UNDERSTANDING VOLCANIC DEPOSITS IN SEDIMENTARY BASINS

Sedimentary basins frequently contain voluminous igneous complexes, forming so-called volcanic basins. Volcanic processes and deposits may have an important impact on the sedimentary basin structure and development, influencing the maturation and migration of hydrocarbons and the formation of ore deposits, and causing eruption of huge volumes of greenhouse and toxic gasses triggering global warming and mass extinctions. Recently, extensive 2D and 3D seismic surveys have been acquired in volcanic basins worldwide, including the continental margins along the NE and NW Atlantic and S Atlantic oceans. We have developed and refined interpretational methods to identify and map volcanic deposits in these regions, including integrated seismic-gravity-magnetic interpretation, seismic volcanostratigraphy, and igneous seismic geomorphology. Seismic interpretations have been calibrated by borehole data and field analogues. Facies mapping is particularly important to understand volcanic deposits in the field, on seismic data, and in boreholes. The main volcanic seismic facies units identified on the mid-Norwegian margin are Seaward Dipping Reflectors, Landward Flows, Lava Delta, and Inner Flows. These facies units are interpreted as sequences of subaerial basaltic lava flows, coastal prograding hyaloclastite deltas, and subaqueous basalt deposits. Interpretation of recent 3D seismic data using Igneous seismic geomorphological on the Vøring Marginal High reveals volcanic flow fields on the marginal high and volcanogenic debris flows along the Vøring Escarpment forming the Lava Delta facies unit. Several scientific and industry boreholes in the NE Atlantic constrain these interpretations, whereas spectacular field outcrops on the Nuussuaq Peninsula, west-central Greenland, reveal similar facies. The eruptive processes that formed these ancient deposits can be inspected in spectacular detail on modern day Hawaii where lava flows reach the ocean and rapidly quench to form hyaloclastite deltas along large sections of the coastline. Petrophysical properties and facies of the lava flow field and volcanogenic sediments derived from boreholes on Hawaii provide a link between the field and seismic data, constraining the seismic interpretations of volcanic basins.