A Holocene record of gradual, catastrophic and human-influenced sedimentation from a backbarrier wetland, northern New Zealand

Abstract

An infilled backbarrier wetland located behind a stationary-type coastal bay-barrier is used to reconstruct a 6000 year paleo-environmental record that incorporates gradual, catastrophic and human-influenced sedimentation styles on the New Zealand coast. The record is assembled from a range of proxy indicators (grain size, magnetic susceptibility, organic content, diatoms and pollen) and is temporally constrained by tephrochronology, radiocarbon dating and optical dating.

Postglacial sea-level rise, volcanism, tsunami and catchment clearance are all evident in the sediment record, either as artifacts or indirect indicators. Results from optical dating also provide insights into the process of sediment reworking and mixing from multiple sources during tsunami transport. We argue that backbarrier wetlands formed behind stationary-type (aggraded) bay-barriers are of greater value (more sensitive) for longer term paleo-environmental reconstruction than wetlands associated with prograded-type and receded-type barriers where the sediment record is typically less complete.

Keywords

Coastal geomorphology, sediments, optical dating, tsunami, New Zealand.