Recent stratigraphy of the John O'Groats Wetland, Fiordland

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Clark, K.J.; Cochran, U.A.; Howarth, J.D.; Villamor, P.; Langridge, R.M.; Vandergoes, M.J.; Berryman, K.R. 2014 Recent stratigraphy of the John O'Groats Wetland, Fiordland. Lower Hutt, N.Z.: GNS Science. GNS Science report 2014/09 101 p.

Abstract: The John O’Groats wetland is ponded against an upstream-facing scarp of the Alpine Fault at the southern end of the onshore fault trace in Fiordland, New Zealand. Preliminary investigations suggested the wetland may contain a record of paleoenvironmental change associated with past Alpine Fault earthquakes, similar to the sequence found at Hokuri Creek, 20 km northeast along the fault. In order to investigate a potential paleoearthquake record at the John O’Groats wetland, a field campaign was carried out in March 2013 during which the wetland was surveyed and eight sediment cores were collected. This report presents the field study methods, detailed stratigraphy of the cores and preliminary dating of paleoenvironmetal changes in the John O’Groats wetland. A piston corer was used to collect eight cores from the John O’Groats wetland. The cores reached depths 7.5 m and were located along transects roughly parallel and perpendicular to the fault scarp. The intersection of the transects was at the approximate “centre” of the wetland basin. Two profiles, parallel and normal with the fault scarp, were surveyed and along these profiles ground-penetrating radar was used to map the subsurface structures of the wetland. The sediments of all cores were photographed and logged in the field, and checked in the laboratory. Sedimentary units were described at a centimetre-decimetre scale, and also categorised using a modified Troels-Smith sediment classification system. Cluster analysis was used to group the sedimentary units into ten sedimentary facies. All cores contain a spectrum of sedimentary facies from coarse clastic units to dark brown peats. All cores contain alternating packages of clastic-dominated and organic-dominated sediments, some alternations are at a >decimetre-scale (e.g., cores JOG-3, -4 and -8) and others are at a