Tracking the Triassic – A summary of the Longyearbyen CO2 Lab field-season
Text and photo: Ingrid Anell, Postdoc UNIS
Standing just outside Longyearbyen in Adventdalen we know that somewhere deep beneath our feet we have a Triassic reservoir that we hope to use for injection of CO2 for long-term storage. The Mesozoic rocks are deeply buried beneath thick Mesozoic and Tertiary basins and in order to fully understand the reservoir and cap-rock we head across the mountains to the north to study fractures, and far to the east to remote Triassic outcrops.
Photo 1 Geologists look out on the sealing shales of the Aghardfjellet Fm halvway up Janusfjellet
To the North of Adventdalen, at Deltaneset, both the cabin and the Triassic outcrops dip. The result is acrobatic sleep positions and long winding beaches revealing progressively younger and younger rocks. The location is well studied from previous years but being on site once again gave the geologists from UNIS and UiB/UNI CIPR the chance to expand the dense scan-line network and delve deeper (and higher) into the cap-rock above. The cap-rock, of late Jurassic age, is a thick dark shale (Photo 1). While paleontologists scour this rock for remains of giant marine Plesiosaurs our group is more interested in its ability to provide a tight seal.
Photo 2. The sun sets on the fantastic Triassic cliff exposures of Kvalpynten on the southwest coast of Edgeøya
Seven geologists from UNIS, UiB and the University of Nebraska at Omaha, went for eight full days of fieldwork onshore Edgeøya (Fig. 2). Edgeøya is known for its polar-bear density and its magnificent Mesozoic outcrops. Luckily for us the latter was far more prominent. Working on the steep cliffs of Kvalpynten the geologists logged perilous sections and performed detailed studies of the unique growth faults exposed along the beach (Fig. 3).
Photo 3. Section of Kvalpynten showing 2 major growth-faults
These faults, first described by Edwards (1976), are found in the Tschermakfjellet and DeGeerdal Formations, in pro-delta and delta deposits. Their origin has been ascribed to a combination of denser sands on less dense clays with excess pore-fluids, a southward slope or paleoslope, differential loading or a tectonic trigger (earthquake) (Edwards, 1976). The factors contributing to their formation are of key importance to understanding the Mesozoic development of the region. In addition to conducting detailed studies of the onshore exposures we also aim to compare them to the offshore seismic data. The hope is to be able to resolve similar features in the offshore data and provide definitive answers on links to deeper processes. Studying the onshore exposures also provides a link to understanding the offshore development as part of a regional mapping of the Mesozoic to tie back to the Lonyearbyen injection site.
The trip also allowed new PhD student Berit Husteli, working on the GeC project, to begin data-collection for her studies by detailing lateral variations in tidal delta deposits. The Kvalpynten cliffs provide excellent exposures of tidal dominated deltaic deposits reveal sedimentological features over several parasequences and display beautiful examples of sand-wave migration, large and small-scale herringbone cross stratification, scours and small channels, rip-up clasts and rejuventation surfaces, varying crossbedding and planar parallel deposits and variations in lithology (Fig. 4-5). The analysis will further refine the reservoir model and constrain parameters for understanding CO2 migration through the Longyearbyen reservoir.