Karen Higgins

Ion microprobe (SHRIMP) U–Pb dating of Upper Cretaceous volcanics from the northern Lord Howe Rise, Tasman Sea

Rock samples recovered during the Australian–French AUSFAIR MD153 Survey in 2006 from the northern Lord Howe Rise and the Fairway Ridge provide new constraints on the tectonostratigraphic evolution of the region and represent significant new information from a region in which few rocks have been dated. SHRIMP U–Pb dating of zircon from rocks from the Lord Howe Rise indicates alkali volcanism in the area at 97 Ma (trachyte) and 74 Ma (latite). The older volcanic activity is probably related to the widespread Late Cretaceous magmatism along the eastern Gondwana margin, whereas the younger activity may be related to the opening of the Tasman Sea or rifting in the New Caledonia Basin. The pebbly clasts and shell fossils in some of the associated volcaniclastic rocks provide evidence for the existence of landmasses as a sediment source area in the northern Lord Howe Rise region, and the initial marine incursion into the area around Campanian time.

Structural analysis of extended Australian continental crust: Capel and Faust basins, Lord Howe Rise

Abstract The Capel and Faust basins (northern Lord Howe Rise) are located in the SW Pacific between Australia, New Zealand and New Caledonia. New seismic, gravity, magnetic and bathymetry data and rock samples have enabled the construction of a three-dimensional geological model providing insights into the crustal architecture and basin stratigraphy. Multiple large depocentres up to 150 km long and 40 km wide, containing over 6 km of sediment, have been identified. These basins probably evolved through two major Early Cretaceous rifting episodes leading to the final break-up of the eastern Gondwanan margin. Pre-break-up plate restorations and potential field data suggest that pre-rift basement is a collage of several discrete terranes, including a Palaeozoic orogen, pre-rift sedimentary basins and rift-precursor igneous rocks. It is likely that a pre-existing NW-trending basement fabric, inherited from the New England Orogen (onshore eastern Australia), had a strong influence on the evolution of basin architecture. This basement fabric was subjected to oblique rifting along an east–west vector in the ?Early Cretaceous to Cenomanian and NE–SW-oriented orthogonal rifting in the ?Cenomanian to Campanian. This has resulted in three structural provinces in the study area: Eastern Flank, Central Belt and Western Flank.

Integrated petroleum systems analysis to understand the source of fluids in the Browse Basin, Australia

The Browse Basin is located offshore on Australia’s North West Shelf and is a proven hydrocarbon province, hosting gas with associated condensate in an area where oil reserves are typically small. The assessment of a basin’s oil potential traditionally focuses on the presence or absence of oil-prone source rocks. However, light oil can be found in basins where source rocks are gas-prone and the primary hydrocarbon type is gas-condensate. Oil rims form whenever such fluids migrate into reservoirs at pressures less than their dew point (saturation) pressure. By combining petroleum systems analysis with geochemical studies of source rocks and fluids (gases and liquids), four Mesozoic petroleum systems have been identified in the basin. This study applies petroleum systems analysis to understand the source of fluids and their phase behaviour in the Browse Basin. Source rock richness, thickness and quality are mapped from well control. Petroleum systems modelling that integrates source rock property maps, basin-specific kinetics, 1D burial history models and regional 3D surfaces, provides new insights into source rock maturity, generation and expelled fluid composition. The principal source rocks are Early–Middle Jurassic fluvio-deltaic coaly shales and shales within the J10–J20 supersequences (Plover Formation), Middle–Late Jurassic to Early Cretaceous sub-oxic marine shales within the J30–K10 supersequences (Vulcan and Montara formations) and K20–K30 supersequences (Echuca Shoals Formation). These source rocks contain significant contributions of terrestrial organic matter, and within the Caswell Sub-basin, have reached sufficient maturities to have transformed most of the kerogen into hydrocarbons, with the majority of expulsion occurring from the Late Cretaceous until present.