New record of siliceous, marine, later Eocene from Kalbarri, Western Australia

Weathered residue of a previously undetected thin Eocene unit at elevation of 220 m AHD east of Kalbarri includes silicified sponge-rich calcarenite and argillite. Sponges (intact forms and spicules) dominate the silicified fauna but common smaller benthic and planktonic foraminifers, molluscs (gastropods, bivalves, scaphopods, and nautiloids), bryozoans, solitary corals, and serpulid worms are also present. The planktonic foraminifers indicate that the unit lies within the Zone P13 to P16 interval of the Middle to Late Eocene (40.5 - 34.0 Ma BKSA95). In comparison to the Giralia Calcarenite of upper Zone P12, the fossil assemblage indicates that significant cooling in the shallow inner neritic zone apparently took place within the basin during the later Eocene. The ages of known marine Eocene occurrences in the basin, and the contrast between these and underlying formations, indicate major erosion during the interval 53 - 41.5 Ma (late Early to early Middle Eocene) preceding deposition of Zone P12-16 units.