Mechanisms of sediment movement from topset to toeset in the Cenozoic clinoforming NW Australian margin, and implications for reservoir development, a seismic geomorphology study

Abstract

The boundary between continental or shelf-delta scale foresets and toesets is a place of dynamic flow transition, but few studies have tried to image or examine this transition zone in seismic data. It is physically modelled as an area of high erosion where supercritical flows cascade down the clinoforming foresets and transitions to subcritical flows, eroding and depositing sediments as back-stepping cyclic steps (Ono and Plink-Bjorkland, in press; Kostic and Parker 2007). More recent modern systems work in lakes (Gardner et al., 1998), marine fjords (Mosher and Thomson, 2002) and in Cenozoic outcrops (West et al., 2019) have documented these cyclic steps and their relationship to steep shelf-margin and steep deltaic-margin slopes, and downslope current interaction. This study initially utilized a data set of extremely large shelf clinoforms offshore Guyana. The current project will use a 3D data volume of well-imaged foreset-to-toeset clinoform transition zones in the Cenozoic deposits offshore NW Australia to examine the seismic expression of these processes. These clinoforms are deposited in ~ 6 packages that exhibit different degrees of progradation/aggradation architectures, seismic geomorphologic features and overall clinoform geometries. We will compare and contrast these different spatial and temporal clinoforming systems, and examine the influence of controls on the foreset to toeset transition zone. The overall evolution of the clinoform packages, specific clinoform morphologies (sediment waves, slope gullies, mass transport deposits), and well log information will provide valuable insight into the ancient processes affecting the system and the sediment budget. This study has the following goals: 1) to utilize an integrated set of geologic and geophysical data to identify processes driving topset-to-foreset-to-toeset basin sedimentation and their resultant deposits, 2) to map the geomorphology and deposits of the complex zone of flow transitions in the foreset-to-toeset along this margin, 3) to understand any genetic links between clinoform progradation/ aggradation architectures, seismic geomorphologic features and the overall clinoform geometries, and 4) to speculate on the implications of these processes and deposits for reservoir and seal potential in such ancient margins around the world.