Publications

The Tipuma Formation is one of several quartz-rich sandstone formations from the Bird’s Head. Its age has been estimated as Triassic to Jurassic based on its stratigraphic position and it has been interpreted as derived from a continental source. The age estimate is supported new U-Pb dating of detrital zircons but studies of light and heavy minerals, quartz cathodoluminescence and zircon age data suggest a more complex provenance. Acid plutonic, metamorphic, and recycled sedimentary rocks were derived from the North Australian continent but angular quartz and elongate euhedral zircons indicate a contribution from previously unrecognised contemporaneous acid volcanics. The importance of volcanic quartz is supported by cathodoluminescence (CL) characteristics which depend on variations in temperature, pressure, and geochemical environment during crystal growth and subsequent events. The CL spectra of sandstones from the Lower, Middle and Upper Members of the Tipuma Formation show they are dominated by quartz of low-T metamorphic and volcanic origin with little plutonic quartz. Most Tipuma Formation sandstones contain Permo–Triassic (205–275 Ma), Neoproterozoic (c. 975 Ma), Early Mesoproterozoic (1.4–1.6 Ga), and Paleoproterozoic (1.8–2.0 Ga) populations, with a few grains of Archaean age (2.8–3.2 Ga). The Permo–Triassic acid volcanic material is interpreted to be derived from an Andean-type arc in the northern Bird’s Head. There is some variation with stratigraphic position and in the Middle Member the abundance of volcanic quartz declines. This is correlated with a decline in Permo–Triassic zircons and an increase in Carboniferous and Proterozoic zircons. We interpret this to indicate a reduced contribution of sediment from the arc and an increased contribution of sediment from northern Australia. A small number of sandstone samples assigned to the Tipuma Formation from the Bird’s Body have also been studied. These are dominated by quartz of low-T metamorphic origin with subordinate volcanic and plutonic quartz. Geochronological results show Triassic zircons are absent but other zircon populations are similar to the Bird’s Head. The differences between sandstones of the Bird’s Head and Body could be explained if the Bird’s Body sandstones are Permian in age and not correlatives of the Tipuma Formation. However, these sandstones resemble the Middle Member of the Bird’s Head Tipuma Formation and their character is consistent with their geographic location which would have been much further from the northern Andean arc but much closer to the northern Australia continent.