Fluvial channel Meander-belt sandstone
Description
The sandstone body exposed in the cliff section is 1.8km long and is on average 6m thick. It has an erosional basal surface which cuts into mottled mudrocks with root traces interpreted as palaeosols developed in floodplain deposits. Similar mudrock facies overlie the sandstone which is interpreted as the fill of a river channel. The strata are in the core of a broad anticline and are horizontal in the centre of the section, dipping  a few degrees NW and SE at either end of the outcrop. Low-angle inclined surface within the sandstone have been interpreted as having been formed by lateral migration of point bar surfaces in a meandering river channel. These lateral accretion surfaces are particularly well developed in the Sudmoor Point Sandstone, making it an excellent example of a fluvial channel sandstone body deposited by a meandering river. The sandstone displays multiple scales of heterogeneity. It can be divided laterally into 6 separate units each of which shows different angles of lateral accretion surfaces and representing stages in the development of the meander belt (Stewart, 1981). The lateral accretion surfaces themselves are picked out by changes in sediment grain size, with mudstones separating the inclined sandstone layers which are centimetres to tens of centimetres thick.  There is also heterogeneity within the inclined sandstone units themselves as they show local variations in grain sizes, thickness, scoured surfaces and cross-bedding.
Viewing the Image
The internal structures of the Sudmoor Point Sandstone are best viewed in the south eastern (right hand end) of the image. The purple mudrocks at the base of the cliff are overbank deposits with palaeosol development. The lower part of the sandstone body is pale brown in colour, becoming white-brown colour towards the top. It is overlain by dark grey mudrocks. The depositional horizontal is picked out by the boundary between the white sandstone and dark mudrocks above. Within the pale brown sandstones the lateral accretion surfaces are clear, dipping at a low angle to the right (south east). Towards the far end of the outcrop, where the base of the sandstone is below the beach level, the heterogeneity within the inclined surfaces is evident, with local scours and fills and thickness variations.