Application of seismic and sequence stratigraphic concepts to a lava‐fed delta system in the Faroe‐Shetland Basin, UK and Faroes

Abstract

Detailed seismic stratigraphic analysis of 2D seismic data over the Faroe-Shetland Escarpment has identi¢ed 13 seismic re£ection units that record lava-fed delta deposition during discrete periods of volcanism. Deposition was dominated by progradation, during which the time shoreline migrated a maximum distance of $44 km in an ESE direction. Localised collapse of the delta front followed the end of progradation, as a decrease in volcanic activity left the delta unstable. Comparison with modern lavafed delta systems on Hawaii suggests that syn-volcanic subsidence is a potential mechanism for apparent relative sea level rise and creation of new accommodation space during lava-fed delta deposition. After the main phase of progradation, retrogradation of the delta occurred during a basinwide syn-volcanic relative sea level rise where the shoreline migrated a maximum distance of $75 km in a NNW direction. This rise in relative sea level was of the order of 175^200 m, and was followed by the progradation of smaller, perched lava-fed deltas into the newly created accommodation space. Active delta deposition and the emplacement of lava £ows feeding the delta front lasted $2600 years, although the total duration of the lava-fed delta system, including pauses between eruptions, may have been much longer.

Igneous seismic geomorphology of buried lava fields and coastal escarpments on the Vøring volcanic rifted margin

“…Initial flood basalt volcanism commonly occurs in a sedimentary basin environment, forming shallow intrusions, peperites, or hydrovolcanic deposits generated by magma-wet sediment interaction, with subaerial lava flows occurring on basin margins and basinal highs (Planke et al, 2000;Wright et al, 2012). Continued flood basalt volcanism leads to more effusive, sub-aerial volcanism where lavas progressively in-fill topographic lows and basins .…”

“…These may be further utilized by later structural movements but may also influence the development of drainage systems (e.g., Schofield and Jolley, 2013). Where Lava Deltas reach significant thickness, erosion and slumping may play an important role for the final morphology of parts of the escarpment Wright et al, 2012;Abdelmalak et al, 2016b). The key to the study of the igneous seismic geomorphology, is to investigate both primary volcanic and secondary structural/erosional elements of volcanic terrains in order to develop the best possible model of the subsurface geology and the volcanic emplacement environment.…”

“…In this scenario the Inner Flows represent an aggradational bottom-set consisting of volcaniclastic sediments mixed with pillow-basalt and massive sheet flows (e.g., Nehyba and Nyvlt, 2015). Lava Deltas are recognized by prograding internal architecture (e.g., Wright et al, 2012) whereas the Landward Flows form sheets of stacked subaerial lavas which transition into Lava Delta facies at the escarpment (e.g. Figure 2).…”

Regional distribution of volcanism within the North Atlantic Igneous Province

“…The escarpments are found between the inner flows and landward lava flows (Figs 2 & 5) and are interpreted to represent a period of volcanism associated with subsidence below sea level, generating prograding lava deltas into shallow water, thus marking a palaeoshoreline (e.g. Wright et al 2011). The age of the escarpment is not known from direct dating.…”

“…Indications for subaerial v. subaqueous extrusion and indicators for water depth provide information regarding palaeogeography during breakup and initial rifted margin evolution (e.g. Wright et al 2011). In addition, detailed mapping of key units is the first step towards establishing the volume of material extruded and intruded, which when combined with accurate geochronology can constrain productivity rates.…”