Description and Analysis of Facies on the Waipaoa Continental Margin, New Zealand

Major paradigm shifts in the study of sedimentology have revolutionized the way fine-grained sediments are studied on continental margins. Although muds are the most abundant natural material on the Earth's surface by volume, the fundamental mechanisms of their transport, dispersal, and deposition are still debated. To better interpret ancient cores from shallow marine environments, observing how to transport and depositional mechanisms are preserved in the stratigraphic record of the modern is essential. This study provides a facies analysis of six modern box cores collected in the Tūranganui-a-Kiwa/Poverty Bay and on the distal Poverty Shelf in New Zealand, where the Waipaoa River delivers sediment directly into the bay. These short cores were collected in May 2010 and are oriented in a northwest to southeast transect from Tūranganui-a-Kiwa/Poverty Bay to the Outer Poverty Shelf, through the Poverty Gap. Grain sizes vary from clay to very fine sand, however, the majority of the cores were clay and silt-rich. Facies identified were: Laminated Very Fine Sand, Normal Grading, Structureless Mud, Laminated Silt and Mud, and Biogenically Mottled Silt and Mud. The main ichnofacies present were Skolithos and Phycosiphon assemblages, with identified species including Skolithos, Phycosiphon, Planolites, and Chondrites. There was overall low ichnological diversity along the studied transect; however, diversity increased distally from the Waipaoa River mouth. Wave reworking from dry storm processes dominates the sediment proximal to the Waipaoa River mouth, while biogenic reworking dominates the lower energy Outer Poverty Shelf.