Early Cretaceous syn- to post-rift evolution of the Mentelle Basin on the southwest Australian rifted margin (IODP Expedition 369 Sites U1513–U1516)

The Mentelle Basin is a large and deep-water sedimentary basin located on the southwest Australian rifted margin. The basin lies west of the Perth Basin, east of the Naturaliste Plateau and south of the Perth Abyssal Plain. The rifted margin formed when the Greater Indian plate separated from the Australian-Antarctic plate during the Jurassic to early Cretaceous. Based on seismic reflection data, several km thick sediments infilling the basin have been interpreted. However, due to lack of geological and geophysical data, the basin has not been studied enough to understand its evolution. In 2017, International Ocean Discovery Program (IODP) Expedition 369 drilled four sites, U1513–U1516, in the Mentelle Basin and recovered important cores including late Jurassic to Early Cretaceous sections. At Site U1515 on the eastern margin of the basin, drilling penetrated below the seismically imaged breakup unconformity into the middle Jurassic to earliest Cretaceous syn-rift strata. Holes at Site U1513 on the western margin cored the syn-rift volcanic sequence, the Hauterivian to early Aptian volcaniclastic-rich sandstone sequence spanning the syn- to post-rift phase, and the Aptian to Albian post-rift claystone sequence. Drilling at Sites U1514 and U1516 in the central part reached the Albian post-rift sequence. Using a combination of shipboard and post-expedition data, we interpret the lithological, paleontological and geochemical characteristics of the syn- to post-rift sequences. The results allowed us to reconstruct the Early Cretaceous stratigraphy, tectonics, paleo-environment, and basin evolution of the Mentelle Basin. During the syn-rift phase, the middle Jurassic to lower Cretaceous non-marine sediments were deposited in the eastern Mentelle Basin, while volcanic rocks were emplaced in the western part. The 82 m thick volcanic sequence consists of alternating basalt flows and volcaniclastics with dolerite dikes, which indicate multiple volcanic eruption events in subaerial to shallow water environments. It was overlain by the 235 m thick volcaniclastic-rich sequence consisting of massive or laminated sandstone layers, deposited in shelf to upper bathyal depths. The deposition period spans the syn- to post-rift phase of the basin but decreasing sedimentation rate and shallow marine setting suggest that the post-rift thermal subsidence did not immediately follow the final continental breakup. We interpret that the delayed thermal subsidence was likely to be induced by adjacent mantle plume activities. Deep marine claystone sequences blanketing most of the basin indicate Aptian to Albian post-rift thermal subsidence.