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ABSTRACT: Sediment Body Quantification: Examples from a Late Permian Mixed Influence Deltaic System, Bowen Basin, Australia

Andrew Falkner, Christopher Fielding

The Bowen basin open-cut coal mines of central Queensland, Australia, provide some of the best exposures of alluvial and fluviodeltaic sequences in the world. Within the Bowen basin coal is mined extensively along a strike length of 5-600 km exposing various parts of an Upper Permian terrestrial to shallow-marine sequence. Individual mines cover 10-30 km of strike and may work several different seams that are correlatable between mines.

The project described here is aimed at providing a detailed database on facies geometry within coal-bearing alluvial and fluviodeltaic sequences of the Bowen basin. Data has been collected from the profusion of very large open-cut coal mine exposures in eastern Queensland, Australia, and rationalized into a form useful for hydrocarbon reservoir description.

High-quality geometrical data is obtained from controlled photomosaics of highwalls supplemented by information from close-spaced borehole networks. Detailed information from core and accessible exposures allows accurate sedimentological interpretation.

Interpretation of the German Creek Formation, one of the coal-bearing units of the Bowen basin, suggests that accumulation occurred on an extensive lower delta plain, within a mixed (i.e., wave-tide-fluvial influenced) delta. Four facies have been identified, two of which are possible reservoirs: facies A, major channelized sandstone bodies (4-11 m thick and 0.5-5 km wide, elongate perpendicular to basin edge), interpreted as deltaic distributary channel fills; and facies B, tabular sandstone bodies (9-20 m thick, tens of km in areal extent, elongate parallel to basin margin) internally dominated by hummocky cross-stratification, interpreted as proximal mouth bar deposits.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990