High resolution digital outcrop model of faults and fractures in caprock shales, Konusdalen West, central Spitsbergen
Authors: Betlem Peter , Birchall Thomas , Lord Gareth , Oldfield Simon , Nakken Lise , Ogata Kei , Senger Kim 
Published: August 2022

Abstract. Structure-from-motion (SfM) photogrammetry has become an important tool for quantitative characterisation of outcrops. Digital outcrop models (DOMs) allow for the mapping of stratigraphy and discontinuous structures like folds, faults and fractures from cm to km scale and provide solutions that are difficult to constrain through subsurface data alone. With pristine, treeless exposures, the outcropping strata in Svalbard, Arctic Norway, hold exceptional potential for analogue studies and are ideally suited for the acquisition of high-resolution DOMs. We here present the acquisition, processing and integration of the Konusdalen West digital model data set, comprising both DOM and derived digital terrain model (DTM) data. Dronebased image acquisition took place over two weeks in July and August 2020. Fifteen differential GNSS control points were used to georeference and quality assure the model, five of which functioning as reference checkpoints. SfM processing of 5512 acquired images resulted in high-confidence, cm-scale resolution point clouds, textured mesh (DOM), tiled model, orthomosaics, and a DTM. The confidence-filtered dense cloud features a median inter-point distance of 1.57 cm and has an average point density of 3824.9 points m-2. For the five checkpoints, the dense cloud features root mean square errors of 2.0 cm in X, 1.3 cm in Y, 5.2 cm in Z, and 5.7 cm in XYZ. Drops in point confidence and point density are mainly found in areas with reduced image densities, and on the backside of boulders. Increased confidences and densities are present along the western flank of the Konusdalen West outcrop, where a fault-fracture network in mudstone-dominated stata is best exposed and photographed most extensively. The Konusdalen West DOM and DTM cover a 0.12 km2 area and span a 170 m elevation difference. The mean of the altitude of the checkpoints versus elevation of the dense cloud-derived DTM differed by less than a cm. The dense cloud-derived DTM closely matches an existing lower-resolution reference DTM of the area. The DOM covers the upper two-third of the mudstonedominated Late Jurassic-Early Cretaceous Agardhfjellet Formation. The Agardhfjellet Formation and its time-equivalents are regional cap rocks for CO2 sequestration and petroleum accumulations both on the offshore Barents Shelf and onshore Svalbard. Faults, formation members and established marker beds can be traced in the high-resolution model and have been used for the stratigraphic integration. Additional structural measurements and observations were taken in June 2021 to place the data in the geological context. Top and side-view orthomosaics feature maximum resolutions of 8 mm per pixel, enabling the mapping of fractures and other sub-cm features. The Konusdalen West digital model data set, together with the extensive drill cores through the same section near Longyearbyen, forms an ideal starting point for the generation of high-resolution, outcrop-truthed geomodels that are suitable for numerical modelling of fluid flow and appraisal of the regionally important caprock. Data described in this manuscript can be accessed at Norstore under https://doi.org/10.11582/2022.00027 (Betlem, 2022b).