Anatomy of a Submarine Fan Complex, Exmouth Sub-basin, Western Australia

Peter A. Arditto

A process sedimentologic and sequence straigraphic study of the base Berriasian-aged Barrow Group was undertaken within the Macedon Gas Field, WA-155-P, Exmouth Sub-basin, using conventional core and wireline log data. Due to poor data quality the 3D seismic could not be integrated into the study. The study concentrated on basal sandstone reservoirs now interpreted to be submarine debris flow and grain flow fan complex. These sands developed as result of rapid sediment loading of the prograding Barrow Group shelf margin with subsequent collapse of the margin and sediment transport to an offshore setting. Detailed core process sedimentology tied into wireline log motifs indicates that sediment transport was by grain flow and minor debris flow; trne turbidites are rare. The inferred sediment source were shelf margin barrier bar and stream mouth bar units located to the southeast. This postulated source area has been subsequently uplifted and removed through erosion by regional intra-Valanginian tectonism.

A well correlation diagram was constrncted to help delineate the distribution of five fan cycles. A regionally significant third-order maximum flooding surface, slightly younger than the fan complex, was used as a stratigraphic datum for the correlation. lsopach and percent sand maps for each of the fans display a general east to southeast progressive displacement in both depocentre and maximum sand content. This is interpreted to be a response to a more general transgressive event within the basal portion of the Barrow Group, culminating in the third-order maximum flooding surface used as the stratigraphic datum. The entire fan complex appears to have limited areal extent which may limit both the capture area for gas charging and the water drive capacity for gas production.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California