Subaerial-subaqueous morphology of some Sydney rocky shores

<p dir="ltr">Morphological features of the inner shelf along Sydney's northern beaches can be divided into three areas of bedrock exposure and paleodrainage, that relate to distinct structural domains.</p><p dir="ltr">Subaqueous headland morphology are also controlled by lithology and structure with bench and gulley orientation related to jointing, and bench height related to bed thickness. These same controls determine boulder size and shape.</p><p dir="ltr">Nearshore topography displays increased abrasion features shorewards, as wave energy increases at the seabed and, waves are refracted towards bathymetric highs.</p><p dir="ltr">Three distinct wave energy zones that relate to wave base were identified~zones of 'Free', 'Limited' and 'No' movement. The zone of 'No Movement', Zone 3, occurs between the inner shelf (-60m) and the nearshore zone where relief is very low. Zone 2, the zone of 'Limited Movement', occurs within the nearshore zone where abrasion increases shorewards, and relief is moderate. Zone 1, the zone of 'Free Movement' occurs where boulders (<2m dia.) are freely moved about (above -6m contour), and relief is high. Within this upper zone wave type controls both the level and rate of modifying processes.</p><p dir="ltr">Drowned aerial features such as undercut bench faces, cemented boulders (talus) at the foot of large subaqueous cliffs, tessellated pavement, raised iron coated joints have been preserved on steep nearshore areas (above the -10m contour) where toolstones have had little opportunity to operate.</p><p dir="ltr">Carbonate growths identified near the boundary of Zones 2 and 3 may relate to a galeolaria zone of an earlier but recent stillstand, possibly 7,000 years B.P. Boulder concentrations at the head of benches, over 1km off Careel Head, may also represent a previous stillstand.</p>