ABSTRACT: Facies analysis and a depositional model for the Lower Cretaceous Flag Sandstone, Barrow Sub-basin (Carnarvon Basin), Western Australia
Cope, Patricia1, Annette George1,
and James Crowley2
(1) University of Western Australia, Perth, Australia
(2) Apache Energy Limited, West Perth, Australia
The Lower Cretaceous Flag Sandstone is a significant hydrocarbon reservoir in the northern Barrow Sub-Basin (Carnarvon Basin) on Australia's North West Shelf. Well and seismic data show that the Flag Sandstone is up to 230 m thick and has a tabular geometry that extends 40-50 km laterally. Detailed sedimentological logging of cored intervals from 12 wells intersecting the upper part of the Flag Sandstone has identified 10 different sedimentary facies dominated by amalgamated massive sandstones, very thick bedded sandstone-mudstone couplets, and medium-bedded graded sandstone-mudstone couplets. The coarser sandstone facies are interpreted to be the product of high-density turbidity currents, though minor sandy debris flow deposits are recognised. The remainder of the facies are interpreted as the products of lower-density turbidity currents, minor silty debris flow and hemipelagic deposition. Facies associations show a gradual decrease in sand:mud ratio from southeast to northwest and are interpreted to best fit the inner, middle and outer fan depositional environments of submarine fan. Petrological investigation shows that the sandstones are composed predominantly of quartz with minor alkali feldspar and lithic fragments of sedimentary and volcanic origin indicating a polygenetic origin from reworked sedimentary and cratonic sources. Comparison of the Flag Sandstone detrital composition with Barrow Group sandstones confirms a common provenance located to the southeast. The sedimentological and petrological studies also discovered that minor but distinctive sediment was supplied via localised points along the palaeo-shelf east of the depocentre.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia