Role of climate in partial drowning of the Queensland Plateau carbonate platform (northeastern Australia)

Abstract

Ocean Drilling Program Leg 133 core data, samples, and geophysical data (logs and seismics) were analyzed to document late Miocene-early Pliocene partial drowning of the Queensland Plateau carbonate platform off Northeast Australia. The modern plateau consists of a mosaic of pinnacle reefs and larger (10 × 50 km) reefs representing relicts of early to middle Miocene buildups. Late Miocene-early Pliocene floatstones, packstones, and mudstones, rich in the larger benthic foraminifers Lepidocyclina and Cycloclypeus, drilled in a transect of sites across the drowned margin of a middle Miocene buildup show that the late Pliocene partial drowning of the platform was preceded by 4 Myr of neritic carbonate deposition without any reefs. The carbonate factory was unable to aggrade to sea level during this period as indicated by the lack of any shallowing trend in the succession. Monitoring of the Miocene to Recent neritic shedding pattern on the windward and leeward side of a pinnacle reef on the Queensland Plateau supports this interpretation. Shedding on the leeward side of the reef, which records periods of active reef growth, played a minor role during the late Miocene, increased during the Pliocene, and reached very high values during the late Pliocene and Pleistocene. Shedding on the windward side of the reef, which was active during lowstands of relative sea level, occurred during the late middle-early late Miocene and during the Pliocene-Quaternary. The data presented here, when combined with paleoceanographic data points to low surface water temperatures (17°–19°C) as a major factor which suppressed reef growth during the late Miocene-early Pliocene period.