A gravity survey of Woy Woy district, New South Wales, and its interpretation

Abstract

A gravity survey of the Woy Woy district, south of Gosford, New South Wales, comprising some 500 gravity stations is conducted to an accuracy of 1 GU in Bouguer anomalies. The resulting map shows predominance of a regional gradient mainly associated with the continental margin. It is suggested that a first degree surface for the regional effect is preferable to a second or higher degree surface. It is shown that the orientation of the linear gradient can be explained almost completely by the attitude of the continental slope and the regional southward dip of the underlying Permian rocks. The residual anomalies show a main gravity low over the townships of Woy Woy and Ettalong. The low reaches a minimum of 18 GU and trends north-south, a major regional drainage direction. It is interpreted to reveal an ancient channel of Brisbane Water, now filled with unconsolidated young sediments replacing the rocks of the Gosford Formation and reaching a maximum thickness of about 90 m.