PESA Vic/Tas February Technical Meeting – Ancient volcanic plumbing systems in sedimentary basins: a guide for hydrocarbon explorers

An important geological risk associated with exploration in many sedimentary basins, particularly those that formed due to lithosphere extension, is the presence of igneous rocks. Whilst hydrocarbon exploration has traditionally overlooked basins containing igneous rocks, the past decade has witnessed the development of an array of new interpretative tools and workflows for characterising both intrusive and extrusive igneous rocks and related phenomena using 3D seismic data. This presentation will highlight the application of 3D seismic data to understand the plumbing systems of ancient, buried volcanic provinces in both frontier and mature regions for hydrocarbon exploration.

A frontier example is provided by the Bight Basin, where 3D seismic data permit the study of an extensive province buried volcanoes and their intrusive plumbing system in unprecedented detail. Although situated on a passive margin, early Cenozoic magmatism in the Bight Basin occurred subsequent to continental breakup and is expressed by a variety of submarine volcanic landforms, fed by abundant sills, dykes and laccoliths emplaced into underlying deltaic sequences.

The Bight Basin is contrasted with the Jurassic Rattray Volcanic Province, located at the triple junction of the North Sea rift system, and the Warnie Volcanic Province in the Eromanga Basin. The Rattray Volcanic Province is long thought to be sourced from a series of large central volcanoes, but the re-interpretation of 3D seismic and well data shows that no such volcanic centres exist, and that the volcanics were erupted through dyke-fed linear fissure zones. The Warnie Volcanic Province is a recently discovered system of >100 buried Jurassic monogenetic volcanoes that has gone largely unnoticed, despite decades of exploration within the Cooper-Eromanga basins. The presentation will examine the implications for hydrocarbon exploration in these study areas, and in other extensional basins containing syn and post-rift igneous rocks.