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2.1.3 Conceptual modelThe South Perth Basin trending along the southern end of the western Australian coast is formed by aPermian to Holocene succession of sediments overlying a Precambrian basement. The basin’s easternboundary is marked by the Darling Fault and the Yilgarn Craton while its western boundary is markedby a thinning of the sedimentary sequence toward oceanic crust in deeper water.The structurally complex Perth Basin was formed during the separation of Australia and Greater Indiain the Permian to early Cretaceous (Crostella and Backhouse, 2000). It includes a significant onshorecomponent in the South and in the North extends offshore to the edge of the continental crust in waterdepths of up to 4500 m. Sandier facies in the South Perth Basin (Sabina Sandstones) suggest that thebasin was closed in the early Triassic and being filled from the South. Further subsidence of the basinlead to regional marine transgression in the early Triassic (Wonnerup) followed by a regression to deltaicand fluvial facies (Myallup) throughout the middle to late Triassic. Triassic rivers flowed from the southor southwest and are assumed to have covered both the Perth Basin and much of the Yilgarn Craton.In the early and middle Jurassic fluvial and marshy sedimentation was white spread in the South. Inthe late Jurassic continental sedimentation was again widespread. The ongoing northwest-southeastextension from the middle Jurassic to earliest Cretaceous culminated in the break-up of Australia andGreater India. The break up in the early Cretaceous was associated with widespread uplift and erosionand possibly also with volcanism. A renewed phase of subsidence followed, where localised saggingallowed for the deposition of submarine sediments, including turbidites. The geological setting of theSW Hub is illustrated in Figure 2.6. Correlation of geological facies across the basin is presented inFigure 2.7.The SW Hub project focuses on the Harvey ridge, a faulted anticline structure 47 km north of Bunburythat forms the boundary between the Bunbury Trough and the Mandurah Terrace. The structure showssigns of four-way dip closure but is cut by several large faults and was first identified by gravity surveys.Lake Preston 1 is currently the closest well and was drilled on the western flank of the anticline.Because of the paucity of adequate data in and around the SW Hub, it does not make sense to constructa complex model. Instead, we focus on conceptual models which capture salient geological features.There are a number of possibilities for creating such models. If we make the decision to base the modelon existing core and available well data, then the conceptual model should be based on GA2011-LL1, thenorthernmost of the recent vintage seismic lines. However, if we decide to base the conceptual model onthe 2012 Harvey 1 well location and core, then the conceptual model should be based on GA2011-LL2,the next most southern line. It is important to note that at the time of writing, data from this well was notpublically available. Figure 2.8 compares seismic data from GA2011-LL1 and LL2. Although there isa similarity between structures that could reasonably be interpreted on both lines, there are differencesalso. These differences strongly influence the construction of the conceptual model.| 17