Sedimentary rocks typically have variable inorganic geochemistry, even in apparently uniform successions. This is driven by subtle changes in mineralogy, often associated with accessory phases such as heavy minerals, but also by the type and abundance of framework grains (lithics and feldspars for example). Chemostratigraphy is based on the characterisation of sedimentary rocks using elemental data (bulk-rock inorganic geochemistry) to detect these changes. Discrete packages of sediment are identified based on geochemical trends and these are then correlated across wells.

Chemostrat Australia recently completed an extensive chemostratigraphy study in the Victorian onshore Otway Basin for the Geological Survey of Victoria (GSV). This talk highlights some of the key findings from this work which covers the majority of formations penetrated in the onshore Otway Basin across 11 wells.

Thirty-seven chemically distinct packages were identified and chemostratigraphic interpretation allowed correlation of units regardless of lithology. Some of the key findings include the division of the Crayfish Subgroup and correlation into South Australian wells, and a subdivision and correlation of the Eumeralla Fm. The data also allow for assessment of the nature and evolution of the volcanogenic component of the basin fill in the Otway Group.

Link to Report