Abstract:
Tectonically active areas will have a strong influence on relative sea level change in coastal environments, and subsequently the biological communities inhabiting coastal and other associated marine environments. Paleoenvironmental reconstruction provides insights of the nature of coastal/marine response to tectonic activity, and how similar environments may be expected to respond in modern environments. The Early Miocene Waitemata Group strata outcropping at Mathesons Bay near Leigh, North Island, New Zealand is an example of a coastal environment which has significantly changed in response to active tectonics in the region. The strata at Mathesons Bay conforms to 10 lithofacies units that represent the existence of a number of different depositional environments developed during sea level transgression over an irregular Mesozoic Waipapa Group surface. Divided into the basal coarser grained Kawau Subgroup and the turbidite-dominated Warkworth Subgroup, they demonstrate a period of rapid subsidence in the intra-arc Waitemata Basin beginning ~22 Ma. These strata record the evolution of Mathesons Bay throughout this subsidence in four distinct stages, including: the transgressing of a rocky coast; basinal subsidence during a period of sediment starvation; the reinitiation of sedimentation, and the formation of an unusual hydrocarbon cold seep. This study utilised lithologic, paleoecologic and petrographic analyses to identify and characterise lithofacies units and reconstruct the paleoenvironment. This was achieved through the construction of field maps and lithologic logs, the sampling of different lithologic units and associated macrofossils, petrographic analysis, and fossil/paleoecological identification.
