Seismic Stratigraphy and Geomorphology of Palaeocene Volcanic Rocks, Faroe-Shetland Basin

Abstract

2D and 3D seismic reflection data in the Faroe-Shetland Basin have been used to remotely study buried, large-scale Palaeocene volcanic structures emplaced during continental flood basalt volcanism in the Faroe-Shetland Basin. The flood basalts were emplaced as thick and extensive pāhoehoe lava flows from multiple sources, including fissure systems close to the Faroese shelf and from volcanic centres within the basin. This thesis has investigated the distribution and internal structure of the flood basalts based on the hypothesis that volcanic eruptions produce volcanic depositional successions that record the temporal and spatial variations of the basin into which they are emplaced. Multiple eruptions will produce cycles of volcanic deposition that are delineated by hiatal surfaces. These successions can be recognised in seismic reflection data by applying seismic stratigraphic concepts in order to gain insights into the evolution of volcanic basin-fill.

The Faroe-Shetland Basin contains a variety of depositional environments, including a deepening marine basin where continental flood basalts reached a palaeo-shoreline and constructed an extensive lava-fed delta system >1000 m thick. The delta is composed of 13 seismic reflection units whose stacking architecture primarily records variations in lava supply and accommodation. Modification of the delta front was by erosion and debris avalanches. The second environment is subaerial to shallow marine where the continental flood basalts emplaced multiple lava flows 10 - 60 m thick which coalesced to form extensive and overlapping lava flow fields. Four seismic reflection units have been recognised and record variations in source and supply of the lava flows. During reoccurring periods of volcanic quiescence, fluvial channels 350 – 500 m wide incised across the lava flow fields, constrained by flow field topography.

The volcanic depositional successions used to reconstruct the volcanic basin-fill history of the Faroe-Shetland Basin indicate that eruptive styles and volcanic structures varying significantly over relatively small areas (tens of km2). Many of the seismic observations have been compared to outcrop analogues, are scale-independent and are indicative of emplacement environment. Analysis has also led to the development of a volcanic seismic stratigraphic model as depositional patterns produced during volcanic activity are primarily driven by volcanic supply. The results presented in this thesis have many important implications for stratigraphy, hydrocarbon exploration and basin modelling in the Faroe-Shetland Basin and therefore can be applied beyond the fields of volcanology or seismic interpretation.