A gravity survey of Woy Woy district and its local and regional geological significance

Abstract

A detailed gravity survey of the Woy Woy district, south of Gosford, New South Wales, was undertaken in order to determine the thickness of young, unconsolidated sediments overlying the Gosford Formation belonging to the Narrabeen Group of the Triassic. The district is situated within a valley which has a maximum width of 5 km, south of the Blackwall Mountain (Fig. 1). The valley is cut into the sandstone of the Gosford Formation by the Brisbane Water which occupies the valley almost entirely to the north. Near Woy Woy, the water channel bifurcates about St. Hubert's Island and further south it narrows down to a width of only 300 m near Bucher Bay (point D in Fig. 1). Near Ocean Beach at the southern boundary of the district, the channel widens again and joins up with the Broken Bay. The sides of the valley formed by the sandstone are generally steep and the valley floor in Woy Woy quite flat except for the intervention of the Blackwall Mountain, a monadnock over 115 m high.