Characterising Permo-Carboniferous Glaciogenic Reservoirs on the Margin of the Lenard Shelf, Canning Basin, Western Australia

Al-Hinaai, Jalal; Redfern, Jonathan
University of Manchester, Manchester, United Kingdom

Interpretation of a recent high quality 3D seismic data acquired on the Lennard Shelf, Canning Basin integrated with data from 17 wells within the survey area, allows analysis of seismic facies and the depositional architecture of Permo-Carboniferous glaciogenic sediments. The results offer new insights into the influence of tectonics and climate on ice sheet dynamics and distribution in the region.

The basal unit of the Grant Group (120-360 m thick) consists of mostly of sandstone with minor conglomerate and shale. This is deposited on a deeply incised unconformity. Below the unconformity, NW-SE to NE-SW oriented normal faults can be mapped, producing a series of half grabens, horsts and tilted fault blocks. Although these pre-Grant faults were not active during Grant Group deposition, they have influenced the later glacial topography.

A series of valleys can be mapped, infilled by low amplitude discontinuous reflectors, interpreted to record a complex suite of glaciogenic facies. Discrete channels can be imaged, oriented NW-SE to N-S and ranging from 1500 to 3200 m wide and up to 240 m deep.

The middle unit (85-200 m thick) is characterised by continuous high amplitude reflectors. It is dominated by mudstones, comprising characteristic fining upward sequences. The formation generally thickens toward the southwest indicating an increase in accommodation toward the Fitzroy Trough. In addition, thickening is observed toward the southern margin, into a major underfilled glacial valley, which supports a local southward direction of ice movement.

The upper package (140-560 m thick) consists of massive and cross-bedded sandstones, and mudstones. Seismic facies vary from chaotic high amplitude reflectors to discontinuous low amplitude reflectors. Its maximum thickness is observed in a north-south trending valley that in places completely eroding the underlying section almost down to the basal Grant unconformity. RMS attribute extractions also show the presence of a network of anastomosing northwest-southeast oriented channels running oblique to the regional trend of the Fitzroy Trough. The morphology and size of this large valley system suggests glacial erosion, and this is interpreted to record the latest glacial advance, and a final glacial phase previously unrecorded in the basin.

These results provide valuable data on the glacial evolution of the basin and development of channel systems, within a section that has proven hydrocarbon potential.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012