3D seismic expression of fluid migration and mud remobilization on the Gjallar Ridge, offshore mid‐Norway

Abstract

This paper presents a three‐dimensional (3D) seismic analysis of sediment remobilization and fluid migration in a 2000‐km2 area above the Gjallar Ridge located in the Vøring Basin, offshore Norway. Three distinct types of mounded structures have been identified as resulting from focused fluid/gas migration and associated mud remobilization and intrusion. Type A structures are gently mounded, and we infer that these structures formed because of in situ remobilization of Middle Eocene to Lower–Middle Oligocene fine‐grained sediments in response to fluid and minor sediment injection via deep‐seated normal faults. Type B structures comprise relatively steep‐sided mounds and are restricted to the pre‐Miocene interval. They are often located above narrow zones of discontinuous low‐amplitude reflections resembling gas chimneys. Some of the Type B structures are associated with stacked amplitude anomalies and possible mud volcanoes at the base Pleistocene indicating their long‐term significance as vertical fluid conduits. Type C structures comprise discrete mound features that seem to jack up the Top Palaeocene (Top Brygge) horizon. These are similar to hydrothermal mounds found elsewhere on the Norwegian Margin and associated with igneous sill intrusion during North Atlantic breakup. This study highlights the utility of 3D seismic data for mapping of fluid and sediment mobilization through time over large basinal areas.

Seal bypass at the Giant Gjallar Vent (Norwegian Sea): Indications for a new phase of fluid venting at a 56-Ma-old fluid migration system

“…High-amplitude reflections also exist in 3D data within the two pipes down to Top Brygge level ( Fig. 6), as previously noted by Hansen et al (2005) and Gay et al (2012).…”

“…2). This reflector has been previously called Base Late Pliocene Unconformity (Hjelstuen et al, 1997(Hjelstuen et al, , 1999a, Base Pliocene reflector (Reemst et al, 1996), Base Upper Pliocene (Eidvin et al 1998;Corfield et al, 2004), and Top Kai (Hansen et al, 2005;Gay et al, 2012). Throughout this paper, we use the term Base Pleistocene Unconformity (BPU), which is in agreement with the Geologic Time Scale of 2012 (Gradstein et al, 2012).…”

“…The vent is characterized by two pipe-like structures extending upwards from the Eocene sequence, each forming a V-shaped structure that terminates at the BPU . Both pipes are marked by stacked high-amplitude reflections and chaotic reflectivity above the Top Brygge horizon (Hansen et al, 2005). Hummocky reflections characterize the BPU and overlying strata at the GGV .…”

“…1B). The data have a dominant frequency of ~40-50 Hz and an inline and crossline spacing of 56 m. Vertical and horizontal resolutions are approximately 10 m and 30-50 m, respectively (Hansen et al 2005). The data underwent standard industry processing including time migration.…”

3D structure and formation of hydrothermal vent complexes at the Paleocene-Eocene transition, the Møre Basin, mid-Norwegian margin

“…The climatic records during this period are well documented from several sections worldwide (Zachos et al, 2001;Zachos et al, 2008), and recent results show that the only drilled HTVC in the Vøring Basin (borehole 6607/12-1) formed during the PETM plateau, thereby demonstrating a relationship between the long duration of the PETM and the gas venting (Frieling et al, 2016). Similar kilometer-scale hydrothermal vent structures have been described elsewhere in seismic data (Hansen et al, 2005;Planke et al, 2005;Grove, 2013;Berndt et al, 2016) and in outcrops (Svensen et al, 2006) in several basins. These vent structures all share structural similarities, including complete brecciation, fluidization, and inward-dipping reflections.…”