Christopher N. Todd1, Eric M. Roberts1
1Geosciences, James Cook University, Townsville, Queensland 4811, Australia
The Phanerozoic tectono-sedimentary evolution of Eastern Australia is generally well understood, with considerable agreement on the plate dynamics and basin development during the Paleozoic to early Mesozoic and from the late Mesozoic to Cenozoic. However, basin development and plate tectonic patterns during the mid-Mesozoic, particularly for north-eastern Australia, remain enigmatic due to the scarcity of well-preserved magmatic rocks of this age along the continental margin. To decipher the tectonic framework and drivers of basin development during this time, sedimentary provenance analysis, involving palaeocurrent measurements, pebble counts, sandstone petrography, and U–Pb detrital zircon geochronology, was conducted on upper Paleozoic to late Mesozoic strata of the north-eastern Galilee and Eromanga basins. The results establish the presence of syn-depositional magmatism along the eastern margin of north-eastern Queensland during the Triassic and Jurassic; however, sandstone petrography and detrital zircon geochronology indicate that these were distal sources that account for only a small proportion of the total sediment input into the study region during this time. Sandstone petrography points towards a recycled orogenic source for the Triassic samples, whereas the Jurassic samples suggest a cratonic source signature; indicating that most of the syn-depositional volcanic input into the basin during this time was likely through distal airfall ash deposits. However, it is also possible that minor erosion of intrusive, arc-related rocks may have intermittently entered the basin from the east. Palaeocurrent and detrital zircon provenance analysis demonstrates that fluvial drainage patterns during the late Permian to Middle Jurassic were dominated by south to south-west palaeoflow with sediment sourced from the Etheridge Province and the Kennedy Igneous Association to the north. A significant Late Jurassic palaeocurrent reversal (flow to the north/north-east) is documented in the upper Blantyre Sandstone, which is interpreted to reflect an uplift event on the eastern Australian margin. This drainage reversal is confirmed by a change in the detrital zircon provenance evidenced by input of zircon populations eroded from the Anakie Inlier, located to the south-east of the study area. These populations are characterised by polyphase zircons that were likely recycled from the central Australian Musgrave Complex, the Ross-Delamerian Orogen, and Patterson-Petermann Orogen. As the basin filled, palaeoflow shifted to west-south-west in the Early Cretaceous, with the dominant detrital zircon population returning to Kennedy Igneous Association sources. Lower Cretaceous strata also yield significant syn-depositional detrital zircons, with a range of 135–120 Ma grains that are interpreted to be sourced from the Whitsunday Igneous Province. This study not only demonstrates that sediments for the northern Galilee and Eromanga basins are primarily sourced from Paleozoic terranes to the north-north-east, but also documents the presence of a continuum of Mesozoic magmatic zircons whose sources lie somewhere to the east of the present coastline of north-eastern Australia, which most likely entered the basin as airfall deposits.
Christopher is a sedimentologist at James Cook University in Queensland. His research focuses on the sedimentology and stratigraphy, ichnology, palaeontology, U–Pb geochronology, and tectonics of Palaeozoic and Mesozoic basins in Australia.