Publications

The Bird’s Head of West Papua is underlain by Australian continental crust and has a relatively complete Silurian to Recent stratigraphy. It is surrounded by active or recently active tectonic zones. The Tipuma Formation of the Bird’s Head is a potentially important hydrocarbon reservoir and it also records part of the region’s Mesozoic tectonic history. However, little is known about variations in lithologies and their composition, and nothing is known about its provenance. New field and laboratory studies are providing new information, which suggests a more complex history than the continental block setting widely accepted previously. The age of the Tipuma Formation is uncertain due to the absence of fossils, and its suggested Triassic age has been based solely on stratigraphic position. The formation rests unconformably on the Silurian-Devonian Kemum Formation and conformably on the Permian Aifam Formation and is overlain by the Cretaceous Jass Formation. It is dominated by red to cream well-bedded mudstones, sandstones and conglomerates deposited in a fluviatile setting. Sandstones are generally compositionally and texturally immature. They are quartz-rich and mostsamples contain volcanic quartz. In order to better constrain the age of sedimentation and to identify major sediment sources, LA-ICPMS and SHRIMP U–Pb ages of detrital zircons were obtained from a total of 11 Tipuma Formation sandstone samples. Results show abundant Permo–Triassic (200–280 Ma), Mesoproterozoic (1.4–1.6 Ga) and Paleoproterozoic (1.8–2.3 Ga) zircon populations. Morphological studies suggest that Permo-Triassic zircons are igneous/volcanic and * SE Asia Research Group, RHUL older zircons were recycled from igneous and metamorphic rocks. The geochronological results show that the maximum age of deposition of the Tipuma Formation is Late Triassic. Fresh volcanic quartz and zircon suggest igneous activity in the Bird’s Head during the deposition of the Tipuma Formation. Intrusive bodies and volcanic rocks outcropping to the north of the Tipuma Formation are a possible source of some material, and a North Australian cratonic origin is proposed for Precambrian zircons. It is suggested that there was a Gondwana Andean-type margin from Eastern Australia through New Guinea to the Bird’s Head in the Late Palaeozoic and Triassic.