Evidence for non-marine Jurassic to earliest Cretaceous sediments in the pre-breakup section of the Mentelle Basin, southwestern Australia

The Mentelle Basin, located off the southwestern continental Australian margin, is an underexplored deep-water basin that developed during the breakup of eastern Gondwana in the Middle Jurassic through to the Early Cretaceous. There is a high degree of uncertainty in stratigraphic interpretations of the basin owing to the lack of well and seismic data in the region. As a consequence, there has been a heavy reliance on data from the neighbouring Perth Basin to infer the geological history of the Mentelle Basin. During Expedition 369 of the International Ocean Discovery Program, a single hole was drilled with a rotary core bit to 517.10m below seafloor at Site U1515 on the continental slope in the eastern Mentelle Basin. The aim was to sample and date the inferred Permian to Jurassic pre-breakup strata. The presence of palynomorphs including Murospora florida and Retitriletes watherooensis in the fluvio-lacustrine succession below the Valanginian breakup unconformity indicates a Jurassic to earliest Cretaceous age for the upper part of the pre-rift sedimentary succession. Notable characteristics of this succession include intervals with high percentages of total organic carbon (up to 44wt%) and high hydrogen index values (Type I source rocks) associated with an increase in Botryococcus and other freshwater algae that accumulated in shallow lakes and waterlogged floodplains. A possible example of dinoturbation was also noted in this core. The discovery of Jurassic to earliest Cretaceous pre-breakup strata at Site U1515 suggests that Jurassic rifting was not constrained to the western depocentre of the Mentelle Basin, but also extended to a number of depocentres in the eastern Mentelle Basin. This has significant implications for the understanding of the regional tectonic history and the Mentelle Basin’s petroleum potential. - Pre-breakup strata sampled in the eastern Mentelle Basin for the first time by IODP Expedition 369 - Upper Jurassic–Lower Cretaceous non-marine strata below the Valanginian Unconformity - High TOC’s, high abundances of Botryococcus algae in a few horizons and a possible example of dinoturbation - Jurassic rifting not constrained to the western Mentelle Basin, but to depocentres in the east