DENISON TROUGH, QUEENSLAND – NEW SEISMIC INFORMATION AND ITS HYDROCARBON IMPLICATIONS

Abstract

New data from a digital six-fold CDP seismic survey in the Permo-Triassic Denison Trough, Queensland by the Bureau of Mineral Resources in conjunction with the Geological Survey of Queensland are markedly better than the old. They improve the hydrocarbon prospects of the trough by showing (a) structures within the Reids Dome Beds which have clearly formed early in the history of the trough, including one with a probable flat spot, (b) pinchouts in the Reids Dome Beds and younger units, and (c) pronounced faulting which occurred at the commencement of Cattle Creek Formation deposition. Major thrusting is shown to have occurred on the Merivale Fault during Middle to Late Triassic, and a conjugate thrust fault is identified. Localised faulting of known gas fields is suspected. A reflection within the Black Alley Shale and lower Bandanna Formation interval showing angular discordance with the formation boundaries is thought to arise from a tuff band marking an isochronous surface; this establishes the direction of progradation of the upper Black Alley Shale and Bandanna Formation. The overall structure of the trough is considered to be less complex than previously thought. In the light of the much improved seismic data, a reassessment of hydrocarbon plays in the Denison Trough appears warranted.