Cryptic Middle to Late Jurassic marine incursions into northeastern Gondwana: An integrated sedimentological, ichnological and geochronological approach

Abstract

Sedimentary deposits of the Great Australian Superbasin, extensively developed across eastern Australia and covering almost a fifth of the continent, chronicle a rich record of palaeoenvironmental changes in northeastern Gondwana through the Jurassic and basal Cretaceous (Berriasian to Barremian). However, aside from the Surat Basin in the southeastern sector of the superbasin, little of this record has been examined closely. Likewise, the chronostratigraphy of the northern superbasin succession is poorly constrained. This study documents palaeoenvironmental and palaeogeographic records of the Carpentaria Basin at the northern extremity of the superbasin by integrating detailed sedimentary facies analysis with ichnology, palynology and U-Pb detrital zircon geochronology. This new geochronological data provides a refined age framework for the basin. At broad scale, the succession records the transition from a mixed paralic/fluviatile setting (Middle to Late Jurassic) to fully marine (Early Cretaceous) conditions. The depositional surface during basin accumulation stood close to sea level for which minor fluctuations induced a complex facies mosaic resulting in marked lithostratigraphic diachroneity for the basin fill. Two hitherto undocumented, discrete transgressive marine intervals, in the Middle Jurassic (Bajocian-Bathonian) and Late Jurassic (~Kimmeridgian-Tithonian) are identified. The former correlates with marine influence recorded in the Eromanga and Surat basins, and reflects extensive marine ingression from the north into the superbasin. The latter correlates with previously documented marine influence in the southeastern Carpentaria basin and the Surat Basin, indicating that a southeasterly-directed marine seaway existed across the Great Australian Superbasin during the Middle to Late Jurassic.