Cretaceous and Tertiary sedimentation on the western margin of the Eucla Basin

Abstract

Sedimentation on the northwestern margin of the Eucla Basin has been defined by drilling and palaeontological data to include Early Cretaceous to Miocene sequences. Channel, floodplain and lacustrine deposits of the Loongana Sandstone and Madura Formation indicate that the Early Cretaceous sea did not reach the Kitchener area. Middle to Late Eocene deposits unconformably overlie the Cretaceous sequence and extend up the Lefroy Palaeoriver towards Norseman where they merge with the Bremer Basin sediments. The Hampton Sandstone extends up the Lefroy Palaeoriver and was deposited under shallow high energy marine conditions probably in a well‐flushed large estuary. An erosional break at the top of the Hampton Sandstone and a wedge of fluvial sand in the Chifley palaeochannel provide evidence for a regression. The succeeding Late Eocene transgression covered wide areas around the Lefroy Palaeoriver and led to deposition of the Princess Royal Spongolite. Low oxygen levels and abundant silica, possibly derived from volcanic ash, allowed sponges to thrive in areas with restricted circulation on the basin margin while limestone accumulated in the sediment starved centre of the basin. The break between the Hampton Sandstone and Princess Royal Spongolite in the Harris Lake area is probably equivalent to the major sea level lowstand at 39.5 Ma.