Peter Reynolds

Subsurface fluid flow focused by buried volcanoes in sedimentary basins: Evidence from 3D seismic data, Bass Basin, offshore southeastern Australia

AbstractThere is growing evidence that intrusive magmatic bodies such as sills and dikes can influence the migration of fluids in the deep subsurface. This influence is largely due to permeability contrasts with surrounding sedimentary rocks or because of interconnected open fractures within and around intrusions acting as conduits for migrating fluids. The role of buried volcanoes in influencing crossstratal fluid migration in sedimentary basins is less well-established. However, several studies have highlighted spatial linkages between extinct hydrothermal vent complexes and fluid seepage, suggesting that buried extrusive features can also influence subsurface fluid-flow pathways, potentially leading to migration of hydrocarbon fluids between the source and reservoir. We have developed 3D seismic reflection data from the Bass Basin in offshore southeastern Australia that image an early Miocene volcanic complex with exceptional clarity. This volcanic complex is now buried by <1.3  km of younger sediments...

The importance of subsurface lithology in controlling magma storage v. eruption: an example from offshore southern Australia

The volumetric relationship between the intrusive and extrusive components of volcanic fields is difficult to constrain. This is because either the erupted products are commonly eroded or the intrusions are concealed by overburden. Three-dimensional seismic data therefore offer a unique opportunity to study ancient volcanic provinces, as these datasets can image both components without the need for erosional dissection. This study is based on 3D seismic data from the Bight Basin Igneous Complex (BBIC), a volcanic province constructed within a sedimentary basin, offshore southern Australia. We demonstrate that the BBIC contains abundant sills and laccoliths emplaced within deltaic sediments. The intrusions have a total volume of 92–111 km3, and the lava flows and volcanoes have a combined volume of 66–76 km3 (Dense Rock Equivalent). This indicates that the ratio of intrusive:extrusive products for the BBIC is between 1:1 and 2:1. The architecture of the BBIC contrasts markedly with the neighbouring Newer Volcanics Province (NVP), which lacks abundant sills and laccoliths. Because lava flows and volcanoes in the NVP were dominantly fed by dykes hosted in basement rock, we suggest that subsurface lithology plays an important role in causing sill formation and determining the total volume of magma stored in the subsurface.

Three-Dimensional Seismic Imaging of Ancient Submarine Lava Flows : An Example From the Southern Australian Margin

This work comprises a part of the Great Australian Bight Deepwater Marine Program (GABDMP) for funding this project. The GABDMP is a CSIRO research program, sponsored by Chevron Australia the results of which will be made publicly available. 3D seismic data was gratefully provided by TGS. IHS are thanked for access to seismic interpretation software. Spectral decomposition was carried out using Foster-Findlay Associates Geoteric Software. Sverre Planke and Tracy Gregg are thanked for constructive reviews.