Reports: UNI855156-UNI8: Cenozoic Evolution of the Southwestern Norwegian Passive Margin

Jeni A. McDermott, PhD, University of St Thomas

The first major activity for the study this year was to prepare the two student researchers (Jenna Abrahamson and Elliott Allen) for their individual responsibilities within the overarching project. Jenna Abrahamson is focusing primarily on the Surnadalen region where we see dramatic asymmetry across the main valley and high vertical fluvial incision rates in the mountains on the southern side. To better understand the causes for such incision, Jenna processed detrital samples (8 total) and sent them for 10Be and 26Al cosmogenic analysis at the PRIME lab at Purdue University. Jenna also gathered geologic and structural data for the region and generated several balanced cross-sections across the valley. Jenna merged geomorphic data collected during the 2016 fieldwork along with high resolution imagery available with ArcGIS and Google Earth to create detailed geomorphic maps of the entire Surndalen region. Finally, she learned how to process river profiles using both the 'profiler' method, which integrates ArcGIS and Matlab to analyze longitudinal profiles in slope-area space, and the chi-plot method, which uses only Matlab to analyze slightly different parameters of the fluvial systems. Elliott's work focused on the paired samples taken across the Laerdal Gjende and Nord Fjord Sogn fault systems. His time was spent processing rock samples taken during the 2016 fieldwork, and individually selecting appropriate apatite grains for (U-Th)/He analysis. Three samples were sent for final analysis to Arizona State University; the samples were collected across a fault, and although the error is large, there does not appear to be a cooling age discontinuity across the structure. Elliott also began investigating stream capture and river reorganization in Norway. To do this, he completed a literature search, and spent significant time Jenna and Elliott presented their work at the University of St Thomas student research symposium. The second major activity performed for this study was to prepare and implement 2 weeks of fieldwork in June/July of 2017. 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 >25 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) Revisit the Surnadalen region to collect more detailed incision data using a laser range finder and investigate possible evidence for drainage basin reorganization, (2) Explore several other drainage basins for geomorphic evidence for reorganization/river capture and collect samples to constrain the timing of such events. During fieldwork, the team revisited the Surna valley, carefully resurveying the incision with a laser range finder in the Folda valley. Although the Vindola valley was also revisited, poor weather conditions (rain and lack of visibility) prevented use of the laser range finder. In lieu of this tool, 1 m DEMs were obtained through Tim Redfield's account and incision was calculated in that way. Additionally, several new drainages in the Surna region were explored, and fluvial incision was found in the Bolu, Rinda, Tiaa, and Orkla drainages. Detailed goemoprhic mapping of the incision sites, augmented with the laser range finder when possible, were completed. After several days spent in the Surna valley, we continued on to examine the Sunndal, Rauma, and Driva drainages for evidence for drainage reorganization. Several tasks were completed along these drainages and their tributaries: (a) detailed geomorphic mapping to identify barbed drainages, underfit streams, wind gaps, and low-relief divides; (b) sedimentological analysis of deposits found in cut banks and sand quarries; (c) bedrock sampling of strath terraces for cosmogenic surface dating when strath terraces were present; (d) rock sampling from the base and top of high relief valleys for 4He/3He dating. The third major activity, which is ongoing, is sample and data processing. This consists of several parts: ongoing preparation of low-temperature thermochronologic samples, processing of cosmogenic surface samples from strath terraces, augmenting and writing code to extract drainage area and longitudinal distance along a stream for use in identifying river capture locations, sedimentological analysis of sediment cross-sections mapped in the field and interpretation for comparison to drainage reorganization, detailed calculations of incision using laser range finder data and 1 DEMs, and detailed analysis of river longitudinal profiles, now that known incision has been documented in the field, to determine what parameters are best for indicating such incision. The final major activity is the presentation of the work at the Geological Society of America's national meeting in Seattle in late October and the writing up of the work for submission to GSA Bulletin. Three abstracts were submitted to the GSA meeting: my abstract was awarded an oral presentation while Jenna and Elliott will each be presenting individual posters in the undergraduate student research session. Manuscript writing is ongoing, with a goal of submission by December, 2017.