Deciphering Late Cretaceous palaeo‐river catchments in eastern Australia: Recognition of distinct northern and southern drainage basins

Abstract

During the Early Cretaceous, Australia was flooded by the epicontinental Eromanga Sea, deposits of which occur across the Great Australian Superbasin. However, the mid‐Cretaceous retreat of this shallow sea, and the resultant palaeogeographic and sediment distribution patterns, are poorly understood. This study chronicles the Eromanga Sea's northward regression through the Carpentaria Basin as captured in the sedimentary record of the Normanton Formation. We achieve this by integrating sedimentary facies analysis of cores from across the Carpentaria Basin with palynology, sandstone petrography and U‐Pb detrital zircon geochronology. Results indicate that the Normanton Formation was deposited between ca. 100 and 96 Ma, and that it represents a large, northward‐prograding, likely river‐dominated delta system. The unit's volcanoclastic nature is exhibited through abundant lithic volcanics and devitrified glass, with a prominent, near‐depositional detrital zircon population attributed to a proximal continental magmatic arc‐derived source hypothesised to parallel the eastern seaboard of Australia at this time. The Normanton Formation is temporally correlative with the lower‐middle portions of the similarly volcanoclastic Winton Formation in the Eromanga Basin, which drained southwards into the Cenomanian‐Santonian Ceduna River Delta system. However, Normanton Formation strata display subtly different provenance signatures and drainage patterns, indicating input from similar, but likely more northern source terrains than much of the contemporaneous Winton Formation. These sediments were unlikely recycled southwards into the Ceduna Delta like those of the Winton Formation; rather they drained northward following the retreat of the Eromanga Sea through the Carpentaria Basin, indicating a Cretaceous drainage divide between two river systems, with distinct northern and southern drainage catchments. The mid‐Cretaceous palaeogeography of eastern Australia is analogous to that of the Late Cretaceous Western Interior Seaway of North America, in which the retreat of a shallow epicontinental sea is marked by the rapid deposition and progradation of multiple large, geographically distinct clastic wedges.