Lithofacies and Depositional Facies of a Slope-Apron Depositional System: Early Cretaceous Barrow Group, North West Shelf, Australia

T. A. (MAC) McGilvery, W. E. Galloway, S. M. Polomka

Deep water depositional systems developed within the Barrow Group succession include both shelf-fed apron and submarine fan complexes. Conventional core from 43 wells was used to define lithofacies and process-facies which characterize Barrow Group strata. These facies where integrated with log motif and seismic facies to interpret depositional facies and paleogeographic evolution.

Twenty-two lithofacies characterize the Barrow Group. Dominant lithofacies include: massive, ripple cross laminated, laminated and bioturbated sandstones; interbedded sandstone and shale which are ripple cross laminated, laminated or bioturbated; and massive to laminated shale. Gravity mass transport processes, which included cohesive to fluidized flow, and turbidity flow, dominated deposition. Additional processes included tractional transport and suspension settling.

Depositional facies include: channel and lobe complexes composed of amalgamated, high-density turbidites, sheet turbidites, channel overbank or levee complexes (unconfined high-density turbidites), small scale channel flank or lobe margin slumps, large scale canyon fill and toe-of-slope slumps and hemipelagic drape and fill.

These facies integrated with log motif, seismic facies and sequence stratigraphic framework define a submarine ramp or apron dominated slope/basin depositional system. Serrate, aggradational gamma-ray log motifs are consistent with episodic sedimentation along the lower slope and adjacent basin floor. Seismic facies indicate development of multiple small submarine canyons or channels which fed the apron and lobe complexes in addition to unconfined gravity flows originating directly from the shorezone or narrow shelf. The resulting depositional complex is a linear-sourced mud/sand-rich apron.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995