Two samples of folded Adelaidean equivalent age sediments which form the basement to the (?) Cambro-Ordovician Officer Basin, obtained from rock outcrops in the Chambers Bluff region of the north-eastern Officer Basin, were analysed geochronologically to try to constrain the age estimates for the commencement of sedimentation in the basin. Rubidium/strontium isotope ratios suggest that the two Sturtian age rocks studied have not been affected by the mid-Ordovician Delamerian Orogeny, but instead have had their Rb/Sr isotopic system reset by folding and mild metamorphism in the late Precambrian. This would indicate that sedimentation in the Officer Basin may have commenced in very early Cambrian times.