Submarine hydrothermal vent complexes in the Paleocene of the Faroe-Shetland Basin: Insights from three-dimensional seismic and petrographical data

Abstract

This work presents a new method of coarse-grained sediment input into a deep sedimentary basin and presents a new example of igneous processes controlling sedimentary facies. The Mesozoic-Cenozoic Faroe-Shetland Basin sediments are intruded by Late Paleocene igneous sills and dikes. Sill intrusions are frequently expressed on the paleosurface as hydrothermal mounds and vents occurring directly above sill tips. Three-dimensional seismic data are used to image a Paleocene submarine mounded structure that has been penetrated by an exploration well drilled in A.D. 1984. Seismic morphology is combined with petrographic data to show that the mound was erupted from a central vent as a series of sediment pulses consisting of sediments disaggregated and recycled from depth-a submarine sediment volcano. INTRODUCTIONThe exploration well 214/28-1 was drilled in A.D. 1984 in the Faroe-Shetland Basin (Andersen, 1988;Smallwood et al., 2004); one of the targets was the mound structure that forms the basis of this contribution. The predrill interpretation was a Paleocene turbidite lobe, either mounded or subject to differential compaction, based on A.D. 1981 vintage twodimensional seismic data.The new interpretation in this paper uses recent three-dimensional seismic data and state-of-the-art seismic attribute computations to map the structure drilled in 1984. Interpretation of these three-dimensional seismic data reveals multiple subcircular mounds, along a north-south trend, dominated by a major conical mound ~380 m high and 3000 m diameter (Fig. 1), which dips 0° to 3° away from the center. The mound is linked by a chimney structure to seismically resolvable and exploration-well-penetrated transgressive dolerite sill intrusions at 0.7-3 km paleodepth below the seabed (now 2.5-4.7 km subsea) (Fig. 2, A-A′).When combined with petrological interpretation of samples taken from a cored section within the mound, it is suggested that the mounds are subsea sediment volcanoes resulting from intrusion-driven disaggregation of lithifi ed sediment, which was subsequently transported to the surface where it erupted to form the conical mounds imaged.The hydrothermal vents recognized in three dimensions in the Faroe-Shetland Basin are similar in morphology and petrography to vent complexes found in the Karoo Basin, South Africa Svensen et al., 2006), suggesting that the "chimney" structures are probably sediment pipes and dikes. Seismic morphologies of hydrothermal vents studied here are identical to those reported in the Vøring and Møre Basins (Norway) by Planke et al. (2005) and regionally by Hansen (2006). The only other offshore example that has been drilled is reported by Svensen et al. (2003) in the Vøring Basin, which is seep carbonate-rich and fi ner-grained than the 214/28-1 example. Previously, hydrothermal mounds have been linked to global climate change , but due to lack of offshore data their importance in linking igneous intrusions to offshore sedimentology has not been appreciated.It is believed this is the fi rst time the lit...

Lateral Magma Flow in Mafic Sill‐complexes

“…This tuning response promotes uncertainty in the interpretation of the true intrusion geometry because it is difficult to determine the difference between real features and geophysical artifacts (Smallwood and Maresh, 2002;Magee et al, 2015). Several studies have, however, used borehole data to corroborate that interpreted magmatic and volcanic bodies are igneous (e.g., Smallwood and Maresh, 2002;Peron-Pinvidic et al, 2010;Grove, 2013;Rateau et al, 2013;Schofield et al, 2015). Synthetic seismic forward models, designed to test the seismic expression of igneous intrusion properties observed in the field, can also be utilized to assess the validity of seismic interpretations (Magee et al, 2015).…”

The architecture of submarine monogenetic volcanoes – insights from 3D seismic data

“…Bell & Butcher, ; Davies et al ., ; Thomson, ; Wall et al ., ; Calvès et al ., ; Jackson, ; Magee et al ., ; Zhao et al ., ; Schofield et al ., ) or hydrothermal in origin (e.g. Jamtveit et al ., ; Svensen et al ., ; Planke et al ., ; Hansen, ; Grove, ; Magee et al ., , b, ; Alvarenga et al ., ). However, the criteria for distinguishing these vents in seismic data were until now lacking.…”

“…Hydrothermal vents have eye, dome or crater‐like shaped upper parts (Planke et al ., ; Grove, ) underlain by a sandstone dyke or breccia pipe that connects at depth to the tips of a sill (Jamtveit et al ., ). Based on observations from seismic data, these connection zones have confusingly been referred to as diatremes (Hansen, ) a feature diagnostic of volcanoes (White & Ross, ).…”

“…Hydrothermal vents may act as fluid migration pathways long after their burial (Svensen et al ., ). Moreover, their upper parts may represent a hydrocarbon play (Grove, ). The vents have been interpreted to arise from either phreatic or phreatomagmatic activity (Jamtveit et al ., ) yet there are no descriptions of the juvenile clasts indicative of a phreatomagmatic origin.…”

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.…”