Paleothermal and seismic constraints on late Miocene-Pliocene uplift and deformation in the Torquay sub-basin, southern Australian margin

The passive southern margin of the Australian continent contains a rich record of late Miocene-Pliocene neotectonic deformation and uplift that continues to the present day as witnessed by unusually high levels of seismicity for a so-called ‘stable continental region’. To date however, few studies have sought to estimate the magnitude of exhumation triggered by this deformation and uplift. Here we combine apatite fission track analysis (AFTA), apatite (U-Th)/He dating and vitrinite reflectance (VR) data from the Nerita-1 well in the Torquay sub-basin with seismic reflection data from this basin and the adjoining Otway Ranges to constrain the magnitude and driving mechanisms of exhumation in this part of the southern Australian margin. The Cenozoic succession in this basin has been deformed by folding and reverse faulting and contains a major, low-angle mid-Miocene unconformity that can be traced for distances of ~1500 km along the margin. Palaeothermal data from Nerita-1 show that the sub-mid-Miocene succession has been more deeply buried by ~1 km of now missing section, and indicate that exhumation began between 10 and 5 Ma, in excellent agreement with stratigraphic constraints. Our estimates of removed section and higher than previous estimates based on extrapolation of seismic reflectors, but are corroborated by AFTA results from nearby wells. Seismic data show that late Miocene-onwards intraplate deformation in the Torquay-sub-basin and Otway Ranges has been accomplished by reverse-reactivation of normal faults within Cretaceous-early Palaeogene syn-rift successions, resulting in folding of overlying post-rift late Palaeogene-Neogene sediments. The probable cause of this deformation and uplift is increased levels of intraplate stress induced by enhanced coupling of the Indo-Australian and Pacific plates ~10 Myr ago, and our results thus demonstrate the key role that plate boundary-controlled stress fields play in intraplate uplift and deformation

3D structural and stratigraphic model of the Perth Basin, Western Australia: Implications for sub-basin evolution

The history of rifting and breakup of eastern Gondwana is recorded by the development and fill of the Perth Basin in Western Australia. Knowledge of the structural architecture and stratigraphic geometry of the Perth Basin is essential to understand the evolution of the Western Australian margin and its applications to hydrocarbon and geothermal prospects, and effective aquifer management. This study integrates existing, publicly available geological, gravity, magnetic and digital elevation data to develop the first refined, regional structural and stratigraphic interpretation of the entire onshore and offshore Perth Basin, Western Australia. This new 3D model offers formation depth and thickness predictions in areas of sparse or no data. The model shows significant heterogeneity in the preserved formation thicknesses and depths at both local and regional scales. These differences may have resulted from differential subsidence and/or differential exhumation, but the formation geometries alone cannot distinguish between these two models if any erosion has occurred. Only the Lower to Middle Jurassic stratigraphy has been minimally eroded and thereby records the net subsidence. This stratigraphic interval shows that subsidence was broadly hinged from south to north, with a greater subsidence rate in the southern and central Perth Basin. Localised differences in thicknesses across adjacent sub-basins were likely controlled by differential displacement along sub-basin bounding faults during subsidence and, subsequently, during exhumation episodes. This new 3D model of the entire Perth Basin provides a framework for numerical simulations of fluid and heat flow and large-scale tectonic analysis, such as stratigraphic forward modelling of the southwestern Australian margin

Assessing palaeobathymetry and sedimentation rates using palynomaceral analysis: a study of modern sediments from the Gulf of Papua, offshore Papua New Guinea

© 2015 © 2015 AASP - The Palynological Society. Palynologists interested in better understanding the sedimentation and energy of depositional environments have often included studies of palynomaceral fragments, particularly when performing palynofacies analyses. Due to the difficult nature of classifying these fragments, researchers have developed numerous, often overlapping, classification schemes. These different schemes make it difficult to compare and contrast between research projects. Determining the appropriate scheme to apply when counting these fragments can be confusing, and application of these schemes can yield inconclusive results, especially when sedimentation and energy are in constant flux. A scheme of five categories, including brown wood (palynomaceral 1-2), leaf cuticle (palynomaceral 3), black debris (palynomaceral 4), structureless organic matter (SOM) and resin, is utilised here. It is applied to the analysis of 64 modern samples from the top 0-4 cm of sediment collected throughout the Gulf of Papua, Papua New Guinea. These samples span a suite of common marine depositional environments: river mouths and deltas, the proximal portion of the continental shelf dominated by a large clinoform, and turbidite and hemipelagic/pelagic deposits on the slope and in the deep ocean basin. Principal component analysis (PCA) confirms this simplified classification scheme provides an indirect means of assessing distance from shore and shelf-slope break, overall water depth and sediment accumulation rate, but other factors, such as processing technique, marine productivity, sediment source, time in transport and residence and bioturbation, are taken into account to fully explain distribution