Reiseblogg fra den arktiske sommeren: geologisk feltarbeid på Østgrønland
Denne sommeren reiste et team med strukturgeologer og sedimentologer fra UiB og UiT - Norges Arktiske Universitet over Nord-Atlanteren for å besøke Wollaston Forland på Nordøst-Grønland. Grunnen? For å studere den strukturelle, avsetningsmessige og diagenetiske historien til et rift-basseng med dypvannsavsetninger fra juratiden.
In the heat of the Arctic summer – geological travel blog from East Greenland
Text and photos: Sten-Andreas Grundvåg (UiT), with contributions from Dr. Eric Salomon, Dr. Gijs Henstra, Dr. Thomas Berg Kristensen, and Prof. Atle Rotevatn (all UiB)
Greenland. Close your eyes and think of it for a moment. Anticipation. Breathe in the cold Arctic air and listen to the howling wind as it whispers into your ears. The call of the wild. To most people Greenland is associated with glaciers and icebergs, deep fiords, muskox and polar bears. For a good reason. The majority of Greenland is covered all-year-round by a vast ice shield, up to several thousand meters thick, and the island hosts the World’s largest national park. However, most of the coastlines are practically devoid of ice and snow during the two-three months of Arctic summer. To geologists, the short and intense Arctic summer is a blessing. That is at least how it should be in theory.
Looking out the window from our Twin Otter propeller plane revealed a different story. Despite being early August, the past weeks of heat in Europe had translated to a cold summer in East Greenland: sea ice still covered the fiords, and many mountains and valleys were peacefully hiding under a white coat. ‘Will we be able to land in Lindeman Fiord?’ Just one of the many questions I asked to myself while looking out the window in despair. Since we had left Reykjavik in Iceland some days earlier, we had been stuck at the airstrip at Constable Point (CNP) waiting on better flight conditions up north. Ironically, the sun was shining at CNP, transforming the runway in to a dusty desert-like habitat full of thriving mosquitos. What a great feeling to finally be on our way. Northbound. To our surprise and great luck, the amount of snow and the extent of the sea ice cover far below us, slowly diminished as the small aircraft proceeded northward. Of less fortune was the increasing amount of fog protruding from the ocean into the narrow fiords. Thus, instead of Lindeman Fiord, the pilots chose a much safer alternative and left us at the Danish research station in Zackenberg, 20–30 km south of our planned final destination. More waiting and waste of valuable field days ahead. Despite the Danes treating us friendly and feeding us superb supper every night, we struggled to settle in. One day we found some pieces of outcrop some 10 swampy kilometers north of the station. The effect of the discovery was just as our commander (read. Prof. Rotevatn) had hoped. After nearly a week on hold, the team was on the edge, but eventually doing something intellectually satisfying together increased the moral. Not only did the crumbly rocks strengthen our desire to get to Lindeman Fiord, but it also extinguished a rising mutiny (with four team members planning an escape from Zackenberg with a pulkka mounted on a sea-ice raft). The next day we got what we hoped for: sun, no fog, and a Twin Otter with the finest Icelandic pilots there is. After one quick flyby and some hardcore action movie-style landing maneuvers, we were safely on the ground on the “runway” in Lindeman Fiord, Wollaston Forland. To call this 100 m long and 40 m wide gravel terrace a runway is an exaggeration at best (all honor to the skilled and brave pilots). Nonetheless, this terrace would serve as our home the next week or so. Establishing a basecamp for five persons always takes some time. First tents, then a lavvo, all secured with rocks, and finally a trip wire fence armed with pyro to alert us in case of visitors in the shape of white fury beasts. For some reasons unknown, the fence tended to attract more professors than polar bears.
What is great about doing fieldwork in the high Arctic, with Wollaston Forland being no exception, is the unevenly distributed and sparse vegetation cover. Thus, when the snow melts, a fascinating landscape reveals itself. Alpine mountain peaks and nunataks, glacial valleys, and coastal cliffs, all full of excellently exposed rocks. In our study area in Lindeman Fiord, both Caledonian metamorphic basement rocks, as well as younger sedimentary rocks of predominantly Mesozoic age are present. What is unique with the study area is the Dombjerg Fault, a border fault that juxtaposes syn-rift deep-water hanging-wall clastics against a footwall of crystalline basement (Henstra et al., 2016; Kristensen et al., 2016; see ARCEx archive to download these papers). The fault belongs to a series of east-stepping faults that together define the western boundary of the East Greenland Fault system (Rotevatn et al., 2018). The exposed basin fill succession is also unique in that sense that it represent exhumed deep-marine gravity flow deposits, which accumulated during rifting and possibly rift climax (Henstra et al., 2016). Similar deposits form important reservoirs in several basins along the western margin of the Norwegian Continental Shelf. The aim of the trip was therefore two-fold: one group were to focus on the structural geology and structural diagenesis associated with the Dombjerg Fault, and the second to focus on the sedimentology and diagenesis of the syn-rift strata of the so-called Wollaston Forland Group. Because we also visited the same area back in 2014 during a more regional-scale study, we had pre-designed a detailed plan for which outcrops to visit and what specific sections to focus on. In regards to our late arrival as narrated above, this plan increased the effectiveness of the days we actually spent in the field.
For example, the structural group managed to sample several tens of veins along the Dombjerg Fault itself, and documented the structural fabric within the basin clastics at selected outcrops in a proximal to distal transect normal to the fault. We hope that these samples may reveal the diagenetic history of the fault and basin and tell us what type of fluids that once used the fault and its associated fracture systems as their fairways. For the sedimentology part, the focus this time was to detail the architecture of the syn-rift gravity flow deposits at sub-seismic-scale resolution. In addition to sedimentary logs and rock samples for petrographic analyses, we also collected numerous photos, drone footage and videos so that we can make digital 3D models of our main outcrops. This means that we will be able to enjoy the outcrops in Wollaston Forland from our comfortable office chairs in the years to come. For a small teaser of one of our preliminary models (low resolution), have a look at this video made by Gijs Henstra: https://drive.google.com/file/d/1bh1vHOv9D40mRIF7I4awi5mW3U7AEGxY/view
PS! Just to let you know: we got safely back to Norway after ten fantastic days in the field. So look out for upcoming publications at www.arcex.no and other forums.
Henstra, G., Grundvåg, S.-A., Johannessen, E.P., Kristensen, T., Midtkandal, I., Nystuen, J.-P., Rotevatn, A., Surlyk, F., Sæther, T. & Windelstad, J. (2016): Depositional processes and stratigraphic architecture within a coarse-grained rift-margin turbidite system: the Wollaston Forland Group, East Greenland. Marine and Petroleum Geology, Volume 76, September 2016, Pages 187–209. [http://dx.doi.org/10.1016/j.marpetgeo.2016.05.018] [intranet]
Kristensen, T.B., Rotevatn, A., Peacock, D.C.P., Henstra, G.A., Midtkandal, I. and Grundvåg, S.-A. (2016): Structure and flow properties of syn-rift border faults: the interplay between fault damage and fault-related chemical alteration (Dombjerg Fault, Wollaston Forland, NE Greenland). Journal of Structural Geology, Volume 92, November 2016, Pages 99-115. DOI: 10.1016/j.jsg.2016.09.012[intranet]
Rotevatn, A., Kristensen, T.B., Ksienzyk, A., Wemmer, K., Henstra, G.A., Midtkandal, I., Grundvåg, S.-A. & Andresen, A. (2018) Structural inheritance and rapid rift-length establishment in a multiphase rift: the East Greenland rift system and its Caledonian orogenic ancestry. Tectonics, 2018, Vol.37(6), p.1858-1875. DOI: 10.1029/2018TC005018 [intranet]