Structural interpretation of a sedimentary basin using high-resolution magnetic and gravity data

Abstract

The Merlinleigh Sub-basin in the onshore Southern Carnarvon Basin is a frontier area for petroleum exploration, with limited seismic coverage and only two deep exploration wells. High-resolution aeromagnetic and semi-detailed helicopter-supported gravity surveys were conducted in 1995 to assist with the structural interpretation of the sub-basin. An evenly spaced grid of potential field data provided relatively cheap structural information, compared with the cost of acquiring seismic data, and an opportunity to test the relative effectiveness of gravity and magnetic data in a sedimentary basin. In the Merlinleigh Sub-basin, magnetic anomalies are dominated by near-surface and intra-basement sources. Gravity anomalies provide reliable definition of the structures at basement level and within the sedimentary sequence. Some of the gravity lineaments are consistent with fault trends mapped with seismic data, whereas others were undetected in the other datasets. Northwesterly oriented gravity lineaments represent transfer faults generated by the breakup of Gondwanaland in the Early Cretaceous. Acquisition costs for the similar sized aeromagnetic and helicopter-supported gravity surveys were similarly priced. In contrast to gravity data, aeromagnetic data provided only a small contribution to the structural knowledge of the area. Gravity data collected on an evenly spaced grid are likely to provide more structural information than aeromagnetic data within this sedimentary basin.