Sorted bedforms on the inner shelf off northeastern New Zealand: spatiotemporal relationships and potential paleo-environmental implications

Sorted bedforms are heterogeneous shelf seabed features found ubiquitously on the inner shelf of New Zealand and around the world. In this study we examine the shallow stratigraphy of sorted bedforms using diver-collected short cores together with the textural analysis of the associated surface sediments in the Tairua-Pauanui embayment on the northeast coast of the North Island of New Zealand. Combining sonar and textural analysis together with the local oceanographic conditions provides new insight into the interpretation of sorted bedform features. In this regional case study, sorted bedforms are found to have a stratigraphic signature characterized by alternating fine and coarse sequences that does not reflect alternating calm (low-energy) and storm (high-energy) cycles. Instead, the core sequences suggest the signature of a heterogeneous inner shelf sedimentary facies developed from morphodynamic feedback mechanisms operating at the scale of the bottom boundary layer. The resulting sedimentary sequence (alternating coarse and fine units) found throughout this study site is the result of contemporaneous sorting processes.