Pinnacle features at the base of isolated carbonate buildups marking point sources of fluid offshore Northwest Australia

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 km 3 to 11,105 km 3 . Most of the pinnacles, however, are less than 2000 km 3 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.

Seismic and Petrographic Characterisation of the Zechstein Hauptdolomit Platforms Around the Elbow Spit High, Dutch Offshore

“…Another explanation for the highly rugous signal at the top of the Zechstein could be that it represents back-barrier pinnacle or patch reefs. Isolated upper Oligocene -Miocene pinnacle reefs are present for example in offshore NW Australia and display a seismic geometry that, especially on 2D seismic lines, resembles the structures observed during the current study (Van Tuyl et al, 2018, Hendry et al, 2021. However, when seen in map view, the high-rugosity structures appear to be oriented in lines, and lack the typical conical shape associated with pinnacle reefs such as those described by Van Tuyl et al(2018).…”

Massive seafloor mounds depict potential for seafloor mineral deposits in the Great South Basin (GSB) offshore New Zealand

“…Although, the seafloor mounds show some similarities with methane-derived carbonate mounds such as high reflectivity and by being underlain by poorly imaged zones 61 , 62 . However, their geometries, large sizes, lack of internal layering, and sharp boundaries signify that they are unlikely to have evolved mainly as methane-derived carbonates on the seafloor.…”

Differentiating reefal ridges from relict coastal ridges: Lessons from the seismic geomorphologic study of buried Miocene buildups (North West Shelf, Australia)

“…These ridges extended southward to the Cape Range anticline, which was not yet formed (McCaffrey et al, 2020;Young et al, 2001; Figure 1, MioR-1 and MioR-2 on Figure 2). The Miocene ridges present there, which are the focus of this study, are only documented from 2D seismic lines (McCaffrey et al, 2020;Young, 2001), as 3D seismic geomorphologic studies are limited to the Browse Basin and Timor Sea, in the northernmost portion of the NWS (Belde et al, 2017;Gorter et al, 2002;Rankey, 2020;Rosleff-Soerensen et al, 2012;Saqab & Bourget, 2016;Thronberens et al, 2022;Van Tuyl et al, 2018a, 2018b, where both ridges and circular buildups are present. The presence of middle Miocene outcrops of a tropical lagoon with corals in the Cape Range anticline, designated as Trealla Limestone and adjacent to the ridges studied here (Figure 1), indicates that the environment was warm, and possibly favourable to coral reef development (Riera et al, 2019(Riera et al, , 2021.…”