Contrasting facies patterns in subtropical and temperate continental slope sediments: inferences from east Australian late Quaternary records

Studies of latest Quaternary continental slope sediments at two localities on the east Australian margin have revealed markedly different responses to late Quaternary sea level fluctuations. Offshore of Noosa, in the sub-tropics, the sediment is predominantly a mixture of fine metastable carbonate, siliciclastic material, and pelagic carbonate. Important features of the stratigraphy include a siliciclastic-dominated facies deposited relatively slowly during the last glacial lowstand (sedimentation rate ≤8 cm/ka), and a calcareous facies, rich in metastable carbonate, deposited more rapidly during the late post-glacial transgression (sedimentation rates 15–24 cm/ka). Highstand and transgressive sedimentation rates are greater than lowstand rates by a factor of 2.5–6 due to increased shelf carbonate productivity after flooding of the mid-shelf. Off Sydney, in temperate latitudes, continental slope sediment is largely a mixture of fine siliciclastic material and pelagic carbonate. Mean sedimentation rates range from 2 to 5 cm/ka over the last four oxygen isotope stages, with mean glacial/interstadial rates higher than Holocene rates by a factor of ～1.36. This largely reflects the transfer of siliciclastic mud from the shelf to the slope during sea level regression. In both localities, facies changes on the slope are not related to specific sea level states (e.g. lowstand facies, transgressive facies, etc.), but reflect instead the interaction of changing sea level with shelf morphology.