Thesis: Depositional history and sequence-stratigraphic framework of an Early Permian shallow-marine sedimentary system, Northern Perth Basin, Australia
Shallow marine settings that include marginal-marine, paralic, and nearshore environments, record the complex interplay between wave, tide, and river processes where dominant and subordinate processes form discrete arrangements of depositional elements and thus determine the morphology and evolution of coastal systems. In the ancient rock record, numerous studies have focused on recognising depositional processes and developing sedimentary models to better understand stratigraphic organisation, and sand body geometry and distribution. These studies have emphasized the importance of alongshore variations in mixed-process systems (e.g. active and inactive lobes of deltas) that can greatly influence three-dimensional architectural models.
The Early Permian (Artinskian) Irwin River Coal Measures (IRCM) in the Northern Perth Basin consist of conglomerates, sandstones, mudstones, and coals attributed to deltaic depositional environments in cool-temperate settings, and constitute the focus of this study. The IRCM overlie nearshore facies of the High Cliff Sandstone, and are overlain by marginal-marine to deep-marine mudstones and sandstones of the Carynginia Formation. The complex stratigraphic arrangement and lateral heterogeneity of the Irwin River Coal Measures require facies analysis and correlation of measured sections to establish process-based depositional models and decipher stratal architecture to reconstruct the evolution of the deltaic system. Sequence-stratigraphic interpretations for Early Permian shallow marine successions deposited in Gondwanan basins are few. Interestingly, stratigraphic cycles of this time period are likely to record intricate interactions between eustatic sea-level changes, instability in glaciated source regions, and growth fault reactivations, combined with more autogenic shoreline processes. Furthermore, the complex tectonic history of the Perth Basin, which was bounded to the east, south and west by continental blocks during the Permian rifting, is likely to result in multiple potential source terranes for the basin-fill, and provides the impetus for sediment provenance analyses in this study.
Why my research is important
The Perth Basin is a proven petroleum province with a considerable onshore production of gas, oil, and condensates from conventional reservoirs since the 1960s, mostly in post-rift Late Permian sandstones and limestones. The majority of the hydrocarbons were sourced from an extensive Lower Triassic mudstone (the Kockatea Shale) that also constitutes the main regional seal, and together with Permian reservoirs, form the Gondwanan petroleum system. Recent discoveries of economic significance in conventional onshore and offshore fields has changed the perception of the Early Permian depositional record of the Northern Perth Basin. In particular, the Waitsia gas field appraised in 2015 is considered to be the largest conventional onshore discovery in Australia in the past 30 years. Moreover, unconventional reservoirs are currently under appraisal in Early Permian tight sandstones and shales.
It is timely given renewed petroleum exploration, including for unconventional resources such as shale gas, to develop a 3D architectural model and the sequence-stratigraphic framework for the Early Permian succession. Considerable uncertainties remain as to the environmental and structural controls on Early Permian sedimentation because of the geological heterogeneity and lateral discontinuity of these strata across the basin.