Seismic Stratigraphy, Facies, and Geomorphology of the Jurassic Legendre Delta, North West Shelf, Australia: Implications for Subaqueous Clinoforms and Sediment Gravity Flow

Abstract

In the Jurassic (Pliensbachian-Oxfordian) a large fluviodeltaic system (the Legendre Delta) was deposited in the central area of North West Shelf, Australia. Detailed interpretation of high-quality 3D seismic data has revealed a set of subaqueous clinoforms (tens of kilometres wide, hundreds of meters high) in the distal area of the system and is interpreted as a mud-dominated shelf-slope. The flat shelf-edge trajectory indicate it was deposited during a long-term stable / falling sea-level stage. Four maximum flooding surfaces were identified within the succession and suggest it was formed as a result of multiple waning-waxing cycles of sediment inputs and/or short-term sea-level fluctuation. Two submarine channels were developed during one of the waning stages of sediment supply, followed by the waxing of mud-dominated sediments. The channels have low-sinuosity and are highly erosive, and are characterized by sediment gravity flow bypass on the steep slope. They become very sinuous, less erosive to the gently dipping downslope, and gravity flow bypass effects decrease as gravity flow deposits are present within the channel meanders. Terminal fan lobes are developed on the flat basin floor.

The results of this study provide insights into the links between channelized sediment gravity flow and the background sediment supply, sea-level fluctuation, topographic and sub-environmental contexts in the deep-water of fluviodeltaic dominated margins, which are of great importance for understanding the processes governing channelized sediment gravity flow.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018