The interpretation of volcanic vents and fields in 3D seismic data, with an example from the Browse Basin, North West Shelf.
Jeuken, Frederick W.
Honours Degree 2009
University of Adelaide
Volcanoes make up only a fraction of the earth’s surface yet the effect they have on sedimentary environments is significant. It has been estimated that over a quarter of Post Archean sedimentary rocks are of volcanic origin. With the improvement in resolution and imaging of 3D seismic surveys, volcanic influence on ancient sedimentary environments is becoming increasingly identifiable.
Many authors have examined igneous facies in the subsurface and studies have focused on the seismic response and characterisation of preserved flood basalts and intrusive igneous bodies such as dikes and sills. In this study, attention is turned to a systematic study of preserved extrusive volcanic vent structures which are commonly associated with rift tectonics e.g. cinder and tuff cones, tuff-rings or maars and basaltic shield volcanoes.
A general methodology is devised to identify and characterise these vent structures in 3D seismic datasets. This uses the expected expression of vent structures based on modern outcrop models to develop a classification system which assesses the type of volcanic vent. A rating scheme then measures the likelihood of that feature being a preserved volcanic vent. This methodology is applied to an example 3D seismic dataset which contains an interval known as the Plover Formation in a region of the Browse Basin, off North West Australia. An extensive monogenetic basaltic volcanic field is interpreted to be preserved in this interval.
An examination of the spatial and temporal characteristics and distributions of these volcanic vents, as well as some modern analogue fields, is made. Using developed relationships, an approximation is made of the number of volcanic vents not readily resolvable in 3D seismic. With this information and utilising defined relationships, the volume and type of erupted material is estimated, namely cinders, tuffs, associated lava flows and airborne ash. The study goes on to assess the probable distribution of erupted material and the relative timing of volcanic events.
With further relation to modern analogues and outcrop models, a determination of the influence of these interpreted volcanic vents on the depositional environment at the time of eruption is made. This information is used to reconstruct a probable ancient volcanic landscape of the survey area in the Browse Basin at the time of eruption, along with a description of the effects on sedimentation.