SALT-MARSH STRATIGRAPHY OF THE CHATHAM ISLANDS, NEW ZEALAND

The Chatham Islands are located on the edge of the Zealandia continental fragment, over 800 km distant from the nearest plate boundary. Unlike most other isolated oceanic islands, which are dominated by volcanic and sedimentary rocks, continental rocks are exposed above sea level in the Chathams. Recent studies show that the emergence of the Chatham Islands is extremely recent, having occurred within the last 2Ma. Submarine volcaniclastics with abundant fossils found near the highest point of the islands (~280 m elevation) were deposited between 4.5 and 2.5 million years ago. The existence of the Chatham Islands on a bulge at the edge of the Chatham Rise and the fact that this uplift is recent is intriguing and hints at currently undefined dynamics. We propose using salt marsh stratigraphic records to constrain the spatial and temporal variability of the uplift. Analysis of salt-marsh peat and agglutinated foraminifera will be used to investigate the millennial-scale record of sea-level change at this location. Coring transects will be sited behind an extensive barrier system, extending over 10 km on the eastern side of the island, enclosing the Te Whanga Lagoon. We hypothesize a regressive salt-marsh stratigraphy, and will focus coring efforts on the proximal end of the barrier to recover the oldest peats.