Tectono-sedimentary history of the Forlandsundet Graben

• Main Author: Schaaf, Niklas Wilko
• Format: Master Thesis
• Language: English
• Published: 2018
• Subjects: Svalbard; Svalbard Archipelago; Prins Karls Forland; Forlandsundet; Sarsøyra; Sarsbukta; Sarstangen; Svalbard margin; Spitsbergen
• Online Access: http://hdl.handle.net/10852/67489; http://urn.nb.no/URN:NBN:no-70664

The Forlandsundet Graben is an understudied Paleogene sedimentary basin, located between the islands Spitsbergen and Prins Karls Forland that belong to the Svalbard Archipelago. It represents a unique opportunity to study the evolution of the western Svalbard margin from a transpressional fold-and-thrust belt into a sharply tapered transform margin during the Cenozoic. The basin is bound by a N-S trending fault zone in the east and exhibits a half- graben to graben geometry. The bounding lineaments crosscut the structures of the Paleocene- Eocene West Spitsbergen fold-and-thrust-belt, suggesting an Oligocene age for at least parts of the Forlandsundet Graben, albeit age-relationships are debated. This thesis is based on sedimentological and structural field data collected during two field seasons on Sarsøyra, a strandflat along the eastern basin boundary. Here, the two youngest sedimentary units of the Forlandsundet Graben, namely the Sarsbukta and Sarstangen Formations, are exposed. In total, 370 m of to date largely undescribed sedimentary sections were measured and a detailed assessment of the sedimentary architecture is provided. Also, the contact relationships between the sedimentary basin fill and the adjacent metamorphic basement were documented. The structural database includes kinematic measurements (~500) from basement and the sedimentary units. The field observations are supplemented with subsurface data and discussed in the light of low temperature geochronology and paleolimnology data collected under the project and kindly provided by the respective authors. The results are used to construct a tectono-sedimentary model of Sarsøyra and suggest that reverse faulting affected the eastern basin boundary at 53.5 Ma followed by oblique normal faulting. The sedimentary units on Sarsøyra were deposited during two phases of oblique, northwest directed rifting. The Sarsbukta Formation records interfingering of alluvial fans and fluvial deposits that were affected by transtensional folding as well as faulting. Afterwards, the Sarstangen Formation was deposited along a major intrabasinal normal fault as fan delta succession. New paleolimnological analyses suggest an Early to Middle Oligocene age for the Sarstangen Formation. The findings are synthesized into two tectono-thermal end-member models for the evolution of the Forlandsundet Graben as a whole. The first model considers that the Forlandsundet Graben experienced a multiphase deformation history, consisting of contraction followed by transtension. The second model explores whether the Forlandsundet Graben could have formed in a purely transtensional setting along with the exhumation of a metamorphic core complex on Prins Karls Forland. Further research is suggested to better constrain the evolution of the Forlandsundet Graben as it represents a rare onshore analogue to the offshore basins of the Svalbard margin and transform margins elsewhere.