Abstract
We investigated pinnacle features at the base of late Oligocene–Miocene isolated carbonate buildups using three-dimensional seismic and borehole data from the Browse Basin, Northwest Australia. Brightened seismic reflections, dim spots, and other evidence of fluid accumulation occur below most pinnacle features. An important observation is that all pinnacles generated topography on successive late Oligocene–Miocene paleoseafloors, therefore forming preferential zones for the settlement of reef-building organisms by raising the paleo-seafloor into the photic zone. Their height ranges from 31 m to 174 m, for a volume varying from 33 km3 to 11,105 km3. Most of the pinnacles, however, are less than 2000 km3 in volume and present heights of 61–80 m. As a result of this work, pinnacles are explained as the first patch reefs formed in association with mud volcanoes or methanogenic carbonates, and they are considered as precluding the growth of the larger isolated carbonate buildups. We postulate that pinnacle features above fluidflow conduits demonstrate a valid seep-reef relationship, and we propose them to be refined diagnostic features for understanding fluid flow through geological time.
Highlights
Carbonate strata dominate the Miocene stra tigraphy of the Browse Basin, Northwest Aus tralia (Rosleff-Soerensen et al, 2012), and depo sition on other equatorial margins (Brouwer and Schwander, 1987; Eberli and Ginsburg, 1987; Grötsch and Mercadier, 1999; Wil son et al, 2000; Pomar, 2001; Fournier et al, 2005)
The Browse Basin records a change from a carbonate ramp to a rimmed platform during the Cenozoic, with regional data documenting the contiguous growth of carbonate buildups in the shallowest parts
Howarth and Alves (2016) mapped clustered fluid-flow features above late Oligo cene–Miocene karst systems and within iso lated carbonate buildups. These fluid-flow fea tures were interpreted as being associated with a salt diapir at depth, despite: (1) the absence of thick evaporites in great parts of the Browse Basin, and (2) the presence of the shallow-water Seringapatam Reef in the area interpreted by Howarth and Alves (2016)
Summary
Carbonate strata dominate the Miocene stra tigraphy of the Browse Basin, Northwest Aus tralia (Rosleff-Soerensen et al, 2012), and depo sition on other equatorial margins (Brouwer and Schwander, 1987; Eberli and Ginsburg, 1987; Grötsch and Mercadier, 1999; Wil son et al, 2000; Pomar, 2001; Fournier et al, 2005). Howarth and Alves (2016) mapped clustered fluid-flow features above late Oligo cene–Miocene karst systems and within iso lated carbonate buildups These fluid-flow fea tures were interpreted as being associated with a salt diapir at depth, despite: (1) the absence of thick evaporites in great parts of the Browse Basin, and (2) the presence of the shallow-water Seringapatam Reef in the area interpreted by Howarth and Alves (2016). We document for the first time the relationship between fluid flow and the growth of late Oligocene–Miocene isolated car bonate buildups in the Browse Basin through the interpretation of the Poseidon three-dimen sional (3-D) seismic volume This was done regardless of the presence of the Seringapatam Reef in the study area, as it forms a prominent near-surface carbonate platform that is distinct from the pinnacle features documented in this paper.
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