ABSTRACT

Numerous tabular bodies of sedimentary rock cut discordantly through bedded Oligocene volcaniclastic sediments along the coast at Oamaru, South Island, New Zealand. Most such dikes represent infilling of irregular fissures which opened spasmodically along the crests of submerged volcanogenic mounds. Infillings predominantly comprise biogenic debris in a wide variety of texture and composition.

Dikes are multilayered, with layers either parallel to the walls or at various angles. Layers of different lithotypes, phases, reflect significant temporal differences between episodes of infilling. Layers of similar lithotypes, pulses, reflect relatively short temporal differences or fluctuations in the filling process during a single episode of infilling. Processes of infill range from gravitationally-induced cohesionless grain flow and viscous mudflow to hydrodynamic injections resulting from opening and closing of the fissures.

Dike microfacies represent seafloor sediments from probable Lower Oligocene into Lower Miocene time. Some phases reflect transient deposits that are not present in the normal stratigraphic sequence of the coastal region. All fissures did not open at the same time or always follow the same routes, and a definitive regional sequence of phase emplacement cannot be determined.