The Wianamatta Group (English: Wianamatta Shale or Wianamatta Group) is the youngest geological formation in the Sydney Basin in New South Wales, Australia. In this formation originated in the Triassic Bändertone and mudstones, which contain a few small sandstone deposits.
The Wianamatta Group shows the following stratigraphic sequence: Bringelly Shale ( Bringelly Shale ), Minchinbury Sandstone ( Minchinbury Sandstone ) and Ashfield Shale ( Ashfield Shale ).
The Wianamatta Group superimposed on the sequence of the Hawkesbury Sandstone ( Hawkesbury Sandstone ).
The Wianamatta Group is the youngest geological layer member of the Sydney Basin, and therefore is as the top layer member at the highest point. It was deposited in connection with a large river delta which has shifted over time from west to east. This is indicated by the sequence of the layer members which clearly show the transition from marine deposits in front of the Delta incurred on land deposits: The Ashfield Shale was formed of clayey marine sediments. The subsequent Minchinbury Sandstone emerged from beach- Nehrungs Islands. The Bringelly Shale was deposited in a marshy plain of alluvial soil in the Delta, meandered through the rivers and were deposited at different, each limited points of sand, which later solidified into sandstone.
Today's weathering of the mudstone occurring at the surface generates plenty of sound, which leads to the formation of clay soils with low water permeability, as they occur for example on the Cumberland Plain common. Here podzol soils are widespread, which swell with the supply of water and shrink when drying.
Be water-bearing layers can form on the pitches of Wianamatta Group. Low-lying and large clay deposits of this formation are able to collect groundwater; if they are at or near the surface, but can form salted dry land in evaporation of the water. The quality of groundwater on the pitches can be good, so that potable water can be found, or it may be too salty so strong and be inedible. The deeper aquifers in the rocks of the Wianamatta Group are generally less saline than the near-surface deposits.