Burial Diagenesis in the Upper Devonian Reef Complexes of the Geikie Gorge Region, Canning Basin, Western Australia (1)

Abstract

The Devonian carbonates of the Geikie Gorge region, Canning basin, have undergone a long and complex diagenetic history that began in Devonian seawater with extensive marine cementation of platform-margin lithologies. Devonian-Lower Carboniferous burial diagenesis was the most important porosity occluding episode because almost all primary porosity was destroyed by equant calcite cements (nonluminescent to brightly luminescent to dully luminescent) during this interval. Dolomitization and consequent secondary porosity development also occurred during early burial diagenesis. The distribution and geochemistry of the major calcite cements and dolomite types are consistent with these phases having been precipitated from connate marine or basinal brines. Karstification and mi or calcite cementation took place during Late Carboniferous subaerial exposure. Minor calcite cementation occurred during Permian-Cenozoic burial, predominantly in secondary porosity within pervasively dolomitized lithologies. Karstification, dedolomitization, and calcite recrystallization took place in association with Cenozoic meteoric diagenesis. Secondary moldic and intercrystalline porosity within the completely dolomitized lithologies were the longest lived porosity types in the carbonates. Some secondary porosity escaped both Devonian-Carboniferous and Permian-Cenozoic burial cementation, probably due to a lack of nucleation sites for calcite cements within completely dolomitized lithologies.