INTEGRATING SEISMIC, GRAVITY AND AEROMAGNETIC DATA IN THE STRUCTURAL INTERPRETATION OF THE MERLINLEIGH SUB-BASIN, WESTERN AUSTRALIA

Abstract

The southern Merlinleigh Sub-basin is a frontier area for petroleum exploration within the onshore Southern Carnarvon Basin, with limited seismic coverage and only two deep exploration wells. High resolution aeromag- netic and semi-detailed gravity data acquired in 1995 provide relatively low cost structural inf ormation"comple- mentary to the regional seismic coverage.

Two-dimensional seismic data can be mapped with confidence if the lines are closely spaced. By identifying lineaments on potential-field images, orientations for structures within the sedimentary succession, and at basement or intra-basement levels, can assist in the interpretation of faults and structures in areas of limited seismic coverage, and to extrapolate them outside areas of seismic control. Consequently, by integrating seismic and potential-field data, a more rigorous interpretation of the structural geometry can be achieved and thereby assists in reconstructing the evolution of a sedimentary basin.

The aeromagnetic data provided only limited information about the structure of the Merlinleigh Sub-basin because magnetic anomalies appear to be dominated either by near-surface or deep intra-basement sources. In contrast, the gravity data provide a more reliable definition of the structure at basement level and, to a lesser extent, within the sedimentary sequence.

Seismic, gravity and magnetic data show that the region is a large north-trending Late Carboniferous to Permian depocentre and can be sub-divided into two main troughs east of the Wandagee and Kennedy Range Faults. These are en-echelon fault systems with syn- depositional growth during the main period of rifting in the Late Carboniferous to Early Permian.