on the project have both graduated, so I have hired two new undergraduate students who are tackling this step. Both students (Jenna Abrahamson and Elliott Allen) have been trained in thin-section chip cutting, rock crushing, wet sieving, magnetic separation on a Frantz, density separation using lithium polytungstate and methylene iodide, and hand-picking individual mineral grains (apatite and zircon). Jenna Abrahamson is focusing primarily on processing the detrital samples and four of those samples have been fully processed and sent to the PRIME lab at Purdue University for 10Be and 26Al cosmogenic analysis. The other five detrital samples are being processed currently. Elliott Allen is the primary undergraduate student focusing on the paired samples taken across the Laerdal Gjende and Nord Fjord Sogn fault systems. Five of the eight highest priority samples have been processed up to hand-picking under the microscope, with the other three nearly ready. I expect selected apatite grains to be sent to Arizona State University for (U-Th)/He analysis by the end of October 2016.