Methanogenetic evolution of a buried pinnacle structure overlying a fluid-escape pipe in the Western Exmouth Plateau, Australia

Abstract

The formation and evolution of carbonate pinnacles in sedimentary basins remain a subject of significant scientific interest, particularly in relation to their interaction with subsurface fluid migration. This study uses high-resolution three-dimensional (3D) seismic reflection data to investigate an isolated and buried carbonate pinnacle (∼700 m wide and 99 m high) in the Exmouth Plateau, offshore Australia. The pinnacle shows a cone-shaped morphology with internally admixed low- to moderate-amplitude seismic reflections and is spatially associated with an underlying vertical zone of low-amplitude and chaotic reflections, interpreted as a fluid-escape pipe. The presence of this pipe suggests focused vertical fluid migration from a potential deep-seated source, likely the early Triassic Locker Shale. Seismic onlap of overlying sediments on the pinnacle flanks precludes its interpretation as a seismic artifact, supporting its in situ origin. The observed structural and stratigraphic relationships indicate that episodic methane expulsion influenced pinnacle development, suggesting a methanogenetic origin. These findings provide added insights into the role of fluid migration in carbonate system evolution and have broader implications for understanding reservoir formation, diagenetic alteration, and subsurface fluid storage. Importantly, our study advances the geoscientific understanding of carbonate diagenesis and basin evolution in both modern and ancient settings by elucidating the interaction between fluid escape features and carbonate build-ups.