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PESA WA August Luncheon: Evolution of “Tres Hombres”: A Large Mid-crustal Structure within the Northern Beagle Sub-basin, Offshore WA

Thursday, August 16 @ 12:00 - 14:00

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Guest Speaker: Gerry O'Halloran

Gerry O’Halloran

Graduated from Adelaide University in 1992 with a BSc (Hons) in Geology and gained a PhD in Geology from Monash University (Stratigraphic and Structural Evolution of the Late Devonian of Central Victoria).

From 1996 he worked as a geoscientist at ExxonMobil in both exploration and development roles in a variety of basins including the Gippsland Basin and the Papuan Fold Belt.

He has worked for BHP since 2004 as a Geoscientist, again in a variety of exploration and development roles in basins within Australia (Exmouth, Browse, NWS, Beagle and Otway Basins) and in the UK (North Sea and Irish Sea).

He is currently working in BHP’s Exploration Group based in Perth which is focussed on progressing exploration opportunities within Australia.

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Evolution of “Tres Hombres”: A Large Mid-crustal Structure within the Northern Beagle Sub-basin, Offshore WA

Gerry O’Halloran

BHP Billiton Petroleum


The northern Beagle Sub-basin lies within the Carnarvon Basin, offshore Western Australia.  It comprises a thick (~ 5km) Jurassic syn-post rift sedimentary succession. In many respects it has a relatively conventional rift basin architecture, with large normal faults defining thickening growth sequences within an overall NNW trending Jurassic depocentre. There is, however, one large and obvious mid crustal domal structure (“Tres Hombres”) that impinges upon the overlying basin geometry. This talk explores the origin, timing and tectonic significance of this somewhat enigmatic structure using insights from high quality, deep record, modern 3D seismic data.

Seismic mapping reveals a dome-like structure with a diameter of more than 30km, and with vertical relief of over 5km, elevating the overlying basin sequences above regional levels. The dome has clearly influenced fault architecture in the overlying basin, which is revealed in in exquisite detail in complex map patterns of faulting within the Jurassic intervals. This faulting is also seen to detach within a lower Triassic shale prone section, and is intimately related to an even older Permian sequence, in which large scale carbonate shelf units act as localised mechanical discordances upon which faults appear to nucleate. The spatial distribution of these Permian carbonate shelf sequences also provides some evidence for the relative timing of the overall doming, as do isopach maps within the overlying Triassic and Jurassic section.

Several potential mechanisms have been considered for the emplacement of this feature, including; basement cored compression, reactivated extensional basement faulting, remnant Palaeozoic topographic relief, salt-related diapirism, or plutonic/igneous intrusive activity. Pros and cons for each of these mechanisms are discussed, each of which have important implications for the tectonic and thermal evolution of the Beagle Basin.


Thursday, August 16
12:00 - 14:00


Parmelia HIlton
14 Mill Street, Perth, WA 6000 Australia


PESA Western Australia

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