Regional Steep Fracture Patterns throughout the Triassic De Geerdalen Formation of Svalbard

Gareth Lord

Following extensive periods of field data collection throughout Svalbard, a regional dataset of fracture orientations and types that are seen within the Triassic De Geerdalen Formation has been established. Analysis of this dataset has determined that regional fracture orientations are relatively uniform throughout central Spitsbergen to western Edgeøya, with subtle overprinting being observed on the island of Hopen in south-eastern Svalbard. Due to this uniform pattern of fracture orientations throughout the region, it has been determined that conjugate shear fracture sets they are primarily controlled by compressional stresses related to the formation of the Western Spitsbergen Fold and Thrust Belt. Whilst irregular or more vertical extensional fracture sets, are most probably formed as a component of regional uplift. Throughout central Spitsbergen, local folding, thrusting and the presence of Cretaceous dolerite intrusions have also been considered as potential causes for fracturing, within the Triassic succession to the east of the Central Tertiary Basin. Throughout eastern Spitsbergen and the west coast of Edgeøya, dolerite intrusions are also present; however these are more distant from exposures seen during field work in this area. It is therefore concluded that fracture development in these areas is primarily controlled by Cenozoic compression and uplift. It is to be of note that within the De Geerdalen Formation on Edgeøya and Hopen, facies are more fluvial, whereas in central Spitsbergen units feature a greater marine influence. On Edgeøya and Hopen, these fluvial facies feature thicker packages of sandstones, which display almost purely extensional jointing, are existent. Overlying Beds to these units are relatively thinner and host more conjugate fracture sets, in combination with large scale through-going extensional jointing. Furthermore this variation in facies type and increased thickness of sand bodies within the De Geerdalen of Eastern Svalbard has inherent implications for the distribution fracture densities. As a result of this it has been seen that fractures are increasingly dispersed within these thicker sand bodies. Fractures and joints observed on the island of Hopen in south-eastern Svalbard hold a similar distribution of fracture orientations to those of Spitsbergen and Edgeøya. With conjugate shear fracturing and extensional jointing being determined to have been formed in relation to the uplift of the Barents Sea shelf. However, on Hopen there is seen to be a secondary fracture subset hosting a prominently different orientation. These fractures are suggested to have formed in association to faulting which culminated in the the formation of the Hopen High, a local horst block bound to the south east by the Olga Basin.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013