Palaeokarst development in a lower Frasnian (Devonian) platform succession, Canning Basin, northwestern Australia

Recognition of palaeokarst in the oldest exposed Devonian (Givetian-lower F rasnian) platform successions of the Canning Basin reef complexes has elude d investigators for over forty years. The first evidence for palaeokarst, d eveloped on microbial mud-mounds in a single stratigraphic horizon, is docu mented and records an episode of exposure during early carbonate platform d evelopment. Surface palaeokarst features are scalloped surfaces, solution p its and a pipe, underlain by fenestral limestone with sediment-filled fossi l moulds and vugs. The platform succession has variably developed metre-sca le cycles which are composed predominantly of shallowing-upward subtidal fa cies, with some cycles having fenestral peloidal mudstone caps. Changes in facies type and stratigraphic arrangement up the succession define two deep ening-upward units (similar to 70 and 180 m thick), with the palaeokarst su rface representing emergence following rapid shallowing at the top of the l ower unit. The stratigraphic position of the palaeokarst between these two units suggests it may represent a sequence boundary. This may have been cau sed by a low-magnitude eustatic fall or footwall-uplift event superimposed on a rapidly subsiding basin margin.