From “source to sink” – A new perspective on the past dynamics of the Murray Canyon Group from benthic foraminiferal communities

Abstract

We present fossil benthic foraminiferal assemblage data from marine sediment core SS02/06-GC2 located in the abyssal plain of the Murray Canyon Group (offshore South Australia). The sedimentological characteristics indicate the presence of turbidite deposits showing classical Bouma-like sequences, dated between ~40 and 12 cal ka BP. These results confirm the previous interpretation of the observed large deep-water holes in the abyssal area where the core was sampled as being gouged by surges of high-energy turbidity currents. The presence of good indicator taxa and unique assemblages occupying specific bathymetric depths allows the determination of the source origin of the sediments making the turbidites. Three distinct faunal groups are found: 1) mostly shelf species, 2) mostly bathyal species and 3) mostly abyssal species. In the sediment core, these groups present a quasi-systematic succession, with nearly all Bouma-like sequences starting with the dominance of bathyal species in the coarse-grained base, followed by the dominance of shallow species in the silty part, and finally with abyssal species in the clays. To explain such phenomena, turbidites triggered by mixed hyperpycnal/hypopycnal flow processes and turbidity currents during periods of river floods are considered for the first time within the Murray Canyon Group. They are mostly related to periods of increased fluvial discharges during wet phases in the Murray-Darling Basin. • The presence of turbidite deposits showing classical Bouma-like sequences. • Relative abundance of benthic bathymetric foraminiferal groups indicates the source of turbidites. • The presence of upper inner shelf/estuarine foraminifera indicates a river in flood origin. • A strong link with humid climate over the Murray-Darling Basin is hypothesized.