Decoding sill emplacement and forced fold growth in the Exmouth Sub-basin, offshore northwest Australia: Implications for hydrocarbon exploration

Unravelling intrusion-induced forced fold kinematics and ground deformation using 3D seismic reflection data

“…The forced folds deform potential Late Cretaceous and Eocene reservoir rocks, creating possible structural traps (Figure 2, 3, and 6). Other potential traps associated with the forced folds are created by the onlap of strata onto the domes (Figure 6) [Smallwood and Maresh 2002;Magee et al 2017b]. Overall, whilst it is difficult to assess whether sill emplacement had a beneficial or adverse effect on petroleum system development, our study highlights that it is critical to not only elucidate magma emplacement mechanics, but also to determine the timing of magmatism relative to hydrocarbon generation and migration.…”

“…fluidisation and porosity reduction), fold amplitude will be less than the thickness of the intrusion [e.g. Jackson et al 2013;Magee et al 2013;Magee et al 2017b]. …”

In-context interpretation: Avoiding pitfalls in misidentification of igneous bodies in seismic data

“…Applying the same in-context interpretation concept to Figure 18, we recognize other key clues that would Interpretation / November 2018 SL37 help to infer the composition of the mound-like features. Among these clues are (1) saucer-shaped, highamplitude sills around the mounds, (2) forced folds that are formed due to the emplacement of the sills (Hansen and Cartwright, 2006;Holford et al, 2012;Jackson et al, 2013;Magee et al, 2014Magee et al, , 2017Infante-Paez and Marfurt, 2017;Schmiedel et al, 2017;Schofield et al, 2017) (red arrows), and (3) a subvertical, narrow, low-amplitude pattern in the section below these mounds that appears to disrupt the reflections for significant vertical distances (2250-3500 ms TWT, or more than 1 km) just below the mounds. Implementing an in-context interpretation, the presence of all these elements (saucer-shaped sills and forced folds in addition to the mounds) indicates an igneous composition of the mounds (Figure 20).…”

Unravelling intrusion-induced forced fold kinematics and ground deformation using 3D seismic reflection data

“…Other potential traps associated with the forced folds are created by the onlap of strata onto the domes (Fig. 6) (Smallwood and Maresh, 2002;Magee et al, 2017b). Overall, whilst it is difficult to assess whether sill emplacement had a beneficial or adverse effect on petroleum system development, our study highlights that it is critical to not only elucidate magma emplacement mechanics, but also to determine 15 the timing of magmatism relative to hydrocarbon generation and migration.…”

“…Inversion of ground deformation data collected from active volcanoes and related to subsurface magma movement also typically assumes that host rock deformation occurs via elastic bending, such that the size and location of the surface uplift and/or subsidence is expected to broadly reflect the volume and position of the magma body (e.g., Biggs et al, 2011;Galland, 2012;Pagli et al, 2012). If space for magma emplacement is also generated by the contemporaneous occurrence of inelastic host rock deformation processes (e.g., fluidisation and porosity reduction), fold 5 amplitude will be less than the thickness of the intrusion (e.g., Jackson et al, 2013;Magee et al, 2013;Magee et al, 2017b). Figure 11: (A) Schematic summarising the expected fold geometry and onlap relationships for forced folds, specifically folds 1 and 3.…”