- Location Map
- Basin Details and Geological Overview
- Structural Elements
- Regional Cross-sections
- Petroleum Systems and Hydrocarbon Potential
- Key References
Basin Details and Geological Overview
The Vlaming Sub-basin is an elongate, north-south trending depocentre that lies on the shelf and upper continental slope (20–1000 m water depth) in the offshore southern Perth Basin (Figure 1). It is bordered by the Mandurah Terrace in the east, Edward’s Island Block in the north and in the west it is separated from the Mentelle Basin by the Yallingup Shelf.
Among the Perth Basin main depocentres the Vlaming Sub-basin is the major Jurassic-Early Cretaceous depocentre. Structurally it belongs to an extensional system on Australia’s southwestern margin that formed during the Palaeozoic to Mesozoic rifting of eastern Gondwana. The architecture of the Vlaming Sub-basin is a result of the northeast-southwest extension during the Permian followed by predominantly east-west extension during the Middle Jurassic–Early Cretaceous.
The Vlaming Sub-basin contains more than 12 km of sedimentary section, the bulk of which is Jurassic to Cainozoic in age. No wells in the central Vlaming Sub-basin have penetrated below the Middle Jurassic Yarragadee Formation. Permian rocks have, however, been recovered on the flanks of the sub-basin.
The Vlaming Sub-basin contains an active petroleum system with several source rocks generating hydrocarbons from the latest Jurassic–Early Cretaceous to the present day. The basin contains multiple good quality reservoirs a range of regional and intraformational seals. Possible structural and stratigraphic traps have been identified throughout the basin at multiple stratigraphic levels.
- ProvExplorer - Vlaming Sub-basin Details and Geological Overview
The Vlaming Sub-basin has complex architecture resulting from the multiple extensional and transtensional episodes combined with the influence of the pre-existing basement structures. Proterozoic igneous and metamorphic rocks of the Pinjarra Orogen, an interconti nental mobile belt that separated the Australian and Indian parts of eastern Gondwana, underlie the sub-basin. The Pinjarra Orogen is characterised by major long lived north-south and northwest-southeast trending crustal structures that probably controlled the segmentation of the Vlaming Sub-basin and other depocentres along Australia’s southwestern margin.
The northwest-southeast trending Harvey Transfer is a major accommodation zone separating northern and southern parts of the Vlaming Sub-basin. The other major structural elements of the Vlaming Sub-basin include the Roe and Parmelia highs, Bathurst Syncline, Edward’s Island Block, Rottnest Trough, Peel Arch, Sugarloaf Arch and Badaminna Fault System (Figure 2). These structures are northerly to north-westerly trending, and formed during Middle Jurassic–Early Cretaceous extension (Crostella and Backhouse, 2000; Bradshaw et al, 2003). Syn-rift faulting in the sub-basin produced a series of half graben and associated anticlinal rollovers with collapse systems on the updip flanks (Spring and Newell, 1993). The 20–25 km wide Peel and Sugarloaf arches are examples of these crestal collapse structures. Their complex architecture can be partly attributed to breakup-related fault reactivation.
Major fault reactivation, block rotation, uplift and erosion occurred across the sub-basin during the Valanginian. Between 250 and 2,000 m of syn-rift section was removed with maximum erosion in the west and northwest. Compaction related subsidence in depocentres on either side of the Harvey Transfer formed two palaeo-lows on the Valanginian unconformity and focussed post rift sedimentation. After the breakup, most of the syn-rift faults remained inactive, with the exception of minor reactivation on the sub-basin flanks to accommodate increasing sag fill.
The Vlaming Sub-basin contains more than 12 km of sediments (Figure 3). During the Jurassic–Early Cretaceous syn-rift extension, more than 10 km of fluvio-lacustrine sediments accumulated in the northern and central parts of the Vlaming Sub-basin. The syn-rift accumulation stopped in the Valanginian as a result of the breakup between Australia and India. Uplift prior to the breakup led to wide-spread erosion creating a prominent, often angular unconformity. Significant parts of the Mesozoic section were eroded and in these areas older syn-rift sequences outcrop below the breakup unconformity.
The postrift sequence (Late Valanginian to Campanian) is thickest (up to 2,500 m) in the central part of the Vlaming Sub-basin. In the Early Cretaceous, two major deltaic systems operated in the region: one originated in uplifted areas in the northern part of the sub-basin and prograded southward while a smaller one drained uplifted areas adjacent to the Leeuwin Block and prograded to the north. Regionally, a significant part of the post-rift section shows deltaic affinities commonly exemplified by prograding clinoforms on seismic images.
Interpretation of seismic and well data, major tectonic phases and petroleum system elements are summarised in the tectonostratigraphic chart (Figure 4). For more information on stratigraphy of each megasequence download Nicholson et al., 2008.
Figure 5 - Cross-section trough the northern Vlaming Sub-basin featuring Jurassic half-graben (Bathurst Syncline) and eroded
crestal collapse structure (Peel Arch). © Geoscience Australia
Figure 6 - Cross-section trough the southern Vlaming Sub-basin showing Permian section intersected by Felix 1 and transition to predominantly Jurassic depocentre to the east © Geoscience Australia
Petroleum Systems and Hydrocarbon Potential
Hydrocarbons discoveries in the Vlaming Sub-basin include a non-commercial oil accumulation (Gage Roads 1) and small gas accumulation (Marri 1). Five of the 17 exploration wells drilled in the basin recovered oil/and or gas shows (eg. Tuart 1, Gage Roads 2, Araucaria 1).
So far exploration activity has been focussed in the northern and central parts of the sub-basin, where South Perth Shale provides regional seal for potential plays. A more structurally complex southern part of the basin is less explored. It has a higher proportion of sandstones in its syn-rift section and the seals are intraformational.
Three potential source rock intervals have been identified in wells from the Vlaming Sub-basin:
- Lower Cretaceous marine shales of the South Perth Shale
- Lower Cretaceous lacustrine shales in the Parmelia Group (Otorowiri and Carnac Fm)
- Middle–Upper Jurassic non-marine coals and carbonaceous shales in the Yarragadee Formation
The Yarragadee Formation is considered the principal source rock unit based on the quantity, quality and maturation of carbonaceous shales (Miyazaki et al, 1996). A recent study of oil-source correlations (Boreham, 2008) has shown that the predominant source input of terrestrial and aquatic (non-marine) organic matter to the Vlaming Sub-basin oils (Gage Roads 1 oil and the Araucaria 1 oil stain) are from the Early-Middle Jurassic (lower Yarragadee Fm) source rocks (Figure 7).
Good reservoir rocks exist throughout Late Jurassic and Early Cretaceous strata in the Vlaming Sub-basin. These include the Leederville Formation, the Gage Sandstone, the Charlotte Sandstone, the Jervoise Sandstone, and the upper part of the Yarragadee Formation (Miyazaki et al, 1996). Several seal intervals are present in the Vlaming Sub-basin above and below the Valanginian breakup unconformity. The best sub-unconformity seal potential relates to mudstone-dominated, amalgamated lacustrine shales and siltstones that were deposited during at least three intervals in the Berriasian Parmelia Group. These intervals are mappable, regionally consistent mudstone-dominated packages of 40 to 50 metres in thickness and include the Otorowiri and Carnac formations.
Multistage rifting and complex structuring in the Vlaming Sub-basin has led to the development of a variety of possible structural and stratigraphic plays. Most of these plays are associated with the Valanginian breakup unconformity (sub-unconformity truncations, palaeotopographic highs and post-breakup pinch-outs) with the South Perth Shale forming a top seal to sandstones of the Parmelia Group beneath the unconformity, or the Gage Sandstone above the unconformity (Figure 8). Seismic mapping has also shown that fault block plays occur at different stratigraphic levels where Jurassic and Early Cretaceous lacustrine shales provide effective seals. These shaly intervals may provide a seal in sub-unconformity anticlinal rollovers and horst-block plays.
||Basic Data Results from new geochemical sampling of offshore wells from the Vlaming Sub-basin, Western Australia: Part 2. Geoscience Australia, Professional Opinion No. 2008/01|
|Bradshaw, B.E., Rollet, N., Totterdell, J.M. and Borissova, I.||2003
||A revised structural framework for frontier basins on the southern and southwestern Australian continental margin. Geoscience Australia Record 2003/03|
|Crostella, A. and Backhouse, J.||2000
||Geology and petroleum exploration of the central and southernPerth Basin, Western Australia. Western Australia Geological Survey, Report 57, 75p|
||Structural and tectonic synthesis for the Perth Basin, Western Australia Journal of Petroleum Geology Vol.17, pp. 129-156|
|Iasky, R. P.||1993||A structural study of the southern Perth basin: Western Australia Geological Survey, Report 31|
|Kempton, R.H., Liu, K., Boreham, C., Bradshaw, B.E., Eadington, P.J. and Passmore, V.||2002
||Oil migration and accumulation in the offshore Perth Basin, Western Australia. CSIRO Petroleum, Open file report, January 2002. Report to Geoscience Australia|
|Marshall, J.F., Ramsay, D.C., Lavering, I., Swift, M.G. and Shafik, S.||1989
||Hydrocarbon prospectivity of the offshore South Perth Basin BMR Record 1989/23|
|Marshall, J.F., Ramsay, D.C., Moore, A.M.G., Shafik, S., Graham, T.G. and Needham, J.||1993
||The Vlaming Sub-basin, offshore South Perth Basin. AGSO, Continental Margins Folio 7|
|Miyazaki, S., Cadman, S.J., Vuckovic, V., Davey, S.J. and Conolly, J.R.||1996
||Vlaming Sub-basin Petroleum Prospectivity. Bureau of Resource Sciences, Petroleum Prospectivity Bulletin 1996/1|
|Monteil, E. Boreham, C. and Krassay, A.||2006
||Basic Data Results from new biostratigraphic and geochemical sampling and analysis of offshore wells from the Vlaming Sub-basin, Western Australia. Geoscience Australia, Professional Opinion No. 2006/05 (Report for Approval to Sample No S31784)|
||Tectonic and stratigraphic history of the Perth Basin, Geoscience Australia Record, 2004/16|
|Owad-Jones, D.L. and Ellis, G.K.||2000
||Western Australia atlas of petroleum fields, Onshore Perth Basin: Petroleum Division, DMEWA, Volume 1|
|Nicholson, C.J., Borissova, I., Krassay, A.A., Boreham, C.J., Monteil, E., Neumann, V., di Primio, R. and Bradshaw B.E.||2008
||New exploration opportunities in the southern Vlaming Sub-basin, APPEA Journal, Vol. 48, Issue:1, pp. 371-379|
||Geological cross-sections of the Vlaming Sub-basin, South Perth Basin. Bureau of Mineral Resources, Geology and Geophysics, Record 1990/64 (geocat 14386)|
|Song, T. and Cawood, P.A.||2000
||Structural styles in the Perth Basin associated with the Mesozoic breakup of Greater India and Australia. Tectonophysics, Vol. 317, pp. 55-72|
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