Nadege Rollet

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.

Triassic–Jurassic granites on the Lord Howe Rise, northern Zealandia

We present U–Pb zircon ages from a phosphate-cemented pebbly sandstone dredged from the central Lord Howe Rise and a 97 Ma rhyolite drilled on the southern Lord Howe Rise. Four granitoid pebbles from the sandstone give U–Pb ages in the range 216–183 Ma. Most detrital zircons in the bulk sandstone are also Late Triassic–Early Jurassic, but subordinate populations of Late Cretaceous and Precambrian zircons are present. The pebbly sandstones highly restricted Late Triassic–Early Jurassic zircon population indicates the nearby occurrence of underlying basement plutons that are the same age as parts of the I-type Darran Suite, Median Batholith of New Zealand and supports a continuation of the Early Mesozoic magmatic arc northwest from New Zealand. Zircon cores from the southern Lord Howe Rise rhyolite do not yield ages older than 97 Ma and thus provide no information about older basement.

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.

Paleogeographic Evolution of Early Campanian to Maastrichtian Supersequences in the Caswell Sub-Basin—Implications for CO2 Storage and Hydrocarbon Entrapment

The Caswell Sub-basin is a northeast-trending Paleozoic to Cenozoic depocentre in the Browse Basin, on the Northwest Shelf, offshore Western Australia. As part of a recent study to investigate the CO2 storage potential of the sub-basin, sequences within the latest Cretaceous section have been high-graded as potential CO2 storage targets based in part on their sequence stratigraphic and paleogeographic characteristics. Sequence stratigraphic analyses were used to improve the understanding of sequence architecture, facies and palaeogeography during early Campanian-Maastrichtian, a time of relative sea level fall in the basin. This phase is characterised by two supersequences (K60a and K60b), with maximum regression reached by the end of the Maastrichtian Sequence (K60b). During the early Campanian (K60a), a major sea level fall resulted in deep incision and channeling at the base of the supersequence. Wide fluvial systems draining to the north from the Kimberley Craton were captured by east-west channels that fed large submarine fan complexes across the Caswell Sub-basin. This was followed by highstand fluvio-deltaic systems that prograded to the north over the structurally controlled ramp-like inner shelf. Supersequence K60b (near base to late Maastrichtian) was initiated by eustatic sea level fall punctuated by deep incision into K60a. Large EW-trending incised valleys and wide fluvial belts provided sediment pathways from to the basin during lowstand conditions. Outboard, transgressive pro-delta shales of the younger supersequence (K60b) provide a seal for the submarine fans. As for the K60a supersequence and in comparison with sediment transport direction for the lowstand fans, the fluvio-deltaic highstand successions are characterised by rapid northward progradation along the shelf margin. The submarine fan complexes of these two supersequences formed isolated sand-rich bodies sealed by thick transgressive and downlapping highstand shales. Containment risk for the evaluation of these fans as potential CO2 storage targets considered updip continuity of sand bodies, incision by channels, faulting and top/base seal. The studies identified a variety of CO2 storage sites and examined the area for potential conflict with active hydrocarbon exploration.

Geophysical studies of Australia's remote eastern deep-water frontier: results from the Capel and Faust Basins

Introduction The Capel and Faust basins are located in a frontier part of offshore eastern Australia, about 800 km east of Brisbane in 1000–3000 m of water (Fig. 1). These basins are being evaluated for their petroleum potential as part of the Australian Government’s Offshore Energy Security Program. This article outlines the current status of integrated interpretation of 2D seismic reflection, sonobuoy refraction and potential-field data acquired during Geoscience Australia marine survey GA-302 conducted between late 2006 and early 2007. This survey collected 5920 km of high-quality 106-fold seismic reflection data using an 8 km streamer to 12 s two-way time at 37.5 m shot interval and a line spacing of 20–50 km. A subsequent swath-bathymetry and geological sampling survey (GA-2436), completed in late 2007, also collected potential-field data in the north-west of the study area with a 3–4 km line spacing (Fig. 1). These data have been integrated in 3D to help constrain the geometry and thickness of sediment depocentres in the region.